Impairments of Endocrine Functions: Causes and Consequences - Ecological Biomarkers: Indicators of Ecotoxicological Effects - page 195

al. (2011) demonstrated that contaminants within Newark Bay, USA, exert both estrogenic
and antiestrogenic responses that result in an overtly antiestrogenic phenotype in the fish
Fundulus heteroclitus , with reduced egg production due to inhibition of vitellogenesis. In many
European estuaries, from the UK to France and Portugal, intersex has been revealed in the
endobenthic bivalve Scrobicularia plana (Langston et al. 2007; Gomes et al. 2009; Fossi Tankoua
et al. 2012). These disturbances are most probably attributable to the presence of EDCs but, at
least in the French sites, no direct correlation was found between percentage of intersex and
proportion of cellular responses in bioassays or organic compound concentrations detected
by chemical analyses (Fossi Tankoua, Budzinski, and Aït Aïssa, personal communication).
In a recent study, Sárria et al. (2011) have exposed juvenile black-striped pipefish
( Syngnathus abaster ) to the estrogenic chemical ethinylestradiol (EE2) and the androgenic
chemical TBT, single and in binary mixtures. The obtained results indicated that EE2, TBT,
or their combined exposure, influence morphological and behavioral development during
the early life of the pipefish. The authors stressed that mixtures significantly modulate
newborn responses in distinct ways when compared to individual chemical exposures
and the combined effects of the selected contaminants are far from being predictable. This
unpredictability underlines the importance of considering mixture effects in environmen-
tal risk assessment and particularly the issue of mixtures of EDCs acting through dissimi-
lar modes of action (MOAs).
The presence of steroidogenesis disruptors in the environment may be also revealed through
the assessment of different end-points linked to reproduction such as the Daphnia 21d repro-
duction test (Dang et al. 2012) and the Fish Sexual Development Test (FSDT) (Holbech et al.
2012) included in the OECD working program. Compiling 142 data sets for 21-day fish assays
and 38 data sets for a fish sexual development test, encompassing 62 chemicals with different
MOAs, Dang et al. (2011) concluded that fecundity and gonad histology are the most sensi-
tive endpoints for fathead minnow Pimephales promelas , medaka Oryzias latipes , and zebraf-
ish Danio rerio in 21-day ish assays, whereas secondary sex characteristics are less sensitive
endpoints and are likely to be inadequate to detect all known MOAs. Intersex in fish and
bivalves and imposex in gastropods are well documented (Chapter 9). In certain cases, even
sex reversal has been observed in fish (Iwamatsu et al. 2006) and frogs (Pettersson et al. 2006).
The reproductive status of fish and invertebrates is also commonly used by determining
gonadosomatic indices (e.g., Vijayavel and Balasubramanian 2008 in crustaceans; Nadzialek
et al. 2010 in fish; Pellerin et al. 2009 in bivalves) or sexual maturation stages (Siah et al. 2003;
Durou and Mouneyrac 2007). Indeed, temporal changes in the maturation of sexual products
may be influenced by environmental stress, but this tool suffers a lack of specificity because
natural factors (temperature, food availability) can interact with contamination factors.
All these different bioassays in vitro and in vivo can generally be applied both in the labo-
ratory and in the field. An intermediate step consists of field experiments such as caging,
which is discussed in Chapter 2. Field experiments have already been used in ecotoxico-
logical studies with EDCs, providing results of great value because of their environmental
realism (Gust et al. 2010b; Vajda et al. 2011).
8.4 Thyroid Endocrine Disruptors
Several classes of chemicals are now suspected or even proved to be disruptive to thyroid
function at several levels. However, evidence for thyroid disrupting activity is often not