4b: Contaminated site assessment and management: Lessons for technical assistance under the Minamata Convention

Landfills have been identified as vital source of mercury (Hg) emissions to the environment. Although there are some reports available for understanding influence of landfill site on environmental mercury pollution, only a few studies were carried out for assessment of mobility of mercury inside landfill site, which might be significant for environmental sound management of mercury waste. Therefore in the present study, core samplings in two landfills were conducted to evaluate stability of mercury in waste and gaseous phase Hg speciation was examined using Ontario Hydro (OH) Method with the aim of distinguishing elemental Hg and oxidized Hg in landfill gas (LFG). Leachate from two landfills was also collected seasonally. Total Hg (T-Hg) concentration in Landfill A ranged from 4 to 1910 μg kg-1 with a geometric mean of 292 μg kg-1 (n=29), meanwhile, T-Hg concentration in Landfill B ranged from 3 to 1368 μg kg-1 with a geometric mean of 556 μg kg-1 (n=35). Generally, T-Hg of Landfill B was higher than that of Landfill A, which is possibly because incineration fly ash which contained more Hg were accepted. Results of Japanese leaching test (JLT-13) which was applied to evaluate the Hg mobility from solid phase to liquid phase were under the detection limit and might indicate Hg was still stabilized in solid phase. The gaseous Hg in LFG was in the μg m-3 range of two landfills, which was similar to previous reports of gaseous Hg emission from landfills (e.g. the Florida case and the Seoul case). The ratio of oxidized Hg varied a lot ranged from 40% to 60% while literatures reported methylated compounds occupied about 10% in the US landfills, which might because ionic Hg was also absorbed as oxidized speciation in OH Method. In the case of leachate, T-Hg was slightly detected in Landfill A at the range of 0.1 μg L-1, on the country, no detection from Landfill B, which coincided with the results of JLT-13. Hg in the solid phase was highly detected as other studies and Hg disposed in landfills usually caused concern about its mobility to natural environment. Nevertheless, the low level results of leaching test and leachate collected on site corroborated the safety of the two landfills. Compared with leachate, LFG seemed to be a predominant release pathway of Hg. All these results indicated the vast majority of Hg remained in the solid phase and was stabilized to some extent.

Mercury is listed by the USEPA as among the most toxic chemicals on earth due to its natural occurrence and persistence in the environment, and its highly toxic nature. The toxicity of mercury became apparent after the Minamata disease which first occurred in the 1950s. Still, there are many recent and ongoing researches investigating other pathways of mercury to the human system and the diseases it brings about. Various studies around the world investigated and described mercury accumulation in soils, plants, bodies of water, and fish species in various locations around the world. With the variation of soil types and contamination sources, several characterization and speciation methods were also designed, implemented and investigated for adequacy and efficiency. Thermal treatment has already been in use as a remediation method for soil contaminated by heavy metals even before its application to the characterization of mercury in soil. More recent studies have analyzed and proven its potential and validity to remediate mercury contaminated soils. Thermal desorption studies show that in comparison to desorption time, temperature has a greater effect on the mercury removal rate. These studies, however, gave different values of temperature (100°C and 400°C) at which mercury removal becomes very efficient. This difference can be justified by the variations in the mercury species and their corresponding concentrations in the soil samples studied. It may then be necessary to further study at which temperatures each mercury species get to be removed from the soil. Quartz columns are filled with mercury contaminated soil and are secured using glass wool. Heat is applied to the column while N2 gas carries mercury species into the cold vapor atomic fluorescence spectrometry (CVAFS) detector. SnCl2 reduction, purge and trap gold amalgamation pre-concentration, and cold vapor atomic fluorescence spectrometry (CVAFS) detection as per US EPA Method 1631 were implemented for standardization. Experimental results show that at low temperatures (<200°C), HgCl2 desorption amount is higher than HgO, HgS. At temperatures equal to or greater than 300°C, about 97 to 99% of HgO, HgS and HgCl2 contaminated soils are removed from the sample within a span of six hours, respectively. The effect of varying temperatures applied and air flow rates to the thermal desorption kinetics were studied.

The Abbadia San Salvatore mercury (Hg) mine was the largest mine of the Mount Amiata Hg ore district (Central Italy) and the third largest site of Hg production during the 20th Century. Despite the cessation of operations in 1983 and recent remediation work, the mine remains a major source of Hg to the environment, especially the atmosphere. To map the atmospheric dispersion of gaseous Hg in the region we employed our recently calibrated passive air sampler for gaseous Hg. Sampling was conducted across two 7-by-7 sampling grids: at a fine-spatial scale (~1 km2 total area) around the mine itself (week long deployments in October 2015 and July 2016) and in a coarser grid (~50 km2 total area) across the western slope of Mt. Amiata (four 3-month deployments in 2015/16). This constitutes the first highly spatially resolved mapping of concurrent, time-averaged gaseous Hg concentrations in and around a major Hg source. Concentrations are in good agreement with instantaneous, but non-concurrent measurements previously reported for the mine site. In the mine area concentrations reach as high as 12,500 ng m-3 and decline rapidly with distance from the most contaminated site. In July, concentrations are higher than in October, especially around the central, most contaminated sites and sites downwind (to the east). This causes concentrations in the closest residential areas of the town of Abbadia San Salvatore to reach or even exceed chronic exposure guideline levels (200 ng m-3). Seasonal deployments across the larger Mt Amiata region also show elevated concentrations in the summer closer to the mine, presumably because emissions increase with temperature. Further from the mine concentrations are remarkably consistent between seasons and show a concentric pattern of rapid decline with distance from the mine, which is skewed to the east by the dominant westerly winds. Background concentrations are observed at sites furthest to the west of the mine. The incremental increase in concentrations moving from upwind background sites towards the mine demonstrates the capability of the sampler to resolve fine differences at background concentrations with a high level of precision and accuracy (<0.2 ng m-3).