Human exposure to thallium through tap water: A study from Valdicastello Carducci and Pietrasanta (northern Tuscany, Italy)

•Thallium (Tl) is a heavy metal with high toxicity for living organisms.•Tap water was contaminated with Tl up to 10 μg/L in Tuscany (Italy).•318 hair and 150 urine samples analyzed to show human contamination.•People significantly accumulated Tl compared to European reference values.

A geological study evidenced the presence of thallium (Tl) at concentrations of concern in groundwaters near Valdicastello Carducci (Tuscany, Italy). The source of contamination has been identified in the Tl-bearing pyrite ores occurring in the abandoned mining sites of the area. The strongly acidic internal waters flowing in the mining tunnels can reach exceptional Tl concentrations, up to 9000 μg/L. In September 2014 Tl contamination was also found in the tap water distributed in the same area (from 2 to 10 μg/L). On October 3, 2014 the local authorities imposed a Do Not Drink order to the population.Here we report the results of the exposure study carried out from October 2014 to October 2015, and aimed at quantifying Tl levels in 150 urine and 318 hair samples from the population of Valdicastello Carducci and Pietrasanta. Thallium was quantified by inductively coupled plasma - mass spectrometry (ICP-MS). Urine and hair were chosen as model matrices indicative of different time periods of exposure (short-term and long-term, respectively).Thallium values found in biological samples were correlated with Tl concentrations found in tap water in the living area of each citizen, and with his/her habits. Thallium concentration range found in hair and urine was 1-498 ng/g (values in unexposed subjects 0.1-6 ng/g) and 0.046-5.44 μg/L (reference value for the European population 0.006 μg/L), respectively. Results show that Tl levels in biological samples were significantly associated with residency in zones containing elevated water Tl levels. The kinetics of decay of Tl concentration in urine samples was also investigated. At the best of our knowledge, this is the first study on human contamination by Tl through water involving such a high number of samples.

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