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1984; Chu and Lapeyre 1989). More recently, Gagnaire et al. (2007) measured the reduced
gene expression of several enzymes in hemocytes from oysters
Crassostrea gigas
exposed
to pesticides.
6.2.5 Comparison between Markers and Adverse Effects
Pipe and Coles (1995) have attempted to correlate the response of different immunologi-
cal biomarkers and the presence of a variety of contaminants in
Mytilus galloprovincialis
living in different sections of the Venice lagoon. The biomarkers consisted of hemocyte
number and viability, phagocytosis, the release of lysosomal enzymes, and the produc-
tion of oxygen derivatives. Contaminants measured were metals and organochlorine (OC)
compounds including PCBs. All measured parameters showed seasonal fluctuations. In
many cases, a correlation was found between the immunological response and contami-
nant concentration measured in mussel tissues. In addition, hemocytes appear more abun-
dant at sites with low metal concentrations compared to the total number of circulating
hemocytes in mussels at more contaminated sites. A tendency to inhibition of phagocy-
tosis was observed in mussels exposed to high concentrations of metals, a phenomenon
also encountered after exposure to PAHs. In mussels exposed to low concentrations of
contaminants, an increase in the production of oxygen species was observed. A negative
correlation between the production of oxygen derivatives and decreasing concentrations
of organic contaminants was also noted.
Moreover, the use of multiple immunomarkers could be of value in understanding the
mode of action of chemicals, especially for complex mixtures. Municipal effluents are well
known to be major sources of contamination in aquatic ecosystems. In addition to trace
metals and polyaromatic hydrocarbons, they contain pharmaceutical and personal care
products (Kummerer 2001), as well as well-known endocrine disruptors such as 17α-,17β-
ethynylestradiol (active ingredient in birth control pills), nonylphenol (breakdown prod-
uct of alkylphenol polyethoxylate surfactants), bisphenol A, and the natural estrogen
17β-estradiol (Sumpter and Jobling 1995; Sabik et al. 2003; Vethaak et al. 2005). Effluent dis-
charges also contain potentially pathogenic microorganisms (Farcy
et al. 2011). Municipal
effluents have been the object of many studies using freshwater bivalves.
Caged
E. complanata
, a freshwater mussel, placed downstream of an effluent discharge
point revealed that hemocyte viability was significantly affected between sites, and phago-
cytosis was significantly reduced (Bouchard et al. 2009). In another study, phagocytic activ-
ity, nitrite oxide (NO), and cyclooxygenase (COX) activity were induced in hemocytes of
E. complanata
exposed to aeration lagoon effluents containing several pharmaceuticals as
well as high bacterial loads (Gagné et al. 2006a, 2006b, 2012). Discriminant function analy-
sis has enabled the separation of the effects of microparticles and microorganisms on the
immune parameters of
E. complanata
. Although the effects on intracellular ROS and thiol
levels were more pronounced with exposure to filtered effluent, phagocytosis, NO levels,
COX, and lysozyme activities were higher with unfiltered effluent. This is in agreement
with a previous study in rainbow trout
Oncorhynchus mykiss
exposed
in vivo
to the same
municipal effluent (Hébert et al. 2008). Phagocytosis and natural cytotoxic cell activities
were more affected by the insoluble (particles and microorganisms) fraction of the munic-
ipal effluent. However, the presence of estrogenic compounds could also influence the
immune system in mollusks (Canesi et al. 2007a, 2007b, 2007c). Exposures to estrogenic
chemicals found in municipal effluents (17α-ethynyl estradiol, mestranol, nonylphenol,
nonylphenol monoethoxylate carboxylate, bisphenol A, benzophenone) were shown to
decrease phagocytosis, lysosome membrane stability, and lysozyme release in mussels.
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