The fate of fenitrothion in a stream environment and its effect on the fauna, following aerial spraying of a Scottish forest.

In order to control an infestation of Pine Beauty moth (Panolis flammea Schiff.) fenitrothion was applied at a rate of 300 g ha-1 to a forest plantation consisting primarily of Lodgepole Pine (Pinus contorta Loud.) and Sitka Spruce (Picea sitchensis Carriere) using the ultra-low volume spraying technique. The concentration of fenitrothion in the forest stream rose to a maximum of 18 micrograms l-1 within the treated area an hour after spraying, but fell to 0.5 microgram l-1 after 24 hs. There was no evidence that the resident fish population was disturbed by the treatment and no short term effects were noticeable in caged fish. The concentration--time profile in the fish followed closely the profile in the water, and in each of the four fish tissues studied fell to 0.02 mg kg-1 after 24 hs. Invertebrate drift increased markedly 12--16 hs after spraying, but decreased to around pre-treatment levels within 48 hs. Caged insects remained alive during the five-day post-spray observation period, suggesting that drifting insects were displaced rather than killed by the insecticide. Concentration of fenitrothion in Willow Moss (Fontinalis antipyretica) fell from 0.139 mg kg-1 to 0.003 mg kg-1 (wet weight) after 48 hs. Fenitrothion was not detected in sediment but this was possibly due to the low surface area/weight ratio of the particles.