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

Comparison of measured and predicted herbicide concentrations in surface water catchments in Belgium

In the process of approval of active substances and authorization in the European Union and at the member state level, it must be shown by the applicant that an unacceptable risk for nontarget organisms in the aquatic environment by the active substance can be excluded. To achieve this aim, standardized models, scenarios, and agreed pesticide input parameters have to be used to calculate the exposure as defined by the FOrum for the Co-ordination of pesticide fate models and their Use (FOCUS). During a period of daily surface water sampling lasting 3.5 years, a survey was conducted among farmers in the highly vulnerable catchment of Grote Kemmelbeek in Belgium to collect agronomic data on crops, application dates, and application rates of 12 applied herbicides and one metabolite. Daily surface water concentrations for the same herbicides were measured over 2.5 years for a second, much larger but less vulnerable, catchment of Kleine Aa (KAa). A comparison of realistic worst-case predicted environmental concentrations in surface water (PECsw) according to FOCUS with measured concentrations shows that, in the GKb catchment, the PECsw was never exceeded for six substances, was exceeded on only 1-2 days for five substances, and was exceeded on 9-27 days for two substances. For the KAa catchment, the PECsw was only exceeded on two days for one compound and never for the other 12 compounds. These numbers correspond to a level of protection of the FOCUS PECsw between 100% and 97% and are much higher than the regulatory protection goal of 90%. These two case studies demonstrate the protectiveness of the FOCUS surface water approach. Integr Environ Assess Manag 2024;20:1447-1462. © 2024 Bayer AG. Integrated Environmental Assessment and Management published by Wiley Periodicals LLC on behalf of Society of Environmental Toxicology & Chemistry (SETAC).

Linking chemical surface water monitoring and pesticide regulation in selected European countries

The progress in chemical analytics and understanding of pesticide dynamics in surface waters allows establishing robust data on compounds with frequent exceedances of quality standards. The current chemical, temporal, and spatial coverage of the pesticide monitoring campaigns differs strongly between European countries. A questionnaire revealed differences in monitoring strategies in seven selected European countries; Nordic countries prioritize temporal coverage, while others focus on spatial coverage. Chemical coverage has increased, especially for non-polar classes like synthetic pyrethroids. Sweden combines monitoring data with agricultural practices for derived quantities, while the Netherlands emphasizes spatial coverage to trace contamination sources. None of the EU member states currently has established a process for linking chemical surface water monitoring data with regulatory risk assessment, while Switzerland has recently established a legally defined feedback loop. Due to their design and objectives, most strategies do not capture concentration peaks, especially 2-week composite samples, but also grab samples. Nevertheless, for substances that appear problematic in many data sets, the need for action is evident even without harmonization of monitoring programs. Harmonization would be beneficial, however, for cross-national assessment including risk reduction measures.

TWAc-Check: A New Approach to Determine the Appropriate Use of Time-Weighted Average Concentration in Aquatic Risk Assessment

In pesticide risk assessment, regulatory acceptable concentrations for surface water bodies (RACsw,ch) are used that are derived from standard studies with continuous exposure of organisms to a test compound for days or months. These RACsw,ch are compared with the maximum tested concentration of more realistic exposure scenarios. However, the actual exposure duration could be notably shorter (e.g., hours) than the standard study, which intentionally leads to an overly conservative Tier 1 risk assessment. This discrepancy can be addressed in a risk assessment using the time-weighted average concentration (TWAc). In Europe, the applicability of TWAc for a particular risk assessment is evaluated using a complex decision scheme, which has been controversial; thus we propose an alternative approach: We used TWAc-check (which is based on the idea that the TWAc concept is just a model for aquatic risk assessment) to test whether the use of a TWAc is appropriate for such assessment. The TWAc-check method works by using predicted-measured diagrams to test how well the TWAc model predicts experimental data from peak exposure experiments. Overestimated effects are accepted because the conservatism of the TWAc model is prioritized over the goodness of fit. We illustrate the applicability of TWAc-check by applying it to various data sets for different species and substances. We demonstrate that the applicability is case dependent. Specifically, TWAc-check correctly identifies that the use of TWAc is not appropriate for early onset of effects or delayed effects. The proposed concept shows that the time window is a decisive factor as to whether or not the model is acceptable and that this concept can be used as a potential refinement option prior to the use of toxicokinetic-toxicodynamic models. Environ Toxicol Chem 2022;41:1778-1787. © 2022 Bayer AG. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

A critical review of effect modeling for ecological risk assessment of plant protection products

