Nicola Pirrone

A Synthesis of Progress and Uncertainties in Attributing the Sources of Mercury in Deposition

Abstract A panel of international experts was convened in Madison, Wisconsin, in 2005, as part of the 8th International Conference on Mercury as a Global Pollutant. Our charge was to address the state of science pertinent to source attribution, specifically our key question was: “For a given location, can we ascertain with confidence the relative contributions of local, regional, and global sources, and of natural versus anthropogenic emissions to mercury deposition?” The panel synthesized new research pertinent to this question published over the past decade, with emphasis on four major research topics: long-term anthropogenic change, current emission and deposition trends, chemical transformations and cycling, and modeling and uncertainty. Within each topic, the panel drew a series of conclusions, which are presented in this paper. These conclusions led us to concur that the answer to our question is a “qualified yes,” with the qualification being dependent upon the level of uncertainty one is willing to accept. We agreed that the uncertainty is strongly dependent upon scale and that our question as stated is answerable with greater confidence both very near and very far from major point sources, assuming that the “global pool” is a recognizable “source.” Many regions of interest from an ecosystem-exposure standpoint lie in between, where source attribution carries the greatest degree of uncertainty.

Mercury as a Global Pollutant: Sources, Pathways, and Effects

Mercury (Hg) is a global pollutant that affects human and ecosystem health. We synthesize understanding of sources, atmosphere-land-ocean Hg dynamics and health effects, and consider the implications of Hg-control policies. Primary anthropogenic Hg emissions greatly exceed natural geogenic sources, resulting in increases in Hg reservoirs and subsequent secondary Hg emissions that facilitate its global distribution. The ultimate fate of emitted Hg is primarily recalcitrant soil pools and deep ocean waters and sediments. Transfers of Hg emissions to largely unavailable reservoirs occur over the time scale of centuries, and are primarily mediated through atmospheric exchanges of wet/dry deposition and evasion from vegetation, soil organic matter and ocean surfaces. A key link between inorganic Hg inputs and exposure of humans and wildlife is the net production of methylmercury, which occurs mainly in reducing zones in freshwater, terrestrial, and coastal environments, and the subsurface ocean. Elevated human exposure to methylmercury primarily results from consumption of estuarine and marine fish. Developing fetuses are most at risk from this neurotoxin but health effects of highly exposed populations and wildlife are also a concern. Integration of Hg science with national and international policy efforts is needed to target efforts and evaluate efficacy.

Regional differences in worldwide emissions of mercury to the atmosphere

Annual emissions of anthropogenic Hg to the atmosphere in different regions of the world during the last decade show an interesting dichotomy: the emissions in the developed countries increased at the rate of about 4.5–5.5% yr−1 up to 1989 and have since remained nearly constant, while in developing countries the emissions continue to rise steadily at the rate of 2.7–4.5% yr−1. On a global basis, however, the total anthropogenic emissions of Hg increased by about 4% yr−1 during the 1980s, peaked in 1989 at about 2290 t and are currently decreasing at the rate of about 1.3% yr−1. Solid waste disposal through incineration processes is the dominant source of atmospheric mercury in North America (∼ 40%), Central and South America (∼34%), western Europe (∼28%) and Africa (∼30%), whereas coal combustion remains the dominant source in Asia (∼42%) and eastern Europe and the former USSR (∼40%). Mining and smelting of Zn and Pb represent the major industrial source of Hg in Oceania (∼35%).

Particulate mercury in the atmosphere: its significance, transport, transformation and sources

The importance of particulate mercury (Hg(p)) in the transport, chemistry and deposition of this toxic metal has long been underestimated and largely ignored. While it was once believed to constitute a small percentage of total atmospheric mercury, Hg(p) may contribute a significant portion of the deposition of this metal to adjacent natural waters. Recent measurements of Hg(p) in several urban/industrial areas have documented that Hg can be associated with large particles (>2.5 µm) and in concentrations similar to those of the vapor phase Hg (ng/m3). As part of ongoing effort to diagnose the sources, transport and deposition of Hg to the Great Lakes and other Great Waters, the University of Michigan Air Quality Laboratory (UMAQL) has investigated the physical and chemical properties of particulate-phase Hg in both urban and rural locations. It appears that particulate Hg may be the one of the most difficult of the Hg measurements to perform, and perhaps the one of the most important for deposition and source apportionment studies. Particulate Hg concentrations measured in rural areas of the Great Lakes Region and Vermont ranged from 1 to 86 pg/m3 whereas Hg(p) levels in urban/industrialized areas were in the range 15 pg/m3 to 1.2 ng/m3.

