Geology Reference
In-Depth Information
Figure 15 Plot of weathering ratio (C3-dibenzothiophenes/C3-chrysenes) vs. source ratio
(C3-dibenzothiophenes/C3-phenanthrenes) for fresh and degraded oil samples
from three different crude oil spills
(Adapted from Douglas et al., 1996.
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)
much material can only be classified as an unresolved complex mixture
(UCM), many individual aliphatic and aromatic compounds can be
routinely determined. Total petroleum hydrocarbon distributions, as
shown in Figure 16 for the Caspian Sea, provide evidence of pollution
''hot spots''.
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In this case, the highest concentrations were observed in
Azerbaijan. Given that several individual PAHs can be ascribed to
different origins, plots of the relative amounts allows an assessment to
be made of the relative importance of petrogenic (fossil oil), pyrolytic
(combustion products) and natural (in situ biological activity) sources.
As shown in Figure 17, most of the PAHs in the Caspian Sea sediments
were derived from fossil oil.
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This technique cannot distinguish between
material derived from natural seeps or anthropogenic activity. Other-
wise, the contribution of combustion products was evident in Russia and
natural sources were only observed in the Iranian sector.
4.5.2 Plastic Debris
The accumulation of litter and debris along shorelines epitomises a
general deterioration of environmental quality on the high seas. The
material originates not only from coastal sources, but also from the
ancient custom of dumping garbage from ships. Drilling rigs and
offshore production platforms have similarly acted as sources of con-
tamination. Some degree of protection in recent years has accrued from
both the London Dumping Convention (LDC) and the International
