Bio


Leckie investigates chemical pollutant behavior in natural aquatic systems and engineered processes, specifically the environmental aspects of surface and colloid chemistry and the geochemistry of trace elements. New research efforts are focused on the development of techniques and models for assessment of exposure of humans to toxic chemicals. Specific attention has been paid to the evaluation of exposure of young children to toxic chemicals. Other interests include technology transfer and the development of environmental science programs in developing nations.

Academic Appointments


  • Professor, Civil and Environmental Engineering
  • Professor (By courtesy), Geological and Environmental Sciences

Boards, Advisory Committees, Professional Organizations


  • Elected Member, National Academy of Engineering (2013 - Present)
  • Appointed Chair Professor in the Department of Environmental Science and Engineering, Tsinghua University, Beijing, China (2013 - Present)

Professional Education


  • PhD, Harvard University (1970)

2013-14 Courses


Journal Articles


  • Enterococcus spp on fomites and hands indicate increased risk of respiratory illness in child care centers AMERICAN JOURNAL OF INFECTION CONTROL Julian, T. R., Pickering, A. J., Leckie, J. O., Boehm, A. B. 2013; 41 (8): 728-733

    Abstract

    BACKGROUND: Surface-mediated transmission is a potential route for respiratory disease in child care centers, but evidence of its importance relative to other routes (eg, airborne) is limited. METHODS: We tracked respiratory disease and monitored bacteria contamination on hands and fomites over 4 months during 64 visits at 2 child care centers. Staff monitored health daily by recording respiratory symptoms. We measured concentrations of Escherichia coli, Enterococcus spp, and fecal coliform in hand rinses and on select fomites. RESULTS: We demonstrated that symptomatic respiratory illness was positively associated with microbial contamination on hands and fomites, as measured using Enterococcus spp. Enterococcus spp were 0.28 (95% confidence interval: 0.08-0.48)-log(10) (colony-forming units per 2 hands) higher when an individual had symptomatic respiratory illness. Susceptible individuals were 1.62 (95% confidence interval: 1.06-2.46) times more likely to develop respiratory illness within 4 days with every log(10) increase of Enterococcus spp on hands. CONCLUSION: The findings imply that hand contamination as measured using Enterococcus spp is a risk factor for onset of respiratory illness and highlight the utility of fecal indicator bacteria as a metric for hand and fomite contamination.

    View details for DOI 10.1016/j.ajic.2012.10.013

    View details for Web of Science ID 000322641100014

    View details for PubMedID 23394857

  • Critical Review of Desalination Concentrate Management, Treatment and Beneficial Use ENVIRONMENTAL ENGINEERING SCIENCE Xu, P., Cath, T. Y., Robertson, A. P., Reinhard, M., Leckie, J. O., Drewes, J. E. 2013; 30 (8): 502-514
  • Methodology to Capture Children's Non-Dietary Ingestion Exposure Activities During Meal Events HUMAN AND ECOLOGICAL RISK ASSESSMENT Ferguson, A., Canales, R., Vieira, V., Leckie, J. 2013; 19 (4): 944-958
  • Effects of Chlorine Exposure Conditions on Physiochemical Properties and Performance of a Polyamide Membrane-Mechanisms and Implications ENVIRONMENTAL SCIENCE & TECHNOLOGY Van Thanh Do, V. T., Tang, C. Y., Reinhard, M., Leckie, J. O. 2012; 46 (24): 13184-13192

    View details for DOI 10.1021/es302867f

    View details for Web of Science ID 000312432200021

  • Effects of hypochlorous acid exposure on the rejection of salt, polyethylene glycols, boron and arsenic(V) by nanofiltration and reverse osmosis membranes WATER RESEARCH Van Thanh Do, V. T., Tang, C. Y., Reinhard, M., Leckie, J. O. 2012; 46 (16): 5217-5223
  • Adsorption of perfluorinated compounds on thin-film composite polyamide membranes JOURNAL OF APPLIED POLYMER SCIENCE Kwon, Y., Shih, K., Tang, C., Leckie, J. O. 2012; 124 (2): 1042-1049

    View details for DOI 10.1002/app.35182

    View details for Web of Science ID 000298672800019

  • Degradation of Polyamide Nanofiltration and Reverse Osmosis Membranes by Hypochlorite ENVIRONMENTAL SCIENCE & TECHNOLOGY Van Thanh Do, V. T., Tang, C. Y., Reinhard, M., Leckie, J. O. 2012; 46 (2): 852-859

    Abstract

    The degradation of polyamide (PA) nanofiltration and reverse osmosis membranes by chlorine needs to be understood in order to develop chlorine-resistant membranes. Coated and uncoated fully aromatic (FA) and piperazine (PIP) semi-aromatic PA membranes were treated with hypochlorite solution and analyzed by X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR). XPS results showed that in chlorine treated FA PA membranes the ratio of bound chlorine to surface nitrogen was 1:1 whereas it was only 1:6 in the case of PIP PA membranes. Surface oxygen of uncoated FA and PIP membranes increased with increasing hypochlorite concentration whereas it decreased for coated FA membranes. High resolution XPS data support that chlorination increased the number of carboxylic groups on the PA surface, which appear to form by hydrolysis of the amide bonds (C(O)-N). FTIR data indicated the disappearance of the amide II band (1541 cm(-1)) and aromatic amide peak (1609 cm(-1)) in both coated and uncoated chlorinated FA membranes, consistent with the N-chlorination suggested by the XPS results. Furthermore, the surface charge of chlorinated membranes at low pH (<6) became negative, consistent with amide-nitrogen chlorination. Chlorination appeared to both increase and decrease membrane hydrophobicity depending on chlorination exposure conditions, which implied that N-chlorination and hydrolysis may be competing processes. The effects of property changes on the membrane performance were also observed for NF90, BW30, and NF270 membranes.

    View details for DOI 10.1021/es203090y

    View details for Web of Science ID 000299136200038

    View details for PubMedID 22221176

  • Quantified outdoor micro-activity data for children aged 7-12-years old JOURNAL OF EXPOSURE SCIENCE AND ENVIRONMENTAL EPIDEMIOLOGY Beamer, P. I., Luik, C. E., Canales, R. A., Leckie, J. O. 2012; 22 (1): 82-92

    Abstract

    Estimation of aggregate exposure and risk requires detailed information regarding dermal contact and mouthing activity. We analyzed micro-level activity time series (MLATS) of children aged 7-12 years to quantify these contact behaviors and evaluate differences by age and gender. In all, 18 children, aged 7-12 years, were videotaped while playing outdoors. Video footage was transcribed via Virtual Timing Device (VTD) software. We calculated the hand and mouth contact frequency, hourly duration and median duration of contact with 16 object categories. Median mouthing frequencies were 12.6 events/h and 2.6 events/h for hands and non-dietary objects, respectively. Median hourly mouthing duration was 0.4 min/h and 0.1 min/h with hands and objects. Median mouthing contact duration was 1 s and 1.5 s with hands and objects, respectively. The median object contact frequency for both the hands combined was 537.3 events/h with an hourly contact duration of 81.8 min/h and a median contact duration of 3 s. There were no significant differences in the mouthing activity between genders or age groups. Female children had longer and more frequent hand contacts with several surface types. Age was negatively correlated with hand contacts of floor and wood surfaces. Contact frequencies in this study are higher than current regulatory recommendations for this age group.

    View details for DOI 10.1038/jes.2011.34

    View details for Web of Science ID 000298248200009

    View details for PubMedID 21989500

  • An Ontology-based Service Model For Smart Infrastructure Design 2012 INTERNATIONAL CONFERENCE ON CLOUD COMPUTING AND SERVICE COMPUTING (CSC) Chu, T., Wang, J., Leckie, J. O. 2012: 17-24
  • Relative Pesticide and Exposure Route Contribution to Aggregate and Cumulative Dose in Young Farmworker Children INTERNATIONAL JOURNAL OF ENVIRONMENTAL RESEARCH AND PUBLIC HEALTH Beamer, P. I., Canales, R. A., Ferguson, A. C., Leckie, J. O., Bradman, A. 2012; 9 (1): 73-96

    Abstract

    The Child-Specific Aggregate Cumulative Human Exposure and Dose (CACHED) framework integrates micro-level activity time series with mechanistic exposure equations, environmental concentration distributions, and physiologically-based pharmacokinetic components to estimate exposure for multiple routes and chemicals. CACHED was utilized to quantify cumulative and aggregate exposure and dose estimates for a population of young farmworker children and to evaluate the model for chlorpyrifos and diazinon. Micro-activities of farmworker children collected concurrently with residential measurements of pesticides were used in the CACHED framework to simulate 115,000 exposure scenarios and quantify cumulative and aggregate exposure and dose estimates. Modeled metabolite urine concentrations were not statistically different than concentrations measured in the urine of children, indicating that CACHED can provide realistic biomarker estimates. Analysis of the relative contribution of exposure route and pesticide indicates that in general, chlorpyrifos non-dietary ingestion exposure accounts for the largest dose, confirming the importance of the micro-activity approach. The risk metrics computed from the 115,000 simulations, indicate that greater than 95% of these scenarios might pose a risk to children's health from aggregate chlorpyrifos exposure. The variability observed in the route and pesticide contributions to urine biomarker levels demonstrate the importance of accounting for aggregate and cumulative exposure in establishing pesticide residue tolerances in food.

    View details for DOI 10.3390/ijerph9010073

    View details for Web of Science ID 000299532000006

    View details for PubMedID 22470279

  • Effect of bromide on the chlorination of a polyamide membrane DESALINATION Kwon, Y., Joksimovic, R., Kim, I., Leckie, J. O. 2011; 280 (1-3): 80-86
  • Comparison of Surface Sampling Methods for Virus Recovery from Fomites APPLIED AND ENVIRONMENTAL MICROBIOLOGY Julian, T. R., Tamayo, F. J., Leckie, J. O., Boehm, A. B. 2011; 77 (19): 6918-6925

    Abstract

    The role of fomites in infectious disease transmission relative to other exposure routes is difficult to discern due, in part, to the lack of information on the level and distribution of virus contamination on surfaces. Comparisons of studies intending to fill this gap are difficult because multiple different sampling methods are employed and authors rarely report their method's lower limit of detection. In the present study, we compare a subset of sampling methods identified from a literature review to demonstrate that sampling method significantly influences study outcomes. We then compare a subset of methods identified from the review to determine the most efficient methods for recovering virus from surfaces in a laboratory trial using MS2 bacteriophage as a model virus. Recoveries of infective MS2 and MS2 RNA are determined using both a plaque assay and quantitative reverse transcription-PCR, respectively. We conclude that the method that most effectively recovers virus from nonporous fomites uses polyester-tipped swabs prewetted in either one-quarter-strength Ringer's solution or saline solution. This method recovers a median fraction for infective MS2 of 0.40 and for MS2 RNA of 0.07. Use of the proposed method for virus recovery in future fomite sampling studies would provide opportunities to compare findings across multiple studies.

