The use of pesticides, particular herbicides, on arable crops may affect not only target organisms, but can also influence aquatic communities of small water bodies due to drift, run-off and drainage incidents. For the registration of a plant protection product, this concern is normally evaluated in the first tier of testing by using the floating aquatic macrophyte Lemna sp. Although Lemna sp. is widespread and common in UK waters, its physiology and life cycle are not representative of many species of aquatic plants found in UK water bodies. Water bodies are dominated by rooted emergent macrophytes, with floating macrophytes representing the smallest fraction of the community (ref. PN0931).
The effects of pesticide exposure on rooted macrophytes may not be adequately addressed in the current risk assessment framework and it may be necessary to develop standardised test procedures for one or more aquatic macrophyte species. These would need to be representative of sensitive macrophyte species exposed through spray drift (exposed macrophytes), run-off and drain flow (submerged and rooted macrophytes). Such tests may help to reduce the uncertainties associated with interspecies variability and also allow impacts of exposure through sediment to be addressed.
A wide variety of species and endpoints have been used in research in an attempt to address these issues. Species have included Myriophyllum spicatum and Myriophyllum sibiricum, Potamogeton pectinatus, Eriocaulon septangulare, Juncus effuses, Oryza sativa, Vallisneria americana, Ceratophyllum sp., Najas sp., Elodea sp. and of course Lemna sp.. Endpoints have included plant length, root growth, number of nodes, wet and dry mass, visual observations, residue, leaf and root surfaces area, leaf-to-root surface area ratio, leaf-to-root mass ratio, shoot density and number of short shoots, chlorophyll-a, chlorophyll-b, carotenoid content, citric acid levels, Chlorophyll-a fluorescence induction, peroxidase (POD) activity and stress protein (SP) synthesis (Lytle et al. (2005); Davies et al. (2003); Hanson et al. (2002); Marwood et al. (2001); Stewart (1999); Fairchild et al. (1998); Biernacki et al. (1997); Siesko et al. (1997); Powell et al. (1996)).
In the light of these observations, an ideal testing strategy would incorporate more macrophyte species. The difficulty facing the regulatory community is the identification of species that are representative of relatively sensitive species in the environment, express toxicity associated with relevant exposure routes, can be maintained in laboratory conditions and have reliable endpoints with low inherent variability. Basic information on these issues is provided by the final report of the DEFRA research project PN0804 (Development of toxicity tests for assessing pesticide effects on non-target aquatic plants). However, further research is required e.g. regarding maintanance of laboratory cultures, quantification of the ability to recover from effects of sub-lethal herbicide doses and in determination if recovery in Lemna can be extrapolated to other species.
As a first step, current practices, additional requirements across the EU and areas of concerns with current methods as well as expertise and capabilities will be identified. Information on the range and reliability of existing protocols will be collated and the main conclusions and findings will be documented in a summary report.
This will be achieved by firstly designing a questionaire to seek information on the key issues, for distribution to relevant institutions and experts from the five regulatory authorities proposed by PSD. Responses via email will then be collated. Face to face meetings or telephone discussions will be conducted with institutions and regulatory authorities as required.