Mercury Speciation Data Research Articles

Mercury-polluted sediments in confined disposal areas: a new modeling approach

Risk assessment was carried out to determine the compatibility of dredged sediments contaminated by mercury with the disposal in a confined structure, to be used as a wharf. Different risk assessment procedures were applied based on the utilization both of total concentration data and of speciation data input and on different transport models. Different strategies of disposal within the confined structure were tested too. A detailed site-specific modeling approach showed the best implementation of risk assessment. In particular, mercury speciation data and the application of three-layer finite system transport model were used. The limitations of the traditional models, even with some improvements proposed by literature, have been stressed in comparison with the proposed three-layer finite system transport model. The raising awareness in the advantages of a detailed site-specific investigation, modeling and consequently risk assessment leads to a more sustainable choice for a site-specific solution. On the other hand, this proposal follows European Union Strategies about waste prevention and recycling in the context of sustainable use of resources; alternatively, polluted sediments should be disposed of in dedicated sites such as landfill out of Italy with too much expensive costs and very high risks.

Atmospheric mercury speciation and mercury in snow over time at Alert, Canada

Abstract. Ten years of atmospheric mercury speciation data and 14 years of mercury in snow data from Alert, Nunavut, Canada, are examined. The speciation data, collected from 2002 to 2011, includes gaseous elemental mercury (GEM), particulate mercury (PHg) and reactive gaseous mercury (RGM). During the winter-spring period of atmospheric mercury depletion events (AMDEs), when GEM is close to being completely depleted from the air, the concentration of both PHg and RGM rise significantly. During this period, the median concentrations for PHg is 28.2 pgm−3 and RGM is 23.9 pgm−3, from March to June, in comparison to the annual median concentrations of 11.3 and 3.2 pgm−3 for PHg and RGM, respectively. In each of the ten years of sampling, the concentration of PHg increases steadily from January through March and is higher than the concentration of RGM. This pattern begins to change in April when the levels of PHg peak and RGM begin to increase. In May, the high PHg and low RGM concentration regime observed in the early spring undergoes a transition to a regime with higher RGM and much lower PHg concentrations. The higher RGM concentration continues into June. The transition is driven by the atmospheric conditions of air temperature and particle availability. Firstly, a high ratio of the concentrations of PHg to RGM is reported at low temperatures which suggests that oxidized gaseous mercury partitions to available particles to form PHg. Prior to the transition, the median air temperature is −24.8 °C and after the transition the median air temperature is −5.8 °C. Secondly, the high PHg concentrations occur in the spring when high particle concentrations are present. The high particle concentrations are principally due to Arctic haze and sea salts. In the snow, the concentrations of mercury peak in May for all years. Springtime deposition of total mercury to the snow at Alert peaks in May when atmospheric conditions favour higher levels of RGM. Therefore, the conditions in the atmosphere directly impact when the highest amount of mercury will be deposited to the snow during the Arctic spring.

Mercury in the Mediterranean. Part 2: processes and mass balance

Mass balance of contaminants can provide useful information on the processes that influence their concentrations in various environmental compartments. The most important sources, sinks and the equilibrium or non-equilibrium state of the contaminant in individual environmental compartments can also be identified. Using the latest mercury speciation data, the results of numerical models and the results of recent studies on mercury transport and transformation processes in the marine environment, we have re-evaluated the total mercury (HgT) mass balance in the Mediterranean Sea. New calculations have been performed employing three distinct marine layers: the surface layer, the thermocline and the deep sea. New transport mechanisms, deep water formation and density-driven sinking and upwelling, were included in the mass balance calculations. The most recent data have even enabled the calculation of an approximate methylmercury (MeHg) mass balance. HgT is well balanced in the entire Mediterranean, and the discrepancies between inputs and outputs in individual layers do not exceed 20 %. The MeHg balance shows larger discrepancies between gains and losses due to measurement uncertainties and gaps in our knowledge of Hg species transformation processes. Nonetheless, the main sources and sinks of HgT (deposition and evasion) and MeHg (fluxes from sediment, outflow through the Gibraltar Strait) are in accordance with previous studies on mercury in the Mediterranean Basin. Mercury in the Mediterranean fish harvest is the second largest MeHg sink; about 300 kg of this toxic substance is consumed annually with sea food.

