A comparison of flux chambers and ambient air sampling to measure γ-hexachlorocyclohexane volatilisation from canola (Brassica napus) fields

The insecticide γ-hexachlorocyclohexane (γ-HCH) is primarily used in Canada in treatments of canola (Brassica napus) seed. It has been shown that γ-HCH so applied will volatilise with 12–30% entering the atmosphere within 6 wk after the seed is planted. Both flux chambers and high-volume air samplers were used to measure γ-HCH volatilisation from a canola field and the results from each method compared. Daily samples were collected from three flux chambers located on the field. γ-HCH was found in the air of the chambers on the first day after planting. Volatilisation rates were low for the first 7 d (40.0 mg ha−1 wk−1) but increased during the second week (143.8 mg ha−1 wk−1). This was consistent with previous studies. Weekly composite air samples, from three heights above the canola field, were used to calculate volatilisation rates from the field. These were 190 mg ha−1 wk−1 (week 1) and 420 mg ha−1 wk−1 (week 2). Soil temperatures in the open field were warmer than those under the flux chambers and this may have contributed to the higher ambient air measurements.