Pesticides in Iowa Precipitation Rainfall has been sampled for pesticides at eight sites in Iowa since 1987 to assess the occurrence of pesticides in rainfall and the contribution of precipitation inputs to water resources. Six of the sites were in a rural setting and two in an urban setting. Eighteen pesticides were detected, including 12 herbicides and six insecticides. Atrazine, alachlor, cyanazine, and metolachlor were the most commonly detected herbicides, with one or more of these four herbicides found in almost every rainfall sample during the growing season. Pesticide concentrations ranged from 0.10 to 40.00 µg/L, with most detections less than 1.00 µg/L. Pesticide detections began in April and ended in July or August. Samples from the urban site had detections of the same agricultural chemicals found at the rural sites, but in lesser quantities. In addition to the commonly detected herbicides, 60% of the insecticides detected were in rain from the urban sites. Variation of pesticide detections were related to regional and local use patterns. Pesticide concentrations were greater at sampling sites near fields where pesticides were applied, and were highest at the beginning of a rainfall event with concentrations becoming lower in samples taken later in the event. For more information contact Bob Libra (Robert.Libra@dnr.iowa.gov) at (319)335-1575. References: Nations, B.K., and Hallberg, G.R., 1992, Pesticides in Iowa precipitation: Journal of Environmental Quality, v. 21, no. 3, p. 486-492. Nations, B.K., Hallberg, G.R., Libra, R.D., Kanwar, R.S., and Alexander, E.C., Jr., 1993, Pesticides in precipitation: implications for water quality monitoring: Proceedings from Agricultural Research to Protect Water Quality, Soil and Water Conservation Society, Ankeny, Iowa, p. 142-145.