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

and the analyses expanded to include elution of the filtered
water through an XAD column followed by hexane extraction of the
eluate. This allowed the column retention and efficiency to be
determined directly for surface sea water.
The results of the second XAD validation experiment, which
are summarised for the HCHs in Table 3.1 and presented in full in
Appendix C , indicate similar results to the first validation
experiment of a 64% column efficiency for a-HCH for the in-situ
sampler extraction. However, only 1.3% alpha and 3.2 % gamma -
HCH were found in the column output indicating an extraction
efficiency of > 96%. The XAD column efficency from water sampled
by NBS drop sampler agreed well for beta and gamma HCH but was
substantially higher for alpha HCH than for the in-situ sampler
(6700 pg/L vs 4400 pg/L). This would suggest some alteration of
the sample during storage and lab processing to change the
availability of the alpha HCH to the XAD resin.
Surface seawater was also analysed during June 1987 by
Greg Patton of the University of South Carolina (Patton al,
1987). Sea water samples (2 -3L) were collected from lorn by NBS
drop sampler, filtered in the Ice Island laboratory (Gelman 47mm
binderless glass fiber filters), extracted onto bonded octyl
silica gel cartridges (500mg, J.T.Baker C8-SPE) and analysed
independantly at USC. The HCHs were the only organochlorines
detected in extracts from these cartridges (Table 3.2) and are
compared to the in-situ sampler and XAD validation results in
Table 3.3.
HCH concentrations sampled by NBS and extracted by XAD or
bonded n-octyl silica are comparable and are similar to NBS
sampled-hexane extracted samples collected August 86. The reason
for the lower values in 1987 by in-situ sampler and NBS/hexane
extraction is not clear.
There has been no correction of the XAD tabulated data for
column extraction/recovery efficency. The USC data includes a
uniform recovery efficiency factor of 78% which has been applied
to all organochlorine concentrations to compensate for method
losses.