ON THE SPATIAL AND TEMPORAL VARIATIONS IN ATMOSPHERIC CONCENTRATIONS OF HEXACHLOROBENZENE AND HEXACHLOROCYCLOHEXANE ISOMERS AT SEVERAL LOCATIONS IN THE PROVINCE OF ONTARIO, CANADA

Hexachlorobenzene (HCB), as well as alpha- and gamma-hexachlorocyclohexane (HCH) have been measured at seven sites in Ontario, Canada during the years 1985-1989. While two of the locations were close to a suspected source of the organochlorines, five were sites that reflected the non-urban airshed loadings which are considered to be regionally representative of the Great Lakes. At the non-urban locations, the gamma-HCH (lindane) and alpha-HCH concentrations ranged from 15 to 190 pg m-3 (mean of 47 pg m-3) and 50 to 660 pg m-3 (mean of 240 pg m-3), respectively. The HCB concentrations varied from 20 to 310 pg m-3 (mean of 94 pg m-3). At the suspected source locations, the alpha:gamma HCH ratio was less than unity while at locations distant from known or suspected sources, the alpha:gamma ratio was usually greater than 7. At the non-urban locations, the highest concentrations of the alpha- and gamma-HCH isomers were observed during the summer and the lowest concentrations were seen during the winter. The concentration of HCB, however, remained relatively constant throughout the year.