    View details for DOI 10.1128/AEM.05709-11

    View details for Web of Science ID 000295123300023

    View details for PubMedID 21821742

  • Sequestration of cadmium ions using titanate nanotube JOURNAL OF HAZARDOUS MATERIALS Du, A. J., Sun, D. D., Leckie, J. O. 2011; 187 (1-3): 401-406

    Abstract

    In this manuscript, titanate (Na(2)Ti(3)O(7)) nanotubes synthesized from alkali hydrothermal route, with high BET surface area (206 m(2)/g), were used as an effective sorbent to remove cadmium ions from water. Sorption capacity (q(m,Langmuir) = 1.1 mmol/g at pH 7) was higher than other sorbents. X-ray photoelectron spectroscopy (XPS) analyses performed on fresh and cadmium-sorbed samples reveal intensities of Na 1s peak decreased after sorption indicating ion-exchanging between cadmium and sodium ions occurred at interlayer of nanotubes. However kinetic study did not show a stoichiometrically equivalent amount of Na(+) being released suggesting Cd uptake was not due solely to ion-exchange mechanism. Batch tests also showed that cadmium uptake was not significantly affected by variation in ionic strength, signifying cadmium ions form an inner-sphere complexation with surface hydroxyl groups. Finally, surface complexation modeling was performed based on charge distribution multisite ion complexation (CDMUSIC) model. It was found that CDMUSIC was able to fit the experimental data best when inner-sphere complexation and ion-exchange were applied together.

    View details for DOI 10.1016/j.jhazmat.2011.01.053

    View details for Web of Science ID 000288630800049

    View details for PubMedID 21295400

  • Selective sorption of divalent cations using a high capacity sorbent JOURNAL OF HAZARDOUS MATERIALS Du, A. J., Sun, D. D., Leckie, J. O. 2011; 187 (1-3): 96-100

    Abstract

    This manuscript describes the application of a novel sorbent, sodium titanate nanotube (STN) on partitioning of various divalent cations. Seven divalent cations, from alkaline earth, transition and post-transition groups, were used to determine the capacity and selectivity of STN. At pH 3 ± 0.02 and 0.1M ionic strength, STN displayed high capacity for Pb and Cd (1.27 and 0.39 mmol/g, correspondingly). The affinity of divalent cations was in the order Pb ? Cd>Cu>Zn>Ca>Sr>Ni. For six of the tested cations, their sorption capacity can be linearly correlated to its hydrolysis constant and electronegativity. STN has unusually low affinity for Ni and correlations of sorption capacity of Ni falls outside the 95% confidence intervals. Furthermore, it exhibited sorption behavior similar to alkaline earth cations, significant uptakes occurred only when pH>point of zero charge. In competitive sorption tests, STN preferentially sorb Cd over other metals (Zn, Ni, Ca and Sr) which coexist in industrial wastewater. As such STN is a potential novel sorbent useful for partitioning Cd from other metals in industrial wastewater.

    View details for DOI 10.1016/j.jhazmat.2010.12.120

    View details for Web of Science ID 000288630800011

    View details for PubMedID 21295911

  • Systematic study on calcium-alginate interaction in a hybrid coagulation-nanofiltration system JOURNAL OF MEMBRANE SCIENCE Listiarini, K., Tan, L., Sun, D. D., Leckie, J. O. 2011; 370 (1-2): 109-115
  • A decision-support system for smarter city planning and management IBM JOURNAL OF RESEARCH AND DEVELOPMENT Juan, Y., Wang, L., Wang, J., Leckie, J. O., Li, K. 2011; 55 (1-2)
  • Virus transfer between fingerpads and fomites JOURNAL OF APPLIED MICROBIOLOGY JULIAN, T. R., Leckie, J. O., Boehm, A. B. 2010; 109 (6): 1868-1874

    Abstract

    Virus transfer between individuals and fomites is an important route of transmission for both gastrointestinal and respiratory illness. The present study examines how direction of transfer, virus species, time since last handwashing, gender, and titre affect viral transfer between fingerpads and glass.Six hundred fifty-six total transfer events, performed by 20 volunteers using MS2, ?X174, and fr indicated 0·23 ± 0·22 (mean and standard deviation) of virus is readily transferred on contact. Virus transfer is significantly influenced by virus species and time since last handwashing. Transfer of fr bacteriophage is significantly higher than both MS2 and ?X174. Virus transfer between surfaces is reduced for recently washed hands.Viruses are readily transferred between skin and surfaces on contact. The fraction of virus transferred is dependent on multiple factors including virus species, recently washing hands, and direction of transfer likely because of surface physicochemical interactions.The study is the first to provide a large data set of virus transfer events describing the central tendency and distribution of fraction virus transferred between fingers and glass. The data set from the study, along with the quantified effect sizes of the factors explored, inform studies examining role of fomites in disease transmission.

    View details for DOI 10.1111/j.1365-2672.2010.04814.x

    View details for Web of Science ID 000284170300002

    View details for PubMedID 20659186

  • Hybrid coagulation-nanofiltration membrane for removal of bromate and humic acid in water JOURNAL OF MEMBRANE SCIENCE Listiarini, K., Tor, J. T., Sun, D. D., Leckie, J. O. 2010; 365 (1-2): 154-159
  • Formation of copper aluminate spinel and cuprous aluminate delafossite to thermally stabilize simulated copper-laden sludge JOURNAL OF HAZARDOUS MATERIALS Hu, C., Shih, K., Leckie, J. O. 2010; 181 (1-3): 399-404

    Abstract

    The study reported herein indicated the stabilization mechanisms at work when copper-laden sludge is thermally treated with gamma-alumina and kaolinite precursors, and evaluated the prolonged leachability of their product phases. Four copper-containing phases - copper oxide (CuO), cuprous oxide (Cu(2)O), copper aluminate spinel (CuAl(2)O(4)), and cuprous aluminate delafossite (CuAlO(2)) - were found in the thermal reactions of the investigated systems. These phases were independently synthesized for leaching by 0.1M HCl aqueous solution, and the relative leachabilities were found to be CuAl(2)O(4)

    View details for DOI 10.1016/j.jhazmat.2010.05.024

    View details for Web of Science ID 000280601300051

    View details for PubMedID 20570043

  • Characterization of isolated polyamide thin films of RO and NF membranes using novel TEM techniques JOURNAL OF MEMBRANE SCIENCE Pacheco, F. A., Pinnau, I., Reinhard, M., Leckie, J. O. 2010; 358 (1-2): 51-59
  • Effect of solution chemistry on the adsorption of perfluorooctane sulfonate onto mineral surfaces WATER RESEARCH Tang, C. Y., Fu, Q. S., Gao, D., Criddle, C. S., Leckie, J. O. 2010; 44 (8): 2654-2662
  • Effect of solution chemistry on the adsorption of perfluorooctanesulfonate onto mineral surfaces Water Research Tang, C., Y., Shiang, Q., Fu, Gao, D., Criddle, C., S., Leckie, J., O. 2010; 8 (44): 2654 – 2662
  • Fouling mechanism and resistance analyses of systems containing sodium alginate, calcium, alum and their combination in dead-end fouling of nanofiltration membranes JOURNAL OF MEMBRANE SCIENCE Listiarini, K., Chun, W., Sun, D. D., Leckie, J. O. 2009; 344 (1-2): 244-251
  • Farmworker children's residential non-dietary exposure estimates from micro-level activity time series ENVIRONMENT INTERNATIONAL Beamer, P. I., Canales, R. A., Bradman, A., Leckie, J. O. 2009; 35 (8): 1202-1209

    Abstract

    Farmworkers' children may have increased pesticide exposure through dermal absorption and non-dietary ingestion, routes that are difficult to measure and model. The Cumulative Aggregate Simulation of Exposure (CASE) model, integrates the complexity of human behavior and variability of exposure processes by combining micro-level activity time series (MLATS) and mechanistic exposure equations. CASE was used to estimate residential non-dietary organophosphate pesticide exposure (i.e., inhalation, dermal, and non-dietary ingestion) to California farmworker children and evaluate the micro-activity approach. MLATS collected from children and distributions developed from pesticide measurements in farmworkers' residences served as inputs. While estimated diazinon exposure was greater for inhalation, chlorpyrifos exposure was greater for the other routes. Greater variability existed between children (sigma(B)(2)=0.22-0.39) than within each child's simulations (sigma(W)(2)=0.01-0.02) for dermal and non-dietary ingestion. Dermal exposure simulations were not significantly different than measured values from dosimeters worn by the children. Non-dietary ingestion exposure estimates were comparable to duplicate diet measurements, indicating this route may contribute substantially to aggregate exposure. The results suggest the importance of the micro-activity approach for estimating non-dietary exposure. Other methods may underestimate exposure via these routes. Model simulations can be used to identify at-risk children and target intervention strategies.

    View details for DOI 10.1016/j.envint.2009.08.003

    View details for Web of Science ID 000271360900014

    View details for PubMedID 19744713

  • Influence of a prolonged solid retention time environment on nitrification/denitrification and sludge production in a submerged membrane bioreactor DESALINATION Teck, H. C., Loong, K. S., Sun, D. D., Leckie, J. O. 2009; 245 (1-3): 28-43
  • Effect of membrane chemistry and coating layer on physiochemical properties of thin film composite polyamide RO and NF membranes II. Membrane physiochemical properties and their dependence on polyamide and coating layers DESALINATION Tang, C. Y., Kwon, Y., Leckie, J. O. 2009; 242 (1-3): 168-182
  • Effect of membrane chemistry and coating layer on physiochemical properties of thin film composite polyamide RO and NF membranes I. FTIR and XPS characterization of polyamide and coating layer chemistry DESALINATION Tang, C. Y., Kwon, Y., Leckie, J. O. 2009; 242 (1-3): 149-167
  • Fabrication and photocatalytic activity of porous TiO2 nanowire microspheres by surfactant-mediated spray drying process MATERIALS RESEARCH BULLETIN Zhang, X., Pan, J. H., Du, A. J., Ng, J., Sun, D. D., Leckie, J. O. 2009; 44 (5): 1070-1076
  • A Model of Exposure to Rotavirus from Nondietary Ingestion Iterated by Simulated Intermittent Contacts RISK ANALYSIS Julian, T. R., Canales, R. A., Leckie, J. O., Boehm, A. B. 2009; 29 (5): 617-632

    Abstract

    Existing microbial risk assessment models rarely incorporate detailed descriptions of human interaction with fomites. We develop a stochastic-mechanistic model of exposure to rotavirus from nondietary ingestion iterated by simulated intermittent fomes-mouth, hand-mouth, and hand-fomes contacts typical of a child under six years of age. This exposure is subsequently translated to risk using a simple static dose-response relationship. Through laboratory experiments, we quantified the mean rate of inactivation for MS2 phage on glass (0.0052/hr) and mean transfer between fingertips and glass (36%). Simulations using these parameters demonstrated that a child's ingested dose from a rotavirus-contaminated ball ranges from 2 to 1,000 virus over a period of one hour, with a median value of 42 virus. These results were heavily influenced by selected values of model parameters, most notably the concentration of rotavirus on fomes, frequency of fomes-mouth contacts, frequency of hand-mouth contacts, and virus transferred from fomes to mouth. The model demonstrated that mouthing of fomes is the primary exposure route, with hand mouthing contributions accounting for less than one-fifth of the child's dose over the first 10 minutes of interaction.

