Aquatic macrophyte growth season in Central and Northern European Union and the implications for aquatic macrophyte risk assessments for herbicides

Under current European Union regulation, the risks to aquatic organisms must be assessed for uses of plant protection products (PPPs) that may result in exposure to the environment. For herbicidal PPPs, aquatic macrophytes are often the most sensitive taxa. For some herbicidal modes of action, macrophytes may be affected only while they are actively growing. For the risk assessment, it is therefore useful to know whether application timings would result in surface water exposure during periods when aquatic macrophytes are actively growing (therefore potentially resulting in effects). Toxicity endpoints, which are based on studies with active growth, may be overconservative in cases where exposure of PPPs will not co-occur with active macrophyte growth. A comprehensive literature search was performed, using systematic and manual approaches, with the aim of identifying the main active growth period for macrophytes in natural freshwater bodies in climates relevant to the Central and Northern zones of the European Union. The results of the searches were screened initially to identify all potentially relevant references, for which a full evaluation was then performed. Reliability was assessed using the principles of the Klimisch scoring system. As part of the full evaluation, growth periods were identified for each macrophyte species studied. Finally, the extracted growth periods were considered together to determine an overall active growth period for aquatic macrophytes representative of the Central and Northern EU zones. Based on this literature review, the active growth period identified for most aquatic macrophyte species representative of the Central and Northern EU zones is April to September. Relating to the regulatory implication of these results, it may be possible to conclude a low risk for aquatic macrophytes if the predicted surface water exposure period for certain PPPs is demonstrated to be outside the periods of active growth. Integr Environ Assess Manag 2023;00:1-15. (c) 2023 The Authors. Integrated Environmental Assessment and Management published by Wiley Periodicals LLC on behalf of Society of Environmental Toxicology & Chemistry (SETAC). A literature search was performed with the aim of identifying aquatic macrophyte growth periods relevant to the Central zone (CZ) and the Northern zone (NZ) of the European Union.Following a data mining exercise using peer-reviewed journals, 25 publications were reviewed and considered relevant to the aims of this report, from which 43 collated growth periods were extracted.The extracted data were concluded to support a growth period for aquatic macrophytes in CZ and NZ EU beginning in April and ending in September.This has implications for the authorization of plant protection products with herbicidal modes of action, which act on macrophytes when they are actively growing.