Use of prospective and retrospective risk assessment methods that simplify chemical mixtures associated with treated domestic wastewater discharges

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. C

Prospective mixture risk assessment and management prioritizations for river catchments with diverse land uses

“…Each scenario layout was modeled for 20 yr, with daily quantifications of PECs for the each of the studied chemicals. Details are in the Supplemental Data (section 1) and the scenario reviews (Holmes et al 2018; Diamond et al 2018; de Zwart et al 2018). …”

“…The aims of the present study were to combine the land‐use scenarios of the associated manuscripts of the Pellston workshop, references Holmes et al (2018), Diamond et al (2018), and de Zwart et al (2018), to investigate these questions for catchments with different combinations of land use.…”

“…Prospective, catchment‐scale prioritization of chemical mixture risks can assist decision‐making regarding risk‐mitigation strategies (Ginebreda et al 2013; Coppens et al 2015; Sobek et al 2016; Brack et al 2017). The present study expands on and integrates 3 detailed analyses of land use–related scenarios, investigating the specific chemical signatures of an agriculture scenario (emissions from agricultural land dictated by rainfall, soils, and PPP use [Holmes et al 2018]), a treated domestic wastewater scenario (daily use of household chemicals [Diamond et al 2018]), and an urban runoff scenario (rainfall‐mediated emissions from city surface areas [de Zwart et al 2018]).…”

Prospective aquatic risk assessment for chemical mixtures in agricultural landscapes

“…Examples of the single‐unit scenarios are feedlots, fields, pasture, aquaculture production areas, and potentially other inputs from nonagricultural point discharges (de Zwart et al 2018; Diamond et al 2018), as in case study 1.…”

“…The aims of the present study were to investigate these questions using standard agricultural aquatic exposure models and scenarios. Associated articles adopted the same working hypothesis to evaluate the risk of chemical mixtures from 2 other land‐use types (de Zwart et al 2018; Diamond et al 2018), whereas a combination of the 3 land‐use scenarios was generated to investigate these questions for catchments with different combinations of land use (Posthuma et al 2018). …”