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G3 Sources and emissions

Wednesday, 31 December, 1969

TG3-P1 — 11:00-12:00 and 17:30-18:30
OBSERVATIONS OF PLUMES OF POLLUTED AIR AT CAPE POINT
Authors: BRUNKE, E.-G.1, EBINGHAUS, R.2, KOCK, H.H.3, LABUSCHAGNE, C.1, SLEMR, F.4
(1) South African Weather Service, ernst.brunke@weathersa.co.za; (2) GKSS Forschungszentrum Geessthacht GmbH; (3) GKSS Forschungszentrum Geesthacht GmbH; (4) Max-Planck-Institute for Chemistry.

Since the beginning of the continuous measurements of gaseous mercury at Cape Point (South Africa) in March 2007 until December 2009 about 67 plumes with enhanced mercury concentrations had been observed. Significant positive correlations of mercury concentrations with CO, CO2 and 222Rn were observed in 46, 44, and 24 plumes, respectively. Most of the Hg/CO slopes lie within a band of 1 – 7 pg/m3 ppb, bracketed by emissions from biomass burning on the low side and industrial/urban emissions on the high side. Only a few of the plumes could be attributed to originate from the industrialized provinces of Gauteng and Mpumalanga but their Hg/CO and Hg/CO2 emission ratios do not confirm the anomalously high emissions in this region presumed by some emission inventories. Using the backward trajectories the plumes will be classified according to their origin. The relation of their characteristics to their origin will also be discussed.

TG3-P2 — 11:00-12:00 and 17:30-18:30
REVIEW OF UNITED STATES PORTLAND CEMENT MANUFACTURING FACILITIES MERCURY INPUTS, ATMOSPHERIC EMISSIONS, CONTROLS, AND REGULATIONS
Authors: SIKKEMA, Joel K1, ALLEMAN, James E1, ONG, Say Kee1
(1) Iowa State University, jsikkema@iastate.edu

United States portland cement facilities face stringent regulatory challenges due to a new USEPA limit on atmospheric mercury emissions and its short three-year compliance window. By 2013, existing non-hazardous waste burning facility emissions will be restricted to 55 pounds mercury/million metric tons clinker (equivalent to 10 micrograms/dry standard cubic meter). Effectively, emissions must be reduced from 8 to 0.5 tons per year. New facilities must achieve a 21 pounds mercury/million metric tons clinker (4 micrograms/dry standard cubic meter) limit. The regulations are based upon measured emissions at the 11 lowest emitting facilities in the industry. These plants use feedstock and fuel inputs naturally low in mercury and, having no need to develop tailpipe control technologies, consequently also have no technologies to apply to non-compliant facilities. New and non-compliant plants must modify technologies used in other industries or develop controls specific to cement manufacture. In addition, each facility must assess its own particular feedstock and fuel inputs. Considerable variation in mercury concentration occurs within inputs used at individual facilities and therefore available data does not support a ‘typically observed’ concentration assumption or even a correlation to mercury levels observed in limestone (approximately 85% of feedstock mixture). Furthermore, unlike coal-fired power plants, cement facilities with in-line feedstock mills display internal control mechanisms that loop and concentrate mercury between the low-temperature feedstock mill and high-temperature kiln. Neither of the two reported emissions models are based on data from the components that drive internal control nor do they distinguish between mercury species, which have differing desorption and sorption properties. Reported control technologies, listed from highest to lowest mercury removal, include dry and semi-dry scrubbing, dry sorbent injection, cleaning mercury enriched dust, wet scrubbing, feedstock and fuel changes, and purging baghouse dust or raw meal. Impacts on removal mechanism effectiveness due to facility operating conditions and modes, mercury species, and feedstock and fuel inputs are not well researched. Minimizing harm to United States cement production while concurrently reducing mercury related health risks necessitates research that broadens understanding of control technologies, mercury inputs, and mercury species sorption and desorption dynamics.

