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These authors also list practical considerations (economic, easy to perform, reliable).
However, biomarkers have been criticized for their lack of specificity since they can
respond to several classes of contaminants and to nonchemical stressors (confounding
factors) and their lack of ecological relevance (Forbes et al. 2006). In order to mitigate these
disadvantages, different strategies are proposed in the next sections for a sound use of
biomarkers for environmental quality assessment as well as predictive risk assessment.
16.2 Using Biomarkers to Assess Environmental Quality
Although biomarkers are being increasingly studied (Jemec et al. 2010) and used in bio-
monitoring (Chapter 15), a number of serious problems still need to be solved. An impor-
tant one is our ability to distinguish between normal fluctuations of biological responses
used as biomarkers and fluctuations attributable to stress, particularly chemical stress
induced by pollutants (Figure 1.6).
16.2.1 Confounding Factors
Confounding factors include both extrinsic factors (temperature, pH, redox status, hard-
ness in freshwaters, salinity in estuarine waters, food availability, parasitism) and intrin-
sic factors (weight/size/age, sex, reproductive status, tolerance acquired by populations
chronically exposed to contaminants in their environment). Seasonal fluctuations that
have been evoked as influencing most of the biomarkers examined in the different chapters
of this topic include both extrinsic and intrinsic factors, among which the most important
are certainly temperature, food availability, and reproductive status, but also the pollutant
inputs associated with different river flows and applications of pesticide treatments.
Despite this limitation, most of the existing information on the influence of tempera-
ture on biomarker responses has been collected as part of field surveys covering tempo-
ral variations. However, according to the fundamentals of biochemistry, temperature is
recognized as influencing the activity of enzymes by changing the protein conformation
and their catalytic efficiency or binding capacity. This is important for the methodology
of biomarkers since many subindividual markers are based on enzymatic activities. In
estuarine and coastal environments, salinity is also an important source of variability for
numerous biomarkers, as exemplified in the endobenthic invertebrates Scrobicularia plana
and Nereis diversicolor (Kalman et al. 2010; Fossi Tankoua et al. 2011 and references quoted
by these authors). The influence of the size/weight/age complex on biomarker responses to
toxicants is at least partly the consequence of differences in uptake of contaminants, which
are well documented after many previous studies on contamination biomonitors such as
the bivalves used in Mussel Watch programs (NAS 1980). It is also evident that biomarkers
of contaminants that interfere specifically with development or reproduction (Chapters 8
and 9) are strongly influenced by the life history stage (larvae, embryos, juveniles, adults)
or sex and sexual status of the relevant organism. Molting, which is a key period in the
life span of arthropods, must be taken into account for a sound interpretation of biological
responses in species belonging to this zoological group (Chapter 8).
Other factors have been less documented. However, the influence of pH and oxygenation
on biomarker responses was shown for several enzyme activities in the freshwater bivalves
Corbicula fluminea and Anodonta cygnea (Vidal et al. 2002; Robillard et al. 2003), whereas
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