Microbial controls of hydrophobic organic chemical bioavailability in sediments

本研究将证明微生物在沉积物有机质处理过程中的功能与疏水有机化学（HOC）生物利用度之间的联系。生物利用度是生态毒理学的一个分支，涉及测量环境介质（如沉积物）中存在的总化学物质的比例，这些化学物质可以被生物体吸收并导致化学物质暴露。本研究的重点是以工业过程中广泛使用的多氯联苯（PCBs）等遗留污染物为代表的hoc，这些污染物在全球范围内分散，但仍在鱼类体内持续积累和生物放大，导致人类对食用受污染鱼类的健康担忧。迄今为止，大多数关于沉积物中有机碳化学生物利用度的研究都集中在沉积物对非生物（非生物）成分的化学吸附上，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沉积物有机碳总量的贡献通常是在传统技术中测量的。此外，微生物活动介导了沉积颗粒和溶解有机物质的转化。这些转化改变了沉淀碳的吸附能力，假设通过两种方式改变HOC的生物利用度：1)当不稳定碳被快速矿化时，孔隙水中的HOC浓度增加，和/或2)微生物生物量和不稳定碳被底栖无脊椎动物消耗导致生物放大。目标1-2将证明，在添加新鲜碳以启动系统后，灭菌与非灭菌沉积物中HOC的孔隙水化学性质发生了变化，孔隙水HOC化学的变化转化为无脊椎动物HOC生物积累的差异。测定hoc的非生物相和微生物相分布的先进技术将允许对比孔隙水和微生物生物量中的化学活性，以检验上述假设。目标3将通过对生产力和氧化还原程度不同的湖泊沉积物岩心的深度研究HOC孔隙水浓度和微生物群落组成/功能，以确定HOC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在测量湖泊碳收支所需的碳矿化方面的效用。目标4将展示应用概念，测量先前恢复的沉积物中HOC生物利用度的差异，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积累模型，以评估和指导受污染沉积物的恢复，并证明多种压力因素（例如污染物混合物和气候变化）共同作用，改变微生物功能，降低生态系统对有毒污染物的能力。

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.