Threshold concepts of toxicological concern are based on the possibility of establishing an exposure threshold value for chemicals below which no significant risk is to be expected. The objective of the present study is to address environmental thresholds of no toxicological concern for freshwater systems (ETNCaq) for organic chemicals. We analyzed environmental toxicological databases (acute and chronic endpoints) and substance hazard assessments. Lowest numbers and 95th‐percentile values were derived using data stratification based on mode of action (MOA; 1 = inert chemicals; 2 = less inert chemicals; 3 = reactive chemicals; 4 = specifically acting chemicals). The ETNCaq values were derived by multiplying the lowest 95th percentile values with appropriate application factors; ETNCaq,MOA1–3 is approximately 0.1 μg/L. A preliminary analysis with complete MOA stratification of the databases shows that in the case of MOA1 or MOA2, the ETNCaq value could be even higher than 0.1 μg/L. A significantly lower ETNCaqMOA4 value was observed based on the long‐term toxicity information in the European Centre for the Ecotoxicology and Toxicology of Chemicals database. Application of the ETNCaq value in a tiered risk‐assessment scheme may help chemical producers to set data‐generation priorities and to refine or reduce animal use. It also may help to inform downstream users concerning the relative risk associated with their specific uses and be of value in putting environmental monitoring data into a risk‐assessment perspective.

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An extensive monitoring program was executed jointly by the Dutch Soap Association (NVZ) and the Dutch authorities. Flow proportional samples of raw, settled, and treated sewage from seven representative municipal sewage treatment plants were collected over three consecutive days. The samples were analyzed for detergent surfactants, including linear alkylbenzene sulfonate (LAS), alcohol ethoxylate (AE), alcohol ethoxylated sulfate (AES), alcohol sulfate, (AS) and soap, using state-of-the-art analytical methods. All surfactants were removed by more than 99% during sewage treatment. The concentrations of the surfactants in the treated sewage averaged 39 g/L for LAS, 6.2 g/L for AE, 6.5 g/L for AES, 5.7 g/L for AS, and 174 g/L for soap. These measured surfactant concentrations form the basis for the exposure element of the aquatic risk assessment for the surfactants studied. In addition, the field studies indicated that in-sewer removal can play a significant role in reducing the concentrations of surfactants entering the sewage treatment plant.

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There is generally a lack of saltwater ecotoxicity data for risk assessment purposes, leaving an unknown margin of uncertainty in saltwater assessments that utilize surrogate freshwater data. Consequently, a need for sound scientific advice on the suitability of using freshwater data to extrapolate to saltwater effects exists. Here we use species sensitivity distributions to determine if freshwater datasets are adequately protective of saltwater species assemblages for 21 chemical substances. For ammonia and the metal compounds among these data, freshwater data were generally protective because freshwater organisms tended to be more sensitive. In contrast, for pesticide and narcotic compounds, saltwater species tended to be more sensitive and a suitable uncertainty factor would need to be applied to surrogate freshwater data. Biological and physicochemical factors contribute to such differences in freshwater and saltwater species sensitivities, but the species compositions of datasets used are also important.