THALLIUM LEVELS AND BIOACCUMULATION IN ENVIRONMENTAL SAMPLES OF NORTHERN CHILE: HUMAN HEALTH RISKS

Thallium (Tl) is a highly toxic heavy metal; however there is an increasing demand for thallium in the high-technology and, a lack of information in the literature. On the other hand, under natural conditions, Tl occurs in large quantities rarely and plays no role in the metabolism of plants or animal. Studies on the presence of Tl in the vicinity of a copper mining-impacted region in northern Chile were carried out. A number of different types of environmental samples such as crop plants (potato, broad bean and maize), water, algae (Myriophyllum acuaticum, Zannichellia palustris L.) and one plant species (Tessaria absinthioides) growing wildly in the same area, were examined. All of them are exposed to a natural environmental contamination and to the impact of the copper mining activity throughout the region. Thallium concentration in plants exhibits species-dependent preferences. Thus, the enrichment of Tl in the edible parts of crop species decreases in the following order: potato > broad bean > maize grain. Thallium contents, expressed as dry weight (d.w.), varied from < 0.001 to 6.8 mu gg(-1) in crop plants, from 0.295 to 8.3 mu gg(-1) in algae, and between 0.010 and 0.501 mu gg(-1) in plant samples (2-10 times the level normally found in plants, 0.05 mu gg(-1) dry wt). Dissolved Tl concentrations in rivers were found to be 6 to 120 ngL(-1). In the current study, the risk for adverse health effects derived from ingestion from potatoes was assessed. It shows that there is an important risk for the infantile and adult population at present.