    View details for DOI 10.1111/j.1539-6924.2008.01193.x

    View details for Web of Science ID 000264892100002

    View details for PubMedID 19187484

  • Organic fouling of nanofiltration membranes: Evaluating the effects of humic acid, calcium, alum coagulant and their combinations on the specific cake resistance JOURNAL OF MEMBRANE SCIENCE Listiarini, K., Sun, D. D., Leckie, J. O. 2009; 332 (1-2): 56-62
  • Developing probability distributions for transfer efficiencies for dermal exposure JOURNAL OF EXPOSURE SCIENCE AND ENVIRONMENTAL EPIDEMIOLOGY Beamer, P., Canales, R. A., Leckie, J. O. 2009; 19 (3): 274-283

    Abstract

    Many dermal exposure models use stochastic techniques to sample parameter distributions derived from experimental data to more accurately represent variability and uncertainty. Transfer efficiencies represent the fraction of a surface contaminant transferred from the surface to the skin during a contact event. Although an important parameter for assessing dermal exposure, examination of the literature confirms that no single study is large enough to provide a basis for a transfer efficiency distribution for use in stochastic dermal exposure models. It is therefore necessary to combine data sets from multiple studies to achieve the largest data set possible for distribution analysis. A literature review was conducted to identify publications reporting transfer efficiencies. Data sets were compared using the Kruskal-Wallis test to determine whether they arise from the same distribution. Combined data were evaluated for several theoretical distributions using the Kolmogorov-Smirnov and chi(2)-goodness-of-fit tests. Our literature review identified 35 studies comprising 25 different sampling methods, 25 chemicals, and 10 surface types. Distributions were developed for three different chemicals (chlorpyrifos, pyrethrin I, and piperonyl butoxide) on three different surface types (carpet, vinyl, and foil). Only the lognormal distribution was consistently accepted for each chemical and surface combination. Fitted distributions were significantly different (Kruskal-Wallis test; P<0.001) across chemicals and surface types. In future studies, increased effort should be placed on developing large studies, which more accurately represent transfer to human skin from surfaces, and on developing a normative transfer efficiency measure so that data from different methodologies can be compared.

    View details for DOI 10.1038/jes.2008.16

    View details for Web of Science ID 000263457600004

    View details for PubMedID 18385671

  • Combination of one-dimensional TiO2 nanowire photocatalytic oxidation with microfiltration for water treatment WATER RESEARCH Zhang, X., Pan, J. H., Du, A. J., Fu, W., Sun, D. D., Leckie, J. O. 2009; 43 (5): 1179-1186

    Abstract

    This paper proposed the fabrication of two different diameter one-dimensional TiO2 nanowires, 10 nm TNW10 and 20-100 nm TNW20, via hydrothermal process using different alkaline sources. TNW10 and TNW20 were used as photocatalysts for the degradation of humic acid (HA), the major natural organic matters (NOMs) in surface and ground water, followed by microfiltration. The evaluation of photocatalytic activities of them showed that TNW10 was superior to the commercial P25 TiO2 while TNW20 was as good as P25. The membrane filtration verified that the two types of nanowires could be completely reclaimed. The membrane fouling caused by TNW10 and TNW20 was much less than that of P25 due to more porous cake and less pore plugging. No apparent decrease on their photocatalytic activity was observed in repeated reuse experiments. These one-dimensional TiO2 nanowires would provide a new route for the combination of photocatalytic oxidation and membrane filtration for water treatment.

    View details for DOI 10.1016/j.watres.2008.12.021

    View details for Web of Science ID 000264616300003

    View details for PubMedID 19157486

  • The role of foulant-foulant electrostatic interaction on limiting flux for RO and NF membranes during humic acid fouling-Theoretical basis, experimental evidence, and AFM interaction force measurement JOURNAL OF MEMBRANE SCIENCE Tang, C. Y., Kwon, Y., Leckie, J. O. 2009; 326 (2): 526-532
  • A Model of Exposure to Rotavirus from Non-Dietary Ingestion Iterated by Simulated Intermittent Contacts Risk Analysis Julian, T., Canales, R., Leckie, R., A., Boehm, J., O. 2009; 5 (29): 617-632
  • Effect of membrane chemistry and coating layer on physiochemical properties of thin film composite polyamide RO and NF membranes. II. Membrane physiochemical properties and their dependence on polyamide and coating layers Desalination Tang, C., Y., Kwon, Y., N., Leckie, J., O. 2009; 1-3 (242): 168 – 182
  • Fabrication and photocatalytic activity of porous TiO nanowire microspheres by surfactant-mediated spray drying process Materials Research Bulletin Zhang, X., Pan, J., H., Du, A., J., Ng, J., Sun, D., D., Leckie, J., O. 2009; 5 (44): 1070 - 1076
  • Effect of membrane chemistry and coating layer on physiochemical properties of thin film composite polyamide RO and NF membranes. I. FTIR and XPS characterization of polyamide and coating layer chemistry Desalination Tang, C., Y., Kwon, Y., N., Leckie, J., O. 2009; 1-3 (242): 149 – 167
  • Combination of one-dimensional TiO nanowire photocatalytic oxidation with microfiltration for water treatment Water Research Zhang, X., Pan, J., H., Du, A., J., Fu, W., Sun, D., D., Leckie, J., O. 2009; 5 (43): 1179 – 1186
  • The fraction of total hand surface area involved in young children's outdoor hand-to-object contacts ENVIRONMENTAL RESEARCH Auyeung, W., Canales, R. A., Leckie, J. O. 2008; 108 (3): 294-299

    Abstract

    Information on the fraction of total hand surface area touching a contaminated object is necessary in accurately estimating contaminant (e.g., pesticides, pathogens) loadings onto the hands during hand-to-object contacts. While several existing physical-stochastic human exposure models require such surface area data to estimate dermal and non-dietary ingestion exposure, there are very limited data sets. This paper provides statistical distributions of fractional surface areas (FSAs) for children's outdoor hand contacts. These distributions were constructed by combining information collected from two distinct studies exploring children's activity patterns and quantifying hand contact surface area. Results show that for outdoor contacts with "All Objects", a range of 0.13-0.27 captured median FSAs, while a range of 0.12-0.24 captured time-weighted FSAs. Overall, an FSA of 0.31 captured 80-100% of FSAs involved in each child's outdoor hand contacts, depending upon the object of interest. These values are much lower than the often conservative assumptions of up to 1 (i.e., the entire hand) that researchers currently make regarding FSAs involved in indoor and outdoor contacts [USEPA, 1997. Standard operating procedures (SOPs) for residential exposure assessments. Contract no. 68-W6-0030. http://www.epa.gov/pesticides/trac/science/trac6a05.pdf].

    View details for DOI 10.1016/j.envres.2008.07.010

    View details for Web of Science ID 000260660000004

    View details for PubMedID 18760778

  • Grafted multifunctional titanium dioxide nanotube membrane: Separation and photodegradation of aquatic pollutant APPLIED CATALYSIS B-ENVIRONMENTAL Zhang, X., Du, A. J., Lee, P., Sun, D. D., Leckie, J. O. 2008; 84 (1-2): 262-267
  • Quantified activity pattern data from 6 to 27-month-old farmworker children for use in exposure assessment ENVIRONMENTAL RESEARCH Beamer, P., Key, M. E., Ferguson, A. C., Canales, R. A., Auyeung, W., Leckie, J. O. 2008; 108 (2): 239-246

    Abstract

    This study was conducted to describe exposure prone behaviors of infants and toddlers in the farmworker community. Analysis of hand and mouth contact frequencies and durations aids understanding of how children interact with their environment and are exposed via contact with surfaces. All 23 participating children (8 female infants, 5 male infants, 5 female toddlers and 5 male toddlers) lived with at least one farmworker. Children were videotaped at home for 2-6 h. Video footage was translated into micro-level activity time series (MLATS) for both hands and the mouth. MLATS were processed to calculate hourly duration in microenvironments, contact frequency, hourly contact duration and median contact duration. The median hourly duration spent indoors was 53 min/h. The median hand-to-mouth frequency was 15.2 events/h and the median object-to-mouth frequency was 27.2 events/h. The hourly mouthing duration was 1.2 and 2.2 min/h with the hands and objects, respectively. The median mouthing duration with hands and objects was 2 s. The median contact frequency for both hands combined was 689.4 events/h with an hourly contact duration of 100.5 min/h and a median contact duration of 3s. Infants had higher mouthing frequencies with non-dietary objects while toddlers had higher mouthing frequencies with objects associated with pica (i.e., paper). Boys had higher contact frequencies while girls had longer contact durations. These sub-group differences indicate factors such as age and gender should be accounted for when conducting exposure assessments. Contact frequencies in this study are higher than current US EPA recommendations, questioning their protective value for infants and toddlers.

    View details for DOI 10.1016/j.envres.2008.07.007

    View details for Web of Science ID 000260132400015

    View details for PubMedID 18723168

  • Self-etching reconstruction of hierarchically mesoporous F-TiO2 hollow microspherical photocatalyst for concurrent membrane water Purifications JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Pan, J. H., Zhang, X., Du, A. J., Sun, D. D., Leckie, J. O. 2008; 130 (34): 11256-?

    Abstract

    We report a large-scale self-etching approach for the synthesis of monodispersed mesoporous F-TiO2 hollow microspheres. The self-etching derived from HF was elucidated by the morphology, chemical composition, and crystal size evolutions from solid to hollow microspheres with the increase in the concentration of H2SO4. The resulting TiO2 hollow microspheres exhibited ease for the concurrent membrane filtration and photocatalysis, providing high potential for engineering application in advanced water treatment, for not only increasing water production but also improving water quality.

    View details for DOI 10.1021/ja803582m

    View details for Web of Science ID 000258660600007

    View details for PubMedID 18680296

  • Synthesis of bimodal porous structured TiO2 microsphere with high photocatalytic activity for water treatment COLLOIDS AND SURFACES A-PHYSICOCHEMICAL AND ENGINEERING ASPECTS Lee, P. F., Zhang, X., Sun, D. D., Du, J., Leckie, J. O. 2008; 324 (1-3): 202-207
  • Change of chemical composition and hydrogen bonding behavior due to chlorination of crosslinked polyamide membranes JOURNAL OF APPLIED POLYMER SCIENCE Kwon, Y., Tang, C. Y., Leckie, J. O. 2008; 108 (4): 2061-2066

    View details for DOI 10.1002/app.25657

    View details for Web of Science ID 000254672800001

  • Palladium-indium catalyzed reduction of N-nitrosodimethylamine: Indium as a promoter metal ENVIRONMENTAL SCIENCE & TECHNOLOGY Davie, M. G., Shih, K., Pacheco, F. A., Leckie, J. O., Reinhard, M. 2008; 42 (8): 3040-3046

    Abstract

    An emerging technology for the removal of N-nitrosodimethylamine (NDMA) from drinking and groundwater is reductive destruction using noble metal catalysts and hydrogen gas as a reducing agent. Bimetallic palladium-indium (Pd-In) supported on alumina combines the ability of Into activate NDMA with the hydrogen activating properties of Pd. This study examined the effect of In addition to a commercial 5% Pd by weight on gamma-Al2O3 catalyst on the efficacy of NDMA reduction. The pseudo-first-order rate constant increased proportionately to In loading from 0.057 h(-1) for 0% In to a maximum of 0.25 h(-1) for 1% In and then decreased with additional in loading. Data suggest that hydrogen activation occurred only on Pd surfaces and In activated NDMA 20 times more effectively than Pd on a mass basis. The rate-limiting factor was NDMA activation for In loadings below 1%. The decrease at higher loadings is interpreted as In blocking pore spaces and limiting access to Pd sites, suggesting monatomic hydrogen limitation. The only products detected were dimethylamine and ammonium with carbon and nitrogen balances in excess of 92%, consistent with a mechanism involving reductive N-N bond cleavage. Results from this study serve as a basis for optimizing bimetallic catalysts for treating NDMA contaminated waters.

