Environmental Engineering Reference
In-Depth Information
H
H
H
H
H
H
H
H
H
C
C
C
C
C
C
C
C
H
H
H
H
H
H
H
H
H
Figure 4.1 Octane molecule, a straight chain hydrocarbon
H
H
C
C
H
C
C
C
H
H
C
C
C
H
C
C
H
H
Figure 4.2 Naphthalene molecule, a polycyclic aromatic hydrocarbon
carcinogenic (cancer-causing), mutagenic (causing genetic
mutations), or teratogenic (causing embryonic malformations).
PAHs are broken down in the liver into compounds that can
be excreted, and generally do not increase in concentration
as they make their way through the food chain. However,
in some cases the intermediate breakdown products can be
more toxic than the original PAHs. In aquatic environments
PAHs may evaporate or be degraded by bacteria, but they
often become more toxic after exposure to light (phototoxic-
ity), and they may become incorporated into sediments where
they degrade very slowly. High concentrations in sediments
are associated with liver and skin cancers in bottom-dwelling
(benthic) fishes. Because mollusks cannot metabolize PAHs,
they continue to accumulate them and are thus useful for
biomonitoring programs, in which their bodies are analyzed
to evaluate the levels of PAH pollution of a particular envi-
ronment. In addition to oil spills, PAHs enter the marine
Search WWH ::
Custom Search