Sedimentological, Mineralogical and Geochemical Features of Late Quaternary Sediment Profiles from the Southern Tuscany Hg Mercury District (Italy): Evidence for the Presence of Pre-Industrial Mercury and Arsenic Concentrations

Abstract

Southern Tuscany (Italy) is an important metallogenic district that hosts relevant S-polymetallic deposits that have intensely been exploited for centuries. Consequently, potential toxic elements, such as Hg and As, are widely distributed in the surrounding environment. In this paper, an extensive sedimentological, mineralogical and geochemical study of two Late Quaternary sediment profiles, partially outcropping along the coast of southern Tuscany (Ansedonia area), was carried out to evaluate the contents and mobility of Hg and As with the aims to contribute to the definition of the geochemical baseline of southern Tuscany before the human intervention and evaluate the potential dispersion of these harmful elements. The sedimentological, mineralogical and geochemical (major elements) features revealed that the studied profiles are mostly related to the local geological characteristics and the Quaternary geological history of the area. The concentrations and the normalized patterns of trace and rare earth elements highlighted the absence of any anthropogenic activity. This implies that the studied samples are to be regarded as good proxies for evaluating the geochemical baseline of southern Tuscany before the intense mining activity. The enrichment factors (EF) of most trace elements were indeed lower or close to 2, indicating a variability close to the average concentration of the Upper Continental Crust (UCC), while other elements slightly enriched, such as Pb, were in agreement with the natural baseline reported for southern Tuscany. Mercury and As displayed EF values >40 when compared to the average contents of UCC, although they decrease down to 4 when compared to the suggested baseline for southern Tuscany. The higher Hg and As contents detected in this study, inferred to natural sources, evidenced (i) the great natural variability occurring in largely mineralized areas and (ii) the importance of estimating reference environmental parameters in order to avoid misleading interpretations of the detected anomalies. Moreover, the results of leaching test on sediment samples denoted a relatively low mobility of Hg and As, suggesting that these elements are preferentially mobilized by transport of clastic sediments and such anomalies may be preserved for relatively long times in Quaternary sediments. However, leachable Hg (0.6–9.7 μg/L) and As (2.1–42.2 μg/L) concentrations are significantly high when compared to those of the Italian limit for groundwater (1 µg/L for Hg and 10 µg/L for As). Quaternary sediments from southern Tuscany could then be a potential, though natural, source of Hg and As to groundwater systems.

New geochemical data for defining origin and distribution of mercury in groundwater of a coastal area in southern Tuscany (Italy)

“…Various studies have been carried out in the Orbetello Lagoon area to determine the origin of the Hg and the processes responsible for its enrichment and distribution in groundwater (Grassi and Netti 2000 ; Protano et al 2000 ; Salleolini et al 2005 ; Bianchi 2018 ; Pasquetti 2019 ; Pasquetti et al 2020 ; De Santis 2021 ).…”

“…In a coastal area of southern Tuscany (Italy) that includes the Lagoon of Orbetello, high concentrations of Hg have been detected in groundwater used in fish farming and agriculture as well as for domestic and drinking purposes. This environmental issue has been the subject of various geochemical studies that have proposed different sources and processes regulating the concentrations, distribution, and behaviour of Hg in the groundwater of the Orbetello Lagoon area (Grassi and Netti 2000 ; Protano et al 2000 ; Salleolini et al 2005 ; Bianchi 2018 ; Pasquetti 2019 ; Pasquetti et al 2020 ; De Santis 2021 ). According to Grassi and Netti ( 2000 ) the interaction of saline water with the solid Hg-bearing constituents of rocks and sediments hosting aquifers affected by seawater intrusion is the main process responsible for Hg release and mobilisation in the groundwater of some coastal aquifers of southern Tuscany, including the carbonate aquifer system in the Orbetello Lagoon area.…”

“…Protano et al ( 2000 ) assumed that the high Hg concentrations in groundwater of the Orbetello Lagoon area were due to upwelling of gaseous elemental mercury (Hg 0 ) into the upper part of the carbonate aquifer system, enhanced by the cone of depression caused by intense pumping of water from numerous wells in this stretch of coast in southern Tuscany. More recently, Pasquetti et al ( 2020 ) determined high Hg concentrations in the Quaternary continental deposits in a coastal plain of the Orbetello Lagoon area (Ansedonia coastal plain) and suggested that these recent deposits could be the source of the Hg in local groundwater. Mercury contamination by human activities, natural rise of Hg-rich geothermal fluids, and diffuse degassing of Hg from deep sources were excluded in this area (Protano et al 2000 ; Bianchi 2018 ; Pasquetti et al 2020 ).…”

“…More recently, Pasquetti et al ( 2020 ) determined high Hg concentrations in the Quaternary continental deposits in a coastal plain of the Orbetello Lagoon area (Ansedonia coastal plain) and suggested that these recent deposits could be the source of the Hg in local groundwater. Mercury contamination by human activities, natural rise of Hg-rich geothermal fluids, and diffuse degassing of Hg from deep sources were excluded in this area (Protano et al 2000 ; Bianchi 2018 ; Pasquetti et al 2020 ).…”

A Long-Term Record of Quaternary Facies Patterns and Palaeonvironmental Trends from the Po Plain (NE Italy) as Revealed by Bio-Sedimentary Data

“…All these processes operate over a wide range of time scales [1][2][3][4][5]. Under the threat of Global Change, these low-lying areas are highly exposed to severe flooding, territory loss and damage of ecosystems [6][7][8], making urgent a robust evaluation of the present-day state of health through monitoring techniques [9][10][11][12] and a correct quantification of the environmentalecological quality status [13][14][15][16][17]. However, an improved comprehension of the depositionalenvironmental responses to external factors through time and space is key to produce reliable projections and conservation-restoration strategies [18].…”