    View details for DOI 10.1021/es7023115

    View details for Web of Science ID 000254890400059

    View details for PubMedID 18497163

  • TiO2 nanowire membrane for concurrent filtration and photocatalytic oxidation of humic acid in water JOURNAL OF MEMBRANE SCIENCE Zhang, X., Du, A. J., Lee, P., Sun, D. D., Leckie, J. O. 2008; 313 (1-2): 44-51
  • TiO nanowire membrane for concurrent filtration and photocatalytic oxidation of humic acid in water Journal of Membrane Science Zhang, X., Du, A., J., Lee, P., Sun, D., D., Leckie, J., O. 2008; 1-2 (313): 44 – 51
  • Aggregating TiO (B) nanowires to porous basketry-like microspheres and their photocatalytic properties Chemistry Letters Zhang, X., Pan, J., H., Du, A., J., Lee, P., F., Sun, D., D., Leckie, J., O. 2008; 4 (37): 424 – 425
  • Synthesis of bimodal porous structured TiO microsphere with high photocatalytic activity for water treatment Colloids and Surfaces A: Physicochemical and Engineering Aspects Lee, P., F., Zhang, X., Sun, D., D., Du, J., Leckie, J., O. 2008; 1-3 (324): 202 - 207
  • Self-etching reconstruction of hierarchically mesoporous F-TiO hollow microsphericalphotocatalyst for concurrent membrane water purifications Journal of the American Chemical Society Pan, J., H., Zhang, X., Du, A., J., Sun, D., D., Leckie, J., O. 2008; 34 (130): 11256 – 11257
  • Biofouling development and rejection enhancement in long SRT MF membrane bioreactor PROCESS BIOCHEMISTRY Khor, S. L., Sun, D. D., Liu, Y., Leckie, J. O. 2007; 42 (12): 1641-1648
  • Application of a stochastic model to estimate children's short-term residential exposure to lead STOCHASTIC ENVIRONMENTAL RESEARCH AND RISK ASSESSMENT Canales, R. A., Leckie, J. O. 2007; 21 (6): 737-745
  • The influence of cobalt doping on photocatalytic nano-titania: Crystal chemistry and amorphicity JOURNAL OF SOLID STATE CHEMISTRY Lim, S. H., Ferraris, C., Schreyer, M., Shih, K., Leckie, J. O., White, T. J. 2007; 180 (10): 2905-2915
  • Photocatalytic oxidation of pharmaceutical compounds: Kinetics and pathways for ibuprofen, clofibric acid, diclofenac and naproxen JOURNAL OF ADVANCED OXIDATION TECHNOLOGIES Thanasawasdi, H., Leckie, J., Mill, T. 2007; 10 (2): 342-348
  • Membrane independent limiting flux for RO and NF membranes fouled by humic acid ENVIRONMENTAL SCIENCE & TECHNOLOGY Tang, C. Y., Leckie, J. O. 2007; 41 (13): 4767-4773

    Abstract

    The flux decline of reverse osmosis and nanofiltration membranes was investigated under constant pressure conditions during humic acid fouling tests. For a given membrane type under a given feedwater composition, increasing pressure resulted in increased flux reduction and foulant accumulation. A limiting flux seems to exist beyond which the membrane flux cannot be sustained. Membranes with initial fluxes greater than the limiting flux experienced severe fouling and their pseudo stable fluxes approached the limiting flux. Flux reduction was much milder when the initial flux was lower than the limiting flux. Furthermore, the limiting flux seems to be independent of membrane properties, probably due to the dominance of foulant--deposited-foulant interaction upon complete foulant coverage over membrane surfaces. On the other hand, strong dependence of the limiting flux on the feedwater composition was observed. The limiting flux was reduced at higher proton, calcium, and/or background electrolytes concentrations, likely due to reduced electrostatic repulsion under these conditions.

    View details for DOI 10.1021/es063105w

    View details for Web of Science ID 000247782500051

    View details for PubMedID 17695927

  • Impact of prolonged sludge retention time on the performance of a submerged membrane bioreactor DESALINATION Sun, D. D., Khor, S. L., Hay, C. T., Leckie, J. O. 2007; 208 (1-3): 101-112
  • An efficient bicomponent TiO2/SnO2 nanofiber photocatalyst fabricated by electrospinning with a side-by-side dual spinneret method NANO LETTERS Liu, Z., Sun, D. D., Guo, P., Leckie, J. O. 2007; 7 (4): 1081-1085

    Abstract

    In this communication, we demonstrate that the electrospinning process with a side-by-side dual spinneret can be a simple approach for fabricating bicomponent TiO2/SnO2 nanofibers with controllable heterojunctions. Specifically, both of the TiO2 and SnO2 components in the nanofibers are fully exposed to the surface. This morphology fully utilized the photogenerated holes and electrons during the photocatalytic process, thus leading to a high photocatalytic activity. We believe that this versatile approach can be extended to fabricate other novel high-efficiency bicomponent photocatalysts.

    View details for DOI 10.1021/nl061898e

    View details for Web of Science ID 000245600500043

    View details for PubMedID 17425281

  • Effect of flux (transmembrane pressure) and membrane properties on fouling and rejection of reverse osmosis and nanofiltration membranes treating perfluorooctane sulfonate containing wastewater ENVIRONMENTAL SCIENCE & TECHNOLOGY Tang, C. Y., Fu, Q. S., Criddle, C. S., Leckie, J. O. 2007; 41 (6): 2008-2014

    Abstract

    Perfluorooctane sulfonate (PFOS) is an emergent contaminant of substantial environmental concerns. In this study, reverse osmosis (RO) and nanofiltration (NF) membranes were used to remove this toxic and persistent compound from PFOS-containing wastewater. Five RO membranes and three NF membranes were tested at a feed concentration of 10 ppm PFOS over 4 days, and the PFOS rejection and permeate flux performances were systematically investigated. PFOS rejection was well correlated to sodium chloride rejection. The rejection efficiencies for the RO membranes were > 99%, and those for the NF membranes ranged from 90-99%. Improvement in PFOS rejection, together with mild flux reduction (< 16%), was observed at longer filtration time. Such shifts in rejection and flux performance were probably due to the increased PFOS accumulation at longer duration, as shown by X-ray photoelectron spectroscopy and liquid chromatograph and tandem mass spectrometry results. A fraction of PFOS molecules might be entrapped in the polyamide layer of the composite membranes, which hindered the further passage of both water and other PFOS molecules. In a similar fashion, PFOS rejection and fouling were enhanced for greater initial flux and/or applied pressure, where PFOS accumulation was promoted probably due to increased hydrodynamic permeate drag. Flux reduction was also shown to correlate to membrane roughness, with the rougher membranes tend to experience more flux reduction than the smoother ones.

    View details for DOI 10.1021/es062052f

    View details for Web of Science ID 000244855100039

    View details for PubMedID 17410798

  • Fouling of reverse osmosis and nanofiltration membranes by humic acid - Effects of solution composition and hydrodynamic conditions JOURNAL OF MEMBRANE SCIENCE Tang, C. Y., Kwon, Y., Leckie, J. O. 2007; 290 (1-2): 86-94
  • Characterization of humic acid fouled reverse osmosis and nanofiltration membranes by transmission electron microscopy and streaming potential measurements ENVIRONMENTAL SCIENCE & TECHNOLOGY Tang, C. Y., Kwon, Y., Leckie, J. O. 2007; 41 (3): 942-949

    Abstract

    Reverse osmosis and nanofiltration membranes fouled by humic acid were systematically characterized by transmission electron microscopy. All fouled membranes, except those with very low initial flux, were completely covered by a layer of humic acid whose thickness and density were greatly affected by the feedwater composition ([H+] and [Ca2+]) and initial flux. A low-density humic layer (about 0.1 g of purified Aldrich humic acid (PAHA)/cm3) was formed at low initial flux (2 m/day or less) at pH 7 without calcium. It was several times denser at a higher initial flux, pH 4.5, or 1 mM Ca2+. Corresponding to the denser foulant layers under these conditions, PAHA accumulation was greatly increased. The denser foulant layers together with the greater PAHA accumulations were responsible for the severe flux reductions. Both virgin and fouled membranes were characterized by streaming potential measurements. While considerable differences existed for virgin membranes, humic acid fouled membranes exhibited identical surface charge properties. The zeta potential of the fouled membranes was controlled by the humic acid layer due to its complete coverage of the membrane surfaces.

    View details for DOI 10.1021/es061322r

    View details for Web of Science ID 000244002800051

    View details for PubMedID 17328207

  • Probing the nano- and micro-scales of reverse osmosis membranes - A comprehensive characterization of physiochemical properties of uncoated and coated membranes by XPS, TEM, ATR-FTIR, and streaming potential measurements JOURNAL OF MEMBRANE SCIENCE Tang, C. Y., Kwon, Y., Leckie, J. O. 2007; 287 (1): 146-156
  • One-step fabrication and high photocatalytic activity of porous TiO2 hollow aggregates by using a low-temperature hydrothermal method without templates CHEMISTRY-A EUROPEAN JOURNAL Liu, Z., Sun, D. D., Guo, P., Leckie, J. O. 2007; 13 (6): 1851-1855

    Abstract

    Porous TiO2 hollow aggregates have been synthesized on a large scale by means of a simple hydrothermal method without using any templates. The as-prepared products were characterized by means of field emission scanning electron microscopy, XRD, TEM, nitrogen adsorption, UV/Vis diffuse reflectance spectroscopy, and FTIR spectroscopy. The photocatalytic activity of the aggregates was demonstrated through the photocatalytic degradation of Rhodamine B. Structural characterization indicates that the porous TiO2 aggregates are 500-800 nm in diameter and display mesoporous structure. The average pore sizes and BET surface areas of the aggregates are 12 nm and 168 m2 g-1, respectively. Optical adsorption investigations show that the aggregates possess an optical band-gap energy of 3.36 eV. The as-prepared products were substantially more effective photocatalysts than the commercially available photocatalyst P25. The dye degradation rate of the porous TiO2 hollow aggregates is more than twice that of P25. The high photoactivities of the aggregates can be attributed to the combined effects of several factors, namely, large surface areas, the existence of mesopores, and the high band-gap energy. In addition, the as-prepared products can be easily recycled.

