Thallium ecosystem diseases in dismissed mine sites as a threat for public health: the Valdicastello-Pietrasanta (Italy) case history

The legacy of mining activity may be the production of metal-rich acidic drainage and the release of toxic compounds to the receiving ecosystem. The mitigation of the environmental impact from metals and metalloids in mine drainages mostly produced by sulfide mineral oxidation is of great environmental concern, and, even if the acidity of drainages often receives most of the attention, the primary sources of toxicity for the biota and humans are the dissolved toxic and potentially toxic metals. Furthermore, the possible increase of pH and alkalinity that occur in superficial- and ground-waters by the interactions of acid waters with carbonate minerals and/or by the admixing of calcium-bicarbonate waters do not necessarily prevent metal transport through waters from causing negative environmental impacts. In fact, even if some metals, such as iron and arsenic, are readily scavenged from the aqueous phase by precipitation and adsorption processes as the pH increases, other ionic species of elements such as thallium may stay in solution in some cases reaching concentrations of concern. Previous studies demonstrated that in the dismissed mine areas of Valdicastello Carducci-Pollone and Mt Arsiccio in the Versilia area (Tuscany Region, Italy) thallium is hosted in base metal sulfides such as pyrite up to wt.% amounts. From these sources thallium is readily mobilized to waters during weathering oxidation of the sulfide minerals, reaching up to 9000 μg/L in drainages, and is dispersed into the ecosystem via water transport pathways with low attenuation when dissolved Fe(II) starts oxidizing and precipitating as insoluble oxyhydroxides. In the study area thallium-contaminated groundwater was used as supply in the potable water distribution network of Valdicastello Carducci and part of Pietrasanta town, and thallium was retained in scale encrustation within the pipeline walls at wt% concentration and then released to drinking waters. A non-invasive study on inhabitants of Valdicastello and Pietrasanta was performed in order to quantify the thallium concentration in urine and hair samples, in addition to saliva samples. The preliminary data show that about 50% of the urine samples are characterized by a thallium concentration above 0.5 μg/L and about 70% of hair samples has a thallium concentration exceeding 10 ng/g. These results highlight the links between changes in the state of the environment and human exposures.