Biology Reference
In-Depth Information
4.2.3 Markers of Genotoxicity
Markers of genotoxicity such as DNA adducts, micronucleus, and Comet assay tests are
well-documented biomarkers of damage (Chapter 13). Recently, several authors have
focused their research on the reproductive consequences of paternal genotoxin expo-
sure in aquatic organisms (Lewis and Galloway 2009; Lacaze et al. 2010; Devaux et al.
2011). DNA damage to sperm was observed in freshwater crustaceans (
Gammarus fossa-
rum
) and fish (
Salmo trutta
,
Salvelinus alpinus
) and in marine polychaetes (
Arenicola marina
)
and bivalves (
Mytilus edulis
) exposed to the model genotoxicant methyl methane sulfonate
and/or to the PAH benzo[
a
]pyrene (B[
a
]P). No effect occurred on fertilization success, but
severe developmental abnormalities were observed in freshwater fish and marine inverte-
brates. Prolonged effects were observed in
S. trutta
such as increased mortality (×3) after 2
months, and increased malformations after 1 year (Devaux et al. 2011). These findings are
in agreement with field observations reported for herring
Clupea pallasi
after the accident
involving the tanker
Exxon Valdez
(for details, see Chapter 13).
4.2.4 Cholinesterases
The majority of insecticides currently in use are organophosphorous, carbamate, and syn-
thetic pyrethroid compounds. Organophosphorous (OP) insecticides produce toxicity by
inhibiting cholinesterase enzymes in the nervous system. Monitoring of AChE inhibition
has been widely used in terrestrial and freshwater aquatic systems as an indicator of OP
exposure and effects (reviews by Galgani and Bocquené 2000; Fulton and Key 2001).
Impairments of AChE activity lead to the accumulation of acetylcholine in neural junc-
tions, responsible for an overstimulation of the peripheral nervous system. The inhibi-
tion of AChE activity can have important effects on individuals, including lethal effects in
the short term if cholinesterase inhibition exceeds a threshold of about 70% in fish brain.
Selected species, however, appear capable of tolerating much higher levels (90%) of brain
AChE inhibition. Less drastic inhibition can also have clear repercussions on behavior:
sublethal effects on stamina have been reported for some estuarine fish in association with
brain AChE inhibition levels as low as 50% (Fulton and Key 2001).
4.2.4.1 AChE Activity Changes Induced by Laboratory or Field Exposure
More recent studies have provided new evidence of the effects of cholinesterase-inhibiting
pesticides both in the laboratory (Table 4.1) and in the field (Table 4.2).
In addition to OP pesticides and carbamates, exposure to other classes of contaminants (met-
als, petroleum, detergents, complex mixtures) as well as natural toxins can inhibit AChE activity
(Table 4.1). Thus, AChE inhibition has been proposed for consideration as a generalist biomarker,
representative of the physiological status of an organism (Leiniö and Lehtonen 2005).
A dose-additive inhibition of Chinook salmon (
Oncorhynchus tshawytscha
) AChE activity
by mixtures of OP and carbamate insecticides has been described by Scholz et al. (2006).
Because both classes of contaminants are concomitantly present in water bodies, a rel-
evant risk assessment must not be focused individually on each of them, a practice that
would lead to an underestimation of potential risk. This topic has been recently reviewed
for invertebrates, and numerous examples of additive, synergistic, but also antagonistic
effects have been registered (Domingues et al. 2010).
Two scallops—the Antarctic
Adamussium colbecki
and the Mediterranean
Pecten jaco-
baeus
—differ widely in AChE molecular forms. However, the presence of inhibitor-sensitive
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