Effects of seven forestry management herbicides on Myriophyllum sibiricum,as compared with other nontarget aquatic organisms

Historically, studies on the nontarget aquatic effects of forest-use herbic ides focused largely on fish and invertebrates despite the ecological impor tance of aquatic plants. Regulatory requirements and the aquatic phytotoxic ity database need to be improved to reflect the importance of aquatic plant s. Based on a review of the scientific literature and results from laborato ry testing with the submersed macrophyte Myriophyllum sibiricum Komarov, th e effects of 2,4 dichlorophenoxyacetic acid (2,4-D), glyphosate, hexazinone , imazapyr, metsulfuron methyl, sulfometuron methyl, acid triclopyr on nont arget aquatic organisms were compared. laboratory results indicate that M, sibiricum is sensitive to herbicide effects, especially those that impact r oot growth. For most herbicides, the inhibitory concentrations 25 and 50 (I C25 and IC50, concentrations that inhibit an endpoint parameter by 25 and 5 0%, respectively) for shoot and root growth were below the expected environ mental concentrations (EEC). For example, the IC50 values for root dry mass were 0.000 12 and 0.000 22 mg active ingredient/L for sulfometuron methyl and metsulfuron methyl, respectively, concentrations that were approximatel y 3100 and 1700 times below the EEC for these compounds. Interspecies compa risons, conducted during this study, demonstrated that M. sibiricum was gen erally equally or more sensitive to these herbicides than other aquatic pla nt species (i.e., floating macrophytes and algae) and, in some cases, mon s ensitive than fish, zooplankton, and other invertebrates. For example, avai lable data demonstrated that 2,4-D, imazapyr, and the sulfonylureas investi gated were more toxic to rooted and floating macrophytes than to other aqua tic organisms, including algae. Because of the high sensitivity and ecologi cal significance of aquatic macrophytes, a greater emphasis should be place d on evaluating aquatic phytotoxicity in future ecotoxicological research.