Effect Modeling Quantifies the Difference Between the Toxicity of Average Pesticide Concentrations and Time‐Variable Exposures from Water Quality Monitoring

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 × 10 10 (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.

Internal Concentrations in Gammarids Reveal Increased Risk of Organic Micropollutants in Wastewater-Impacted Streams

“…This high detection frequency of neonicotinoids was unexpected, considering that these substances are very polar (log D ow 0.6–1.3) and only few detections were found in the water samples at the same sites with maximum concentration of 24 ng/L for thiacloprid . Further, a recent report on the uptake of pesticides applying the toxicokinetic-toxicodynamic model developed by Jager et al (2011) predicts no delayed release of imidacloprid indicating a fast elimination of this substance in gammarids …”

Environmental Risk of Pesticides for Fish in Small- and Medium-Sized Streams of Switzerland

“…In this case, the PNEC i,fish,acute was compared to the MEC of each sample analyzed irrespective of the collection period. For 2017 data, RQ i,acute were determined using MEC of 3.5-day TP composite samples based on [30]. For 2015 and 2017 data, we used 14-day time-weighted (TW) average MEC for the calculation of RQ i,chronic .…”

Use of Postregistration Monitoring Data to Evaluate the Ecotoxicological Risks of Pesticides to Surface Waters: A Case Study with Chlorpyrifos in the Iberian Peninsula

“…Continuous time-proportional sampling with autosamplers or passive sampling devices has been proposed to reduce uncertainties in the risk assessment of pesticides in Mediterranean rivers (Rico et al 2019a). As recommended by Spycher et al (2018), time-weighted average concentrations of 3 d are required as a minimum to reduce uncertainties in acute pesticide risk assessments, and 14-d time-weighted average concentrations have been proposed by Ashauer et al (2020) for chronic risk assessments based on effect modeling. Therefore, focus-based monitoring of insecticides (i.e., with higher sampling frequency and temporal resolution), particularly during heavy precipitation events, is recommended in vulnerable littoral Mediterranean areas impacted by citrus production.…”