Biology Reference
In-Depth Information
13.3 Genotoxicity, Physiological, and Populational Effects
The impact of genotoxicity on populations is a matter of debate in ecotoxicology. However,
there are very few
in situ
studies allowing the establishment of links between genomic
alterations, physiological effects in individuals and populational changes. Two case stud-
ies will be discussed here:
• The impact of the
Exxon Valdez
oil (EVO) spill on fish, especially herring populations
• The relationships between genomic changes and health status of populations
exposed to contaminants, such as mosquito fish
Gambusia affinis
exposed to radio-
active elements and
Daphnia longispina
exposed to chemical pollutants
13.3.1
Exxon Valdez
Accident
On March 24, 1989, 40,000 metric tons of crude oil were spilled into Prince William Sound
(PWS), Alaska, from the tanker
Exxon Valdez
. The accident occurred coincidently with the
spawning of Pacific herring (
Clupea pallasi
) stocks in PWS. The spill trajectory overlapped
the route of the adult herring spawning migration and spawning locations. The herring
did not spawn on the most heavily oiled beaches but did spawn on shorelines considered
to be lightly to moderately oiled.
No mortality of adult fish was reported, but eggs and larvae were severely impacted.
Larvae hatched from contaminated sites had high rates of abnormalities and mortality
(Brown et al. 1996; Hose et al. 1996; Norcross et al. 1996; Marty et al. 1997). A high level
of mitotic aberrations and micronuclei was measured in larvae that had been collected
between 6 and 10 weeks after the grounding (Hose and Brown 1998): 40-51% of aber-
rant anaphases and telophases were recorded in impacted areas, versus <10% in non-
impacted zones. Major oil-associated effects in larvae taken from oiled sites in spring
1989 included small size, ascites, pericardial edema, delayed development, and genetic
damage.
Studies focused on the Pacific herring because of their economic value and the coinci-
dence of the EVO spill with spawning, but similar effects have been observed with pink
salmon (
O. gorbuscha
). Although pink salmon did not spawn until months after the spill,
they deposited their eggs in intertidal stretches of stream deltas. Oiled gravel persisting in
some streams was a continuous source of exposure for pink salmon embryos, resulting in
elevated mortality.
Toxicity was related to the soluble and dispersed PAH fraction in the water column;
sediment concentrations were low in the few specimens collected. Naphthalenes, fluo-
renes, phenanthrenes, and dibenzothiophenes were found in seawater samples at oiled
sites. Total PAH (TPAH) concentrations in water in spring peaked at 1.9 and 2.6 μg L
-1
in
oiled areas, which was considered weak pollution, because it never exceeded water quality
standards. Retrospectively, these considerations were erroneous, since the concentration
thresholds for genomic lesions and morphological abnormalities were estimated later to
range between 0.4 and 0.7 μg TPAHs L
-1
(Carls et al. 2002).
Significant effects on fish populations were not reported in the 2 years following the oil
spill, until a collapse of more than 75% in the adult herring population was recorded dur-
ing the winter 1992-1993, responsible for an economic crash never before seen. A link with
the EVO accident could not be demonstrated, because monitoring studies had stopped
in 1989 for the reason that TPAH concentrations in water were considered too low to be
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