Atmospheric concentrations and dry and wet deposits of some herbicides currently used on the Canadian Prairies.

High volume air sampling in the Canadian Prairies was used to characterize atmospheric concentrations for 10 herbicides (alachlor, atrazine, ethalfluralin, metolachlor, 2,4-D, dicamba, bromoxynil, MCPA, trifluralin, and triallate) along a 500-km north-south transect. Atmospheric concentration measurements at various altitudes identified that of the six herbicides present in the highest concentrations, triallate was strongly influenced by local sources, while 2,4-D, dicamba, bromoxynil, MCPA and trifluralin were dominated by regional atmospheric transport. Concentrations of the herbicides measured at various altitudes were compared with dry deposition rates measured using a dry/wet deposition sampler and used to calculate deposition velocities V(d). The primary atmospheric transport mechanism for MCPA and bromoxynil was shown to be adsorption to particles dispersed in the atmosphere, with the same mechanism also confirmed for 2,4-D and dicamba, while trifluralin was shown to be transported mainly in the gas phase. This method of calculation indicated that transportation of triallate was influenced by particle adsorption. Weekly maximum atmospheric loadings of the major herbicides present in the Prairies were estimated to range from 73 kg for trifluralin to 541 kg for 2,4-D.

Atmospheric movements of lindane (gamma-hexachlorocyclohexane) from canola fields planted with treated seed.

Lindane (gamma-hexachlorocyclohexane [gamma-HCH]) is used as an insecticide in many countries. Concentrations of gamma-HCH have been found in air, water, soil, snow, and tissue samples throughout the world and concerns have been raised for its potential effects on human and ecosystem health. In Canada, gamma-HCH is primarily used as a treatment on canola (Brassica napus L) seed with an estimated 455.3 Mg applied in 1997 and 510.4 Mg in 1998. The purpose of this study was to measure gamma-HCH volatilization from fields planted with treated canola seed. Atmospheric dry and wet deposition and soil samples were collected for two growing seasons (1997 and 1998) from a canola field planted with treated seed. Atmospheric concentrations as high as 16.1 and 7.4 ng m(-3) were measured at 1 m above the canola field compared with maximum concentrations of 2.9 and 2.7 ng m(-3) measured above a grass field located 2 km away (1997 and 1998, respectively). On the basis of measurements made in this study it was estimated that between 12 and 30% of the gamma-HCH applied as canola seed treatment may volatilize and be released to the atmosphere. This would create an atmospheric loading of 66.4 to 188.8 Mg for the 6-wk period following planting, estimated from the quantity of seed sown on the Canadian prairies in 1998. Dry deposition rates and rain concentrations as high as 2,203 ng m(-2) d(-1) and 170 ng L(-1) were measured adjacent to the canola field.

Atmospheric pentachlorophenol concentrations in relation to air temperature at five Canadian locations.

Pentachlorophenol (PCP), used as a wood preservative and as a disinfectant, has been found in human urine samples from Saskatchewan and in air samples from three Canadian sites. To confirm the presence of atmospheric PCP residues and to explore seasonality, weekly samples were collected at five Canadian sites for three consecutive weeks, in the months of July and October, 1995 and January, April and May, 1996, using a high volume sampler equipped with polyurethane foam (PUF) plugs. PCP was present in all samples collected adjacent to a utility pole storage site with concentrations ranging from 0.7 to 1233.0 ng m-3. There was a very strong correlation between average weekly air temperature, measured over a range of -29.3 to +20.0 degrees C, and the log10 of the average weekly concentration of PCP at this site. PCP was measured in 7 of 11 air samples from each of two small cities (concentrations ranging from 0.2 to 6.8 ng m-3) and the correlation between temperature and PCP concentration, for these two city sites, was similar to that for the utility pole storage site. Concentrations of PCP at two rural sites were lower (0.1-1.5 ng m-3) and detected less frequently. As a consequence, the correlation between air temperature and PCP concentration was more variable.