Dispersal of heavy metals from abandoned mine workings and their transference through terrestrial food chains

Abstract

Past exploitation of metalliferous ores has resulted in extensive metal contamination of surface soils in the vicinity of a derelict mine complex. Soil lead and zinc concentrations were found to decrease exponentially with distance downwind of abandoned metalliferous spoil heaps. Dispersal of metal-rich waste materials is attributed mainly to wind erosion, percolating waters and surface drainage waters. The abundance of lead and zinc in surface soils close to spoil heaps largely reflects the chemical composition of the waste material. However, heavy metal ratios in native fauna were inconsistent with those of the indigenous soil and vegetation, reflecting differences in the relative mobilities of metallic pollutants. Examinations of carnivores, herbivores and their estimated diets indicated that cadmium has a greater potential for accumulation through lower terrestrial trophic levels than both lead and zinc. The low transfer potential of zinc may be associated with its essential role in biological systems. The high mobility of cadmium may result from its accumulation in soft tissues rather than skeletal components, the latter constituting the principal sites for deposition of lead.