Sources of Chlorpyrifos and Dacthal to a Small Canadian Prairie Watershed

• Published in: Environmental science & technology 1999-10, Vol.33 (19), p.3317-3323
• Main Authors: Rawn, Dorothea F. K, Muir, Derek C. G
• Format: Article
• Language: English
• Subjects: agricultural watersheds; Agronomy. Soil science and plant productions; Applied sciences; atmospheric deposition; Atmospheric pollution; Biological and medical sciences; Canada, Manitoba; chlorpyrifos; Dacthal; deposition; Exact sciences and technology; Fundamental and applied biological sciences. Psychology; Pollutants physicochemistry study: properties, effects, reactions, transport and distribution; Pollution; Soil and water pollution; Soil science; south tobacco creek watershed; watersheds
• ISSN: 0013-936X; 1520-5851
• DOI: 10.1021/es990290n

Atmospheric deposition and air−water exchange of two semivolatile pesticides, Dacthal and chlorpyrifos, were compared in a small agricultural watershed in southern Manitoba, Canada, between 1994 and 1996. Dacthal was not used in the watershed nor in the surrounding region. Dacthal concentrations were derived from long-range transport and deposition processes and were lower than those of chlorpyrifos, which was applied locally each year of the study. Maximum concentrations of chlorpyrifos in air (103 ng/m3), precipitation (38 ng/L), and creek water (105 ng/L) were observed during local application periods. The highest Dacthal concentrations (4 ng/L) observed in precipitation occurred during intervals when its use in the U.S. was expected, although a seasonal relationship was not established. Precipitation and gas exchange across the air−water boundary were important pathways of movement for both chlorpyrifos and Dacthal. A net volatilization flux from the entire creek surface was observed for chlorpyrifos (1.4 g, 24 000 ng/m2) in 1995 and for Dacthal in both 1995 (0.37 g, 6300 ng/m2) and 1996 (0.15 g, 2600 ng/m2).