Polycyclic aromatic hydrocarbons (PAHs), like many other hydrophobic organic contaminants, are rapidly sorbed to particles and incorporated within sediments in aquatic systems. The PAH composition within the sediments reflects the source(s) from which the PAHs were derived. However the "source signature" may be altered by postdepositional weathering or biodegradation. In the present study, variation in PAH composition was investigated in size-fractionated sediments and depth-fractionated sediments collected from a Canadian fjord contaminated with aluminum smelter derived PAHs. Multivariate analyses of PAH compositional data consistently showed that different sampling sites could be discriminated on the basis of their PAH composition, but smaller versus larger size fractions within a site could not. The composition of unsubstituted and alkyl-substituted PAHs in a sediment core primarily showed changes with depth that were attributable to enhancement of anthropogenic inputs in the upper core segments. No trends with sediment depth, associated with compound-specific weathering or biotransformation, were noted in the composition of anthropogenically generated PAHs. This may indicate a limited chemical and biological availability of the aluminum smelter derived PAHs.
The results of a PCB weathering experiment (i.e.,
losses from soil and changes in PCB composition from
soil over time) at Cambridge Bay, Northwest Ter
ritories, in the Canadian Arctic are presented. Nine
plots representing three different general substrate
types (dry barren, dry moss, and wet grass) were treated
with three different PCB Aroclor formulations (1254,
1260, and a 1:1 mixture). Soil and plant samples
were collected annually over a 5-year period and
analyzed for individual PCB congeners. The results
showed a high degree of variability between treat
ments that was ascribed to the presence of vegetation
as well as non-homogenous PCB application and/or soil heterogeneity (e.g., biomass, organic carbon,
and moisture content) within individual plots. Where
readily interpretable data were available, the first-order
rate constant for the loss of PCBs from the substrate
was calculated to be approximately 0.5 yr-1
(t1/2 =
1.1 yr) (range = 0.3−1.0 yr-1 for
individual congeners).
For the dry barren area, the rate of loss from soil
of individual congeners was negatively correlated with
the planar total surface area of the congener (or
positively correlated with vapor pressure). For a wet
grass area or a dry moss area, the rate of loss was
not correlated with any of the standard physical
constants, suggesting that live and detrital vegetation
may play a key role in the release and retention of
PCBs. The estimated loss rates for the three plots
may or may not be applicable to PCB-contaminated
soils in general, where PCB volatility may be reduced
by the presence of hydrocarbon-based carriers or
influenced by other factors not considered in this
study.
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