European emissions of atmospheric mercury from anthropogenic sources in 1995

Abstract Estimates of atmospheric emissions of mercury from anthropogenic sources in Europe in 1995 are presented with the information on emissions of both total mercury and its major chemical and physical forms. The 1995 anthropogenic emissions of total emissions were estimated to be about 342 tonnes , a decrease of 45% compared to these emissions in 1990. Combustion of fuels, particularly coal has been the major source of anthropogenic emissions contributing to more than half to the total emissions. The emissions from coal combustion have not changed significantly over the past decade. Major decrease has been estimated for emissions from industrial processes, particularly the chlor-alkali production using the Hg cell process. In 1995 the European emissions of anthropogenic mercury contributed about 13% to the global emissions of this element from anthropogenic sources. The anthropogenic Hg emissions in Europe were still higher than the natural emissions in the region, estimated to be about 250– 300 tonnes per year. The accuracy of estimates of anthropogenic emissions of Hg in Europe in 1995 is considered to be between 25 and 50%. The most accurate seem to be the estimates for combustion sources, while the most incomplete data were collected and/or estimated for waste disposal. The emissions of gaseous elemental mercury contributed about 61% to the emissions of the total mercury, while the contribution of gaseous bivalent mercury and particulate mercury was 32 and 7%, respectively.

Mercury emissions to the atmosphere from natural and anthropogenic sources in the Mediterranean region

Abstract This report discusses past, current and projected mercury emissions to the atmosphere from major industrial sources, and presents a first assessment of the contribution to the regional mercury budget from selected natural sources. Emissions (1995 estimates) from fossil fuels combustion (29.8 t yr −1 ) , cement production (28.8 t yr −1 ) and incineration of solid wastes (27.6 t yr −1 ) , all together account for about 82% of the regional anthropogenic total (105.7 t yr −1 ) . Other industrial sources in the region are smelters (4.8 t yr −1 ) , iron–steel plants (4.8 t yr −1 ) and other minor sources (chlor-alkali plants, crematoria, chemicals production) that have been considered together in the miscellaneous category (9.6 t yr −1 ) . Regional emissions from anthropogenic sources increased at a rate of 3% yr −1 from 1983 to 1995 and are projected to increase at a rate of 1.9% yr −1 in the next 25 years, if no improvement in emission control policy occurs. On a country-by-country basis, France is the leading emitter country with 22.6 t yr −1 followed by Turkey (16.1 t yr −1 ) , Italy (11.4 t yr −1 ) , Spain (9.1 t yr −1 ) , the former Yugoslavia 7.9 ( t yr −1 ) , Morocco (6.9 t yr −1 ) , Bulgaria (6.8 t yr −1 ) , Egypt (6.1 t yr −1 ) , Syria (3.6 t yr −1 ) , Libya (2.9 t yr −1 ) , Tunisia (2.8 t yr −1 ) and Greece (2.7 t yr −1 ) , whereas the remaining countries account for less than 7% of the regional total. The annual emission from natural sources is 110 t yr −1 , although this figure only includes the volatilisation of elemental mercury from surface waters and emissions from volcanoes, whereas the contribution due to the degassing of mercury from top soil and vegetation has not been included in this first assessment. Therefore, natural and anthropogenic sources in the Mediterranean region release annually about 215 t of mercury, which represents a significant contribution to the total mercury budget released in Europe and to the global atmosphere.

