Hyporheic Interactions Increase Zinc Exposure and Effects on Hyalella azteca in Sediments under Flow-Through Conditions.

Groundwater-surface water interactions in the hyporheic transition zone can influence contaminant exposure to benthic macroinvertebrates. In streams, hyporheic flows are subject to varying redox conditions, which influence biogeochemical cycling and metal speciation. Despite these relationships, little is known about how these interactions influence the ecological risk of contaminants. The present study investigated the effects of hyporheic flows and zinc (Zn)-contaminated sediments on the amphipod Hyalella azteca. Hyporheic flows were manipulated in laboratory streams during 10-d experiments. Zinc toxicity was evaluated in freshly spiked and aged sediments. Hyporheic flows altered sediment and porewater geochemistry, oxidizing the sediments and causing changes to redox-sensitive endpoints. Amphipod survival was lowest in the Zn sediment exposures with hyporheic flows. In freshly spiked sediments, porewater Zn drove mortality, whereas in aged sediments simultaneously extracted metals (SEM) in excess of acid volatile sulfides (AVS) normalized by the fraction of organic carbon (fOC) [(SEM-AVS)/fOC] influenced amphipod responses. The results highlight the important role of hyporheic flows in determining Zn bioavailability to benthic organisms, information that can be important in ecological risk assessments. Environ Toxicol Chem 2019;38:2447-2458. © 2019 SETAC.