U.S. Geological Survey Toxic Substances Hydrology Program--Proceedings of the Technical Meeting Charleston South Carolina March 8-12,1999--Volume 2 of 3--Contamination of Hydrologic Systems and Related Ecosystems, Water-Resources Investigation Report 99-4018B

An Ecological Risk Assessment of the Potential for Herbicide Impacts on Primary Productivity of the Lower Missouri River

by James F. Fairchild, Linda C. Sappington, and David S. Ruessler

This report is available in pdf format: Fairchild.pdf

ABSTRACT

The Lower Missouri River Basin has been drastically altered due to impoundment, channelization, and conversion of the floodplain to agriculture. Agricultural practices have led to both ecological and human health concerns related to herbicide use. A study was conducted to perform an ecological risk assessment of the potential impacts of herbicides on aquatic plant communities of the Lower Missouri River Basin. Sixteen heribicides (atrazine, metribuzin, simazine, cyanazine, alachlor, metolachlor, chlorsulfuron, metsulfuron, triallate, EPTC, trifluralin, diquat, paraquat, dicamba, bromoxynil, and 2,4-D) were tested using one species of algae (Selenastrum capricornutum) and one floating macrophyte (Lemna minor). These herbicides represented nine chemical classes and several modes of action and were chosen to represent major current uses in the U.S. The triazinone herbicide metribuzin and the sulfonylurea herbicides chlorsulfuron and metsulfuron were highly toxic but do not necessarily represent a large aquatic risk due to the low rates of application. Bromoxynil, dicamba, 2,4-D, and EPTC exhibited low toxicity. Diquat, paraquat, triallate, and trifluralin were relatively toxic but exhibit low environmental mobility. Cyanazine, alachlor, atrazine, and metolachlor pose the greatest risk to aquatic plants. However, a comparison of these toxicity data to published information concerning application rates, chemical fate, and measured environmental concentrations indicates that adverse impacts of herbicides on non-target aquatic plant communities of the Lower Missouri River are unlikely. However, human health concerns will continue to regulate the use of these chemicals.