Agriculture Reference
In-Depth Information
THE USE OF EARTHWORM BIOMARKERS AND
UNDERSTANDING BIOAVAILABILITY
The use of sensitive biomarkers in toxicity tests using earthworms represents a fairly new approach
(A.J. Reinecke and Reinecke 1998). Scott-Fordsmand and Weeks (1998) reviewed biomarkers
comprehensively. A
is defined as a xenobiotically induced variation in cellular or
biochemical components or processes, structures, or functions that is measurable in a biological
system or sample. As such, it constitutes a response to the presence of a stress factor. Relatively
little research has been undertaken so far on biomarkers in earthworms. Biomarkers have been
evaluated in
biomarker
(Goven et al. 1988; Rodriquez et al. 1989; Svendsen and
Weeks 1997; S.A. Reinecke et al. 2002). For instance, a broad spectrum of xenobiotics can alter
the immune function. The immunobiology of earthworms has been studied intensively in immu-
notoxicological studies (Fitzpatrick et al. 1990; Venables et al. 1992; Goven et al. 1994; Marino
and Morgan 1998). Although a number of coelomocyte-based end points have been shown to be
sensitive indicators of the sublethal toxicity of chemicals (Venables et al. 1992) and hold promise
to provide cost-effective assessment of potential risks, evidence of ecological relevance is limited,
although promising (Maboeta et al. 2002). The comet assay (Figure 16.1), measuring the effects
of toxicants on deoxyribonucleic acid (DNA) integrity in earthworms, could also serve as a
biomarker (S.A. Reinecke and Reinecke 2003). This represents a new approach, which may yield
promising results if a battery of biomarkers can be employed, to predict toxic risks to organisms
at higher levels of organization.
An important new development is the application of modern molecular techniques to identify
biomarkers in earthworms. Heavy metal-responsive genetic indexes (Strzenbaum et al. 1998)
may enhance future testing protocols. A number of molecular genetic techniques have already
been utilized to identify genes responsive to certain types of exposure to toxicants. The value of
biomarkers in risk assessment (Weeks 1995) has received increasing attention because of the
problems experienced when trying to relate environmental concentrations of toxicants to their
bioavailable fraction. The bioavailability and toxicity of a chemical may differ considerably in
laboratory tests from those observed in the field. Biomarkers, on the other hand, respond to the
dose of a toxicant entering the animal body.
L. terrestris
and
E. fetida
FIGURE 16.1
The use of the comet assay as a biomarker. An example of changes in the DNA structure of
nuclei of coelomocytes of the earthworm,
Eisenia fetida,
before and after the worms were exposed to nickel.
