Guidance document on the impact of water treatment processes on residues of active substances or their metabolites in water abstracted for the production of drinking water

Pesticide transformation products: a potential new source of interest for drinking water

Pesticide transformation products (TPs) are frequently quantified in aquatic systems, including surface and groundwater. They often present higher polarity than parent compounds, are less volatile and less biodegradable and are therefore more mobile and persistent. These properties make them compounds of main interest in water resources and drinking water. With more than 600 samples collected over two years and nearly 100,000 results available, this study was carried out to evaluate the occurrence of 157 pesticide TPs and certain active substances in raw and drinking water in France. Our study made it possible to assess the potential exposure of the population to pesticides and their metabolites through drinking water consumption and finally to put forward new TPs of interest for the monitoring of drinking water. Among TPs, chlorothalonil R471811 and metolachlor ESA were the most frequently quantified compounds, with quantification in more than 50% of raw and drinking water. TPs dimethachlor CGA369873, chlorothalonil R471811 and R417888, terbuthylazine LM2 and LM6, desphenyl chloridazon (DPC) and methyldesphenyl chloridazon (MeDPC) were monitored for the first time in drinking water in France. Concentrations exceeding the regulatory quality standard of 0.1 µg.L-1 were observed in more than 30% of drinking water samples for chlorothalonil R471811, and a maximum concentration was measured at 9.8 µg.L-1 for DPC in drinking water. The quantification frequencies were relatively similar in raw water and tap water, which appears to indicate poor efficiency of the majority of the currently used drinking water treatment plants. This research confirmed the benefit of focusing on TPs and parent compounds, and also to continue monitoring TPs that originate from compounds already withdrawn from the market for several years that appear to be highly persistent.

Occurrence, dispersal, and associated environmental risk assessment of pesticides and their transformation products in small water bodies of Northeastern France

The widespread use of pesticides, specifically plant protection products (PPPs), has led to their transformation products (TPs) being increasingly detected in various environmental compartments, notably surface waters. This study integrates field-detected TPs into an environmental risk assessment of lentic small water bodies (LSWBs). For this purpose, measured environmental concentrations (MECs) of PPPs and TPs in 12 LSWBs, influenced by tributaries under varying agricultural pressures, were collected. Ecotoxicological data from multiple sources were compiled to calculate risk quotients (RQs) and identify potentially harmful PPPs and TPs. Among 86 molecules investigated, 17 PPPs and 30 TPs were detected, representing nearly half of those initially targeted. Ponds exhibited diverse PPP and TP compositions and levels with 12 substances posing high pesticide risk, primarily atrazine-2-hydroxy, MCPA, and metolachlor. Various pond conditions indicated moderate to high risk to aquatic organisms at corresponding MECs. Despite diverse agricultural pressures, only one site was deemed low-risk, highlighting widespread contamination risk due to co-occurring molecules. Given the prevalence of TPs in water bodies, urgent efforts are needed to gather ecotoxicological data on these contaminants to enhance environmental risk assessments. This study provides novel insights into pesticide risks in a less-studied yet common European landscape, focusing on TPs.

Should Transformation Products Change the Way We Manage Chemicals?

When chemical pollutants enter the environment, they can undergo diverse transformation processes, forming a wide range of transformation products (TPs), some of them benign and others more harmful than their precursors. To date, the majority of TPs remain largely unrecognized and unregulated, particularly as TPs are generally not part of routine chemical risk or hazard assessment. Since many TPs formed from oxidative processes are more polar than their precursors, they may be especially relevant in the context of persistent, mobile, and toxic (PMT) and very persistent and very mobile (vPvM) substances, which are two new hazard classes that have recently been established on a European level. We highlight herein that as a result, TPs deserve more attention in research, chemicals regulation, and chemicals management. This perspective summarizes the main challenges preventing a better integration of TPs in these areas: (1) the lack of reliable high-throughput TP identification methods, (2) uncertainties in TP prediction, (3) inadequately considered TP formation during (advanced) water treatment, and (4) insufficient integration and harmonization of TPs in most regulatory frameworks. A way forward to tackle these challenges and integrate TPs into chemical management is proposed.

Metabolites in the regulatory risk assessment of pesticides in the EU

A large majority of chemicals is converted into metabolites through xenobiotic-metabolising enzymes. Metabolites may present a spectrum of characteristics varying from similar to vastly different compared with the parent compound in terms of both toxicokinetics and toxicodynamics. In the pesticide arena, the role of metabolism and metabolites is increasingly recognised as a significant factor particularly for the design and interpretation of mammalian toxicological studies and in the toxicity assessment of pesticide/metabolite-associated issues for hazard characterization and risk assessment purposes, including the role of metabolites as parts in various residues in ecotoxicological adversities. This is of particular relevance to pesticide metabolites that are unique to humans in comparison with metabolites found in in vitro or in vivo animal studies, but also to disproportionate metabolites (quantitative differences) between humans and mammalian species. Presence of unique or disproportionate metabolites may underlie potential toxicological concerns. This review aims to present the current state-of-the-art of comparative metabolism and metabolites in pesticide research for hazard and risk assessment, including One Health perspectives, and future research needs based on the experiences gained at the European Food Safety Authority.