Conclusions: Biomarkers in Environmental Risk Assessment - Ecological Biomarkers: Indicators of Ecotoxicological Effects - page 415

reproduction biomarkers (% females carrying a dead brood) in the amphipod Monoporeia
affinis were related to oxygen concentration of the bottom water (Eriksson Wiklund and
Sundelin 2004). The importance of parasitism in ecotoxicological studies is highlighted by
changes affecting biomarkers of oxidative stress in freshwater mussels Dreissena polymor-
pha and marine mussels Mytilus galloprovincialis (Minguez et al. 2009; Canesi et al. 2010) or
the impact of the parasitic acanthocephalan worm Echinorhynchus truttae on the feeding
rate of the amphipod Gammarus pulex (Fielding et al. 2003). Infection with another acantho-
cephalan parasite Acanthocephalus tehlequahensis causes a significant and direct energetic
cost to its freshwater isopod intermediate host Caecidotea communis at both individual and
population levels (Lettini and Sukhdeo 2010).
The sampling matrix must also be carefully chosen. For instance, Bechshøft et al. (2011)
have shown that retinol was not uniformly distributed in the kidney of polar bears Ursus
maritimus . Many different tissues have been used for the determination of acetylcholinester-
ase (AChE) activity in different species (Chapter 4). However, after a comparison between
eyes, brain, gills, digestive tract, and muscles of the common prawn Palaemon serratus ,
Frasco et al. (2010) recommend the use of eyes since this tissue expresses the highest levels
of ChE while possessing an enzyme that shows the properties of a vertebrate AChE. In the
case of genotoxic biomarkers, mussels are useful sentinel species in PAH-contaminated
areas, provided DNA adducts are measured in specific tissues (gills or digestive gland), as
opposed to whole tissues that may dilute the adduct pool and weaken the signal (Chapter
13). In the gammarid amphipod crustacean Gammarus fossarum caged upstream and
downstream of wastewater treatment plant effluent output, spermatozoa appeared to be
more susceptible to accumulating DNA damage than hemocytes and oocytes (Lacaze et
al. 2011a). Studying genotoxic damage in polychaetes, Lewis and Galloway (2008) demon-
strated that different cell types within the same species and different species within the
polychaetes show significantly different responses.
It is important to consider the confounding roles of all these factors before using any bio-
marker in any organ or cell of any species in the medium under investigation. However, it
must be duly noted that studies highlighting the influence of certain biological or ecologi-
cal conditions on particular biomarkers also reveal that other biomarkers are robust, not
being influenced or only marginally by confounding factors.
Important differences in responsiveness to both contamination factors and natural fac-
tors appear when comparing different species. Ethoxyresorufin O -deethylase (EROD), and
more recently following the development of molecular biology, CYP genes are frequently
used as core biomarkers of exposure to organic xenobiotics. However, a comparison of
the responses of tomcod Microgadus tomcod and killifish Fundulus heteroclitus submitted
to AH exposure in North American estuaries, underlines that, depending on species and
site, responses may be different with the consequent possibility of false negatives or posi-
tives when interpreting the results of a biomonitoring program (Berthet et al. 2011). In a
comparison of biomarker responses in two endobenthic invertebrates, it appears that the
annelid Nereis diversicolor is less sensitive than the bivalve Scrobicularia plana to the effects
of size and salinity differences (Table 16.1). In addition, this annelid is more responsive
for a number of enzyme activities, as also underlined by Solé et al. (2009), whereas it is
not efficient at revealing metal exposure by use of metallothionein (MT) concentrations
(Poirier et al. 2006). For behavioral tests, in the case of petroleum hydrocarbons, bivalves
( Mercenaria mercenaria , Olla et al. 1983; Protothaca staminea , Pearson et al. 1981) seem more
responsive than annelids ( Nereis virens , Olla et al. 1984), but, at a high degree of mixed
pollution such as in the Seine estuary, France, delayed burrowing was also observed in N.
diversicolor (Mouneyrac et al. 2009). Even within the same taxon, Hagger et al. (2010) report