Impairments of Endocrine Functions: Case Studies - Ecological Biomarkers: Indicators of Ecotoxicological Effects - page 234

mussels exposed to estrogens at the early stage of gametogenesis. In contrast, mature
mussels displayed no statistically significant change in both gene mRNA expressions
(Ciocan et al. 2010). Other reproduction-specific genes, including testis-specific kinases,
vitelline lysin, and envelope protein, are estrogen-regulated during development (Ciocan
et al. 2011). This suggests that the reproductive physiology of mollusks may be suscep-
tible to damage by environmental estrogens at certain points in their gametogenesis pro-
cess. This is especially true for serotonin and cyclooxygenases (involved in prostaglandin
synthesis), which are both important in the endocrinology of mollusks (Cubero-Leon et
al. 2010).
9.2.4 Accumulation and Molecular Effects of Estrogens or Antiandrogens in Fish
Endocrine disrupters are accumulated in fish from the Seine estuary. Detection of these
compounds is particularly evident in fish bile, where many xenobiotics are excreted and
found in high concentrations (Gibson et al. 2005; Smith and Hill 2006). The same com-
pounds as those identified in zebra mussels (mainly steroids) are found in bile of male
roach Rutilus rutilus from the Seine River. However, a larger diversity of compounds has
sometimes been observed in male flounder ( Platichthys flesus) ) living in the estuary and in
the Baie de Seine. Indeed, some compounds whose chemical nature has not been eluci-
dated so far are present in flounder bile, in addition to natural and synthetic steroids and
alkylphenols and bisphenol A (Denier et al. 2008). This increased diversity may be associ-
ated with the habitat of the benthic fish that could lead flounder to be exposed to a larger
number of compounds present in sediments. A lower diversity of compounds is observed
in bile from roach living in rivers and whose lifestyle is not benthic. Nevertheless, as the
most downstream part of the estuary is host to numerous industries and to the large city
of Le Havre, the possibility that flounder are exposed to compounds present in significant
amounts originating from these specific sources cannot be ruled out.
Unlike in mussels, molecular effects of xenoestrogens can easily be demonstrated in
fish by measuring VTG expression in male fish (see Chapter 2). Indeed, VTG is a phospho-
lipoglycoprotein used as reserve substance in eggs in order to allow the development of
fish larvae. It is naturally synthesized by female fish in response to estradiol secreted by
the ovaries during the reproductive cycle. However, the occurrence of VTG in male fish
reveals an exogenous exposure to xenoestrogens and is a biomarker of endocrine disrup-
tion (Van der Ven et al. 2003).
This protein can be measured in plasma or liver of fish and, in the Seine estuary, it has
been demonstrated in male roach and flounder. VTG concentration can be very high in
some male roach sampled in the Seine, with values reaching 10,000 ng mL -1 in plasma.
Eighty percent of the roach analyzed show very significant plasma concentrations, exceed-
ing 200 ng mL -1 (Minier et al. 2005; Geraudie et al. 2010a). The average concentration
observed in flounder plasma collected in 2001 was 125,000 ng mL -1 . Forty-nine percent of
the samples were above 1000 ng mL -1 , a threshold value signifying a clear disruption of
the endocrine system. Compared to plasma VTG measured in flounder from other large
European estuaries, this result shows that the Seine estuary is one of the most contami-
nated estuaries in Europe along with the Mersey and the Tyne (England) but ahead of
other major estuaries such as the Thames, the Scheldt, and the Elbe, still considered to be
contaminated (Kleinkauf et al. 2004; Vethaak et al. 2005).
The presence of large amounts of VTG has been linked to problems of excretion, lead-
ing to kidney dysfunction, since male fish cannot eliminate these large plasma proteins.