A wide diversity of plant protection products (PPP) is used for crop protection leading to the contamination of soil, water, and air, which can have ecotoxicological impacts on living organisms. It is inconceivable to study the effects of each compound on each species from each compartment, experimental studies being time consuming and cost prohibitive, and animal testing having to be avoided. Therefore, numerous models are developed to assess PPP ecotoxicological effects. Our objective was to provide an overview of the modeling approaches enabling the assessment of PPP effects (including biopesticides) on the biota. Six categories of models were inventoried: (Q)SAR, DR and TKTD, population, multi-species, landscape, and mixture models. They were developed for various species (terrestrial and aquatic vertebrates and invertebrates, primary producers, micro-organisms) belonging to diverse environmental compartments, to address different goals (e.g., species sensitivity or PPP bioaccumulation assessment, ecosystem services protection). Among them, mechanistic models are increasingly recognized by EFSA for PPP regulatory risk assessment but, to date, remain not considered in notified guidance documents. The strengths and limits of the reviewed models are discussed together with improvement avenues (multigenerational effects, multiple biotic and abiotic stressors). This review also underlines a lack of model testing by means of field data and of sensitivity and uncertainty analyses. Accurate and robust modeling of PPP effects and other stressors on living organisms, from their application in the field to their functional consequences on the ecosystems at different scales of time and space, would help going toward a more sustainable management of the environment. Graphical Abstract Combination of the keyword lists composing the first bibliographic query. Columns were joined together with the logical operator AND. All keyword lists are available in Supplementary Information at https://doi.org/10.5281/zenodo.5775038 (Larras et al. 2021).

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

This study assessed the acute and chronic risk of pesticides, singly and as mixtures, for fish using comprehensive chemical data of four monitoring studies conducted in small- and medium-sized streams of Switzerland between 2012 and 2018. Pesticides were ranked based on single substance risk quotients and relative contribution to mixture risk. Concentrations of the pyrethroid insecticides, λ-cyhalothrin, cypermethrin and deltamethrin, and the fungicides, carbendazim and fenpropimorph, posed acute or chronic single substance risks. Risk quotients of eighteen additional pesticides were equal or greater than 0.1, and thirteen of those contributed ≥30% to mixture risk. Relatively few substances dominated the mixture risk in most water samples, with chronic and acute maximum cumulative ratios never exceeding 5 and 7, respectively. A literature review of toxicity data showed that concentrations of several pesticides detected in Swiss streams were sufficient to cause direct sublethal effects on fish in laboratory studies. Based on the results of our study, we conclude that pesticides detected in Swiss streams, especially pyrethroid insecticides, fungicides and pesticide mixtures, pose a risk to fish health and can cause direct sublethal effects at environmental concentrations. Sensitive life stages of species with highly specialized life history traits may be particularly vulnerable; however, the lack of toxicity data for non-model species currently prevents a conclusive assessment across species.

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

Chemical monitoring data sets such as those provided by the implementation of the Water Framework Directive (WFD) offer opportunities to evaluate the ecological risks of pesticides under large spatiotemporal scales and to evaluate the protectiveness of the current prospective risk-assessment framework. As a case study, we used the monitoring data set for the insecticide chlorpyrifos to perform a probabilistic risk assessment for Iberian surface-water ecosystems. The specific objectives of the study were 1) to assess the occurrence of chlorpyrifos in relation to different agricultural production land uses, 2) to assess the spatiotemporal variation in the exceedance of the European WFD short- and long-term environmental quality standards (maximum allowable concentration environmental quality standard [MAC-EQS] and annual average [AA] EQS), and 3) to perform a probabilistic risk assessment for freshwater invertebrates. A database that contains chlorpyrifos concentrations from 14 600 surface water samples taken between 2012 and 2017 in the Iberian Peninsula (Spain and Portugal) was analyzed, and chlorpyrifos was detected in 21% of these samples. The MAC-EQS was exceeded in 2% of the cases, whereas the AA-EQS was exceeded in 18% of the cases. The majority of the exceedances took place in the littoral areas of the eastern and southeastern parts of the Iberian Peninsula, particularly in areas with dominant citrus production during late spring, late summer, and autumn. The present study indicates unacceptable risks posed by chlorpyrifos to Iberian surface waters over the study period, although it was approved for use in Europe. The present study supports the need to perform further postregistration monitoring assessments with other pesticides following similar approaches, which can help to identify possible pesticide-misuse practices and improvements of the prospective risk-assessment framework. Environ Toxicol Chem 2021;40:500-512. © 2020 SETAC.