Identification of present-day and historical sources of mercury in a complex industrial area

Mercury levels were measured in soils and earthworms on behalf of a long-term surveillance program of the emissions from the industrial area of Scarlino (Southern Tuscany, Central Italy), where a municipal solid waste incinerator and two main chemical plants are currently operating. The study aimed at establishing preliminary soil data to be used as baseline for long-term monitoring of mercury contamination of soil and soil biota and to assess eventual contribution of the industrial emissions. Overall total mercury concentration of superficial soils (0-5 cm), collected from 44 sampling sites randomly selected within a circular area up to 1.5 km from the center of the industrial area, was in average 0.29 ± 0.27 µg g-1 . This value, which remains well below the screening values (1 µg g-1 ) for contaminated soils set by the Italian regulatory framework for residential areas, is approximately 4-5 times higher than the European topsoil baseline (FOREGS) for mercury and highlights a general enrichment of the metal in the area. This is mainly attributable to widespread geochemical anomalies characterizing the Southern Tuscany and to the historical mineral processing and smelting activities that have been carried out in the Scarlino area until the mid-90s. The highest mercury concentrations were found in soils from sampling sites in direct proximity of industrial/artisanal activities, where concentrations up to 1.59 µg g-1 were reached. Average mercury concentrations (0.25 ± 0.10 µg g-1 ) from agricultural and grazing land soils were also noticeable, although earthworms from the same sites did not show a significant bioaccumulation of the metal (0.11 ± 0.09 µg g-1 ). The generally elevated concentrations and the high variability (overall coefficient of variation = 93%) of mercury soil data from the Scarlino area are questioning the possibility to isolate the influence of a single source of contamination in an environment with a long industrialization history. This is currently prompting further research supported by techniques for monitoring atmospheric depositions (i.e. biomonitoring, passive sampling) to improve estimation of mercury contamination arising from different possible sources in the Scarlino area