Watershed-Scale Risk to Aquatic Organisms from Complex Chemical Mixtures in the Shenandoah River

Abstract

River waters contain complex chemical mixtures derived from natural and anthropogenic sources. Aquatic organisms are exposed to the entire chemical composition of the water, resulting in potential effects at the organismal through ecosystem level. This study applied a holistic approach to assess landscape, hydrological, chemical, and biological variables. On-site mobile laboratory experiments were conducted to evaluate biological effects of exposure to chemical mixtures in the Shenandoah River Watershed. A suite of 534 inorganic and organic constituents were analyzed, of which 273 were detected. A watershed-scale accumulated wastewater model was developed to predict environmental concentrations of chemicals derived from wastewater treatment plants (WWTPs) to assess potential aquatic organism exposure for all stream reaches in the watershed. Measured and modeled concentrations generally were within a factor of 2. Ecotoxicological effects from exposure to individual components of the chemical mixture were evaluated using risk quotients (RQs) based on measured or predicted environmental concentrations and no effect concentrations or chronic toxicity threshold values. Seventy-two percent of the compounds had RQ values <0.1, indicating limited risk from individual chemicals. However, when individual RQs were aggregated into a risk index, most stream reaches receiving WWTP effluent posed potential risk to aquatic organisms from exposure to complex chemical mixtures.

Evaluation of Complex Mixture Toxicity in the Milwaukee Estuary (WI, USA) Using Whole‐Mixture and Component‐Based Evaluation Methods

“…Finally, by employing predictive analysis, we were able to bridge component-based and whole-mixture analyses, providing additional weight-of-evidence for chemical/mixture group prioritizations. Overall, our study represents an important complement to other prioritization analyses and complex mixture assessment in Great Lakes watersheds (e.g., Barber et al, 2022;Corsi et al, 2019;Maloney et al, 2022). Indeed, by identifying diverse target sites, individual chemicals, and simplified mixture groups, we have identified additional targets for ecotoxicological evaluation and increased the weight-of-evidence for high-and low-priority compounds and mixtures across these aquatic systems.…”

“…Thus these mixtures should be considered definitive high‐priority targets for effects‐based monitoring and/or risk assessment within the Milwaukee Estuary. Conversely, sterols are naturally derived, originating from the decomposition of organic matter (Mudge & Lintern, 1999; Murtaugh & Bunch, 1967), demonstrate limit solubilities, and are not expected to be inherently toxic (Barber et al, 2022). However, because sterols have not been thoroughly tested in standard ecotoxicological assays, these mixtures should be considered medium priority contingent on further evidence demonstrating significant risk potential in aquatic environments.…”

Identifying Key Stressors Driving Biological Impairment in Freshwater Streams in the Chesapeake Bay Watershed, USA

“…Point sources, for example, can drastically alter water quality and contaminant loading in reaches immediately downstream from the discharge point, and includes industrial discharges (Hall et al 2009 ; Nedeau et al 2003 ; Echols et al 2009 ; Monda et al 1995 ) and municipal wastewater (Polls et al 1980 ; Birge et al 1989 ). Chemical mixtures containing multiple contaminants can originate from municipal or industrial wastewater discharges, and those mixtures can collectively increase ecotoxicological impacts to aquatic organisms (Barber et al 2022 ). Impacts from point sources can occur in agricultural settings as well, including increased nutrient loading from aquaculture activities (Koetsier 2002 ) or slaughterhouse discharges (Roberts 2005 ).…”

Occurrence of organic pollutants in the River Itchen and River Test—two chalk streams in Southern England, UK

“…The antidepressant venlafaxine and its major metabolite o-desmethylvenlafaxine were frequently found in both rivers and have been shown to affect the behaviour and mortality of fish (Sehonova et al 2018 ). Interestingly, more recent work has started to investigate the impact of chemical mixtures on freshwater ecosystems (Barber et al 2022 ; Covert et al 2020 ; Nowell et al 2018 ).…”