    View details for DOI 10.1002/chem.200601092

    View details for Web of Science ID 000244577400021

    View details for PubMedID 17133639

  • Nickel aluminate spinel formation during sintering of simulated Ni-laden sludge and kaolinite JOURNAL OF THE EUROPEAN CERAMIC SOCIETY Shih, K., Leckie, J. O. 2007; 27 (1): 91-99
  • An efficient bicomponentTiO/SnOnanofiberphotocatalyst fabricated by electrospinning with a side-by-side dual spinneret method Nano Letters Liu, Z., Sun, D., D., Guo, P., Leckie, J., O. 2007; 4 (7): 1081 – 1085
  • Fouling of reverse osmosis and nanofiltration membranes by humic acid-Effects of solution composition and hydrodynamic conditions Journal of Membrane Science Tang, C., Y., Kwon, Y., N., Leckie, J., O. 2007; 1-2 (290): 86 – 94
  • Probing the nano- and micro-scales of reverse osmosis membranes-A comprehensive characterization of physiochemical properties of uncoated and coated membranes by XPS, TEM, ATR-FTIR, and streaming potential measurements Journal of Membrane Science Tang, C., Y., Kwon, Y., N., Leckie, J., O. 2007; 1 (287): 146 – 156
  • Effect of flux (transmembrane pressure) and membrane properties on fouling and rejection of reverse osmosis and nanofiltration membranes treating perfluorooctanesulfonate containing wastewater Environmental Science & Technology Tang, C., Y., Fu, Q., S., Criddle, C., S., Leckie, J., O. 2007; 6 (41): 2008 - 2014
  • The Influence of Cobalt-doping on PhotocatalyticNano-titania: Crystal Chemistry and Amorphicity Journal of Solid State Chemistry Lim, S., H., Ferraris, C., Schreyer, M., Shih, K., Leckie, J., O., White, T., J. 2007; 10 (180): 2905-2915
  • Change of membrane performance due to chlorination of crosslinked polyamide membranes JOURNAL OF APPLIED POLYMER SCIENCE Kwon, Y., Tang, C. Y., Leckie, J. O. 2006; 102 (6): 5895-5902

    View details for DOI 10.1002/app.25071

    View details for Web of Science ID 000241593800101

  • Use of reverse osmosis membranes to remove perfluorooctane sulfonate (PFOS) from semiconductor wastewater ENVIRONMENTAL SCIENCE & TECHNOLOGY Tang, C. Y., Fu, Q. S., Robertson, A. P., Criddle, C. S., Leckie, J. O. 2006; 40 (23): 7343-7349

    Abstract

    Perfluorooctane sulfonate (PFOS) and related substances are persistent, bioaccumulative, and toxic, and thus of substantial environmental concern. PFOS is an essential photolithographic chemical in the semiconductor industry with no substitutes yet identified. The industry seeks effective treatment technologies. The feasibility of using reverse osmosis (RO) membranes for treating semiconductor wastewater containing PFOS has been investigated. Commercial RO membranes were characterized in terms of permeability, salt rejection, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and membrane surface zeta potential (streaming potential measurements). Filtration tests were performed to determine the membrane flux and PFOS rejection. Over a wide range of feed concentrations (0.5 - 1500 ppm), the RO membranes generally rejected 99% or more of the PFOS. Rejection was better for tighter membranes, but was not affected by membrane zeta potential. Flux decreased with increasing PFOS concentration. While the flux reduction was severe for a loose RO membrane probably due to its higher initial flux, very stable flux was maintained for tighter membranes. At a very high feed concentration (about 500 ppm), all the membranes exhibited an identical stable flux. Isopropyl alcohol, present in some semiconductor wastewaters, had a detrimental effect on membrane flux. Where present it needs to be removed from the wastewater prior to using RO membranes.

    View details for DOI 10.1021/es060831q

    View details for Web of Science ID 000242367100040

    View details for PubMedID 17180987

  • Hypochlorite degradation of crosslinked polyamide membranes I. Changes in chemical/morphological properties JOURNAL OF MEMBRANE SCIENCE Kwon, Y., Leckie, J. O. 2006; 283 (1-2): 21-26
  • Hypochlorite degradation of crosslinked polyamide membranes - II. Changes in hydrogen bonding behavior and performance JOURNAL OF MEMBRANE SCIENCE Kwon, Y., Leckie, J. O. 2006; 282 (1-2): 456-464
  • Nickel stabilization efficiency of aluminate and ferrite spinels and their leaching behavior ENVIRONMENTAL SCIENCE & TECHNOLOGY Shih, K., White, T., Leckie, J. O. 2006; 40 (17): 5520-5526

    Abstract

    Stabilization efficiencies of spinel-based construction ceramics incorporating simulated nickel-laden waste sludge were evaluated and the leaching behavior of products investigated. To simulate the process of immobilization, nickel oxide was mixed alternatively with gamma-alumina, kaolinite, and hematite. These tailoring precursors are commonly used to prepare construction ceramics in the building industry. After sintering from 600 to 1480 degrees C at 3 h, the nickel aluminate spinel (NiAl204) and the nickel ferrite spinel (NiFe204) crystallized with the ferrite spinel formation commencing about 200-300 degrees C lower than for the aluminate spinel. All the precursors showed high nickel incorporation efficiencies when sintered at temperatures greater than 1250 degrees C. Prolonged leach tests (up to 26 days) of product phases were carried out using a pH 2.9 acetic acid solution, and the spinel products were invariably superior to nickel oxide for immobilization over longer leaching periods. The leaching behavior of NiAl2O4 was consistent with congruent dissolution without significant reprecipitation, but for NiFe2O4, ferric hydroxide precipitation was evident. The major leaching reaction of sintered kaolinite-based products was the dissolution of cristobalite rather than NiAl2O4. This study demonstrated the feasibility of transforming nickel-laden sludge into spinel phases with the use of readily available and inexpensive ceramic raw materials, and the successful reduction of metal mobility under acidic environments.

    View details for DOI 10.1021/es0601033

    View details for Web of Science ID 000240130200058

    View details for PubMedID 16999134

  • Young children's hand contact activities: An observational study via videotaping in primarily outdoor residential settings JOURNAL OF EXPOSURE SCIENCE AND ENVIRONMENTAL EPIDEMIOLOGY Auyeung, W., Canales, R. A., Beamer, P., Ferguson, A. C., Leckie, J. O. 2006; 16 (5): 434-446

    Abstract

    Microlevel activity time series (MLATS) data were gathered on hand contact activities of 38 children (1-6 years old) by videotaping in primarily outdoor residential environments. The videotape recordings were then translated into text files using a specialized software called VirtualTimingDevicetrade mark. Contact frequency (contacts/h), duration per contact (s/contact), and hourly contact duration (min/h) were summarized for outdoor hand contacts with 15 distinct object/surface categories ("Animal", "Body", "Clothes/Towels", "Fabric", "Floor", "Food", "Footwear", "Metal", "Non-dietary Water", "Paper/Wrapper", "Plastic", "Rock/Brick", "Toys", "Vegetation/Grass", and "Wood") and two aggregate object/surface categories ("Non-dietary objects/surfaces" and "Total objects/surfaces"). For outdoor both hand contacts with "Total objects/surfaces", contact frequencies ranged from 229.9 to 1517.7 contacts/h, median durations/contact ranged from < 1 to 5 s, and hourly contact durations ranged from 42.6 to 102.2 m/h. The data were analyzed for significant differences in hand contact activities as a function of (1) age, (2) location, (3) gender, and (4) hand. Significant differences (P < or = 0.05) were found for all four factors analyzed. Hourly contact durations with "Non-dietary objects/surfaces" and "Total objects/surfaces" increased with age (P = 0.01, rs = 0.42 and P = 0.005, rs = 0.46, respectively), while contact frequencies and hourly contact durations with "Wood" decreased with age (P = 0.02, rs = -0.38 and P = 0.05, rs = -0.32, respectively). Location was found to affect contact frequencies and hourly contact durations with certain objects/surfaces. For example, contact frequencies and hourly contact durations with "Fabric" were higher indoors (P = 0.02 for both), while contact frequencies and hourly contact durations with "Vegetation/Grass" were higher outdoors (P = 0.02 and P = 0.04, respectively). Girls had longer hourly contact durations with "Footwear" (P = 0.02), "Non-dietary objects/surfaces" (P = 0.03), and "Total objects/surfaces" (P = 0.01) than boys. The right hand had longer hourly contact durations with objects that are often manipulated with the hand (e.g., "Toys" (P = 0.0002)), while the left hand had longer hourly contact durations with passively touched objects/surfaces (e.g., "Clothes/Towels" (P = 0.003) and "Floor" (P = 0.04)).

    View details for DOI 10.1038/sj.jes.7500480

    View details for Web of Science ID 000241165900006

    View details for PubMedID 16552427

  • Spinel formation for stabilizing simulated nickel-laden sludge with aluminum-rich ceramic precursors ENVIRONMENTAL SCIENCE & TECHNOLOGY Shih, K., White, T., Leckie, J. O. 2006; 40 (16): 5077-5083

    Abstract

    The feasibility of stabilizing nickel-laden sludge from commonly available Al-rich ceramic precursors was investigated and accomplished with high nickel incorporation efficiency. To simulate the process, nickel oxide was mixed alternatively with gamma-alumina, corundum, kaolinite, and mullite and was sintered from 800 to 1480 degrees C. The nickel aluminate spinel (NiAl2O4) was confirmed as the stabilization phase for nickel and crystallized with efficiencies greater than 90% for all precursors above 1250 degrees C and 3-h sintering. The nickel-incorporation reaction pathways with these precursors were identified, and the microstructure and spinel yield were investigated as a function of sintering temperature with fixed sintering time. This study has demonstrated a promising process for forming nickel spinel to stabilize nickel-laden sludge from a wide range of inexpensive ceramic precursors, which may provide an avenue for economically blending waste metal sludges via the building industry processes to reduce the environmental hazards of toxic metals. The correlation of product textures and nickel incorporation efficiencies through selection of different precursors also provides the option of tailoring property-specific products.

    View details for DOI 10.1021/es052324z

    View details for Web of Science ID 000239684900045

    View details for PubMedID 16955910

  • Video methods in the quantification of children's exposures JOURNAL OF EXPOSURE SCIENCE AND ENVIRONMENTAL EPIDEMIOLOGY Ferguson, A. C., Canales, R. A., Beamer, P., Auyeung, W., Key, M., Munninghoff, A., Lee, K. T., Robertson, A., Leckie, J. O. 2006; 16 (3): 287-298

    Abstract

    In 1994, Stanford University's Exposure Research Group (ERG) conducted its first pilot study to collect micro-level activity time series (MLATS) data for young children. The pilot study involved videotaping four children of farm workers in the Salinas Valley of California and converting their videotaped activities to valuable text files of contact behavior using video-translation techniques. These MLATS are especially useful for describing intermittent dermal (i.e., second-by-second account of surfaces and objects contacted) and non-dietary ingestion (second-by-second account of objects or hands placed in the mouth) contact behavior. Second-by-second records of children contact behavior are amenable to quantitative and statistical analysis and allow for more accurate model estimates of human exposure and dose to environmental contaminants. Activity patterns data for modeling inhalation exposure (i.e., accounts of microenvironments visited) can also be extracted from the MLATS data. Since the pilot study, ERG has collected an immense MLATS data set for 92 children using more developed and refined videotaping and video-translation methodologies. This paper describes all aspects required for the collection of MLATS including: subject recruitment techniques, videotaping and video-translation processes, and potential data analysis. This paper also describes the quality assurance steps employed for these new MLATS projects, including: training, data management, and the application of interobserver and intraobserver agreement during video translation. The discussion of these issues and ERG's experiences in dealing with them can assist other groups in the conduct of research that employs these more quantitative techniques.

    View details for DOI 10.1038/sj.jea.7500459

    View details for Web of Science ID 000237513600008

    View details for PubMedID 16249797

  • Hypochlorite Degradation of CrosslinkedPolyamide Membranes: II. Changes in Hydrogen Bonding Behavior and Performance Journal of Membrane Science Kwon, Y., N., Leckie, J., O. 2006; 282: 456-464
  • Hypochlorite Degradation of CrosslinkedPolyamide Membranes: I. Changes in Chemical/Morphological Properties Journal of Membrane Science Kwon, Y., N., Leckie, J., O. 2006; 282: 21-26
  • An Efficient Bicomponent TiO2/SnO2NanofiberPhotocatalyst Fabricated by Electrospinning with a Side-by-Side Dual Spinneret Method Nano Letters Liu, Z., Y., Sun, D., D., Guo, P., Leckie, J., O. 2006; 4 (7): 1081-1085
  • Managing E-Government IT infrastructure: An approach combining autonomic computing and awareness based collaboration FOURTH INTERNATIONAL CONFERENCE ON COMPUTER AND INFORMATION TECHNOLOGY, PROCEEDINGS Wang, J., Cao, J., Leckie, J. O., Zhang, S. S. 2004: 998-1003
  • Variability in goethite surface site density: evidence from proton and carbonate sorption JOURNAL OF COLLOID AND INTERFACE SCIENCE Villalobos, M., Trotz, M. A., Leckie, J. O. 2003; 268 (2): 273-287

    Abstract

    Goethite is a representative iron oxide in natural environments due to its abundance and thermodynamic stability and may be responsible for many surface-mediated processes, including ion retention and mobility in aqueous settings. A large variability in morphologies and specific surface areas of goethite crystals exists but little work has been done to compare surface reactivity between them. The present work offers experimental evidence for the existence of an inverse relationship between sorption capacity for protons and carbonate ions and specific surface area of goethite for three synthetic goethite preparations spanning surface area differences by a factor of 2. An explanation for this was found by assuming a variable reactive site density between preparations in direct relationship to their sorption capacity based on congruency of carbonate sorption computed on a per-site basis. Previous evidence of maximum sorption capacities supports this explanation, and site density ratios between the goethites studied here were obtained. Triple layer surface complexation modeling was successful in describing adsorption data for all goethite preparations using equal stoichiometries. A new formulation of standard state for activities of surface species based on a 1.0 mole fraction of sites on the solid allowed transformation of the conventional molar concentration-based affinity constants to values based on site occupancy. In this fashion, by applying the appropriate site density ratios, a single set of affinity constant values was found that described accurately the adsorption data for all preparations.

