Mercury in Terrestrial Food Webs of the Idrija Mining Area
307
contaminated area. However, transformations of mercury inside the animal
tissues must not be neglected. The relatively high Me-Hg values in the target
tissues of mercury accumulation suggest that in addition to preferential
accumulation and retention, at least part of the organic mercury may arise from
metabolic biotransformation processes i.e. in-vivo methylation of Hg. The most
favourable factors for in-vivo methylation of Hg are present in the animal's
gastro-intestinal tract. Factors such as the deer's nutritional habits, suitable pH
and temperature in the rumen of herbivores, high concentrations of inorganic
mercury present in the plant foodstuffs, the presence of CO2, CH 4 , and important
microorganisms suggest the existence ofbiomethylation processes. Of course, the
Me-Hg concentration level in each tissue is a result of methylation and
demethylation processes, which additionally complicate the issue.
It is suggested that both various accumulation patterns and important
transformation mechanisms depend on the different toxicological and pharmacological features of the particular Hg species involved and individual characteristics of the animals. A special study is anticipated which will be devoted to
solving problems dealing with Hg transformation and transport processes in
wildlife metabolism, and in the polluted forestal terrestrial ecosystem as a whole.
Also, the significance of some metabolic processes inside the gastrointestinal
tract of ruminants for the biotransformation rate of Hg in herbivore tissues will
be established and evaluated.
4.6
Is Wildlife Particularly Vulnerable
as Concerns Environmental Hg Contamination?
As stressed in the WHO-IPCS Environmental Health Criteria (WHO 1976, 1989,
1990, 1991) and some other reviews (Lindqvist 1991; O'Brien et al. 1993), only a
few studies have been published on truly wild, non-laboratory terrestrial
mammals in relation to their exposure to mercury and its compounds in the
natural environment. From such studies some important information was gained
with respect to mercury toxicity. In one of the first studies performed on wild
mammals (Aulerich et al. 1974), it was shown that mink exposed to enhanced
concentrations of inorganic Hg in their diet (as in the case of natural exposure in
the Idrija area) showed no apparent clinical signs of poisoning, whereas the toxic
effects of Me-Hg were found to be much worse. However, from the small number
of studies concerning mercury concentrations in terrestrial wildlife and the food
chain transfer of the element, such as that of Bull et al. (1977), it was proposed
(WHO 1976, 1989, 1990, 1991) that exposure via soil, soil water and through
terrestrial food webs should be emphasized, rather than through drinking water
and inhalation pathways. These later were found to be of less importance for the
ecotoxicology of terrestrial organisms, even though heavily polluted areas could
be an exception. The results of our present study confirm the above (see Table 4
and Fig. 4). There is a strong correlation between the mercury concentration in
the mixed plant diet samples and mercury concentration values in roe deer
tissues. Thus, the vigorous vegetation feeding characteristics of herbivorous
307
contaminated area. However, transformations of mercury inside the animal
tissues must not be neglected. The relatively high Me-Hg values in the target
tissues of mercury accumulation suggest that in addition to preferential
accumulation and retention, at least part of the organic mercury may arise from
metabolic biotransformation processes i.e. in-vivo methylation of Hg. The most
favourable factors for in-vivo methylation of Hg are present in the animal's
gastro-intestinal tract. Factors such as the deer's nutritional habits, suitable pH
and temperature in the rumen of herbivores, high concentrations of inorganic
mercury present in the plant foodstuffs, the presence of CO2, CH 4 , and important
microorganisms suggest the existence ofbiomethylation processes. Of course, the
Me-Hg concentration level in each tissue is a result of methylation and
demethylation processes, which additionally complicate the issue.
It is suggested that both various accumulation patterns and important
transformation mechanisms depend on the different toxicological and pharmacological features of the particular Hg species involved and individual characteristics of the animals. A special study is anticipated which will be devoted to
solving problems dealing with Hg transformation and transport processes in
wildlife metabolism, and in the polluted forestal terrestrial ecosystem as a whole.
Also, the significance of some metabolic processes inside the gastrointestinal
tract of ruminants for the biotransformation rate of Hg in herbivore tissues will
be established and evaluated.
4.6
Is Wildlife Particularly Vulnerable
as Concerns Environmental Hg Contamination?
As stressed in the WHO-IPCS Environmental Health Criteria (WHO 1976, 1989,
1990, 1991) and some other reviews (Lindqvist 1991; O'Brien et al. 1993), only a
few studies have been published on truly wild, non-laboratory terrestrial
mammals in relation to their exposure to mercury and its compounds in the
natural environment. From such studies some important information was gained
with respect to mercury toxicity. In one of the first studies performed on wild
mammals (Aulerich et al. 1974), it was shown that mink exposed to enhanced
concentrations of inorganic Hg in their diet (as in the case of natural exposure in
the Idrija area) showed no apparent clinical signs of poisoning, whereas the toxic
effects of Me-Hg were found to be much worse. However, from the small number
of studies concerning mercury concentrations in terrestrial wildlife and the food
chain transfer of the element, such as that of Bull et al. (1977), it was proposed
(WHO 1976, 1989, 1990, 1991) that exposure via soil, soil water and through
terrestrial food webs should be emphasized, rather than through drinking water
and inhalation pathways. These later were found to be of less importance for the
ecotoxicology of terrestrial organisms, even though heavily polluted areas could
be an exception. The results of our present study confirm the above (see Table 4
and Fig. 4). There is a strong correlation between the mercury concentration in
the mixed plant diet samples and mercury concentration values in roe deer
tissues. Thus, the vigorous vegetation feeding characteristics of herbivorous