Environmental Engineering Reference
In-Depth Information
plant uptake of metals introduces contaminants into estuarine food webs
(Giblin et al. 1980).
Since the industrial revolution, fossil fuels contribute the largest portion
of world energy demand, in particular for transportation. In addition,
petroleum products are increasingly used in the synthesis of plastics. A major
consequence of use of oil is the release of petroleum-generated compounds
into coastal waters, and transport accidents contribute substantially to
marine pollution. Studies of the ecological consequences of accidental spills
are diffi cult to compare because it is hard to assess the relative exposure
and the types of compounds involved. Although catastrophic oil spills are
a more widely recognized source of marine pollution, these events occur
at local spatial scales, and show recovery in the long term. A more global
problem is the local chronic release of petroleum around areas with much
human activity. The effects of each new input will recede as the oil weathers,
but there are always new little inputs, each of which impacts the same or a
nearby area. This pattern of local, but widespread, repeated perturbations
could have more detrimental and wide-ranging effects than major spills
(Valiela 2006).
In the mid 20th century, synthesis of chlorinated hydrocarbon
compounds led to great advances in public health, agriculture and industries.
In general, human-made chlorinated compounds of low molecular weight
like dichlorethane, vinyl chloride, tetrachloride, trichlorethane, and
trichlorethylene are rather volatile, and do not accumulate in coastal
environments. In contrast, synthetic chlorinated hydrocarbons of larger
molecular weight, particularly DDT and PCBs, raise concern because of their
ability to reach and alter coastal environments. Chlorinated compounds
have been found widely distributed throughout the entire world (Atlas
et al. 1986). About 1,000,000 tons were produced before 1976, and perhaps
100,000 tons have managed to enter natural environments (Axelman and
Broman 2001).
The concentrations of persistent chlorinated hydrocarbons in organisms
are affected by the degree of contamination, biomagnifi cations (the transfer
of contaminant from food to consumer), bioconcentration (storage within
consumers), depuration (the relative ability to metabolize chlorinated
hydrocarbons), and the kind and age of the organisms. The better known
effect of DDT is the thinning of bird eggshells, observed after the 1940s, when
DDT became broadly used (Risebrough 1989). In the west coast on North
America, shell-thinning affected double-crested cormorants ( Phalacrocorax
auritus ), and was responsible for the near extinction of brown Pelicans
( Pelecanus occidentalis ). PCBs reduce growth and photosynthesis in algae
and plants (Mahanty 1986), and create sublethal conditions in invertebrates,
fi sh, and birds, which involve lower reproduction, malformations, altered
liver, thyroid, and circulatory functions, suppression of immunity, and
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