CANADIAN WATER-QUALITY GUIDELINES FOR LINURON

The environmental chemistry, fate, and toxicology of the herbicide, li nuron, is reviewed. Linuron is a phenylurea herbicide used for selecti ve control of annual weeds in fruit and field crops and noncrop areas. Linuron is soluble in water which suggests that it may leach readily through soils. Its log K-oc for soil is 2.83, which indicates a modera te adsorption potential and a moderate mobility. Its half-life is less than 4 weeks in water and approximately 2 months in soil. The primary mode of degradation is microbial. In regions of intensive agriculture , linuron concentrations up to 1100 and 2800 mu g L-1 have been detect ed in Canadian surface waters and ground waters, respectively. Duckwee d (Lemna minor), the most sensitive freshwater species for which data were available, had a 5-d lowest-observed-eff ect level of 70 mu g L-1 for growth inhibition. The most sensitive crop species was the tomato (Lycopersicum esculentum) with a LOEAR of 0.018 kg ha(-1) for reduced fresh weight. Canadian Water Quality Guidelines (CWQG) specify levels of contaminants that should not be exceeded in order to protect and s ustain the major beneficial uses of water in Canada. For linuron, suff icient toxicity data were available to derive an interim CWQG of 7 mu g L-1 for the protection of freshwater life, a full CWQG of 0.071 mu g L-1 for irrigation water to protect cereals, tame hays, and pasture, and an interim CWQG of 3.3 mu g L-1 for irrigation water to protect ot her crops. (C) 1998 by John Wiley & Sons, Inc.