Institute Affiliations

  • Member, Maternal & Child Health Research Institute (MCHRI)

Stanford Advisors

All Publications

  • Biochar promotes arsenic sequestration on iron plaques and cell walls in rice roots. Chemosphere Xu, M., Gao, P., Wu, J., Ma, J., Zhang, X., Yang, G., Long, L., Chen, C., Song, C., Xiao, Y. 2021: 132422


    The iron (Fe) cycle in the rice-soil system affects arsenic (As) uptake by rice. The effect of Fe on As uptake can be influenced by the addition of biochar, but has not been thoroughly investigated. In this study, the effects of maize straw-derived biochar (MB) on Fe and As translocation were determined by analysing the Fe and As concentrations in pore water, dithionite-citrate-bicarbonate (DCB) extracts, and rice plants. As-contaminated soils were supplemented with 0 or 1% biochar and 0 or 90 mg kg-1 P, and rice plants were grown for 70 d. Results indicated that biochar addition increased the concentrations of Fe and As in pore water, while P did not affect them. Additionally, biochar promoted the accumulation of Fe and As in roots. However, the rice biomass increased by 28% upon biochar addition, indicating that the rice plants became more tolerant to As toxicity with biochar. Specifically, biochar increased the root triphenyl tetrazolium chloride (TTC) reductive intensity, reduced the root H2O2 concentration, and promoted iron plaque (IP) formation. Moreover, the positive correlation between IP/DCB-extractable As and crystalline Fe on the rice root surface indicated that crystalline Fe appeared to be the determinant species of IP and played a central role in As segregation. In addition, biochar increased both crystalline Fe formation on the root surface and the Fe content in the cell wall, which enhanced As sequestration. Overall, rice could effectively tolerate As stress under biochar treatment since As could be retained on the root surface and root cell wall with MB.

    View details for DOI 10.1016/j.chemosphere.2021.132422

    View details for PubMedID 34600923

  • Decoding personal biotic and abiotic airborne exposome. Nature protocols Jiang, C., Zhang, X., Gao, P., Chen, Q., Snyder, M. 2021


    The complexity and dynamics of human diseases are driven by the interactions between internal molecular activities and external environmental exposures. Although advances in omics technology have dramatically broadened the understanding of internal molecular and cellular mechanisms, understanding of the external environmental exposures, especially at the personal level, is still rudimentary in comparison. This is largely owing to our limited ability to efficiently collect the personal environmental exposome (PEE) and extract the nucleic acids and chemicals from PEE. Here we describe a protocol that integrates hardware and experimental pipelines to collect and decode biotic and abiotic external exposome at the individual level. The described protocol has several advantages over conventional approaches, such as exposome monitoring at the personal level, decontamination steps to increase sensitivity and simultaneous capture and high-throughput profiling of biotic and abiotic exposures. The protocol takes ~18 h of bench time over 2-3 d to prepare samples for high-throughput profiling and up to a couple of weeks of instrumental time to analyze, depending on the number of samples. Hundreds to thousands of species and organic compounds could be detected in the airborne particulate samples using this protocol. The composition and complexity of the biotic and abiotic substances are heavily influenced by the sampling spatiotemporal factors. Basic skillsets in molecular biology and analytical chemistry are required to carry out this protocol. This protocol could be modified to decode biotic and abiotic substances in other types of low or ultra-low input samples.

    View details for DOI 10.1038/s41596-020-00451-8

    View details for PubMedID 33437065

  • The Exposome in the Era of One Health. Environmental science & technology Gao, P. n. 2021


    Current studies on environmental chemistry mainly focus on a single stressor or single group of stressors, which does not reflect the multiple stressors in the dynamic exposome we are facing. Similarly, current studies on environmental toxicology mostly target humans, animals, or the environment separately, which are inadequate to solve the grand challenge of multiple receptors in One Health. Though chemical, biological, and physical stressors all pose health threats, the susceptibilities of different organisms are different. As such, significant relationships and interactions of the chemical, biological, and physical stressors in the environment and their holistic environmental and biological consequences remain unclear. Fortunately, the rapid developments in various techniques, as well as the concepts of multistressors in the exposome and multireceptor in One Health provide the possibilities to understand our environment better. Since the combined stressor is location-specific and mixture toxicity is species-specific, more comprehensive frameworks to guide risk assessment and environmental treatment are urgently needed. Here, three conceptual frameworks to categorize unknown stressors, spatially visualize the riskiest stressors, and investigate the combined effects of multiple stressors across multiple species within the concepts of the exposome and One Health are proposed for the first time.

