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

a weight:weight basis on all three trips show no depth
gradient. There was a suggestion of a maximum in percent PQC
and PON content of suspended matter in samples at the depth
of the nutrient maximum (100 - 120 m) on all three trips.
This might be expected if flocculent, organic rich particles
were concentrated in the pycnocline. This may also reflect
the continental shelf origins of this water (see section
4.4.1).
4.4.3 Dissolved Pesticide and PCB Concentrations
Data for all compounds and all depths for each sampling
trip are given in Appendix D. Alpha and gamma isomers of
HCH, trans and cis chlordane, dieldrin, heptachlor epoxide,
HCB and PCBs were all present at quantifiable concentrations.
A summary of individual compounds that were above detection
limits and their variation with depth is given in Table 4.5.
The most abundant compounds were the alpha and gamma isomers
of HCH. concentrations of alpha HCH were 4 - 5 ng/L while
gamma HCH levels were 6 to 7 times lower. Concentrations of
all detectable compounds with the exception of dieldrin were
highest in the upper 0 - 50 m well mixed surface layer and
decreased with depth through the halocline. Concentrations
of dieldrin did not exhibit any depth related trend perhaps
as a result of the low concentrations (less than 5 pg/L).
Ratios of the alpha to gamma HCH isomers (5 -7.5) did
not vary significantly with depth despite the more than 20
fold decrease in concentrations from the surface to deep
water. Ratios of trans and cis chlordane did change with
depth however, from values of about 2 in the surface water to
less than 1 in the deep water of the halocline.
There were no significant seasonal differences in the
concentrations of organochlorines in the upper low salinity
water despite lower salinities in August 1986 at the end of
the period of maximum ice melt.