    View details for DOI 10.1016/j.jcis.2003.07.044

    View details for Web of Science ID 000187019200001

    View details for PubMedID 14643228

  • Association of uranyl with the cell wall of Pseudomonas fluorescens inhibits metabolism GEOCHIMICA ET COSMOCHIMICA ACTA Bencheikh-Latmani, R., Leckie, J. O. 2003; 67 (21): 4057-4066
  • Fate of uranyl in a quaternary system composed of uranyl, citrate, goethite, and Pseudomonas fluorescens ENVIRONMENTAL SCIENCE & TECHNOLOGY Bencheikh-Latmani, R., Leckie, J. O., Bargar, J. R. 2003; 37 (16): 3555-3559

    Abstract

    This study investigated the partitioning of uranyl within a quaternary system made up of uranyl, citrate, goethite, and the bacterium Pseudomonas fluorescens. In the absence of cells, uranyl was sorbed to goethite as a complex involving surface groups and/or citrate. Measurements of the evolution of CO2 indicated that the addition of bacterial cells lead to the gradual biodegradation of citrate. Throughout the biodegradation process, uranyl remained sorbed to the insoluble fraction comprised of goethite and cells. EXAFS (Extended X-ray Absorption Fine Structure) measurements showed that bacterial cells outcompeted goethite for uranyl under the experimental conditions and caused the repartitioning of uranyl from goethite to cell matter, independently from citrate degradation. Citrate degradation caused further release of uranyl from goethite surfaces, followed by subsequent association of uranyl with cells. At long equilibration times (3 months), cell lysis and phosphate release resulted in the precipitation of an autunite-like phase. This work suggests that bacterial degradation of uranyl-complexing ligands in contaminated subsurface media containing iron oxides should not necessarily lead to an increase in the mobility of uranyl.

    View details for DOI 10.1021/es0210401

    View details for Web of Science ID 000184803700012

    View details for PubMedID 12953865

  • Surface complexation modeling of carbonate effects on the adsorption of Cr(VI), Pb(II), and U(VI) on goethite ENVIRONMENTAL SCIENCE & TECHNOLOGY Villalobos, M., Trotz, M. A., Leckie, J. O. 2001; 35 (19): 3849-3856

    Abstract

    Dissolved carbonate species are known to affect the sorption behavior of trace species. The macroscopic description of these interactions with a thermodynamic approach has been limited by the lack of data on the binary interaction between carbonate and relevant mineral surfaces. This work follows from two detailed studies of carbonate adsorption on goethite (4, 13). It shows that independent triple-layer surface complexation modeling (TLM) of carbonate adsorption allows successful descriptions of carbonate-trace element ternary sorption on this oxide, using relatively simple and optimal stoichiometries. Carbonate adsorption was considerably enhanced in the presence of Pb(II), despite an invariant total Pb(II) sorption to equilibration with up to 1% C02(g). Both the Pb(II)-carbonate system behavior and the anion-like pH adsorption behavior of U(VI) in the presence of C02 were successfully modeled using binary and ternary metal-bound surface complexes. The significant reduction of Cr(VI) adsorption edges to lower pH values in the presence of C02 was accurately simulated and explained via site competition and surface electrostatic repulsion effects on the predicted inner- and outer-sphere Cr(VI) surface complexes formed. The results of this research are highly relevant to modeling of metal transport field data and of potential soil remediation schemes using carbonate.

    View details for DOI 10.1021/es001748k

    View details for Web of Science ID 000171352500018

    View details for PubMedID 11642443

  • Surface complexation modeling and FTIR study of carbonate adsorption to goethite JOURNAL OF COLLOID AND INTERFACE SCIENCE Villalobos, M., Leckie, J. O. 2001; 235 (1): 15-32
  • Surface Complexation Modeling and FTIR Study of Carbonate Adsorption to Goethite. Journal of colloid and interface science Villalobos, M., Leckie, J. O. 2001; 235 (1): 15-32

    Abstract

    Experimental data for carbonate adsorption onto synthetic goethite, spanning 3 orders of magnitude in carbonate concentrations, were simulated using the triple-layer surface complexation model (TLM). A single set of TLM parameters successfully described the adsorption behavior versus pH over the concentration range obtained from closed and open CO(2) conditions. An optimization analysis was performed for all possible interfacial charge configurations using FITEQL3.2. The results yielded an optimum charge allocation of 0 and -1 in the 0- and beta-planes, respectively, which suggests a monodentate complex most probably in an inner-sphere configuration (SOCOO(-beta)). Fourier transform infrared (FTIR) spectroscopic measurements on open systems at atmospheric P(CO(2)) confirmed this result by showing a clear peak split (155 cm(-1)) of the nu(3) C-O asymmetric stretching frequency of surface-bound carbonate, consistent with that reported for monodentate Co(III)-carbonato inner-sphere solution complexes. An additional Na(+)-ternary complex (SOCOONa) was invoked in the TLM construct to improve simulations of the enhanced carbonate adsorption occurring at high ionic strength and high pH. The model was successful in predicting carbonate adsorption behavior under diffferent conditions than it was calibrated for. Projections for equilibration at higher P(CO(2))'s (1-10%) than those used in this work show the potential for carbonate sorption densities of up to 2.5-3 µmol/m(2). Copyright 2001 Academic Press.

    View details for PubMedID 11237439

  • Carbonate adsorption on goethite under closed and open CO2 conditions GEOCHIMICA ET COSMOCHIMICA ACTA Villalobos, M., Leckie, J. O. 2000; 64 (22): 3787-3802
  • Modeling particle transport and aggregation in a quiescent aqueous environment using the residence-time scheme WATER RESOURCES RESEARCH Perigault, J. G., Leckie, J. O., Kitanidis, P. K. 2000; 36 (8): 2249-2261
  • Development of a simulation system for a continuous flow, quiescent, aqueous environment WATER RESEARCH Ela, W. P., Leckie, J. O. 2000; 34 (5): 1734-1750
  • Comparative assessment of settlement models for municipal solid waste landfill applications WASTE MANAGEMENT & RESEARCH El-Fadel, M., Shazbak, S., Saliby, E., Leckie, J. 1999; 17 (5): 347-368
  • Acid/base, copper binding, and Cu2+/H+ exchange properties of a soil humic acid, an experimental and modeling study ENVIRONMENTAL SCIENCE & TECHNOLOGY Robertson, A. P., Leckie, J. O. 1999; 33 (5): 786-795
  • Neptunium(V) sorption on hematite (alpha-Fe2O3) in aqueous suspension: The effect of CO2 RADIOCHIMICA ACTA Kohler, M., Honeyman, B. D., Leckie, J. O. 1999; 85 (1-2): 33-48
  • Quantified mouthing activity data from a four-child pilot field study JOURNAL OF EXPOSURE ANALYSIS AND ENVIRONMENTAL EPIDEMIOLOGY Zartarian, V. G., Ferguson, A. C., Leckie, J. O. 1998; 8 (4): 543-553
  • Acid/base, copper binding, and Cu2+/H+ exchange properties of goethite, an experimental and modeling study ENVIRONMENTAL SCIENCE & TECHNOLOGY Robertson, A. P., Leckie, J. O. 1998; 32 (17): 2519-2530
  • Quantified dermal activity data from a four-child pilot field study (Reprinted from the Journal of Exposure and Environmental Epidemiology, vol 7, pg 543-552, 1997) JOURNAL OF CLEAN TECHNOLOGY ENVIRONMENTAL TOXICOLOGY AND OCCUPATIONAL MEDICINE Zartarian, V. G., Ferguson, A. C., Leckie, J. O. 1998; 7 (3): 259-268
  • Quantifying videotaped activity patterns: Video translation software and training methodologies (Reprinted from the Journal of Exposure Analysis and Environmental Epidemiology, vol 7, pg 535-542, 1997) JOURNAL OF CLEAN TECHNOLOGY ENVIRONMENTAL TOXICOLOGY AND OCCUPATIONAL MEDICINE Zartarian, V. G., Ferguson, A. C., Ong, C. G., Leckie, J. O. 1998; 7 (3): 251-258
  • Time-dependent adsorption in near coastal marine sediments: a two-step model ADVANCES IN WATER RESOURCES Hansen, A. M., Leckie, J. O. 1998; 21 (6): 523-531
  • Dermal exposure: The missing link ENVIRONMENTAL SCIENCE & TECHNOLOGY Zartarian, V. G., Leckie, J. O. 1998; 32 (5): 134A-137A
  • Quantifying videotaped activity patterns: Video translation software and training methodologies JOURNAL OF EXPOSURE ANALYSIS AND ENVIRONMENTAL EPIDEMIOLOGY Zartarian, V. G., Ferguson, A. C., Ong, C. G., Leckie, J. O. 1997; 7 (4): 535-542

    Abstract

    Questionnaires and diaries, the current methods of human activity data collection, do not accurately capture the detail necessary to quantify exposure incurred through the dermal and non-dietary ingestion routes. Stanford University's Environmental Engineering and Science Program has developed methodologies and software (VideoTraq) for training video translators, determining inter-observer reliability, and translating videotaped micro-activity patterns into computer text files. VideoTraq output files contain duration, in seconds, for each combination of location, activity, and object contacted corresponding to the sequential micro-activities of a videotaped subject's contact boundary (e.g., left hand, right hand, mouth). Such output allows for detailed analyses of micro-activity data, including contact frequency and duration. When coupled with environmental concentrations, these data will allow for more accurate exposure assessments, particularly for the dermal and non-dietary ingestion exposure routes.

    View details for Web of Science ID A1997XW85000008

    View details for PubMedID 9306236

  • Quantified dermal activity data from a four-child pilot field study JOURNAL OF EXPOSURE ANALYSIS AND ENVIRONMENTAL EPIDEMIOLOGY Zartarian, V. G., Ferguson, A. C., Leckie, J. O. 1997; 7 (4): 543-552

    Abstract

    Thirty-three hours of videotape collected in a 1993 pilot study were quantified, via a video translation software application, to obtain left and right hand activity data of four children of farmworkers. Reported here are the children's contact duration and frequency for each object in their environment, duration spent in each location and activity exertion level, and frequency distributions of object contact durations. The pilot study provided valuable information for evaluating and improving videotaping and videotape translation methodologies as a means of gathering activity information that can be used to refine dermal exposure estimates. Although a larger database of children's videotaped activities for different ages and populations is needed before generalizations can be made, the data presented here are the most detailed information to date for children's micro-level dermal activities.

