Conducting groundwater monitoring studies in Europe for pesticide active substances and their metabolites in the context of Regulation (EC) 1107/2009

Executive summary Groundwater monitoring is recommended as a higher-tier option in the regulatory groundwater assessment of plant protection products in the European Union. However, to date little guidance has been provided on study designs. SETAC EMAG-Pest GW, a group of regulatory, academic, and industry scientists, was created in 2015 to establish scientific recommendations for conducting such studies. This report provides the SETAC EMAG-Pest GW group’s recommendations on study designs and study procedures. Because of the need to assess the vulnerability to leaching in both site selection and in extrapolating study results, information on how to assess the vulnerability to leaching is a major topic in this report. In the development of groundwater study designs, which groundwater needs to be protected and to what level are key aspects. In the European Union, a groundwater quality standard of 0.1 µg/L applies to active substances and relevant metabolites, but the groundwater to which this standard is applied varies among the Member States. Also, the definition of the concentration may consider temporal or spatial variability (e.g. a single sample or an average concentration over a period of time or geographic area). The SETAC EMAG-Pest GW group does not endorse any specific exposure assessment option. However, 7 different exposure assessment options that consider only the location of the groundwater to which the ground water quality standard is applied were selected to illustrate the impact of the exposure assessment option on the study design. Monitoring can be performed on many different geographical scales. In-field and edge-of-field monitoring focus on residues from applications to a single field, while catchment and aquifer monitoring focus on residues in groundwater over a larger area. The timing of applications in monitoring studies can vary. In a prospective study, an application is made and the movement and degradation of the residues is followed. In a retrospective study, residues from previous applications are monitored. Some studies are both retrospective and prospective—residues from previous applications are monitored and a new application is made and the residues are followed. In addition to the exposure assessment option, study designs must consider the objectives of the study, the properties of the active substance and its metabolites, and the site characteristics. Usually, the objective is to determine whether a substance can move into the groundwater specified in the exposure assessment option as well as the magnitude of residues in groundwater. The objective may also include determining degradation rates in soil as a function of depth, persistence and movement of residues in groundwater, efficacy of mitigation measures, or confirmation of more detailed studies on a wider range of sites. Sampling schedules should consider the expected time required for an active substance to move through the soil into groundwater, as well as expected persistence in both soil and groundwater. Movement and persistence can be affected by both site characteristics and properties of the active substance and its metabolites. The need to tailor study designs to objectives, exposure assessment options, compound properties and site characteristics complicates the development of standardised study designs. Therefore, this report includes a number of example designs. Other key points that must be addressed by study designs are the vulnerability of the chosen sites compared to the vulnerability of all use areas supported by the study, the product use before and during the study, and the connectivity of the sampled groundwater to treated fields. Demonstrating connectivity (a quality criterion in the EU assessment of monitoring sites to exclude false negative measurements) is more challenging for catchment or aquifer monitoring compared to shallow wells installed as part of in-field or edge-of-field studies. This report includes an extensive discussion on assessing vulnerability of monitoring sites. This includes information on different approaches to vulnerability assessment and mapping as well as for setting monitoring sites into context. Lists of available methods and data sources available at the European level are also included. In addition to information on study design and estimating vulnerability, this report includes information on a number of other topics: avoiding contamination during sampling and/or analysis, avoiding influencing residue movement as a result of purging during sampling, and proper study documentation (Good Laboratory Practices and/or quality criteria). Procedures that are discussed include site selection (new or existing wells), installation of monitoring wells, sample collection, and analysis of samples. The report also provides information on causes of outliers (abnormally high concentrations not the result of normal leaching through soil), the use of public monitoring data, information on further hydrological characterisation (such as use of tracers, groundwater age dating, and geophysical methods), and information that should be included in reports providing results of groundwater studies. Abstract Groundwater monitoring is recommended as a higher-tier option in the regulatory groundwater assessment of crop protection products in the European Union. However, to date little guidance has been provided on the study designs. The SETAC EMAG-Pest GW group (a mixture of regulatory, academic, and industry scientists) was created in 2015 to establish scientific recommendations for conducting such studies. This report provides recommendations for study designs and study procedures made by the Society of Environmental Toxicology and Chemistry (SETAC) Environmental Monitoring Advisory Group on Pesticides (EMAG-Pest). Because of the need to assess the vulnerability to leaching in both site selection and extrapolating study results, information on assessing vulnerability to leaching is also a major topic in this report. The design of groundwater monitoring studies must consider to which groundwater the groundwater quality standard is applicable and the associated spatial and temporal aspects of its application, the objective of the study, the properties of the active substance and its metabolites, and site characteristics. This limits the applicability of standardised study designs. The effect of the choice of groundwater to which the water quality guideline is applied on study design is illustrated and examples of actual study designs are presented.