PERMETHRIN TREATMENTS IN CANADIAN FORESTS .3. ENVIRONMENTAL FATE AND DISTRIBUTION IN STREAMS

Aerial applications of permethrin at 17.5 g ha-1 resulted in maximum concentrations of 0.07-2.50-mu-g litre-1 in stream water. The median maximum concentration was 0.54-mu-g litre-1 in oversprayed streams (n = 35, mean = 0.66) and 0.25-mu-g litre-1 1-1.4 km downstream of treated areas (n = 11, mean = 0.33). Permethrin residues in stream water declined with time and distance, with a mean disappearance rate of 0.106 h-1 and mean half-life of 10.3 h at oversprayed sites, and a mean disappearance rate of 0.202 h-1 and half-life of 3.9 h at downstream sites. Less than 8% of sediment samples from treated streams contained detectable permethrin concentrations (> 5 ng g-1). Approximately 50% of fish from streams in treated areas contained measurable residues (> 5 ng g-1) up to 28 days post-treatment. No residues were detected in fish at 69 or 73 days after the applications. In fish that contained measurable residues, the median bioconcentration factor was 98 (mean = 148).