    View details for Web of Science ID A1997XW85000009

    View details for PubMedID 9306237

  • Modeling leachate generation and transport in solid waste landfills ENVIRONMENTAL TECHNOLOGY Elfadel, M., Findikakis, A. N., Leckie, J. O. 1997; 18 (7): 669-686
  • Environmental impacts of solid waste landfilling JOURNAL OF ENVIRONMENTAL MANAGEMENT Elfadel, M., Findikakis, A. N., Leckie, J. O. 1997; 50 (1): 1-25
  • Cation binding predictions of surface complexation models: Effects of pH, ionic strength, cation loading, surface complex, and model fit JOURNAL OF COLLOID AND INTERFACE SCIENCE Robertson, A. P., Leckie, J. O. 1997; 188 (2): 444-472
  • Numerical modelling of generation and transport of gas and heat in sanitary landfills .3. Sensitivity analysis WASTE MANAGEMENT & RESEARCH Elfadel, M., Findikakis, A. N., Leckie, J. O. 1997; 15 (1): 87-102
  • Gas simulation models for solid waste landfills CRITICAL REVIEWS IN ENVIRONMENTAL SCIENCE AND TECHNOLOGY Elfadel, M., Findikakis, A. N., Leckie, J. O. 1997; 27 (3): 237-283
  • Numerical modelling of generation and transport of gas and heat in sanitary landfills .2. Model application WASTE MANAGEMENT & RESEARCH Elfadel, M., Findikakis, A. N., Leckie, J. O. 1996; 14 (6): 537-551
  • Numerical modelling of generation and transport of gas and heat in landfills .1. Model formulation WASTE MANAGEMENT & RESEARCH Elfadel, M., Findikakis, A. N., Leckie, J. O. 1996; 14 (5): 483-504
  • Temperature effects in modeling solid waste biodegradation ENVIRONMENTAL TECHNOLOGY Elfadel, M., Findikakis, A. N., Leckie, J. O. 1996; 17 (9): 915-935
  • Anion-exchange preparation of a U-232 radiotracer for alpha-particle liquid scintillation counting TALANTA Ong, C. G., Leckie, J. O. 1996; 43 (4): 601-605

    Abstract

    Daughter product ingrowths, which could act as analytical interferences, are removed from (232)U(VI) stock solutions prior to use as an alpha-particle emitting radiotracer in conjunction with detection by liquid scintillation counting. The preparative benchtop separation procedure employs elution with HCl through a BioRad AG1-X8 anion-exchange resin column, and fraction collection. The importance of the separation of the (232)U isotope from daughter products, characterized by high recovery, is illustrated by liquid scintillation energy spectra. Rapid ingrowth in the purified fraction also limits the period of time after purification in which the radiotracer is usable.

    View details for Web of Science ID A1996UT76200012

    View details for PubMedID 18966525

  • EFFECT OF PH, NACL, AND COCKTAIL SELECTION ON U-232 LIQUID SCINTILLATION SPECTRA ANALYTICAL CHEMISTRY Ong, C. G., Prasad, A., Leckie, J. O. 1995; 67 (21): 3893-3896
  • Migration and atmospheric emission of landfill gas HAZARDOUS WASTE & HAZARDOUS MATERIALS Elfadel, M., Findikakis, A. N., Leckie, J. O. 1995; 12 (4): 309-327
  • X-RAY-ABSORPTION SPECTROSCOPIC STUDIES OF CADMIUM AND SELENITE ADSORPTION ON ALUMINUM-OXIDES LANGMUIR Papelis, C., Brown, G. E., Parks, G. A., Leckie, J. O. 1995; 11 (6): 2041-2048
  • MODELING THE RATE OF CADMIUM AND SELENITE ADSORPTION ON MICROPOROUS AND MESOPOROUS TRANSITION ALUMINAS ENVIRONMENTAL SCIENCE & TECHNOLOGY Papelis, C., Roberts, P. V., Leckie, J. O. 1995; 29 (4): 1099-1108

    View details for Web of Science ID A1995QP70900042

    View details for PubMedID 22176419

  • KINETICS OF OXIDATION OF SELENITE TO SELENATE IN THE PRESENCE OF OXYGEN, TITANIA, AND LIGHT ENVIRONMENTAL SCIENCE & TECHNOLOGY GRUEBEL, K. A., Davis, J. A., Leckie, J. O. 1995; 29 (3): 586-594

    View details for Web of Science ID A1995QJ90800020

    View details for PubMedID 22200266

  • A PILOT-STUDY TO COLLECT MICRO-ACTIVITY DATA OF 2-YEAR-OLD TO 4-YEAR-OLD FARM-LABOR CHILDREN IN SALINAS VALLEY, CALIFORNIA JOURNAL OF EXPOSURE ANALYSIS AND ENVIRONMENTAL EPIDEMIOLOGY Zartarian, V. G., STREICKER, J., Rivera, A., CORNEJO, C. S., Molina, S., VALADEZ, O. F., Leckie, J. O. 1995; 5 (1): 21-34

    Abstract

    A pesticide exposure assessment pilot study was conducted in Salinas Valley, California during September, 1993. The pilot study had two main purposes: 1) to develop general methodologies for videotaping micro-activities of a population, and 2) to collect an initial database of activity patterns of two- to four-year-old farm labor children. Tools to accurately determine exposure and dose through all three pathways (dermal, ingestion, and inhalation) are needed to effectively assess and manage health risks posed by pesticides and other environmental pollutants. Eight to ten hours of videotape data were collected for each of four Mexican-American farm labor children. In addition, the researchers administered a day-after recall questionnaire to the caregivers of the children to test (for the study sample) the hypothesis that recall questionnaires are inadequate for collecting detailed information regarding dermal and hand-to-mouth exposures. The results of this study provide the first detailed set of videotape data on farm labor children, a population at high risk to pesticide exposures. In addition, this is the first project in the exposure assessment field to use direct observation videotaping for collecting micro-activity data in order to quantify dermal and ingestion exposure. The comparison of caregivers' recall of children's activities to actual videotapes from the pilot study supports the hypothesis that videotaping may greatly improve the accuracy of activity information used to compute dermal and ingestion exposures. However, as it was clear that the researchers' presence in some cases altered the activities of the subjects, further experiments need to be conducted to minimize interference of videotaping on exposure-related activities. This paper explains the selection of the study population, the methods used to implement the pilot study, and the lessons learned. While the discussion focuses on four case studies in the Mexican-American farm labor population, the data collection methods developed and the lessons learned can be applied to other populations.

    View details for Web of Science ID A1995RE20000002

    View details for PubMedID 7663147

  • INTERACTION BETWEEN AQUEOUS URANIUM(VI) AND SULFIDE MINERALS - SPECTROSCOPIC EVIDENCE FOR SORPTION AND REDUCTION GEOCHIMICA ET COSMOCHIMICA ACTA Wersin, P., Hochella, M. F., Persson, P., Redden, G., Leckie, J. O., Harris, D. W. 1994; 58 (13): 2829-2843
  • COMPLEXATION OF CARBONATE SPECIES AT THE GOETHITE SURFACE - IMPLICATIONS FOR ADSORPTION OF METAL-IONS IN NATURAL-WATERS GEOCHIMICA ET COSMOCHIMICA ACTA VANGEEN, A., Robertson, A. P., Leckie, J. O. 1994; 58 (9): 2073-2086
  • SOLUBILITY-PRODUCT CONSTANT AND THERMODYNAMIC PROPERTIES FOR SYNTHETIC OTAVITE, CDCO3(S), AND AQUEOUS ASSOCIATION CONSTANTS FOR THE CD(II)-CO2-H2O SYSTEM GEOCHIMICA ET COSMOCHIMICA ACTA Stipp, S. L., Parks, G. A., Nordstrom, D. K., Leckie, J. O. 1993; 57 (12): 2699-2713
  • KINETIC-STUDIES OF ADSORPTION-DESORPTION OF CD AND ZN ONTO AL2O3/SOLUTION INTERFACES WATER SCIENCE AND TECHNOLOGY LO, K. S., Leckie, J. O. 1993; 28 (7): 39-45
  • CD2+ UPTAKE BY CALCITE, SOLID-STATE DIFFUSION, AND THE FORMATION OF SOLID-SOLUTION - INTERFACE PROCESSES OBSERVED WITH NEAR-SURFACE SENSITIVE TECHNIQUES (XPS, LEED, AND AES) GEOCHIMICA ET COSMOCHIMICA ACTA STIPP, S. L., Hochella, M. F., Parks, G. A., Leckie, J. O. 1992; 56 (5): 1941-1954
  • COBALT(II) INTERACTIONS WITH NEAR-COASTAL MARINE-SEDIMENTS ENVIRONMENTAL GEOLOGY AND WATER SCIENCES Hansen, A. M., Leckie, J. O., Mee, L. D. 1992; 19 (2): 97-111
  • SURFACE COMPLEXATION MODELS - AN EVALUATION OF MODEL PARAMETER-ESTIMATION USING FITEQL AND OXIDE MINERAL TITRATION DATA JOURNAL OF COLLOID AND INTERFACE SCIENCE Hayes, K. F., Redden, G., ELA, W., Leckie, J. O. 1991; 142 (2): 448-469
  • INSITU X-RAY ABSORPTION STUDY OF LEAD-ION SURFACE COMPLEXES AT THE GOETHITE WATER INTERFACE LANGMUIR Roe, A. L., Hayes, K. F., CHISHOLMBRAUSE, C., Brown, G. E., Parks, G. A., Hodgson, K. O., Leckie, J. O. 1991; 7 (2): 367-373
  • SPECTROSCOPIC INVESTIGATION OF PB(II) COMPLEXES AT THE GAMMA-AL2O3 WATER INTERFACE GEOCHIMICA ET COSMOCHIMICA ACTA CHISHOLMBRAUSE, C. J., Hayes, K. F., Roe, A. L., Brown, G. E., Parks, G. A., Leckie, J. O. 1990; 54 (7): 1897-1909
  • STUDY OF COPPER(II) ASSOCIATION WITH DISSOLVED ORGANIC-MATTER IN SURFACE WATERS OF 3 MEXICAN COASTAL LAGOONS ENVIRONMENTAL SCIENCE & TECHNOLOGY Hansen, A. M., Leckie, J. O., MANDELLI, E. F., Altmann, R. S. 1990; 24 (5): 683-688
  • XANES AND EXAFS STUDY OF AQUEOUS PB(II) ADSORBED ON OXIDE SURFACES PHYSICA B-CONDENSED MATTER CHISHOLMBRAUSE, C. J., Roe, A. L., Hayes, K. F., Brown, G. E., Parks, G. A., Leckie, J. O. 1989; 158 (1-3): 674-675
  • A NUMERICAL-MODEL FOR METHANE PRODUCTION IN MANAGED SANITARY LANDFILLS WASTE MANAGEMENT & RESEARCH Elfadel, M., Findikakis, A. N., Leckie, J. O. 1989; 7 (1): 31-42
  • MODELING IONIC-STRENGTH EFFECTS ON ANION ADSORPTION AT HYDROUS OXIDE SOLUTION INTERFACES JOURNAL OF COLLOID AND INTERFACE SCIENCE Hayes, K. F., Papelis, C., Leckie, J. O. 1988; 125 (2): 717-726
  • MODELING GAS-PRODUCTION IN MANAGED SANITARY LANDFILLS WASTE MANAGEMENT & RESEARCH Findikakis, A. N., Papelis, C., Halvadakis, C. P., Leckie, J. O. 1988; 6 (2): 115-123
  • THE MOUNTAIN-VIEW-CONTROLLED-LANDFILL-PROJECT FIELD EXPERIMENT WASTE MANAGEMENT & RESEARCH Halvadakis, C. P., Findikakis, A. N., Papelis, C., Leckie, J. O. 1988; 6 (2): 103-114
  • THE FEASIBILITY OF USING SEQUENTIAL EXTRACTION TECHNIQUES FOR ARSENIC AND SELENIUM IN SOILS AND SEDIMENTS SOIL SCIENCE SOCIETY OF AMERICA JOURNAL GRUEBEL, K. A., Davis, J. A., Leckie, J. O. 1988; 52 (2): 390-397
  • INSITU X-RAY ABSORPTION STUDY OF SURFACE COMPLEXES - SELENIUM OXYANIONS ON ALPHA-FEOOH SCIENCE Hayes, K. F., Roe, A. L., Brown, G. E., Hodgson, K. O., Leckie, J. O., Parks, G. A. 1987; 238 (4828): 783-786

    Abstract

    A novel application of x-ray absorption spectroscopy has provided structural information for ions sorbed at oxide-water interfaces. As an example, in situ extended x-ray absorption fine structure (EXAFS) measurements of adsorbed selenate and selenite ions at ah alpha-FeOOH(goethite)-water interface have been performed; these measurements show that selenate forms a weakly bonded, outer-sphere complex and that selenite forms a strongly bonded, inner-sphere complex. The selenite ion is bonded directly to the goethite surface in a bidentate fashion with two iron atoms 3.38 angstroms from the selenium atom. Adsorbed selenate has no iron atom in the second coordination shell of selenium, which indicates retention of its hydration sphere upon sorption. This method provides direct structural information for adsorbed species at solid-liquid interfaces.

