Polycyclic Aromatic Hydrocarbons - Organic Pollutants: An Ecotoxicological Perspective - page 185

Induction of P450 1A1/2 provides the basis for biomarker assays for PAHs and
other planar organic pollutants, such as coplanar PCBs, PCDDs, and PCDFs.

9.4 enVIronmentaL fate

Viewed globally, the largest emissions of PAH are into the atmosphere, and the main
source is the products of incomplete combustion of organic compounds. As men-
tioned earlier, emissions are mainly the consequence of human activity, although
certain natural events, for example, forest fires, are sometimes also important.
Emissions into the air are of complex mixtures of different PAHs, including particu-
late matter, as in smoke. PAHs in the vapor phase can be adsorbed on to airborne
particles. Airborne PAHs eventually enter surface waters owing to precipitation of
particles or to diffusion. Once there, because of their high K ow values, they tend to
become adsorbed to the organic material of sediments, and are taken up by aquatic
organisms. Similarly, airborne PAH can eventually reach soil to become adsorbed by
soil colloids, and absorbed by soil organisms.
Apart from release into air, which is important globally, the direct transfer of
PAH to water or land surfaces can be very important locally. Wreckages of oil tank-
ers and discharges from oil terminals cause marine pollution by crude oil, which
contains appreciable quantities of PAH. Disposal of waste containing PAH around
industrial premises has caused serious pollution of land in some localities.
When crude oil is released into the sea, oil films ( slicks ) can spread over a large
area, the extent and direction of movement being determined by wind and tide (see
Clark 1992). The hydrocarbons of lowest molecular weight have the highest vapor
pressures, and tend to volatilize, leaving behind the least volatile components of
crude oil. Eventually, the residue of relatively involatile hydrocarbons will sink to
become associated with sediment. Thus, long after the surface film of oil has disap-
peared, residues of PAH will exist in sediment, where they are available to bottom-
dwelling organisms. To illustrate the range of PAHs found in sediments, some values
follow for PAH residues detected in sediment from the highly polluted Duwamish
waterway in the United States (see Varanasi et al. 1992). All concentrations are given
as mean values expressed as ng/g dry weight.

Naphthalene 400

Fluorene 390

Phenanthrene 2400

Anthracene 610

Fluoranthene 3900

Benz[ a ]anthracene 2000

Chrysene 2900

Benzo[ a ]pyrene 2300

Pyrene 4800

Dibenz[ a,h ]anthracene 470

Perylene 900

Benzofluoranthenes 4900