ABSTRACT
There is clear scientific evidence to support the contention that aquatic macrophytes play a key role in the structure and functioning of aquatic ecosystems and, hence, must be considered within the risk assessment process for plant protection products (see Section 6.1). Under existing risk assessment procedures in the European Union (EU), the risk of herbicides to aquatic plants and algae is initially evaluated by calculating toxicity exposure ratios (TERs) between toxicity endpoints (EC50), derived from standard laboratory tests with 2 algae and one Lemna species, and predicted environmental concentrations (PECs). The resulting TER is compared with a trigger of 10, defined in Annex VI of 91/414/EEC. TER values that exceed this trigger indicate that the compound under evaluation can be considered to pose an acceptable risk to aquatic plants and algae, whereas TER values that fall below this trigger indicate a potential unacceptable risk and the need for a higher-tier risk assessment. However, there is concern that risk assessments based on Lemna endpoints may not be protective of other macrophyte species. Furthermore, there is a lack of guidance on the conduct and design of higher-tier studies focusing on aquatic macrophytes. Both issues were considered during the workshop.
