Mercury in bottled water from Emilia-Romagna and Veneto: ultra-trace amount determination and evaluation of intake using a health risk assessment approach

Mercury (Hg) is a toxic element and a ubiquitous pollutant. Natural sources and processes (e.g. forest fires, volcanic and geothermal activities, rock weathering) and human activities (e.g. power plants, artisanal and small-scale gold and mercury mining) are both responsible for its presence in all environmental matrices (air, water and soil). Even at very low levels in both aquatic and terrestrial ecosystems, all mercury compounds are toxic and can be dangerous to humans and biota. Once in the environment, Hg can enter and accumulate in the food chain causing harmful effects on human health depending on its chemical form (elemental form, inorganic mercury and organic mercury), route, dose and duration of exposure. The most toxic organo-mercurial compound found frequently in the environment is methyl-mercury (MeHg) taken by eating fish, shellfish and fish- derived products through diet. Drinking water is a minor source of mercury (as inorganic, mainly Hg2+) exposure. European and Italian legislation set for drinking water (tap and botted natural mineral) the maximum admitted concentration limit of 1 microgram per litre. A total of 17 bottled water samples from 10 brands, representing 8 still, 7 sparkling and 2 lightly sparkling waters respectively. They were analysed for total mercury (HgT) using cold vapour atomic fluorescence spectrometry following US-EPA1631 version E method. For the first-time, mercury was detected at ultra-trace levels (sub nanogram per litre) in bottled waters from Emilia-Romagna and Veneto regions. HgT analyses were carried out whilst following quality assurance and quality control procedures by analyzing laboratory blanks, initial (IPR) and ongoing (OPR) precision recovery standards, matrix spikes (MSs) and three certified reference materials (CRMs). The results were corroborated by the fruitful participation in an interlaboratory comparison study for total mercury determination in freshwater samples. In addition, through the laboratory results obtained, it was possible to carry out the evaluation of the risk of exposure to mercury through the intake of bottled water evaluated on three age groups of consumers. The daily and weekly exposure assessment will be illustrated, as well as the risk characterization through the hazard quotient (HQ) calculated with respect to the reference dose for mercury (RfD).