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Persistence and Movement of Picloram in a Northern Saskatchewan Watershed

Agric. Canada, Regina Res. Stn., 5000 Wascana Pkwy., P.O. Box 440, Regina, Sask. S4P 3A2 Canada;
Environ. Canada, Regina, Sask. S4P 3R4 Canada.

^* Corresponding author.

ABSTRACT

In the summer of 1982, 477 ha of a weapons range in northern Saskatchewan were treated with a granular formulation of picloram (4-amino-3,5,6-trichloropicolinic acid) at a rate of 3.38 kg ha^–1 (a.i.). For the next 2 yr, the persistence of picloram was monitored in the soil at sites within and outside the treatment area. Picloram was monitored for a 3-yr period in the groundwater at off-target sites and in the surface waters and sediments of a creek and two lakes adjoining the treatment area. Extensive leaching of the herbicide was noted. After 14 months residues were recovered from the 60- to 90-cm soil depths, and after 22 months from the 90- to 120-cm soil layer. After 26 months between 138 and 396 g ha^–1 of picloram were recovered from the top 120-cm soil depths, Picloram was detected in the top 30 cm of soils, approximately 1 km from the treatment area, when sampled 14 and 22 months following the initial application. Picloram (0.25–88.3 µg L^–1) was recovered after 35 months from groundwater samples collected at 120 cm from the same off-target sites. This transfer to nontreated sites was considered to result from a combination of blowing surface soil and groundwater movement from the treated area. Samples of surface waters taken from a lake approximately 1 km from the treatment zone indicated that picloram residues could be detected (0.1–1.15 µg L^–1) in the falls of 1983 and 1984, but not in the summers of 1984 and 1985. Traces of picloram (0.14–0.39 µg L^–1) were recovered in the fall of 1983 and summer of 1985 in creek waters situated approximately 300 m from the edge of the treatment area. Picloram was detected (12 µg kg^–1) in only one lake sediment sample at one sampling period.

Key Words: Groundwater • Herbicide • Leaching • Residues • Soil • Water • 4-Amino-3,5,6-trichloropicolinic acid

Contribution of Environmental Chemistry of Herbicides Section, Res. Stn., Agric. Canada, Regina, Sask. S4P 3A2 Canada, and Environ. Protection Service, Environ. Canada, Regina, Sask. S4P 3R4 Canada.

Received for publication July 15, 1986.