ATMOSPHERIC DEPOSITION OF PESTICIDES IN A SMALL SOUTHERN SASKATCHEWANWATERSHED

Weekly atmospheric deposition samples were collected from early May to early September during 1984 to 1987 in a small agricultural watershed near Regina, Saskatchewan, an area in the midst of extensive agricult ural pesticide use in the Canadian prairies. ''Bulk'' deposition sampl es were collected weekly in duplicate and analyzed for six herbicides (bromoxynil, 2,4-D, dicamba, diclofop, triallate, and trifluralin) and five insecticides (carbaryl, carbofuran, chlorpyrifos, deltamethrin, and dimethoate). In general, no significant differences were found amo ng the duplicate samples. Over the 4-year period, the frequency of wee kly detection of herbicides during the growing seasons was 0, 32, 39, 53, 58, and 67% for trifluralin, bromoxynil, triallate, diclofop, dica mba, and 2,4-D, respectively. For insecticides, only carbaryl and carb ofuran were detected in one to two samples in the years for which the insecticides were analyzed. This infrequent detection reflected the re latively high detection limits set for the insecticides as compared to those for the herbicides. The seasonal herbicide atmospheric deposits during the growing period over the 4-year period (mg ha(-1)) ranged f rom 90 to 234 (bromoxynil), 386 to 1,374 (2,4-D), 20 to 219 (dicamba), 43 to 338 (diclofop), and 9 to 260 (triallate). Highest deposition ra tes were measured during and immediately following the spraying period s, with lesser, but significant, amounts also being detected during th e harvest operations in August.