laboratory-incubated redox oscillation experiment to investigate Hg fluxes from highly contaminated coastal marine sediments (Gulf of Trieste, Northern Adriatic Sea)

• Published in: Environmental science and pollution research international 2014-03, Vol.21 (6), p.4124-4133
• Main Authors: Emili, A, Carrasco, L, Acquavita, A, Covelli, S
• Format: Article
• Language: English
• Subjects: Adsorption; anaerobic conditions; Anoxic conditions; Aquatic life; Aquatic organisms; Aquatic Pollution; Atmospheric Protection/Air Quality Control/Air Pollution; Biogeochemistry; carbon; Contaminated sediments; Demethylation; Dimethylmercury; Dissolved organic carbon; Earth and Environmental Science; Ecotoxicology; Environment; Environmental Chemistry; Environmental Health; Environmental Monitoring; Experiments; Geologic Sediments - chemistry; Heavy Metals in the Environment : Sources; Hydrogen sulfide; Hypoxia; Interactions and Human Health; Investigations; Laboratories; manganese; Marine pollution; Marine sediments; Mercury; Mercury - analysis; Mercury - chemistry; Methylmercury; methylmercury compounds; Mining; Models, Chemical; Nitrates; Nitrogen dioxide; Organic carbon; Oxidation-Reduction; oxygen; Oxygenation; Pollution studies; River mouth; Rivers - chemistry; Seawater - chemistry; Sediment pollution; Sediment-water interface; Sediments; Slovenia; temperature; Temporal variations; Waste Water Technology; Water column; Water Management; Water Pollutants, Chemical - analysis; Water Pollutants, Chemical - chemistry; Water Pollution Control; Water temperature
• ISSN: 0944-1344; 1614-7499
• DOI: 10.1007/s11356-013-2225-5

Mercury (Hg) mobility at the sediment–water interface was investigated during a laboratory incubation experiment conducted with highly contaminated sediments (13 μg g⁻¹) of the Gulf of Trieste. Undisturbed sediment was collected in front of the Isonzo River mouth, which inflows Hg-rich suspended material originating from the Idrija (NW Slovenia) mining district. Since hypoxic and anoxic conditions at the bottom are frequently observed and can influence the Hg biogeochemical behavior, a redox oscillation was simulated in the laboratory, at in situ temperature, using a dark flux chamber. Temporal variations of several parameters were monitored simultaneously: dissolved Hg (DHg) and methylmercury (MeHg), O₂, NH₄ ⁺, NO₃ ⁻ + NO₂ ⁻, PO₄ ³⁻, H₂S, dissolved Mn²⁺, dissolved inorganic and organic carbon (DIC and DOC). Under anoxic conditions, both Hg (665 ng m² day⁻¹) and MeHg (550 ng m² day⁻¹) fluxed from sediments into the water column, whereas re-oxygenation caused concentrations of MeHg and Hg to rapidly drop, probably due to re-adsorption onto Fe/Mn-oxyhydroxides and enhanced demethylation processes. Hence, during anoxic events, sediments of the Gulf of Trieste may be considered as an important source of DHg species for the water column. On the contrary, re-oxygenation of the bottom compartment mitigates Hg and MeHg release from the sediment, thus acting as a natural “defence” from possible interaction between the metal and the aquatic organisms.