A comparison of data quality control protocols for atmospheric mercury speciation measurements

Significant advances in the measurement of atmospheric mercury species have been made in the past 10 years yet limited protocols on quality control (QC) and assurance on this data have been published in the literature. Recently, considerable work has been done to develop quality control and assurance programs within North America. Environment Canada and the National Atmospheric Deposition Network (NADP) independently developed programs, RDMQ™ and AMQC, respectively, to QC atmospheric mercury speciation data (including gaseous elemental mercury (GEM), reactive gaseous mercury (RGM) and mercury associated to particles (PHg)). These 2 programs were assessed by the criteria on which the data is QCed and comparability of the final data products. Results show that the criteria used to flag data compare well within the 4 tested sites and that the number of flags for each criterion is generally comparable. The QC programs were applied to 2 distinct data sets and the final QCed data was compared. From a mid-latitude site, the final data sets compare very well and showed there to be a 0.3, 8.6 and 15% difference in the mean GEM, RGM and PHg concentrations post QC of each program. It is recommended that either the RDMQ or the AMQC programs be employed for a typical mid-latitude site. When the QC programs were applied to highly variable data, the data do not compare as well for RGM and PHg. Results showed a 2.7, 27 and 33% difference in the mean GEM, RGM and PHg concentrations, respectively, post QC of each program. It is recommended that RDMQ be used for data that is highly variable with high RGM/PHg concentrations as it allows for more manual correction over the QCed data. This investigation of 2 QC programs produced comparable data and that either of these programs can be used as standard methods for the quality control of atmospheric mercury speciation data.

An interpretation of flue-gas mercury speciation data from a kinetic point of view ☆

Mercury emission from coal-fired power plants is causing great concern. Thermodynamic equilibrium calculations are commonly used for prediction of Hg speciation in the flue-gas. According to representative calculations, at temperatures below 725 K all Hg should exist in oxidized forms. However, Hg speciation measurements for flue-gas at much lower temperature showed a wide range of oxidized Hg fraction from 30 to 95%. A hypothesis that Hg equilibrium is frozen as the flue-gas cools could describe the data. However, a different interpretation of the measured results can be given based on kinetic considerations. Here, the oxidized Hg fraction is limited by the reaction rate of chlorine with elemental Hg in the flue-gas, while the differences in the degree of oxidation can largely be attributed to different time–temperature histories for the flue-gases. The residence time of flue-gas is likely to be a governing factor for the Hg speciation.

Flue gas Hg measurements from coal-fired boilers equipped with wet scrubbers

The U.S. EPA has indicated they are considering additional SO2 and NOx emission reductions, and EPA is under a consent agreement to propose mercury reduction regulations by 2004 for the utility industry. The boiler manufacturers and the utility industry have developed improved combustion modification techniques to reduce NOx emissions. These advanced combustion modification techniques, plus selective catalytic reduction (SCR), offer the potential to reduce NOx emissions at reduced cost. Wet and dry FGD systems have been shown to reduce SO2 emissions by up to 95%. CONSOL has shown that conventional wet FGD and ESP systems can remove an average of 67±6% of the inlet mercury. These data show that utility boilers equipped with ESP-scrubber combinations are removing two-thirds of the mercury in the as-fired coal at no added cost. The mercury speciation data show that 80 to 95% of the oxidised mercury, as determined by the Ontario Hydro method, is removed by the scrubber. The average mercury material balance closure at the six plants was 103±8%. The mercury removed from the scrubber reported to the scrubber by-product. Standard leachate testing conducted on fixated and unfixated scrubber by-product from one test showed no mercury leaching. Mercury volatility was evaluated by heating the scrubber by-product 140°F for eleven weeks. After eleven weeks, no loss of mercury was reported. Based on these findings, there may be combinations of environmental control systems that can achieve significant SO2, NOx, and mercury reductions at lower cost than the conventional approach of three add-on processes FGD for SO2 control, selective catalytic reduction for NOx control, and carbon injection for mercury control.

Distribution, speciation, and transport of mercury in stream-sediment, stream-water, and fish collected near abandoned mercury mines in southwestern Alaska, USA

