Abstract
A framework is presented that is intended to facilitate the evaluation of potential aquatic ecological risks resulting from discharges of down-the-drain chemicals. A scenario is presented using representatives of many of the types of chemicals that are treated domestically. Predicted environmental chemical concentrations are based on reported loading rates and routine removal rates for 3 types of treatment: trickling filter, activated sludge secondary treatment, and activated sludge plus advanced oxidation process as well as instream effluent dilution. In tier I, predicted effluent concentrations were compared with the lowest predicted-no-effect concentration (PNEC) obtained from the literature using safety factors as needed. A cumulative risk characterization ratio (cumRCR) < 1.0 indicates that risk is unlikely and no further action is needed. Otherwise, a tier 2 assessment is used, in which PNECs are based on trophic level. If tier 2 indicates a possible risk, then a retrospective assessment is recommended. In tier 1, the cumRCR was > 1.0 for all 3 treatment types in our scenario, even though no chemical exceeded a hazard quotient of 1.0 in activated sludge or advanced oxidation process. In tier 2, activated sludge yielded a lower cumRCR than trickling filter because of higher removal rates, and the cumRCR in the advanced oxidation process was << 1.0. Based on the maximum cumulative risk ratio (MCR), more than one-third of the predicted risk was accounted for by one chemical, and at least 90% was accounted for by 3 chemicals, indicating that few chemicals influenced the mixture risk in our scenario. We show how a retrospective assessment can test whether certain chemicals hypothesized as potential drivers in the prospective assessment could have, or are having, deleterious effects on aquatic life. Environ Toxicol Chem 2018;37:690-702. © 2017 The Authors. Environmental Toxicology and Chemistry Published by Wiley Periodicals, Inc. on behalf of SETAC.
Highlights
Regulatory bodies around the world have typically evaluated ecological risks on a chemical-by-chemical basis, in which it is assumed that the environment is protected if each chemical is regulated at or below its safe concentration
This scenario does not intend to be an actual mixture risk assessment of real-world wastewater treatment plant (WWTP) effluents in general; we believe that the framework we present can be used to address a wide range of conditions
Unacceptable mixture risk was hypothesized for all 3 treatment types even though no one chemical exceeded a hazard quotient of 1.0 in either the activated sludge or the advanced oxidation treatment
Summary
Regulatory bodies around the world have typically evaluated ecological risks on a chemical-by-chemical basis, in which it is assumed that the environment is protected if each chemical is regulated at or below its safe concentration. Concerns about underestimating chemical mixture risks to aquatic life have been especially directed toward municipal wastewater treatment plant (WWTP) discharges, which are known to be complex mixtures (Anderson 2008; Diamond et al 2010; Ohlinger et al 2013). Municipal WWTPs are often a source of various types of down-the-drain chemicals from diverse products, but the particular mixture present in a given discharge will depend on the type of wastewater treatment used and its operation efficiency, population size, associated wastewater flow, and perhaps the geographic region and/or climatic regime (Diamond et al 2011). Prospective risk assessments of WWTP discharges have not typically used mixture exposure information in a meaningful way, and incorporating such information is challenging. Prospective assessments of down-the-drain chemicals in WWTP discharges ideally require knowledge of the various chemicals that could be present in the effluent after treatment, as well as knowledge of their potential effects and mode of action. Information pertaining to potential exposure in the receiving waterbody is desirable, which will be influenced at least in part by available effluent dilution and fate properties of the chemicals in the receiving waterbody
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