TG3-P3 — 11:00-12:00 and 17:30-18:30
MERCURY CONCENTRATIONS AND VEGETATION-ATMOSPHERE FLUXES IN SALT-MARSH PLANTS (TAGUS ESTUARY, PORTUGAL)
Authors: CANÁRIO, João1, POISSANT, Laurier2, VALE, Carlos1, PILOTE, Martin2
(1) IPIMAR/INRB IP, jcanario@ipimar.pt; (2) Environment Canada;

A number of studies have shown that natural surfaces (e.g. soil, water, vegetation) contribute to a considerable amount of mercury in the global pool. Since almost 30% of the Earth’s land is covered by vegetation the role of plants in the atmospheric mercury cycling is, therefore important in assessing the mercury fate on regional and global scales. This issue is particularly relevant in salt-marshes where it is known that vegetation in these ecosystems tend to accumulate large amounts of mercury.

In order to assess the role of salt-marsh plants on the mercury vegetation-atmospheric fluxes, three salt marsh plant species, Halimione portulacoides, Sarcocornia fruticosa and Spartina maritima were selected from a moderately contaminated site in the Tagus estuary (Alcochete marsh). Total mercury in stems and leaves for each plant site as well as total gaseous mercury and vegetation-air fluxes were measured over two continuous days. Mercury fluxes was estimated with a dynamic flux Tedlar® bag coupled with an high resolution automated mercury analyzer (Tekran 2537A). Other environmental parameters such as air temperature, relative humidity and net solar radiation were also measured aside.

H. portulacoides showed the highest total mercury concentrations in steams and leaves and the highest surface area of all species. The same was observed for the average vegetation-air flux (0.39±0.24 ng Hg m-2 h-1). Interestingly, S. maritima (Hg flux: 0.12±0.09 ng Hg m-2 h-1) had lower flux and concentration levels then S. fruticosa (Hg flux: 0.23±0.22 ng Hg m-2 h-1) in spite having a higher surface area. These results suggest that Hg vegetation-air flux is apparently more related to the Hg concentration in the above ground plant parts than to the above ground surface area.

The continuous measurements appointed to a daily pattern for all plants with enhanced fluxes during daylight and lower flux during the night. It was noticed that throughout the measurements a negative flux (air-vegetation) were never observed suggesting the absence of net Hg0 deposition.

Based on the above fluxes and the total area occupied by each species we have estimated the total amount of Hg0 emitted from this salt-marsh. It was predict a daily emission of 0.81 mg Hg d-1 from the Alcochete marsh and 119 mg Hg d-1 for the entire salt marsh area of the Tagus estuary.

TG3-P4 — 11:00-12:00 and 17:30-18:30
MERCURY IN SOILS ALONG TWO CONTINENTAL-SCALE TRANSECTS, CANADA AND THE UNITED STATES
Authors: WOODRUFF, Laurel G.1, CANNON, William F.1, SMITH, David B.1
(1) U.S. Geological Survey, woodruff@usgs.gov

The North American Soil Geochemical Landscapes Project is a low-density geochemical and mineralogical soil survey of North America. A 2004 pilot study consisted of soils collected from randomly selected sites (average spacing of 40 km) along two continent-wide transects, one from northern Manitoba to El Paso, TX and the other along the 38th parallel from the Atlantic to the Pacific Oceans. At each site up to 4 samples were collected: 1) soil from 0 to 5 cm depth, regardless of horizon; 2) upper organic soil (O horizon); 3) surface mineral soil (A horizon); and 4) deeper subsoil (B or C horizon). Eight hundred and thirty soil samples were analyzed for 44 elements and forms of carbon. Vertical and spatial distributions of mercury along the transects show influences from geologic, atmospheric, and anthropogenic mercury sources. At sites where 0 to 5 cm depth, O-, A-, and C-horizon soils were collected from a single pit, mercury is invariably highest in the O horizon compared to other soils, with a median value of 0.12 mg/kg (range 0.05 to 0.22 mg/kg). Deeper subsoils have the lowest mercury concentrations, with nearly 60 percent of the samples having values less than the 0.02 mg/kg lower detection limit, and a median value of 0.03 mg/kg (range < 0.02 to 0.14 mg/kg). At two sites in the Coast Range of California and several sites in western Nevada, mercury is high in all soil samples, reflecting contributions from geologic soil parent materials in areas with known mercury mineralization and a history of mercury mining. Lowest overall concentrations of mercury are across the midsection of the US with the exception of two sites with anomalously high mercury in topsoils within areas previously used for animal confinement. Along the west to east transect, mercury concentrations in topsoils increase from the midsection of the US to the east coast. In this region, the vertical distribution of mercury in soil profiles, with highest mercury values in topsoils compared to deeper soils, is consistent with retention of atmospherically-deposited mercury by binding to soil carbon. Normalization of mercury concentrations to carbon concentrations (linked to climate and land cover/land use factors) indicates that the spatial distribution of mercury is highly dependent on carbon concentrations in soils. Thus, at the continental-scale geologic sources of mercury, climate, land use, and possible local or regional anthropogenic sources are critical factors controlling the distribution of mercury in soils.

