Occurrence, temperature and seasonal trends of α- and γ-HCH in air (Québec, Canada)

Atmospheric concentrations of α- and γ-hexachlorocyclohexane (HCH) were measured during 1993–1995 along the St. Lawrence River in Québec, Canada. Average α- and γ-HCH concentrations (pg/m3) were St. Anicet: 93–101; Villeroy: 92–42; Mingan: 96–20, respectively. α-HCH mean concentrations were similar in all sites and appeared to be more influenced by long-range transport than local sources. γ-HCH mean levels in St. Anicet were 2 and 5 times higher than in Villeroy and Mingan, respectively. The time-series of γ-HCH air concentrations at St. Anicet and Villeroy were characterised by highly elevated springtime episodes, which are in agreement with the γ-HCH usage in Québec as corn seed dressing pesticide. No temporal trend was observed for the α-HCH in air. Clausius–Clapeyron plots (log conc. vs. 1/T) showed a stronger correlation between temperature and measured γ-HCH concentrations at St. Anicet and Villeroy than Mingan. On a regional scale, the influence of the local sources of γ-HCH implied a seasonal variability in air concentrations due to its short transport, while at the background site (Mingan), the observed α- and γ-HCH concentrations in air were the result of its long-range transport and/or water/air gas exchanges.