Distribution of Chlorinated Hydrocarbon Pesticides and PCBs in the ...

Technical mixtures used previously in the northern hemisphere
contained approximately 50 to 80% alpha-HCH (the inactive and
stable isomer) with 8 to 15% lindane giving a ratio of a1pha:gamma
5 to 6. Besides the source of HCH, ratios of a1pha:gamma isomers
may be altered by transformation of lindane to the more stable a
isomer on exposure to W radiation and in aerated water (Oehme and
Mano, 1984). High ratios in air vapour in August/September and in
August snow could reflect the loss of the gamma isomer by UV
induced transformation. The ratios for the HCH isomers in
seawater did not vary significantly between sampling trips,
reflecting stability of the large reservoir of HCH1s dissolved in
surface seawater.
HCB concentrations in air vapour measured over the Ice
Island (63 - 109 pg m'3) (Table 4.1) are similar to the lowest
values reported during summer off the Norwegian Arctic coast
(Oehme and Stray, 1982; Oehme and Ottar, 1984), but they are an
order-of-magnitude less than concentrations measured in air over
the continental U.S. and North Atlantic (Bidleman et &., 1987) .
Simultaneous measurements on the Ice Island in August and June by
staff from Bidlemanls lab at USC were 3 times higher in August
1986 and about 50% higher in June 1987 (Table 3.8, Section 3.2.2).
Levels measured in both air and seawater in our study were similar
for the three sampling periods but values in snow were lower in
August/September. Although HCB has a vapour pressure which is low
compared to many other organochlorines (Table 5.1), it is a semivolatile
organic compound. Decreases in concentrations dissolved
in snow could arise from volatilization after deposition in the
early spring.
In general, our values for most organochlorine residues
in snow in 1987 are in agreement with both USC and the National
Water Quality Laboratory. Patton g& &.Is (1988) collected
freshly fallen snow on the Ice Island in June 1987 and showed that
levels of total HCH were two to six times higher than
concentrations present in lloldll subsurface snow. Sublimation of
previously deposited hexachlorocyclo-hexanes could have depleted
concentrations in snow, especially during summer when air