Historical atmospheric mercury emissions and depositions in North America compared to mercury accumulations in sedimentary records

Abstract Gold and silver production in North America (included United States, Canada and Mexico) released a large amount of mercury to the atmosphere until well into this century when mercury (Hg) amalgamation was replaced by cyanide concentration. Since then, emissions from industries have been the dominant anthropogenic sources of atmospheric Hg in North America as a whole. Past Hg emissions from gold and silver extractions in North America during the 1800s do not show a clear evidence of atmospheric deposition occurred at the coring sites considered in this study. Estimated atmospheric emissions of Hg in North America peaked in 1879 (at about 1708 t yr −1 ) and 1920 (at about 940 t yr −1 ), primarily due to Hg emissions from gold and silver mining. After the Great Economic Depression (1929) Hg emissions peaked again in the 1947 (274 t yr −1 ), in 1970 (325 t yr −1 ) and in 1989 (330 t yr −1 ) as result of increased Hg emissions from industrial sources, though improvements in the emissions control technology in United States and Canada have been substantial. Estimates of total atmospheric deposition fluxes of Hg to water and terrestrial receptors were in the range of 14.3–19.8 μg m −2 yr −1 in North America as a whole, and averaged 135 μg m −2 yr −1 (global background + local emissions) in the Great Lakes. These values were in good agreement with recent estimates reported in literature. The comparison of atmospheric Hg deposition fluxes with Hg accumulation rates in sediment cores suggests that atmospheric deposition was the major source of Hg entering the lakes system at coring sites, however, important contributions to Lake Ontario sediment cores sites from 1940 to 1970 were likely originated from local point sources (i.e. direct discharges).

Intercomparison of methods for sampling and analysis of atmospheric mercury species

An intercomparison for sampling and analysis of atmospheric mercury species was held in Tuscany, June 1998. Methods for sampling and analysis of total gaseous mercury (TGM), reactive gaseous mercury (RGM) and total particulate mercury (TPM) were used in parallel sampling over a period of 4 days. The results show that the different methods employed for TGM compared well whereas RGM and TPM showed a somewhat higher variability. Measurement results of RGM and TPM improved over the time period indicating that activities at the sampling site during set-up and initial sampling affected the results. Especially the TPM measurement results were affected. Additional parallel sampling was performed for two of the TPM methods under more controlled conditions which yielded more comparable results.

Volcanoes as emission sources of atmospheric mercury in the Mediterranean basin

Emissions from volcanoes, fumaroles and solfataras as well as contributions from widespread geological anomalies could represent an important source of mercury released to the atmosphere in the Mediterranean basin. Volcanoes located in this area (Etna, Stromboli and Vulcano) are the most active in Europe; therefore, it is extremely important to know their mercury contributions to the regional atmospheric budget. Two main methods are used for the evaluation of volcanic mercury flux: a direct determination of the flux (by measuring in the plume) and an indirect one derived from the determination of the Hg/SO2 (or Hg/S) ratio value, as SO2 emissions are constantly monitored by volcanologists. An attempt to estimate mercury flux from the Vulcano volcano and to establish the Hg/S ratio value has been made along three field campaigns carried out in October 1998, in February and May 1999 sampling several fumaroles. Traditional sampling methods were used to collect both total Hg and S. The average Hg/S ratio value resulted to be 1.2 x 10(-7). From the Hg/S value we derived the Hg/SO2 value, and by assuming that all the volcanoes located in this area have the same Hg/SO2 ratio, mercury emissions from Vulcano and Stromboli were estimated to be in the range 1.3-5.5 kg/year and 7.3-76.6 kg/year respectively, while for Etna mercury flux ranged from 61.8 to 536.5 kg/year. Data reported in literature appear to be overestimated (Fitzgerald WF. Mercury emission from volcanos. In: 4th International conference on mercury as a global pollutant, August 4-8 1996, Hamburg, Germany), volcanic mercury emission does not constitute the main natural source of the metal.

Atmospheric mercury distribution in Northern Europe and in the Mediterranean region

Mercury species in air have been measured at five sites in Northwest Europe and at five coastal sites in the Mediterranean region during measurements at four seasons. Observed concentrations of total gaseous mercury (TGM), total particulate mercury (TPM) and reactive gaseous mercury (RGM) were generally slightly higher in the Mediterranean region than in Northwest Europe. Incoming clean Atlantic air seems to be enriched in TGM in comparison to air in Scandinavia. Trajectory analysis of events where high concentrations of TPM simultaneously were observed at sites in North Europe indicate source areas in Central Europe and provide evidence of transport of mercury on particles on a regional scale.