A PROPOSED OECD TEST GUIDELINE FOR THE SUBMERGED, SEDIMENT-ROOTED MACROPHYTE, MYRIOPHYLLUM

Introduction Currently, the risk of herbicides to aquatic plants is evaluated from data for four algal species and a single macrophyte species, in the US, and from data for two algal species and one macrophyte species, in the EU. In both cases, the standard macrophyte test species is Lemna gibba or L. minor. In the EU, concern has been expressed that risk assessments based on Lemna species may underestimate toxicity of some chemistries to other macrophyte species, particularly sediment-rooted species. Recent guidance published from the SETAC workshop on Aquatic Macrophyte Risk Assessment for Pesticides (AMRAP) proposed that data for a rooted macrophyte species may be required under the following circumstances: • If Lemna is known not to be sensitive to the mode of action. • If Tier 1 Lemna and algal EC50 values are > 1 mg ai/L. • If partitioning to sediment is a concern. The submerged, dicotyledonous species, Myriophyllum, was selected by AMRAP participants as a suitable test species in light of prior experience and its known sensitivity to some herbicide chemistries. A protocol was then developed for validation in a pre-test (11 laboratories) and final ring-test ( 14 laboratories) as shown in Tables 1 and 5.