TG3-P5 — 11:00-12:00 and 17:30-18:30
PROGRESS TOWARD A U.S. NATIONAL MAP OF MERCURY IN SOILS
Authors: CANNON, William F.1, WOODRUFF, Laurel G.2, SMITH, David B.1
(1) U.S. Geological Survey, wcannon@usgs.gov; (2) U.S Geological Survey;

The U.S. Geological Survey is conducting a survey of the geochemistry and mineralogy of soils within the conterminous United States. The work, begun in 2007, is to be completed by 2013 or sooner. The goals of the survey are: 1) develop a national-scale framework for generating and managing geochemical and mineralogical data now and in the future; 2) produce a soils data base, and its representation in map form, generated with consistent and up-to-date protocols for sampling and analyses; and 3) establish an archive of soil samples for future investigators. The completed dataset will identify natural regional background levels and controls on soil geochemistry, as well as identify human impacts on the soil landscape, resulting in a better understanding of links between soil geochemical factors and environmental and human health. The survey is based on widely spaced sampling and intended to define regional trends in the chemical and mineralogical composition of soils. The nominal sample spacing is 40 km within a spatially balanced random array of sites. This results in nearly 5,000 sites across the country. At each site soils were collected from three depths: 1) at about 1 m; 2) a composite of the A-horizon; and 3) the upper most 5 cm of soil regardless of horizon. The <2mm fraction of each sample is digested with an aggressive four-acid technique which results in near-total digestion. The concentrations of a broad suite of elements are quantified mostly with inductively coupled plasma mass spectrometry. Total mercury concentration is determined by cold vapor atomic absorption analysis following digestion in a mixture of nitric and hydrochloric acids. This technique has a detection limit of 0.02 mg Hg/kg.

The sampling phase of the survey was completed in 2010 and the analytical chemistry and mineralogy determinations are in progress. Results for approximately half of the country are now available. The data show about three orders of magnitude variation in total Hg between individual samples and define prominent differences in typical baseline concentrations between regions. Samples from three depths at each site help to define the relative contribution of atmospheric deposition vs. geologic sources for mercury. Data on the concentration of other elements, which can influence mercury concentration, such as organic carbon and sulfur, can also support interpretations of mercury sources and sequestration processes which vary according to factors such as land cover/land use characteristics, climate, and soil parent material.

TG3-P6 — 11:00-12:00 and 17:30-18:30
CURRENT SITUATION AND POTENTIAL FOR RECYCLING OF MERCURY CONTAINING PRODUCTS IN JAPAN
Author: ASARI, Misuzu1
(1) Kyoto University, misuzuasari@eprc.kyoto-u.ac.jp

The collection and recycling of household products containing mercury is important in both advanced countries and developing countries. Then, the current situation and potential in Japan were examined.

In Japan, fluorescent lamps used domestically are typical products containing mercury. But the management of them is up to each local government. And the collection rate stays around 20 %.

On the other hand, for collected products containing mercury, there are 20 private recycling companies at main regions in Japan. For fluorescent lamps, 16 companies recycle them, and the total recycling capacity is 85,656 tones lamps (4.3 tons mercury) per year. This capacity is about five times compared with the current recycling amount, 18,645-tons fluorescent lamps (0.9 tons mercury) per year. Therefore, it seems important how to promote the collection rate of used products containing mercury and recycle them.

