Abstract
Synthetic chemicals are frequently detected in water bodies, and their concentrations vary over time. Water monitoring programs typically employ either a sequence of grab samples or continuous sampling, followed by chemical analysis. Continuous time-proportional sampling yields the time-weighted average concentration, which is taken as proxy for the real, time-variable exposure. However, we do not know how much the toxicity of the average concentration differs from the toxicity of the corresponding fluctuating exposure profile. We used toxicokinetic-toxicodynamic models (invertebrates, fish) and population growth models (algae, duckweed) to calculate the margin of safety in moving time windows across measured aquatic concentration time series (7 pesticides) in 5 streams. A longer sampling period (14 d) for time-proportional sampling leads to more deviations from the real chemical stress than shorter sampling durations (3 d). The associated error is a factor of 4 or less in the margin of safety value toward underestimating and an error of factor 9 toward overestimating chemical stress in the most toxic time windows. Under- and overestimations occur with approximate equal frequency and are very small compared with the overall variation, which ranged from 0.027 to 2.4 × 1010 (margin of safety values). We conclude that continuous, time-proportional sampling for a period of 3 and 14 d for acute and chronic assessment, respectively, yields sufficiently accurate average concentrations to assess ecotoxicological effects. Environ Toxicol Chem 2020;39:2158-2168. © 2020 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.
Highlights
Synthetic chemicals such as pesticides, pharmaceuticals, biocides, industrial chemicals, and veterinary medicines either are released directly into the environment or reach the environment after their intended use and disposal
We analyzed the margin of safety values from the most toxic time windows, that is, those with the smallest margin of safety values (Figure 2)
We found that the time‐proportional sampling method is associated with an error of factor 4 or less in the margin of safety value toward underestimating chemical stress and an error of factor of 9 toward overestimating chemical stress
Summary
Synthetic chemicals such as pesticides, pharmaceuticals, biocides, industrial chemicals, and veterinary medicines either are released directly into the environment or reach the environment after their intended use and disposal. They are often termed “micropollutants” because they occur in the range of micrograms per liter (Schwarzenbach et al 2006). Assessing the risk to the environment of these chemicals requires measuring their presence in water bodies and establishing their temporal concentration profile. Monitoring strategies typically either use a sequence of grab samples (e.g., European Community 2000; Baas et al 2016) or continuous sampling where samples are pooled over a certain time period, followed by chemical analysis of the pooled sample for the whole sampling duration
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