Mercury in Terrestrial Food Webs of the Idrija Mining Area

Abstract

To evaluate the degree of contamination with mercury and its transfer in food webs in the active mercury mining area of Idrija, concentrations in soil profiles, plants and animal tissues were analyzed during the period from 1990 to 1996. Total mercury (T-Hg) and methylmercury concentrations (Me-Hg) were determined in body tissues and fur of roe deer, Capreolus capreolus L. (n = 20), their diet (composite plant samples of a minimum of 40 plant species), soil samples, and in tissues of their predators such as the wolf, Canis lupus L. (n = 2), and lynx, Lynx lynx L. (n = 8). The study was focused on the wider area of the active mercury mine in Idrija, the abandoned mercury mining area in Podljubelj, where mining and smelting ceased in 1900, and five non-polluted locations in Slovenia. Special attention was paid to proper sample collection, preparation and storage. The concentration levels of total and methylmercury in roe deer tissues are correlated with those in their composite vegetal diet, and soil samples from the polluted area. A correlation with the distance from the mercury source was observed (T-Hg: r2 < 0.62; Me-Hg: r2 < 0.73). Herbivore tissues which originate from the active mining area contain up to 350 times higher concentrations of mercury than controls. The tissues of old animals mostly contain high Hg concentrations compared to the corresponding tissues of young animals. However, in the Idrija area the relationship with the age of roe deer was less distinctive due to the influence of the particular spatial exposure gradient. Total mercury concentrations in roe deer organs descend as follows: kidney >> liver > fur > pineal gland >> suprarenal gland > spleen > masseter muscle > lung > pituitary gland > eye sections > sections of the central nervous system (CNS). A large portion of Hg (20 to 85%) in animal tissues from the contaminated area was present as methylmercury (except in the liver and kidney), despite the fact that inorganic Hg and elemental Hg are the primary sources of pollution in the area. The percentage of Me-Hg in composite plant samples and soil profiles was very small (0.14 to 2%). Our data indicate that in the terrestrial environment, roe deer tissues can be successfully used as an indicator of mercury contamination, transfer and accumulation processes. Furthermore, a positive correlation between mercury concentrations in certain roe deer and human tissues from residents of the mining area suggests that roe deer tissues may be successfully used as biomonitors and thus as an early warning of elevated mercury concentration levels in man. However, mercury levels in selected predator species do not follow locally enhanced Hg concentrations in their prey (roe deer) or in vegetation and soils from the polluted area. Since the predators selected occupy larger territories and their prey contains different mercury levels, they are considered less suitable for monitoring of locally enhanced Hg contamination.