Introduction - Ecological Biomarkers: Indicators of Ecotoxicological Effects - page 7

The problem of endocrine disruption was first realized because of the disastrous ecotox-
icological effect of tributyltin (TBT), a compound used in antifouling paints. TBT-mediated
imposex (for details, see Chapter 9) has been observed in more than 195 species of proso-
branch gastropods worldwide (Sternberg et al. 2010). Subsequent population depletion of
such gastropods has been observed in harbors and marinas where many individual snails
were presenting morphological symptoms of imposex. In the case of the dogwhelk Nucella
lapillus , population-level effects on other species (barnacles, fucoid seaweeds, hermit crabs)
belonging to the same ecological community would be attributable to such a population
drop in the affected gastropods (Bryan and Gibbs 1991).
Endocrine glands and the hormones they secrete are not only indispensable to the suc-
cess of reproduction but are also involved in the development of organisms, their growth,
and their behavior. However, most scientific research, particularly in fish, focuses on inter-
actions between pollutants and male and female sexual hormones (Chapters 8 and 9). A
peculiar topic of concern is that the effects of endocrine disruptors on reproduction are
typically subtle, occurring at low doses, in the absence of any other appearance of toxicity.
The spatial distribution of endocrine-disrupting chemicals, particularly steroid estrogens
and nonylphenols, is related to the discharge of domestic and industrial wastewaters every-
where in the world (Jugan et al. 2009; Bertin et al. 2011; Gong et al. 2011; Tetreault et al. 2011).
The presence of intersex (male gonads invaded with oocytes) individuals is increasingly
documented in bivalves and fish. Natural or xenoestrogens could be a contributory factor in
the induction of intersex (Baroiller and D'Cotta 2001; Langston et al. 2007). However, it is still
unclear if intersex can have consequences on the production of progeny (Chapters 8 and 9).
A wide variety of anthropogenic, waterborne contaminants can also affect the
hypothalamic-pituitary-thyroid axis and its role in development and reproduction as
recently reviewed in teleost fish and amphibians (Blanton and Specker 2007; Carr and
Patiño 2011). Impairment of thyroid functioning can influence behavior as neurotoxic
effects such as the inhibition of neurotransmitters (AChE, serotonin) have also been
observed (Figure 1.4). Many aspects of behavior can be affected (Dell'Omo 2002; Amiard-
Triquet 2009; Hellou 2011): avoidance of predators or contaminated sediment or other
habitat, contributing to the defense and survival of organisms; location of sexual partners
and care of juveniles indispensable to reproductive success; feeding behavior and prey
capture important for acquiring energy. Thus, behavioral ecotoxicology is potentially use-
ful to link biochemical impairments to population effects (Chapter 10).
The success of reproduction is clearly linked to the relative energy allocation of an
organism to defense against exposure to chemical stressors, basal metabolism, growth,
and reproduction. Organisms obtain their energy from ingested food. For predators, the
impairment of foraging activity can lead to a shift toward easily accessible food such as
detritus, the energy value of which may be lower. Chemical contaminants can also influ-
ence food assimilation through the impairment of digestive enzyme activity. Lastly, prey
species can be susceptible to environmental contamination, thus leading to decreased
food availability for predators (Chapter 11).
Energy analysis can reveal a disequilibrium in energy balance associated with toxic or
more general stress. Different energy parameters can be used as biomarkers of pollutant
effects (Chapter 12). These parameters can be linked to macroscopic criteria representative
of maintenance and growth (condition indices, size, or biomass increase, etc.) or repro-
duction (gonadosomatic index, egg production, offspring number, etc.). For ecological risk
assessment, it is necessary to determine to what extent populations may be affected when
such adverse effects are revealed (loss of their ecosystem function or even local extinction).
Models that can allow extrapolation from individual- and suborganismal-level responses