I'r - Memorial University of Newfoundland

samples and sources (Fig. 52.1 and 42.5a.b). The distribution ofsam ples and scurces
along the two first PCs suggests presence ofunaccounted sources or processes acting in
lake sediments. A simi lar conclusion followed the analysis ofthe distribution ofsam ples
with respect to primary sources and mixing curves generated from nonnalized mo lecular
composition ofdifferent compounds. It is possible that the pattern represented by the first
and second PCs can be attributed to a variety ofweathering processes !mown to affect
PAH during their transport and afte r deposition.
A number of reasons point to the natural origin ofthe unidentified contributors. All
known anthropogenic sources are concentrated on one end ofboth PCs (fig. 5.2.1; see
also FigA .2.5a.b andSection 4.2.1). On both components. they are at the opposite end of
station 946 with the maximum contribution from the unidentified process/source. Site
946 is located very far from the areas subjected to direct anthropogenic influence and is
characterized by a very low level of total PAH concentration (Fig. 4.1.1). Finally, station
946 exh ibits very low PylPer ratio (0.08; Fig. 4.2.1) wbich is indicative of natural origin
of PAH assemblage (lipiatou and Saliot, 1992; sec also Appendix AS).
It can also bedemonstrated that the observed changes in the PAH assemblage are
more likely to be caused by an ongoing process rathe r than an additional source. The
sites affected the most are located at cons iderable distance from each other (e.g., 946 and
967 . PC I ; 946 and Wh; PC 2; Fig. 4.2.5a.b). It is difficult to suggest a specific source
selectiv ely affe cting different sites on a regional scale. Converse ly, distance is not
important for a process which can be initiated wherever the requiredconditions are met.
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