Metal Fate Dynamics and Ecotoxicology in Hydrologically Variable Aquatic Ecosystems

Predicting the environmental fate and effects of metals is nuanced, due to the diverse interplay of biogeochemical and physicochemical variables, and is vital to protecting and preserving aquatic resources. Regulatory methods for toxicity testing and ecological risk assessment often lack sufficient data to address simple and critical changes in environmental conditions, such as hydrologic extremes (drought/flood), which are predicted to become more severe with climate change. This is a particular concern, as water quality criteria (e.g., regulatory standards for metal thresholds) are defined by laboratory toxicity test methods. In this dissertation, the effects of altered hydrology on sediment metal biogeochemistry and associated effects to aquatic organisms are investigated. Water level fluctuation experiments are conducted on high carbonate sediments collected from coastal wetlands in the Great Lakes region, showing a significant release of porewater Zinc (Zn) due to altered geochemistry following drought conditions, with sublethal effects to benthic macroinvertebrates (Chapter 2-3). In a subsequent study (Chapter 4), Zn-release and effects to organism growth is again observed in more acidic reservoir sediments with different geochemical controls. Vanadium (V) redox biogeochemistry is also investigated and oxidation had relatively little effect on V speciation due to strong complexation with iron oxyhydroxide compounds. In the final chapter (Chapter 5), field validation of Zn-release is performed at the same wetland sites used for laboratory testing and demonstrated positive benthic community responses. The effects of elevated sediment Zn are confounded by a strong positive relationship between benthic community abundance, richness, and diversity with sediment pH. The pH shift was likely driven by periphyton photosynthesis, altering metal speciation and complexation and the periphyton served as a food source benefiting the benthic macroinvertebrate community. General implications of this research are elucidated, including relevance to the management and restoration of aquatic systems, regulatory driven toxicology, and improving the extrapolation of laboratory to field studies. Finally, it appears that increases in hydrologic extremes, as predicted with climate change, will alter metal biogeochemistry in sediments, thereby resulting in wide-ranging effects on benthic macroinvertebrate communities.PHDEarth and Environmental SciencesUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/138720/1/snedrich_1.pd

Preliminary investigation of 6PPD-quinone in surface water and standing road water in Michigan

Recent studies have identified a new emerging contaminant, 6PPD-quinone (N-(1,3-dimethylbutyl)-N-phenyl-p-phenylenediamine), which has been attributed to significant salmon mortality in rivers in the Pacific Northwest (Tian et al., 2021). Sampling for 6PPD-quinone was conducted in surface water and standing road water in 11 watersheds throughout Michigan. Sample sites were selected to address various research questions, including whether 6PPD-quinone release would increase with recycled crumb rubber road paving technologies. Surface water samples (n=17) were collected from rivers or creeks adjacent to or intersecting roadways following storm events in August-September of 2021. Five standing road water (puddle) samples were also collected. Only two of 17 surface water samples exceeded detection limits (MDL = 3 ng/L) at 12 and 37 ng/L., which fell below the reported LC50 for coho salmon of 95 ng/L (Tian et al. 2022). All five puddle samples had elevated concentrations of 6PPD-quinone, ranging from 54-660 ng/L. All surface water sites sampled along crumb rubber mixed asphalt and asphalt rubber chip seal roadways were non-detect for 6PPD-quinone. Additional sampling is proposed for the summer of 2022 to target a river adjacent to a highly trafficked roadway that is reported to support spawning sport fish.Ope

Indirect effects of climate change on zinc cycling in sediments: The role of changing water levels

Increased variability in lake and river water levels associated with changing climate could impact the fate and effects of metals in redox‐sensitive sediments through the alteration of microbial communities and of acid–base and redox chemistry. The objective of the present study was to determine the influence of water level fluctuation on metal speciation in porewater and predict environmental risk to high‐carbonate systems. Using experimental microcosms with sediments collected from 4 metal‐contaminated coastal freshwater wetlands in Michigan, USA, we conducted water level fluctuation experiments. Porewater and sediment metals (Ca, Cu, Fe, Mg, Mn, Ni, Zn) and important metal binding phases (iron‐oxide speciation, acid‐volatile sulfide) were quantified. In a short‐term drying (seiche) experiment, there were decreases in all porewater metals after inundation of saturated sediments. During a drought experiment, re‐inundation of oxidized sediments increased porewater Cu, Zn, Mg, Ca for most sites. Porewater Zn increased after inundation to levels exceeding the US Environmental Protection Agency threshold for chronic toxicity. These data show that the dissolution of metal carbonates and metal sulfates contributes to metal release after re‐flooding and indicate that we might expect increased ecological risk to organisms present in drought‐sensitive regions where altered hydroperiods are likely to increase metal bioavailability. Environ Toxicol Chem 2017;36:2456–2464. © 2017 SETACPeer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/138388/1/etc3783.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/138388/2/etc3783_am.pd

Laboratory and Field‐Based Assessment of the Effects of Sediment Capping Materials on Zinc Flux, Bioavailability, and Toxicity

A former mining site has been the subject of extensive remediation and restoration, with a significant focus on disconnecting mine spoils from groundwater and managing the quantity and quality of runoff. A remaining task is ensuring concentrations of zinc (Zn) in the stream outflow of a pit lake are reduced below water quality standards. The efficacy of multiple capping materials for decreasing Zn dissolution from sediments was conducted under natural and reasonable worst‐case conditions (pH = 5.5). Capping materials included AquaBlok™, limestone, and limestone–bone char. Field exposures were conducted in limnocorrals that isolated overlying water columns above the sediment and capping treatments. Simultaneous in situ and ex situ toxicity tests were conducted using Daphnia magna, Hyalella azteca, and Chironomus dilutus. In situ caged organisms were protected from temperature shock (warm epilimnetic waters) by deploying within a Toxicity Assessment Container System (TACS). Organisms were exposed to surficial sediments, caps, and hypolimnetic overlying waters for 4 d. Ex situ testing was conducted in core tube mesocosms containing sediments and caps at similar temperatures (15–19 °C). Results demonstrated the usefulness of TACS deployment in stratified lake systems. There were no differences in responses between treatments involving sediment capping materials in both in situ and ex situ tests. The lack of differences was likely due to dissolved Zn in surface water being below the hardness‐adjusted threshold effects levels (164 μg L–1). This field‐ and laboratory‐based weight‐of‐evidence study provided site‐specific data to support the selection of an effective remedy, with reduced uncertainty compared to laboratory and chemistry‐only approaches. Environ Toxicol Chem 2019;39:240–249. © 2019 SETACPeer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/152878/1/etc4612.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/152878/2/etc4612_am.pd