Effects of the November 2012 Flood Event on the Mobilization of Hg from the Mount Amiata Mining District to the Sediments of the Paglia River Basin

Abstract

The Mount Amiata mining district (southern Tuscany, Italy) was, for decades, one of the world's largest mercury (Hg) producing regions, where mining activity lasted until the 1980s. The Paglia River drains the eastern part of the district and is also the main western tributary of the Tiber River. Recent studies show that, still today, high total Hg contents severely affect the downstream ecosystems of these rivers. In November 2012, a major flood event occurred in the Paglia River basin, which drastically changed the river morphology and, possibly, the Hg concentrations. In the present work, stream sediment was sampled before and after the flood to evaluate possible changes in sediment total Hg concentrations as a consequence of this event. The comparison between pre-and post-flood Hg concentrations shows that Hg content increased up to an order of magnitude after the flood, suggesting that this event triggered Hg mobilization in the basin rather than its dilution.

From point source to diffuse source of contaminants: The example of mercury dispersion in the Paglia River (Central Italy)

“…As previously noted, a major flood event occurred along the Paglia R. in February 2016. A comparison was made between the Hg concentrations of the overbank deposits of this event, and the deposits of baseflow channel, bar, and floodplain (Table 5), to ascertain whether this event caused an important remobilization of Hg-contaminated sediments, as demonstrated by Pattelli et al (2014) for the November 2012 event.…”

“…In most cases, the Hg concentrations of 2016 overbank flood Table 5 Hg concentration values of baseflow channel (C), bar (B) and floodplain (FP) collected in 2013, and of the overbank deposits of the February 2016 flood. -No data.°( After Pattelli et al, 2014; in parentheses, their sample label is reported). * = mean value between the two banks.…”

“…As stressed by Lafhaj et al (2008), international, especially European, laws became more stringent, and in many areas of the world stream sediments have to be treated as waste material. In many European countries, former point sources of pollution (e.g., waste heaps) were progressively distributed along rivers by runoff, becoming diffuse sources (Pattelli et al, 2014;Hurley et al, 2017). As a consequence, stream sediment management has become an environmental and economical concern for a large number of countries (Lafhaj et al, 2008).…”

“…Gray et al (2014) and Lattanzi et al (2017) documented the long-distance transport of Hg along the Tiber River downstream from the MAMD. Pattelli et al (2014) compared stream sediment contamination of the Paglia and Tiber rivers before and after a large flood event (November 2012) to assess its effects on total Hg contents. Although many aspects related to the contamination deriving from the MAMD have been analysed, an overall study considering the distribution of contaminant in the fluvial system and its links with geomorphological features and past channel changes was not adequately addressed.…”

Mining Waste and Its Sustainable Management: Advances in Worldwide Research

“…Mining waste management includes the characterization and remediation of residues. The state-of-the-art proposes new methods such as the use of mapping to determine the extent of wastes, the use of hyperspectral instruments [25], the mobility of sediments containing toxic residues [26], the mitigation of toxic metals spread in redox areas [27], the use of biochemical and mineral dissolution processes in sulfurous tailings [28], the dilution of tailings products, and the geochemical and mineral elimination of submarine tailings [29]. Other remediation systems include the use of heat to volatilize toxic components, and the use of microorganisms to reduce the reactivity and toxicity [30].…”