    View details for Web of Science ID A1987K681000027

    View details for PubMedID 17814706

  • MACROSCOPIC PARTITIONING COEFFICIENTS FOR METAL-ION ADSORPTION - PROTON STOICHIOMETRY AT VARIABLE PH AND ADSORPTION DENSITY ACS SYMPOSIUM SERIES Honeyman, B. D., Leckie, J. O. 1986; 323: 162-190
  • MECHANISM OF LEAD-ION ADSORPTION AT THE GOETHITE-WATER INTERFACE ACS SYMPOSIUM SERIES Hayes, K. F., Leckie, J. O. 1986; 323: 114-141
  • PROTON STOICHIOMETRY FOR THE ADSORPTION OF CATIONS ON OXIDE SURFACES JOURNAL OF COLLOID AND INTERFACE SCIENCE Perona, M. J., Leckie, J. O. 1985; 106 (1): 64-69
  • SORPTION OF LEAD ONTO 2 GRAM-NEGATIVE MARINE-BACTERIA IN SEAWATER MARINE CHEMISTRY Harvey, R. W., Leckie, J. O. 1985; 15 (4): 333-344
  • A GROUNDWATER MASS-TRANSPORT AND EQUILIBRIUM CHEMISTRY MODEL FOR MULTICOMPONENT SYSTEMS WATER RESOURCES RESEARCH CEDERBERG, G. A., Street, R. L., Leckie, J. O. 1985; 21 (8): 1095-1104
  • PARTICULATE MATTER AT THE ESTUARINE SALT-MARSH SURFACE MICROLAYER - PARTICLE-SIZE DISTRIBUTIONS AND COMPARISON TO BULK SUSPENSION ESTUARINE COASTAL AND SHELF SCIENCE Lion, L. W., Leckie, J. O. 1983; 16 (6): 689-698
  • ENRICHMENT AND ASSOCIATION OF LEAD AND BACTERIA AT PARTICULATE SURFACES IN A SALT-MARSH SURFACE-LAYER JOURNAL OF MARINE RESEARCH Harvey, R. W., Lion, L. W., Young, L. Y., Leckie, J. O. 1982; 40 (4): 1201-1211
  • REMOVAL OF TOXIC METALS FROM POWER-GENERATION WASTE STREAMS BY ADSORPTION AND COPRECIPITATION JOURNAL WATER POLLUTION CONTROL FEDERATION Benjamin, M. M., Hayes, K. F., Leckie, J. O. 1982; 54 (11): 1472-1481
  • TRACE-METAL ADSORPTION CHARACTERISTICS OF ESTUARINE PARTICULATE MATTER - EVALUATION OF CONTRIBUTIONS OF FE/MN OXIDE AND ORGANIC-SURFACE COATINGS ENVIRONMENTAL SCIENCE & TECHNOLOGY Lion, L. W., Altmann, R. S., Leckie, J. O. 1982; 16 (10): 660-666
  • MECHANISMS FOR TRACE-METAL ENRICHMENT AT THE SURFACE MICROLAYER IN AN ESTUARINE SALT-MARSH MARINE CHEMISTRY Lion, L. W., Harvey, R. W., Leckie, J. O. 1982; 11 (3): 235-244
  • ACCUMULATION AND TRANSPORT OF CD, CU, AND PB IN AN ESTUARINE SALT-MARSH SURFACE MICROLAYER LIMNOLOGY AND OCEANOGRAPHY Lion, L. W., Leckie, J. O. 1982; 27 (1): 111-125
  • CONCEPTUAL-MODEL FOR METAL-LIGAND-SURFACE INTERACTIONS DURING ADSORPTION ENVIRONMENTAL SCIENCE & TECHNOLOGY Benjamin, M. M., Leckie, J. O. 1981; 15 (9): 1050-1057

    View details for Web of Science ID A1981MD81900009

    View details for PubMedID 22284108

  • CHEMICAL SPECIATION OF TRACE-METALS AT THE AIR-SEA INTERFACE - THE APPLICATION OF AN EQUILIBRIUM-MODEL ENVIRONMENTAL GEOLOGY Lion, L. W., Leckie, J. O. 1981; 3 (5): 293-314
  • COMPETITIVE ADSORPTION OF CD, CU, ZN, AND PB ON AMORPHOUS IRON OXYHYDROXIDE JOURNAL OF COLLOID AND INTERFACE SCIENCE Benjamin, M. M., Leckie, J. O. 1981; 83 (2): 410-419
  • THE BIOGEOCHEMISTRY OF THE AIR-SEA INTERFACE ANNUAL REVIEW OF EARTH AND PLANETARY SCIENCES Lion, L. W., Leckie, J. O. 1981; 9: 449-486
  • MULTIPLE-SITE ADSORPTION OF CD, CU, ZN, AND PB ON AMORPHOUS IRON OXYHYDROXIDE JOURNAL OF COLLOID AND INTERFACE SCIENCE Benjamin, M. M., Leckie, J. O. 1981; 79 (1): 209-221
  • SURFACE-IONIZATION AND COMPLEXATION AT THE OXIDE-WATER INTERFACE .3. ADSORPTION OF ANIONS JOURNAL OF COLLOID AND INTERFACE SCIENCE Davis, J. A., Leckie, J. O. 1980; 74 (1): 32-43
  • LANDFILL MANAGEMENT WITH MOISTURE CONTROL JOURNAL OF THE ENVIRONMENTAL ENGINEERING DIVISION-ASCE Leckie, J. O., PACEY, J. G., Halvadakis, C. 1979; 105 (2): 337-355
  • NUMERICAL-SIMULATION OF GAS-FLOW IN SANITARY LANDFILLS JOURNAL OF THE ENVIRONMENTAL ENGINEERING DIVISION-ASCE Findikakis, A. N., Leckie, J. O. 1979; 105 (5): 927-945
  • PARTICULATE MATTER - ITS ASSOCIATION WITH MICROORGANISMS AND TRACE-METALS IN AN ESTUARINE SALT-MARSH MICROLAYER ENVIRONMENTAL SCIENCE & TECHNOLOGY Lion, L. W., Harvey, R. W., Young, L. Y., Leckie, J. O. 1979; 13 (12): 1522-1525
  • INVESTIGATION OF SOLUBLE ORGANIC NITROGEN-COMPOUNDS IN MUNICIPAL SECONDARY EFFLUENT JOURNAL WATER POLLUTION CONTROL FEDERATION Keller, J. V., Leckie, J. O., McCarty, P. L. 1978; 50 (11): 2522-2529
  • COMPUTER-SIMULATION OF CONDUCTOMETRIC AND POTENTIOMETRIC TITRATIONS OF SURFACE GROUPS ON IONIZABLE LATEXES JOURNAL OF COLLOID AND INTERFACE SCIENCE James, R. O., Davis, J. A., Leckie, J. O. 1978; 65 (2): 331-344
  • SURFACE IONIZATION AND COMPLEXATION AT OXIDE-WATER INTERFACE .2. SURFACE PROPERTIES OF AMORPHOUS IRON OXYHYDROXIDE AND ADSORPTION OF METAL-IONS JOURNAL OF COLLOID AND INTERFACE SCIENCE Davis, J. A., Leckie, J. O. 1978; 67 (1): 90-107
  • EFFECT OF ADSORBED COMPLEXING LIGANDS ON TRACE-METAL UPTAKE BY HYDROUS OXIDES ENVIRONMENTAL SCIENCE & TECHNOLOGY Davis, J. A., Leckie, J. O. 1978; 12 (12): 1309-1315
  • SURFACE IONIZATION AND COMPLEXATION AT OXIDE-WATER INTERFACE .1. COMPUTATION OF ELECTRICAL DOUBLE-LAYER PROPERTIES IN SIMPLE ELECTROLYTES JOURNAL OF COLLOID AND INTERFACE SCIENCE Davis, J. A., James, R. O., Leckie, J. O. 1978; 63 (3): 480-499

Conference Proceedings


  • Adsorption and photodegradation of humic acids by nano-structured TiO2 for water treatment Lee, P. F., Sun, D. D., Leckie, J. O. SCIENCE & TECHNOLOGY NETWORK INC. 2007: 72-78
  • Photocatalytic oxidation of emerging contaminants: Kinetics and pathways for photocatalytic oxidation of pharmaceutical compounds Tungudomwongsa, H., Leckie, J., Mill, T. SCIENCE & TECHNOLOGY NETWORK INC. 2006: 59-64
  • Effect of 200 days' sludge retention time on performance of a pilot scale submerged membrane bioreactor for high strength industrial wastewater treatment Hay, C. T., Sun, D. D., Khor, S. L., Leckie, J. O. IWA PUBLISHING. 2006: 269-276

    Abstract

    A high strength industrial wastewater was treated using a pilot scale submerged membrane bioreactor (MBR) at a sludge retention time (SRT) of 200 d. The MBR was operated at a high sludge concentration of 20 g/L and a low F/M ratio of 0.11 during 300 d of operation. It was found that the MBR could achieve COD and TOC overall removal efficiencies at more than 99 and 98% TN removal. The turbidity of the permeate was consistently in the range of 0.123 to 0.136 NTU and colour254 absorbance readings varied from 0.0912 to 0.0962 a.u. cm(-1). The sludge concentration was inversely proportional to the hydraulic retention time (HRT), yielded excellent organic removal and extremely low sludge production (0.0016 kgVSS/day).

    View details for DOI 10.2166/wst.2006.362

    View details for Web of Science ID 000239320900033

    View details for PubMedID 16862799

  • Ternary complex formation at mineral solution interfaces Leckie, J. O. ORGANIZATION ECONOMIC COOPERATION & DEVELOPMENT. 1995: 181-212
  • HUMIC ACID GOETHITE INTERACTIONS AND THEIR EFFECT ON COPPER BINDING Robertson, A. P., Leckie, J. O. ELSEVIER SCIENCE BV. 1994: 487-492