History of Biomarkers - Ecological Biomarkers: Indicators of Ecotoxicological Effects - page 26

mode of membrane anchorage in vertebrates (Mora et al. 1999). Some studies suggest that
a polymorphism of ChEs may exist for mollusks. Indeed, two distinct ChEs differentiated
by their solubility and their sensitivity toward organophosphates have been found in the
oyster C. gigas (Bocquené et al. 1997). In some biomonitoring studies, it is not clear whether
only AChEs or also pseudocholinesterases are able to hydrolyze the substrate (acetylthio-
choline) used; thus, authors should choose to use the nonspecific term of cholinesterases
when presenting biological monitoring results.
Measurements carried out on dab (the flatfish Limanda limanda ) along a 360-km tran-
sect in the North Sea (Galgani et al. 1992) showed important inhibitions of various types
of cholinesterases. This effect, mainly observed in animals coming from near the coast,
is due to compounds carried from the estuaries of the Elba and Weser rivers. The iden-
tification of the inhibiting compounds of ChEs nevertheless remains delicate, and it is
not possible to definitely conclude that organophosphorous and carbamates are the only
chemicals responsible for the observed inhibition effects on ChEs in the various marine
compartments. The chemical data on these products are scarce, and marine organisms are
subjected permanently to the effects of complex mixtures of contaminants. Payne et al.
(1996) wonder whether AChE activity is an old biomarker with a new future. Indeed, these
authors show that an inhibition of AChE activity could be associated with an induction
of EROD activity in the livers of trout ( Salmo trutta ) and flounders ( Pleuronectes americanus )
caught in an area contaminated with pulp mill effluents.
Contaminants other than pesticides can inhibit AChE activity. Leiniö and Lehtonen
(2005) report inhibition of AChE by metals, detergents, and algal toxins. These authors
conclude that the inhibition of AChE activity can be regarded as a marker of the physi-
ological state of the animals. Moreover, Pfeifer et al. (2005) emphasize that AChE activity
in mussels Mytilus sp. collected from Baltic Sea is negatively correlated with salinity. The
abiotic parameters of the environment thus need to be taken into account as with other
biomarkers when performing biological monitoring.
2.4.2 Vitellogenin
Biomarkers of endocrine disruption are used more and more since many studies have
shown that the reproduction of fish is very sensitive to chemical pollutants. Among the
chemical compounds reaching the aquatic environment, the first endocrine disruptor
compounds (EDCs) were those acting as estrogens by their capacity to mimic the natural
estrogen, estradiol, thus causing a feminizing action on organisms. The general term of
EDCs now includes molecules of very varied structure and origin (PCBs, tributyltins, or
natural phytoestrogens coming from the metabolism of soya or clover). The incidence
of fish hermaphroditism close to wastewater treatment plants in the United Kingdom
(Purdom et al. 1994) led to a study of the “estrogenicity” of the effluents of the treat-
ment plants. Ethynylestradiol, a synthetic estrogen used as contraceptive, is involved in
these effects (Purdom et al. 1994). Human natural estrogens (17β-estradiol, estriol, and
estrone) and their conjugates, excreted in urine and feces, contribute to estrogenicity
(Larsson et al. 1999). Another chemical molecule is nonylphenol, used as an intermediate
in the industrial production of nonylphenol ethoxylates, a large group of nonionic sur-
factants widely used in plastics, latex paints, household and industrial detergents, and
paper and textile industries (Lee 2002). However, according to Soto et al. (1995), EDCs
mimic not only the sex steroid hormones estrogens but also androgens, by binding to
hormone receptors or influencing cell signaling pathways; they block, prevent, and alter
hormonal binding to hormone receptors or influence cell signaling pathways; they alter