    View details for DOI 10.1021/acs.est.0c07033

    View details for PubMedID 33417434

  • The Exposome in the Era of the Quantified Self. Annual review of biomedical data science Zhang, X., Gao, P., Snyder, M. P. 2021; 4: 255-277


    Human health is regulated by complex interactions among the genome, the microbiome, and the environment. While extensive research has been conducted on the human genome and microbiome, little is known about the human exposome. The exposome comprises the totality of chemical, biological, and physical exposures that individuals encounter over their lifetimes. Traditional environmental and biological monitoring only targets specific substances, whereas exposomic approaches identify and quantify thousands of substances simultaneously using nontargeted high-throughput and high-resolution analyses. The quantified self (QS) aims at enhancing our understanding of human health and disease through self-tracking. QS measurements are critical in exposome research, as external exposures impact an individual's health, behavior, and biology. This review discusses both the achievements and the shortcomings of current research and methodologies on the QS and the exposome and proposes future research directions.

    View details for DOI 10.1146/annurev-biodatasci-012721-122807

    View details for PubMedID 34465170

  • Photochemical impacts on the toxicity of PM2.5 CRITICAL REVIEWS IN ENVIRONMENTAL SCIENCE AND TECHNOLOGY Xu, J., Hu, W., Liang, D., Gao, P. 2020
  • Background concentrations of trace metals As, Ba, Cd, Co, Cu, Ni, Pb, Se, and Zn in 214 Florida urban soils: Different cities and land uses. Environmental pollution (Barking, Essex : 1987) da Silva, E. B., Gao, P. n., Xu, M. n., Guan, D. n., Tang, X. n., Ma, L. Q. 2020; 264: 114737


    Soil contamination in urban environment by trace metals is of public concerns. For better risk assessment, it is important to determine their background concentrations in urban soils. For this study, we determined the background concentrations of 9 trace metals including As, Ba, Cd, Co, Cu, Ni, Pb, Se, and Zn in 214 urban soils in Florida from two large cities (Orlando and Tampa) and 4 small cities (Clay County, Ocala, Pensacola and West Palm Beach). The objectives were to determine: 1) total concentrations of trace metals in urban soils in cities of different size; 2) compare background concentrations to Florida Soil Cleanup Target Levels (FSCTLs); and 3) determine their distribution and variability in urban soils via multivariate statistical analysis. Elemental concentrations in urban soils were variable, with Pb being the highest in 5 cities (165-552 mg kg-1) and Zn being the highest concentration in Tampa (1,000 mg kg-1). Besides, the As and Pb concentrations in some soils exceeded the FSCTL for residential sites at 2.1 mg kg-1 As and 400 mg kg-1 Pb. Among the cities, Clay County and Orlando had the lowest concentrations for most elements, with Cd, Co, and As being the lowest while Ba, Pb and Zn being the highest. Among all values, geometric means were the lowest while 95th percentile was the highest for all metals. Most 95th percentile values were 2-3 folds higher than the GM data, with Pb presenting the greatest difference, being 4 times greater than GM value (58.9 vs. 13.6 mg kg-1). Still they were lower than FSCTL, with As exceeding FSCTL for residential sites at 2.1 mg kg-1. In addition, the linear discriminate analysis showed distinct separation among the cities: Ocala (Ba & Ni) and Pensacola (As & Pb) were distinctly different from each other and from other cities with higher metal concentrations. The large variations among elemental concentrations showed the importance to establish proper background concentrations of trace metals in urban soils.

    View details for DOI 10.1016/j.envpol.2020.114737

    View details for PubMedID 32559860