Emerging contaminants in the environment:
Our ongoing research in this topic area includes 1) plant uptake and accumulation of pharmaceutical and personal care products (PPCPs) during treated wastewater irrigation or biosolids application, 2) transformation pathways of PPCPs in soil and metabolism in plant, and 3) abiotic and biotic processes of brominated flame retardants (BFRs) and bisphenols in the environment. Funding sources: USDA-NIFA, EPA
Bioavailability of organic contaminants:
Organic compounds such as PCBs, PAHs, DDT, PBDEs and pyrethroid insecticides are strongly hydrophobic and they tend to sorb to solid particles and DOM. This phase partitioning behavior dictates that the bioavailability of these compounds in sediment, soil or surface water may not be directly related to their bulk chemical concentration. Our research in this area involves 1) development of bioavailability measurement methods such as solid phase microextraction (SPME), isotope dilution method (IDM), and Tenax extraction, 2) characterization of processes and factors regulating bioavailability, such as aging and black carbon types, and 3) application of bioavailability in improving risk assessment and evaluation of remediation efficiency. Funding sources: NIEHS, CDPR, PWG
Pesticide runoff and mitigation in urban environments:
Pesticides are frequently used by home owners and professional applicators around homes to control structural pests (e.g., termites), ants, and other insects. Such uses have been associated with contamination and aquatic toxicity of urban surface streams. In collaboration with California Department of Pesticide Regulation, the State Water resources Control Board and the Pyrethroid Work Group (PWG), we have been carrying out research to 1) evaluate the sources of urban pesticide contamination, 2) understand the abiotic transformation and sorption processes of pesticides on impervious surfaces such as concrete, and 3) develop mitigation strategies and education/outreach materials for stakeholders. Funding sources: CDPR, SWRCB, PWG.
Chiral contaminants:
A high percentage of current-use pesticides and pharmaceuticals are asymmetrical molecules with chiral centers. These chiral chemicals consist of two or more stereoisomers. While enantiomers have identical physico-chemical properties, their interactions with biological macromolecules are often chiral selective, leading to enantiomer selectivity in biodegradation, ecotoxicity and human health effects. In collaboration with Prof. W.P. Liu at Zhejiang University, China, we have been conducting research to 1) develop analytical methods enabling separation of enantiomers using GC and HPLC, and 2) evaluate chiral selectivity during biodegradation, aquatic toxicity and human health effects. Funding sources: USDA
