Biomarkers of Defense, Tolerance, and Ecological Consequences - Ecological Biomarkers: Indicators of Ecotoxicological Effects - page 65

of hepatic neoplasms has been observed in two populations—killifish Heterandria formosa
from the Elizabeth River and tomcod Microgadus tomcod from the Hudson River, United
States—resistant, respectively, to PAHs and PCBs. Resistant hepatocytes are able to prolif-
erate vigorously, resist cytotoxicity, and exhibit unusual patterns of gene induction (phases
I and II enzymes). Thus, it has been hypothesized that hepatic neoplasia may provide a
complementary mechanism for impacted populations to persist in highly contaminated
environments (considering that cancer is postreproductive in these fish models), but at the
cost of an altered population age structure. Cascading effects at higher levels of biological
organization depend on the role of impacted populations in the structure of communities
and the functioning of ecosystems.
Another ecosystem aspect must be considered to assess the protective value of biomark-
ers of defense. Tolerance allows the persistence of organisms in highly contaminated
environments but perhaps at the cost of contaminant transfer in food webs, which is par-
ticularly worrying for those compounds prone to biomagnification (methylmercury, DDT,
PCBs) or in the case of toxicity transfer between successive links (PAHs). If we include our
own species in the ecosystem, tolerance may be considered more detrimental than ben-
eficial, responsible for the development of bacterial strains coresistant to chemicals and
antibiotics so important in medicine or the development of insect populations resistant to
pesticides, thus requiring insecticides with novel modes of action (Ghanim and Ishaaya in
Amiard-Triquet et al. 2011).
Tolerance clearly poses a problem for risk assessment in contaminated ecosystems. In
regulations for the control of water quality based on toxicity tests, the protective effect
of acclimation is never taken into account. This can generate positive false results since
living organisms are present in areas where contaminant concentrations are so high that
they are not expected to be able to survive. On the other hand, laboratory tests carried out
with tolerant strains or populations can lead to negative false results, with underestimated
toxicological parameters. Consequently, environmental assessment must not be limited to
a chemical approach, which only makes it possible to verify that environmental standards
are enforced, but must also include a biological constituent involving a multibiomarker
approach (Chapter 2).
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