Concentrations of total Hg, Hg (II), and methylmercury were measured in stream-sediment, stream-water, and fish collected downstream from abandoned mercury mines in south-western Alaska to evaluate environmental effects to surrounding ecosystems. These mines are found in a broad belt covering several tens of thousands of square kilometers, primarily in the Kuskokwim River basin. Mercury ore is dominantly cinnabar (HgS), but elemental mercury (Hg o) is present in ore at one mine and near retorts and in streams at several mine sites. Approximately 1400 t of mercury have been produced from the region, which is approximately 99% of all mercury produced from Alaska. These mines are not presently operating because of low prices and low demand for mercury. Stream-sediment samples collected downstream from the mines contain as much as 5500 μg/g Hg. Such high Hg concentrations are related to the abundance of cinnabar, which is highly resistant to physical and chemical weathering, and is visible in streams below mine sites. Although total Hg concentrations in the stream-sediment samples collected near mines are high, Hg speciation data indicate that concentrations of Hg (II) are generally less than 5%, and methylmercury concentrations are less than 1% of the total Hg. Stream waters below the mines are neutral to slightly alkaline (pH 6.8–8.4), which is a result of the insolubility of cinnabar and the lack of acid-generating minerals such as pyrite in the deposits. Unfiltered stream-water samples collected below the mines generally contain 500–2500 ng/l Hg; whereas, corresponding stream-water samples filtered through a 0.45-μm membrane contain less than 50 ng/l Hg. These stream-water results indicate that most of the Hg transported downstream from the mines is as finely-suspended material rather than dissolved Hg. Mercury speciation data show that concentrations of Hg (II) and methylmercury in stream-water samples are typically less than 22 ng/l, and generally less than 5% of the total Hg. Muscle samples of fish collected downstream from mines contain as much as 620 ng/g Hg (wet wt.), of which 90–100% is methylmercury. Although these Hg concentrations are several times higher than that in fish collected from regional baseline sites, the concentration of Hg in fish is below the 1000 ng/g action level for edible fish established by the US Food and Drug Administration (FDA). Salmon contain less than 100 ng/g Hg, which are among the lowest Hg contents observed for fish in the study, and well below the FDA action level.

Derivation of wildlife values for mercury

A procedure has been developed to estimate surface water concentrations of toxicants ("wildlife values") that will protect the viability of wildlife populations associated with aquatic resources. This procedure was designed primarily to protect piscivorous birds and mammals from compounds that bioaccumulate in fish and was used in the Great Lakes Water Quality Initiative (GLI) to calculate wildlife values (WV) for mercury, DDT/DDE, total polychlorinated biphenyls (PCBs), and 2,3,7,8-tetrachlorodibenzodioxin (TCDD). Published in 1995, and expressed as total mercury in unfiltered water, the final wildlife value (WVf) for mercury derived in the GLI was 1300 pg Hg/L. This value was selected as the wildlife criterion (WC) for mercury in the Great Lakes basin. A second WVf for mercury was derived in 1997 as part of a Congressionally mandated report on airborne mercury emissions. These calculations were based upon mercury speciation data that were largely unavailable when the GLI was developed. Important features of the WVf in the Report to Congress include its calculation on a dissolved methylmercury basis and a reliance on field data to estimate fish bioaccumulation factors. Calculated as methylmercury in filtered water, the WVf derived in the report is 50 pg Hg/L (equivalent to 54 pg MeHg/L). A comparison of WV in the GLI and the Report to Congress requires that average values be specified for mercury speciation in natural systems. Based on this information, the WVf given in the report corresponds to a value of 910 pg Hg/L, as total mercury in unfiltered water, or about 70% of the WVf derived in the GLI. In this article we describe the algorithm used to derive WV in the GLI and the Report to Congress and review its application to mercury. Scientific uncertainties in deriving WV, particularly as they apply to mercury, are critically examined.

Mercury mobility at the Carson River Superfund Site, west-central Nevada, USA: Interpretation of mercury speciation data in mill tailings, soils, and sediments

The Carson River Superfund Site in west-central Nevada is an area of Hg-contaminated soil, sediment, water, air, and biola resulting from the amalgamation milling of Ag-Au ores of the Comstock lode worked approximately a century ago. In order to develop an understanding of the behavior, transport, and fate of Hg at this site, a technique was developed to estimate the proportions of total, elemental, exchangeable, organic, and sulfide Hg in soils, sediments, and tailings. Results of this analysis performed on active Carson River sediments indicate that Hg is selectively dissolved out of Hg-Au amalgam particles and subsequently adsorbed to fine-grained sediments which are then deposited in downstream, low-energy reaches of the Carson River and Labontan Reservoir. In the relatively more-reducing environment of the reservoir Hg appears to be converted, in large part, to relatively-insoluble HgS. The original elemental form of Hg released to the environment is the chemical form which is still dominant in most highly-contaminated soils, sediments, and tailings. Deeper, more-reducing soil horizons, however, appear to fix a significant portion of the Hg as HgS, analogous to the Lahontan Reservoir example described above. This fixation as HgS is documented to be largely limited to higher-sulfur areas where sulfide minerals from the Comstock ores increase the total sulfur concentrations of contaminated soils, sediments, and tailings.