Chemistry Reference
In-Depth Information
in germ cells, there are inevitably questions about their effects on progeny. Most
mutations are not beneficial!
There is evidence for immunosuppressive effects of PAHs in rodents (Davila et
al. 1997). For example, strong immunosuppressive effects were reported in mice
that had been dosed with benzo[
a
]pyrene and 3-methyl cholanthrene, effects that
persisted for up to 18 months (Environmental Health Criteria 202). Multiple immu-
notoxic effects have been reported in rodents, and there is evidence that these result
from disturbance of calcium homeostasis (Davila et al. 1997). PAHs can activate
protein tyrosine kinases in T cells that initiate the activation of a form of phospholi-
pase C. Consequently, release of inositol triphosphate—a molecule that immobilizes
Ca
2+
from storage pools in the endoplasmic reticulum—is enhanced.
Turning to the acute toxicity of PAH, terrestrial organisms will be dealt with
before considering aquatic organisms, to which somewhat different considerations
apply. The acute toxicity of PAHs to mammals is relatively low. Naphthalene, for
example, has a mean oral LD50 of 2700 mg/kg to the rat. Similar values have been
found with other PAHs. LC50 values of 150 mg/kg and 170-210 mg/kg have been
reported, for phenanthrene and fluorene, respectively, in the earthworm. The NOEL
level for survival and reproduction in the earthworm was estimated to be 180 mg/
kg dry soil for benzo[
a
]pyrene, chrysene, and benzo[
k
]luoranthene (Environmental
Health Criteria 202).
Toxicity of PAH to aquatic organisms depends on the level of UV radiation to
which the test system is exposed. PAHs can become considerably more toxic in the
presence of radiation, apparently because photooxidation transforms them into toxic
oxidative products. PAHs, such as benzo[
a
]pyrene, can have LC50s as low as a few
micrograms per liter toward fish when there is exposure to UV (Oris and Giesy 1986,
1987). PAHs can also show appreciable toxicity to sediment-dwelling invertebrates.
LC50 values of 0.5-10 mg/kg (concentration in sediment) have been reported for
marine amphipods for benzo[
a
]pyrene, fluranthene, and phenanthrene, used singly
or in mixtures. These values are much lower than the LC50 or NOEL concentrations
for earthworms quoted earlier, which were exposed to contaminated soil. It has also
been shown that exposure of adult fish to anthracene and artificial UV radiation can
impair egg production (Hall and Uris 1991).
9.6 ecoLogIcaL effectS
Serious ecological damage has been caused locally by severe oil pollution. The wreck-
ages of the oil tankers—the
Torrey Canyon
(Cornwall, United Kingdom, 1967), the
Amoco Cadiz
(Brittany, France, 1978), the
Exxon Valdez
(Alaska, United States,
1989), and the
Sea Empress
(South Wales, United Kingdom, 1996)—all caused seri-
ous pollution locally. Less dramatically, leakage from offshore oil operations has
also caused localized pollution problems. Most of the reported harmful effects of
such marine pollution have been due to the physical action of the oil rather than the
toxicity of PAHs. Fish, however, may have been poisoned by oil in situations where
there was strong UV radiation (see Section 9.5). The oiling of seabirds and other
marine organisms has been the cause of some local population declines. Sometimes
the reduction of invertebrate herbivores on polluted beaches and rock pools has led
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