Microbial controls of hydrophobic organic chemical bioavailability in sediments

这项研究将论证沉积物有机物处理的微生物功能与疏水有机化学品(HOC)生物有效性之间的联系。生物利用度是生态毒理学的一个子领域，涉及测量环境介质(如沉积物)中可被吸收并导致有机体中化学物质暴露的总化学物质的比例。这项研究的重点是以工业过程中广泛使用的多氯联苯(PCB)等遗留污染物为代表的HOCs，这些污染物分散在全球各地，但继续促进鱼类的生物积累和生物放大，导致人类对食用受污染鱼类的健康担忧。到目前为止，关于沉积物中HOCs化学生物有效性的研究大多集中在对沉积物中非生物(非生物)组分的化学吸附，包括碎屑有机碳和高度改性的碳(如黑碳)。然而，微生物生物量本身对通常用常规技术测量的沉积物总有机碳有贡献。此外，微生物活动调节沉淀物颗粒和溶解有机物质进入沉积物的转化。这些转变改变了固定碳的吸附能力，这被认为通过两种方式改变了特定的生物可利用性：1)当活性碳被快速矿化时，通过增加孔隙水中的特定浓度和/或2)微生物生物量和底栖无脊椎动物消耗的活性碳导致生物放大。目标1-2将证明在添加新鲜碳来启动系统后，灭菌与未灭菌的沉积物中HOCs的孔隙化学发生改变，并且孔隙化学的变化转化为无脊椎动物HOC生物积累的差异。先进的技术来确定HOCs的非生物和微生物相分布，将允许对比孔隙水中的化学活性和微生物生物量来检验上述假设。目标3将通过不同生产力和氧化还原作用的湖泊沉积物岩心深度来研究特定孔隙水浓度和微生物群落组成/功能，以确定特定孔隙水浓度是由微生物功能和碳处理速率的转变驱动的，展示生态毒理学工具的效用，以衡量整个湖泊碳收支所需的碳矿化。目标4将展示应用的概念，测量以前恢复的沉积物中HOC生物有效性的差异，并结合食物网模型预测缓解方法的选择如何转化为降低鱼类HOC污染。对加拿大的好处包括改进生物累积模型，以评估和指导受污染沉积物的恢复，并证明多种压力因素(如污染物混合物和气候变化)共同作用，改变微生物功能，降低有毒污染物的生态系统容量。

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.