Small mammal populations and community under conditions of extremely high thallium contamination in the environment

Studies were carried out in the vicinity of a zinc smelter in southern Poland, 50 km northwest of Krakow, where the previous measurements with another bioindication method revealed huge thallium levels in the environment. The mammals (106 individuals in total) were captured in four wooded areas situated 1.5 to 2.5 km in various directions from the plant and in two reference sites, located far from industrial emission sources. Very high Tl levels were found in livers and kidneys of all mammals examined from the two areas nearest the smelter. Bank voles were the most loaded (maximum Tl in kidneys, 34.27 microgram/g dry mass; in livers, 14.53 microgram/g; values from unpolluted areas were below the detection limit, 0.07 microgram/g). A distinct decrease in the amount of hair-a characteristic of thallium poisoning-was observed in several individuals. The extreme case was a wood mouse with the rear half of its body almost entirely hairless (!). Densities of single populations and the whole community were very low, up to 4.8 individuals/ha, including insectivores. Numerical proportions between species were changed in comparison to unpolluted areas. The age structure was deformed, with a disproportionate small participation by young generations. Among the males studied, only sexually inactive individuals were found. The condition of populations and the community of small mammals living here was much worse compared with data from the surroundings of other zinc smelters.