Thallium determination in contaminated water and biological samples: a population-based case–control study in Valdicastello Carducci and Pietrasanta (Lucca, Italy)

Water-soluble thallium (Tl) compounds are highly toxic for most living organisms. Tl toxicity to mammals is higher than that of Hg(II), Cd(II) and Pb(II), because it chemically behaves as a heavy metal and because, due to its charge and size, it is an analogous of potassium. Thus, it has been notified as an important EPA priority pollutant. Thallium maximum contaminant level (MCL) in drinking water defined by EPA is 2 μg/L and 0.1 μg/L in China (CNS 2006) [1]. A recent study showed the presence of Tl at high concentrations (up to 9000 μg/L) in groundwater near Valdicastello Carducci (Italy). The contamination is supposedly due to acid drainage from abandoned mining areas. In September 2014 Tl contamination was also found in water intended for human consumption distributed in the same area. We report here the preliminary results of a non-invasive population-based study that aimed to quantify the Tl levels in about 100 urine and 330 hair samples from the population of Valdicastello Carducci and Pietrasanta, Italy. Several saliva samples were also collected in order to explore this matrix as exposure indicator. All samples were analyzed by ICP-MS. Quality assurance of the results was guaranteed analyzing two certified reference material (water and urine from NIST). Tl values found in urine and hair samples were correlated with Tl concentration levels found in tap water in the living area of each citizen and with his/her habits (use of tap water both to drink and to cook or only to cook). The kinetics of decay of Tl concentration in urine samples was also investigated. About 50% of samples had a Tl concentration value above 0,5 microgram/L; about 70% of hair samples had a Tl concentration > 10 ng/g (2 1 ng/g is the value of not exposed people). The high values of thallium found in hair samples suggest a long-term exposure.