COMPARATIVE SENSITIVITY OF 5 SPECIES OF MACROPHYTES AND 6 SPECIES OF ALGAE TO ATRAZINE, METRIBUZIN, ALACHLOR, AND METOLACHLOR

This study determined the relative sensitivity of five species of aqua tic macrophytes and six species of algae to four commonly used herbici des (atrazine, metribuzin, alachlor, and metolachlor). Toxicity tests consisted of 96-h (duckweed and algae) or 14-d (submerged macrophytes) static exposures. The triazine herbicides (atrazine and metribuzin) w ere significantly more toxic to aquatic plants than were the acetanili de herbicides (alachlor and metolachlor). Toxicity studies ranked metr ibuzin > atrazine > alachlor > metolachlor in decreasing order of over all toxicity to aquatic plants. Relative sensitivities of macrophytes to these herbicides decreased in the order of Ceratophyllum > Najas > Elodea > Lemna > Myriophyllum. Relative sensitivities of algae to herb icides decreased in the order of Selenastrum > Chlorella > Chlamydomon as > Microcystis, Scenedesmus > Anabaena. Algae and macrophytes were o f similar overall sensitivities to herbicides. Data indicated that Sel enastrum, a commonly tested green alga, was generally more sensitive c ompared to other plant species. Lemna minor; a commonly tested floatin g vascular plant, was of intermediate sensitivity, and was fivefold le ss sensitive than Ceratophyllum, which was the most sensitive species tested. The results indicated that no species was consistently most se nsitive, and th;at a suits of aquatic plant test species may be needed to perform accurate risk assessments of herbicides.