From other aspects, end of life products which remain in households are also important. At the “home visit survey”, the existence such as used clinical thermometers containing mercury was clarified. It is necessary to prevent unsuitable disposal of them.

For mercury containing products, including the product used in the past, the discussion on the policy is also necessary as the typical example of household hazardous wastes.

TG3-P7 — 11:00-12:00 and 17:30-18:30
EMISSION CHARACTERISTICS OF MERCURY FROM COAL-FIRED POWER PLANTS IN KOREA
Authors: PARK, Jung-Min1, LEE, Sang-Bo1, KIM, Hyung-Chun1, SONG, Duk-Jong1, KANG, Kyoung-Hee1, LEE, Dae-Gyun1, YOO, Chul1, KIM, Min-Jung1, HONG, Ji-Hyung1, LEE, Suk-Jo1
(1) National Institute of Environmental Research, ilikepaul@korea.kr

In this study, mercury emissions from coal-fired power plants in Korea, were measured. Coal-fired power covers about 30% (1.5GW) of total electricity generation capacity in Korea and most of the coal-fired power plants (about 1.2GW) are equipped with both electrostatic precipitator (ESP) and wet flue gas desulfurization (FGD) that are used for particulate and SOx removal, respectively. The US EPA 101A and the Ontario Hydro method were used to sample the mercury containing combustion flue gases, at the inlet of the APCDs and at the stack, in order to understand the change in forms of mercury in such processes. The fates of Hg in a coal-fired power plant and a municipal waste incinerator, including its removal by APCDs were quantified by collecting and analyzing gaseous samples as well as solid and liquid samples such as fuel (coal or wastes), fly ash from hopper, bottom ash, gypsum (by-product from FGD), lime or limestone, and effluents. The assessment of mercury emission and total mercury mass balance from a coal-fired power plant and a municipal waste incinerator were estimated by gathered sample data. Mercury concentration in the flue gas were 1.63~3.03µg/m3 in CPP#1~2 using Anthracite as a fuel, 1.95~3.33µg/m3 in CPP#3~4 using Bituminous. When comparing two methods of error was 10~20%. Distribution of mercury speciation in flue gas were oxidized, elemental, particulate mercury order was emission. Emission factor were estimated as 19.83~32.45 mg/ton in CPP using anthracite as a fuel, 7.43~20.63 mg/ton in CPP using bituminous. Approximately 86% of in/out Hg balance was obtained with this study and major Hg outgoing was fly ash in hopper. Large amount of Hgp, above 50% of Hg could be removed by ESP and Hg compounds seemed to be oxidized to Hg2+ through ESP, which resulted in increase of Hg2+. Then wet FGD unit could remove Hg2+ with lime-slurry scrubber solution, which covers less than 10% of Hg, and about a quarter of mercury emits to the atmosphere through stack. Hg speciation changes with increasing oxidized portion through ESP and reduction of absorbed Hg to Hg0 in the wet FGD scrubber solution are reported from other investigations, however, need more comprehensive study with field experiments.

