Distributions and concentrations of thallium in surface waters of a region impacted by historical metal mining (Cornwall, UK).

Thallium is a highly toxic heavy metal whose concentrations and distributions in the aquatic environment are poorly defined. In this study, concentrations of aqueous and total Tl have been measured in water samples from a variety of rivers and effluents (the latter related to historical metal mining) in the county of Cornwall, SW England. Aqueous concentrations ranged from about 13 ng L(-1) in a river whose catchment contained no metal mines to 2,640 ng L(-1) in water abstracted directly from an abandoned mine shaft. Concentrations of Tl in rivers were greatest in the vicinity of mine-related effluents, with a maximum value measured of about 770 ng L(-1). Thallium was not efficiently removed by the conventional, active treatment of mine water, and displayed little interaction with suspended particles. Its mobility in surface waters, coupled with concentrations that are close to a quality guideline of 800 ng L(-1), is cause for concern. Accordingly, we recommend that the metal is more closely monitored in this and other regions impacted by mining activities.