Nedrich Sara M, Burton G Allen
Department of Earth and Environmental Sciences, The University of Michigan, 2534 CC Little Bldg., 1100 North University Ave., Ann Arbor, MI 48109-1005, United States.
Department of Earth and Environmental Sciences, The University of Michigan, 2534 CC Little Bldg., 1100 North University Ave., Ann Arbor, MI 48109-1005, United States.
Environ Pollut. 2017 Nov;230:1116-1124. doi: 10.1016/j.envpol.2017.07.073. Epub 2017 Aug 7.
Hydrologic variability exacerbated by climate change affects biogeochemical cycling in sediments through changes in pH, redox, and microbial activity. These alterations affect the lability and speciation of metals, such that toxicity may be observed in otherwise non-toxic sediments. In this study, we investigate the effects of drought and reflooding on metal bioavailability in sediments with low to moderate concentrations of Zn (18-270 mg kg). Sediments were collected from coastal wetlands in Michigan, dried (36-days) and re-inundated in lab microcosms. We investigated the relationships between key parameters, for surface/porewater (dissolved and particulate metals, dissolved oxygen, redox (Eh), reduced iron, and temperature) and sediment (simultaneously extracted metals (SEM), acid volatile sulfide (AVS), Fe/Mn-oxyhydroxide, organic carbon, water content analyses, and diffusive gradient in thin films (DGTs) metal concentrations). Porewater Zn increased with inundation of dried sediments for all sediment types, exceeding United States Environmental Protection Agency (U.S. EPA) chronic criteria for freshwater organisms, and decreased as sediments became reduced. Effects on Hyalella azteca (7-day exposure) and Daphnia magna (10-day exposure) were quantified. Results show decreased growth of H. azteca for sites with elevated Zn and increased Zn-body concentration (BC) in the most contaminated sediment type. Further, BC was negatively correlated with H. azteca growth. D. magna survival, growth, and reproduction were not affected. DGT metal concentrations were more reflective of porewater than organism bioaccumulation. Outcomes of predictive toxicology methods are compared to toxicity test results and suggestions are provided for model improvements. This study demonstrates that post-drought re-flooding of sediments affects Zn biogeochemical cycling with potentially adverse effects on benthic organisms, even in sediments with only moderately elevated concentrations (>150 mg kg).
气候变化加剧的水文变异性通过pH值、氧化还原和微生物活动的变化影响沉积物中的生物地球化学循环。这些变化影响金属的活性和形态，从而可能在原本无毒的沉积物中观察到毒性。在本研究中，我们调查了干旱和再淹没对锌浓度低至中等（18 - 270毫克/千克）的沉积物中金属生物有效性的影响。沉积物取自密歇根州的沿海湿地，干燥（36天）后在实验室微观世界中重新淹没。我们研究了表层/孔隙水（溶解态和颗粒态金属、溶解氧、氧化还原电位（Eh）、还原铁和温度）与沉积物（同时提取金属（SEM）、酸挥发性硫化物（AVS）、铁/锰羟基氧化物、有机碳、含水量分析以及薄膜扩散梯度（DGT）金属浓度）的关键参数之间的关系。对于所有沉积物类型，干燥沉积物淹没后孔隙水中的锌含量增加，超过了美国环境保护局（U.S. EPA）对淡水生物的慢性标准，随着沉积物还原，锌含量降低。对墨西哥透明溞（7天暴露）和大型溞（10天暴露）的影响进行了量化。结果表明，锌含量升高的地点墨西哥透明溞的生长下降，在污染最严重的沉积物类型中，锌体浓度（BC）增加。此外，BC与墨西哥透明溞的生长呈负相关。大型溞的生存、生长和繁殖未受影响。DGT金属浓度比生物体生物积累更能反映孔隙水情况。将预测毒理学方法的结果与毒性测试结果进行了比较，并为模型改进提供了建议。本研究表明，干旱后沉积物的再淹没会影响锌的生物地球化学循环，对底栖生物可能产生不利影响，即使在锌浓度仅适度升高（>150毫克/千克）的沉积物中也是如此。