TG3-P8 — 11:00-12:00 and 17:30-18:30
CONTINUOUS AUTOMOBILE HG AIR SURVEYS FOR ATMOSPHERIC ENVIRONMENTAL MONITORING IN DIFFERENT WORLD SCENARIOS.
Authors: HIGUERAS, Pablo L1, ESBRÍ, José M1, OYARZUN, Roberto2, MASHYANOV, Nikolay3, OYARZÚN, Jorge4, CONTRERAS, Felicia5, GOSAR, Mateja6, MILLÁN, Rocío7, GARCÍA, M. Eugenia8, ŠPIRI?, Zdravko9, PANICHEV, Nickolay10, LÓPEZ-BERDONCES, Miguel A1, DRAGAS, Mate9, LLANOS, Wiilians R1, MATURANA, Hugo4, ADAMS, Melitón11, RYZOV, Vladimir3, MCCRINDLE, Rob10
(1)Instituto de Geología Aplicada, UCLM. Pl. Manuel Meca, 1. 13400 Almadén (Ciudad Real), Spain, pablo.higueras@uclm.es; (2) Departamento de Cristalografía y Mineralogía, Universidad Complutense de Madrid. 28071 Madrid, Spain; (3) St. Petersburg State University, St Petersburg, Russia; (4) Departamento de Minas, Universidad de LA Serena. La Serena, Chile; (5) Ministerio del Poder Popular para el Ambiente, Centro Simón Bolívar, Viceministrerio de Ordenación y Administración Ambiental, Caracas (Venezuela); (6) Geological Survey of Slovenia, Ljubljana, Slovenia; (7) Centro de Investigaciones Energéticas, Medio Ambientales y Tecnológicas - CIEMAT. 28071 Madrid, Spain; (8) Universidad Mayor de San Andrés. La Paz (Bolivia); (9) Oikon Ltd., Zagreb, Croatia; (10) Tshwane University of Technology, Pretoria, Republic of South Africa; (11) Petróleos de Venezuela.;

We describe a cost-effective technique for detecting mercury emission sources and polluted sites using continuous automobile Hg air surveys (CAHGS). Large cities, countryside, important sources of Hg gas can be studied in a matter of hours using CAHGS, having a complete picture regarding baseline data and anomalous concentrations.

We have carried out such surveys in Europe, South America and Africa with excellent results, using a LUMEX RA-915+ device coupled with a GPS for data georeferencing. The LUMEX RA-915+ is a well known instrument for continuous monitoring of total mercury in the atmosphere; the analytical procedure is based on Zeeman Atomic Absorption Spectrometry, with a dynamic measuring range between 1 and 25,000 ng m-3.

We have been able to monitor the progressive reduction of Hg emissions from the Almadén district (Spain) while roasting of cinnabar ore at the city was coming to an end. We also measured a significant reduction of Hg from the main waste dump while restoration works were taking place. At Idrija (Slovenia) the results put forward high to very high concentrations in the surroundings of two main local sources: the old roasting plant and a mine ventilation shaft. A cross section of St. Petersburg (Russia) allowed discovery of several unknown sources of mercury emissions from heavily contaminated sites. At the Podravina (Croatia) gas processing facility the results indicated than the pollution hazards were brought to a minimum level since an efficient, closed mercury removal system was built.

Jewelry works using mercury from local artisanal miners at El Callao (Venezuela) produced extremely high concentrations of Hg air, whereas the old mining site of Andacollo (Chile) Andacollo (Chile) only showed high concentrations at the classical artisanal trapiche gold mills. We went further at Chile, visiting more than one site with a mining/metallurgical past, covering about 10,000 km2 in just five days, thus gaining a regional perspective. In Pretoria (South-Africa) we measured background Hg content about 1.7 ng m-3, while at a Portland Cement factory its concentration rises to 30-50 ng m-3.

Besides, we also observed at Potosí (Bolivia), unusually low Hg air emissions from soils can be also the result of biological and physicochemical transformation of metallic mercury to cinnabar/metacinnabar and/or schuetteite. Thus we recommend that as a standard procedure some low concentration areas should be checked by classic, on foot, field collected data.

TG3-P9 — 11:00-12:00 and 17:30-18:30
MERCURY EMISSIONS FROM CREMATORIA USING ONLINE HGCEM
Authors: CORNS, Warren T1, DEXTER, Matthew A1, STOCKWELL, Peter B1
(1) P S Analytical, wtc@psanalytical.com

Anthropogenic emission of mercury into the environment continues to cause concern. Increasing control of atmospheric mercury emissions is resulting in the gradual overall fall in mercury emissions. UK annual mercury emissions are estimated to have fallen dramatically over the last 3 decades. In contrast to the overall fall, mercury emissions from crematoria have increased significantly. The increase in emissions is readily attributable to the use of amalgam fillings and, due to better dental health, a large decrease in the number of people edentate at the time of death. Estimates of the mass of mercury present in an average cremation vary significantly, with estimates generally between 0.9 g and 3.0 g. The mass present depends on dental health practices, thus varying with time period and with country.

