Microbial controls of hydrophobic organic chemical bioavailability in sediments

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This research will demonstrate linkages between microbial function of sediment organic matter processing and hydrophobic organic chemical (HOC) bioavailability. Bioavailability is a subfield of ecotoxicology concerned with measuring the fraction of total chemical present in an environmental media (e.g. sediments) that can be taken up and contribute to chemical exposures in organisms. This research focuses on HOCs represented by legacy pollutants such as polychlorinated biphenyls (PCBs) that were widely used in industrial processes, are globally dispersed, yet continue to contribute to bioaccumulation and biomagnification in fish leading to human health concerns about the consumption of contaminated fish. To date, most research on chemical bioavailability of HOCs in sediments focusses on chemical sorption to abiotic (non-living) components of the sediment including detrital organic carbon and highly modified carbons such as black carbon. However, microbial biomass itself contributes to the total sediment organic carbon commonly measured in conventional techniques. In addition, microbial activity mediates the transformation of settled particulate and dissolved organic material incorporated into sediments. These transformations alter the sorptive capacity of settled carbon that is hypothesized to change HOC bioavailability in two ways: 1) by increasing the HOC concentrations in porewater when labile carbon is rapidly mineralized and/or 2) by microbial biomass and labile carbon being consumed by benthic invertebrates resulting in biomagnification. Objectives 1-2 will demonstrate that porewater chemistry of HOCs is altered in sterilized vs non-sterilized sediments following addition of fresh carbon to prime the system and that changes to porewater HOC chemistry translate to differences in invertebrate HOC bioaccumulation. Advanced techniques to determine abiotic and microbial phase distribution of HOCs will allow contrast of chemical activity in porewater and microbial biomass to test the above hypotheses. Objective 3 will examine HOC porewater concentrations and microbial community composition/function through depth in sediment cores from lakes that vary in productivity and redox to establish that HOC porewater concentrations are driven by transitions in microbial function and carbon processing rates, showcasing the utility of ecotoxicology tools to measure carbon mineralization necessary for lake wide carbon budgets. Objective 4 will demonstrate applied concepts, measuring differences in HOC bioavailability in sediments previously restored coupled with food web models to forecast how choice of mitigation method translates to lowering of fish HOC contamination. Benefits to Canada include improved bioaccumulation models to assess and guide contaminated sediment restoration and demonstration that multiple stressors (e.g. pollutant mixtures and climate change) act together to alter microbial function and decrease ecosystem capacity for toxic pollutants.