Among potentially toxic trace elements introduced in the environment by both natural and anthropogenic sources, mercury (Hg) is a contaminant of major concern due to its toxicity and relatively high bioavailability of its most toxic chemical form, methylmercury (MeHg). Indeed, sediments may act as a sink for Hg but they can also be considered a secondary source of contamination due to resuspension events and geochemical processes at the sediment-water interface with subsequent release of Hg species into the overlying water column. In semi-confined aquatic systems, limited water circulation, elevated production of organic matter and hypoxia/anoxia events may promote Hg methylation and MeHg production which can lead to potential MeHg bioaccumulation in the aquatic biota thus posing a risk to marine life and human health. Against this background, sustainable sorbent amendments may represent a cost-effective and environmentally sustainable way to reduce the amount of bioavailable mercury that can be methylated (Gilmour et al., 2018, 2013). The Marano and Grado Lagoon (northern Adriatic Sea, Italy) has been contaminated with Hg from the second largest Hg mine worldwide (Idrija, Slovenia) and from a decommissioned chlor-alkali plant. Although there has been extensive research on the biogeochemical behavior of Hg in this area (Covelli et al., 2007, 2012), there is still a lack of key information to evaluate whether in situ sustainable remediation can be successfully employed to mitigate Hg mobility in porewaters and potential MeHg production, promoting preservation and restoration of the lagoon environment with the reuse of the sediments, which are considered an important natural resource for the future management of the lagoon. The purpose of this study is to evaluate the potential application of vineyard pruning residues biochar on Hg contaminated sediments at a selected fish farm in the lagoon, which is one of the most productive sites for aquaculture. Leaching tests were conducted on biochar to assess the release of major and potentially toxic elements in solution. To characterize porewaters and sediments, two short sediment cores were collected and the surface sediment layer (0-5 cm) was extruded under an inert atmosphere. One core was amended with biochar (3% w/w) whereas the other was untreated and used as a control sample. In both cases, sediment was divided into different aliquots which were incubated for different time intervals up to 6 months. Periodically, porewaters were extracted from both untreated and amended sediment samples and the effects of biochar on the mobility of Hg and other major and trace elements were evaluated by means of chemical analyses on both solid and dissolved fractions.
May mercury availability to methylation in contaminated sediments be reduced by using biochar as an amendment? Preliminary evidences from laboratory experiments
Pavoni E.
;Petranich E.;Floreani F.;Crosera M.;Marussi G.;Bortolin D.;Covelli S.
2023-01-01
Abstract
Among potentially toxic trace elements introduced in the environment by both natural and anthropogenic sources, mercury (Hg) is a contaminant of major concern due to its toxicity and relatively high bioavailability of its most toxic chemical form, methylmercury (MeHg). Indeed, sediments may act as a sink for Hg but they can also be considered a secondary source of contamination due to resuspension events and geochemical processes at the sediment-water interface with subsequent release of Hg species into the overlying water column. In semi-confined aquatic systems, limited water circulation, elevated production of organic matter and hypoxia/anoxia events may promote Hg methylation and MeHg production which can lead to potential MeHg bioaccumulation in the aquatic biota thus posing a risk to marine life and human health. Against this background, sustainable sorbent amendments may represent a cost-effective and environmentally sustainable way to reduce the amount of bioavailable mercury that can be methylated (Gilmour et al., 2018, 2013). The Marano and Grado Lagoon (northern Adriatic Sea, Italy) has been contaminated with Hg from the second largest Hg mine worldwide (Idrija, Slovenia) and from a decommissioned chlor-alkali plant. Although there has been extensive research on the biogeochemical behavior of Hg in this area (Covelli et al., 2007, 2012), there is still a lack of key information to evaluate whether in situ sustainable remediation can be successfully employed to mitigate Hg mobility in porewaters and potential MeHg production, promoting preservation and restoration of the lagoon environment with the reuse of the sediments, which are considered an important natural resource for the future management of the lagoon. The purpose of this study is to evaluate the potential application of vineyard pruning residues biochar on Hg contaminated sediments at a selected fish farm in the lagoon, which is one of the most productive sites for aquaculture. Leaching tests were conducted on biochar to assess the release of major and potentially toxic elements in solution. To characterize porewaters and sediments, two short sediment cores were collected and the surface sediment layer (0-5 cm) was extruded under an inert atmosphere. One core was amended with biochar (3% w/w) whereas the other was untreated and used as a control sample. In both cases, sediment was divided into different aliquots which were incubated for different time intervals up to 6 months. Periodically, porewaters were extracted from both untreated and amended sediment samples and the effects of biochar on the mobility of Hg and other major and trace elements were evaluated by means of chemical analyses on both solid and dissolved fractions.Pubblicazioni consigliate
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