The Legacy of Hg Contamination in a Past Mining Area (Tuscany, Italy): Hg Speciation and Health Risk Assessment

The World Health Organization included mercury among the ten chemicals posing a major public health concern. The mercury-cell manufacturing process has been extensively used in chloralkali plants to produce chlorine and caustic soda by electrolysis, representing a potential source for Hg release into the environment. Despite a significant decline due to the membrane cell processing alternative, there is still a use of mercury in chlor-alkali facilities globally. In the Tuscany region (Italy), solution mining by pumping water into NaCl deposits was applied to produce brines for a mercury-cell chlor-alkali plant. The Hg-contaminated exhausted brines were reinjected at depth in the NaCl deposit through injection wells, or order to renew the available resources. Activities ceased in 1995 following the dispersion of highly contaminated Hg-bearing brines into the environment, and reclamation started. In the present study, the existing dataset for the pristine soil and water contamination has been evaluated and new data provided. The results indicate the legacy of contamination, with Hg concentration exceeding the regulatory limit in some soil samples. Risk assessment by applying Hg speciation analysis indicates that mercury in soil does not carries a risk of non-cancerous effects for the different exposure routes in case of an outdoor use of the site, but the risk would become unacceptable in case of indoor settings such as residential buildings via vapor intrusion.