Summertime transport of current-use pesticides from California's Central Valley to the Sierra Nevada Mountain Range, USA

Agricultural activity in California's Central Valley may be an important so urce of pesticides that are transported in the air to the: Sierra Nevada Mo untain Range, USA. Pesticides applied to this intensive crop production are a may volatilize under warm temperatures typical of the valley and be trans ported through the atmosphere to be deposited in the cooler, higher elevati on regions of the Sierra Nevada Mountains. To determine the extent of summe rtime atmospheric transport of pesticides to this region, high-volume air, dry deposition, and surface water samples were collected in the Central Val ley and at different elevations in California's Sequoia National Park. Resu lts revealed that the highest residue concentrations were those of compound s with heavy summertime agricultural use. A significant drop in pesticide c oncentrations in both air and water samples was observed within a few 100-m elevation from the valley; however, levels remained relatively constant be tween similar to 500 and 2,000 m. Water concentrations from two areas above 3,000 m contained levels less than a tenth as high as those at lower eleva tions. Possible effects of the pesticides were estimated using measured wat er concentrations to calculate total exposure of three aquatic species to o rganophosphate insecticides. Aggregate exposure calculations showed concent rations were well below 96-h LC50 values for rainbow trout and stonefly but concentrations may be harmful to amphipods.