The Siele mine and its smelting plant are part of the world class Monte Amiata mining district (MAMD – Tuscany, Italy). The mine is located close to the Siele creek (c.), which drains the mining area, then flows to the Paglia River (R.), which in turn is an affluent of Tiber River, flowing through the city of Rome to the Mediterranean Sea. After closure in 1981, the mining area was subjected to the first reclamation in the district (and at the worldwide scale), completed in 2001. In this study, we present new data on Hg concentrations in soils, stream sediments, and air in the Siele mining area and along the Siele c., and we review all previously available data, with the aim of quantifying the Hg contribution from the Siele c. into the Paglia R., and of documenting the evolution of the system following mine reclamation. Hg concentrations (up to 5400 mg/kg) in stream sediments are comparable to pre-reclamation values in the first 500 m downstream the mine site. They decrease downstream to the confluence with the Paglia R., but remain anomalous (i.e., above the 1 mg/kg Italian law limit for residential soil). Comparison of pre- and postremediation data of gaseous elemental mercury (GEM) in air shows that Hg0 emissions in most of the sites within the Siele mining area are lower than pre-reclamation values, but in few outdoor sites, levels are still high (up to 9500 ng/m3), exceeding the existing regulatory limits (“Norma Amiata”: 300 ng/m3 in outdoor sites). On the other hand, Hg mobility, determined by leaching tests, is mostly below the limits defined by pending regulations (1 μg/L), and methyl-Hg concentrations are mostly below 1 ng/kg (with a single value of 6 ng/kg). Results show the Siele c. plays a role by no means negligible in the general picture of the contributions of Hg in the Paglia R. basin, proving to be one of the most critical areas of the entire MAMD. Indeed, concentrations of Hg in sediments and soils in the Siele c. are comparable to those of the Pagliola c., draining the Abbadia S.S. mine (the main site of the MAMD), where reclamation is still under way. Moreover, despite remediation works, Hg emissions from contaminated soil will represent a significant contribution to the atmospheric load of Hg in the future, if no further remediation action is taken. The Siele system has a low resilience and natural recovery will take many years (probably decades), during which the area will remain an important source of Hg for the Paglia and Tiber River systems, and eventually for the Mediterranean Sea. This study provides important background data for local authorities to implement monitoring strategies and find new remediation plans based on the identified critical area. Further, at a global scale, this work contributes additional data to the assessment of the global Hg budget to the atmosphere and the hydrosphere.
Low resilience of a mercury mining area after reclamation: the case of the Siele mine (Mt. Amiata Mining District, Italy)
Fornasaro S.
Primo
;
2021-01-01
Abstract
The Siele mine and its smelting plant are part of the world class Monte Amiata mining district (MAMD – Tuscany, Italy). The mine is located close to the Siele creek (c.), which drains the mining area, then flows to the Paglia River (R.), which in turn is an affluent of Tiber River, flowing through the city of Rome to the Mediterranean Sea. After closure in 1981, the mining area was subjected to the first reclamation in the district (and at the worldwide scale), completed in 2001. In this study, we present new data on Hg concentrations in soils, stream sediments, and air in the Siele mining area and along the Siele c., and we review all previously available data, with the aim of quantifying the Hg contribution from the Siele c. into the Paglia R., and of documenting the evolution of the system following mine reclamation. Hg concentrations (up to 5400 mg/kg) in stream sediments are comparable to pre-reclamation values in the first 500 m downstream the mine site. They decrease downstream to the confluence with the Paglia R., but remain anomalous (i.e., above the 1 mg/kg Italian law limit for residential soil). Comparison of pre- and postremediation data of gaseous elemental mercury (GEM) in air shows that Hg0 emissions in most of the sites within the Siele mining area are lower than pre-reclamation values, but in few outdoor sites, levels are still high (up to 9500 ng/m3), exceeding the existing regulatory limits (“Norma Amiata”: 300 ng/m3 in outdoor sites). On the other hand, Hg mobility, determined by leaching tests, is mostly below the limits defined by pending regulations (1 μg/L), and methyl-Hg concentrations are mostly below 1 ng/kg (with a single value of 6 ng/kg). Results show the Siele c. plays a role by no means negligible in the general picture of the contributions of Hg in the Paglia R. basin, proving to be one of the most critical areas of the entire MAMD. Indeed, concentrations of Hg in sediments and soils in the Siele c. are comparable to those of the Pagliola c., draining the Abbadia S.S. mine (the main site of the MAMD), where reclamation is still under way. Moreover, despite remediation works, Hg emissions from contaminated soil will represent a significant contribution to the atmospheric load of Hg in the future, if no further remediation action is taken. The Siele system has a low resilience and natural recovery will take many years (probably decades), during which the area will remain an important source of Hg for the Paglia and Tiber River systems, and eventually for the Mediterranean Sea. This study provides important background data for local authorities to implement monitoring strategies and find new remediation plans based on the identified critical area. Further, at a global scale, this work contributes additional data to the assessment of the global Hg budget to the atmosphere and the hydrosphere.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
