Biomarkers of Defense, Tolerance, and Ecological Consequences - Ecological Biomarkers: Indicators of Ecotoxicological Effects - page 63

(Boyle et al. 2008). Even if metal detoxification by biomineralization does not guarantee the
“transfer of metal detoxification along marine food chains” according to the expression of
Nott and Nicolaidou (1990), it is a factor limiting the risk of transfer. The physicochemical
form of metals in their prey clearly influences subsequent trophic transfer, but the pat-
tern varies between food items, consumers, and metals. From the different studies syn-
thesized by Rainbow et al. (2011), it may be concluded that what is trophically available to
one predator (feeding on one prey type) is not necessarily trophically available to another
(taxonomically separated) predator even if feeding on the same prey, given the variability
between animal digestive systems (Figure 3.3).
The ecotoxicological risk is greater for metals that have organometallic forms such as
methylmercury, which is prone to biomagnify in aquatic food chains as dramatically dem-
onstrated by the Minamata disaster. Biomagnification is defined as an increase in contami-
nant concentration from one trophic level to the next owing to accumulation from food.
Biomagnification is also well documented for persistent organic contaminants such as
dichlorodiphenyltrichloroethane (DDT), PCBs, and PBDEs. Hydrophobicity is an impor-
tant chemical property favoring biomagnification in biota but it is not the whole story, and
despite being hydrophobic, PAHs are not biomagnified. The fate of organic contaminants
in the food web depends on a set of biological mechanisms including (1) mucus produc-
tion; (2) induction of MXR that, by limiting bioaccumulation in prey species, reduces con-
taminant transfer to predators (Section 3.3.5); (3) biotransformation based on phases I and
II enzymes, which favor excretion (Section 3.3.3) but with side effects linked to the pres-
ence of intermediate reactive metabolites. These genotoxic/carcinogenic metabolites may
be responsible for a transfer of toxicity in the food chain, even in the absence of biomag-
nification. Studies involving PAH-contaminated polychaetes fed to juvenile English sole
or mussels contaminated with hydrocarbons released into the field after the oil spill of the
tanker Erika fed to mammals provide examples of a transfer of toxicity between successive
trophic levels (Amiard-Triquet and Rainbow in Amiard-Triquet et al. 2011).

A

Cellular
debris

Heat-sensitive
proteins

Metallothionein-
like proteins

Metal-rich
granules

Organelles

B

Cellular
debris

Heat-sensitive
proteins

Metallothionein-
like proteins

Metal-rich
granules

Organelles

C

Heat-sensitive
proteins

Metallothionein-
like proteins

Metal-rich
granules

Cellular
debris

Organelles

Soluble fraction

Insoluble fraction

FIGURE 3.3
Fractionation of metal accumulated in prey into five components. (After Wallace, W.G. et al., Mar. Ecol. Prog.
Ser. , 249, 183-197, 2003.) (a) Highlighted areas covering all five fractions to some degree represent metal accu-
mulated in prey trophically available to a neogastropod mollusk (Cheung and Wang 2005; Rainbow et al. 2007).
(b) Highlighted areas (from four fractions) represent metal accumulated in prey trophically available to a preda-
tor with weaker digestive powers than a neogastropod mollusk. (c) Highlighted areas (from two fractions)
represent metal accumulated in prey trophically available to a planktonic copepod filtering phytoplankton
(Reinfelder and Fisher 1991). (From Rainbow, P.S. et al., Environ. Pollut. , 159, 2347-2349, 2011. With permission.)