Mercury emissions during the cremation process are almost entirely due to the presence of amalgam fillings in the cadaver. This leads to very significant variation in the concentration of mercury emitted, in each cremation. Concentrations vary between low ug/m3 to several mg/m3.

The P S Analytical Sir Galahad amalgamation-atomic fluorescence spectrometer is a proven technique for the determination of mercury in a wide range of gaseous media. This paper presents summary results of an initial study of mercury emissions on a single crematory stack at a UK crematorium and introduces a Hg CEM, specifically designed to continuously monitor mercury concentrations in cremation gases for regulatory purposes or online process control of mercury abatement equipment.

TG3-P10 — 11:00-12:00 and 17:30-18:30
NECESSARY MERCURY DIFFUSION COEFFICIENT OF A PROTECTIVE LAYER FOR LONG-TERM UNDERGROUND REPOSITORY OF UNUSED MERCURY
Author: TAKAHASHI, Fumitake1
(1)Kyushu University, f-takahashi@doc.kyushu-u.ac.jp

Owing to adverse impact of mercury on the ecosystem, there have been international efforts to shift to non-mercury industrial processes and products. This requests safe disposal or long-term repository of mercury in post-service phase. Underground repository of unused mercury seems to be a safe and feasible way. For long-term underground repository, two potential corrosions should be considered as a mercury release pathway to the environment: One is inner surface corrosion of a repository vessel owing to amalgam formation. The other is outer surface corrosion owing to groundwater. A cost-effective way to reduce mercury emission owing to these corrosions is to cover a repository vessel with a protective layer material like cement. The objective of this study is to estimate necessary characteristics of a protective layer material for safe long-term underground repository of mercury. In this study, mercury diffusion coefficient and thickness of a protective layer were focused on and estimated based on the risk assessment of a mercury-emission-transfer-exposure scenario. In this scenario, mercury sulfide is stored in a repository vessel. It is leached from the vessel to groundwater through a protective layer and transferred to a lake. Sorption to the soil and methylation/demethlation reactions during the transfer by groundwater are accounted in this model. Mercury is distributed to lake water and the sediment when groundwater reaches to the lake. Further distribution between lake water and the sediment, methylation and demethylation of mercury species in water and sediment mediums are also included. Hydraulic diffusion of lake water reduces mercury burden in the lake. Methylmercury in lake water is biomagnificated through food-chains and exposed to human bodies via contaminated fish food. Calculated mercury intake is compared to tolerable intake reported by WHO to assess health risk. Sensitivity analysis of this model indicated kinetic rate coefficient of methylation and demethylation in the sediment, distribution constant of methylmercury between lake water and the sediment, and biomagnification factor were significant. If negligible risk is requested during more than 10,000 years repository, this model calculation suggested the protective layer should have less than 7.7x10-15 m2/s of mercury diffusion coefficient and more than 15 cm of thickness. This suggested that clay-based material like sand-mixed bentonite might be insufficient as a protective layer. However, cement is applicable as a low-cost coverage material when necessary thickness is insured.

TG3-P11 — 11:00-12:00 and 17:30-18:30
GASEOUS ELEMENTAL MERCURY EMISSIONS FROM THE FOREST FLOOR IN NEW YORK’S ADIRONDACK PARK
Authors: MAXWELL, J. Alex1, HOLSEN, Thomas M.2, CHOI, Hyun-Deok3, HUANG, Jiaoyan2
(1) Clarkson University - Institute for a Sustainable Env., maxwelj@clarkson.edu; (2) Clarkson University - Civil & Env. Engineering; (3) National Institute of Aerospace (NIA);

Soil emissions of gaseous elemental mercury (GEM) ( Hg0) were measured using a dynamic flux chamber (DFC) under deciduous (DF) and conifer forest (CF) canopies in New York’s Adirondack Park. Sampling was conducted during the growing months from 2005 to 2006 (DF) and again from 2009 to 2010 (CF). The inlet and outlet of the DFC was coupled with a Tekran ® Model 2537A mercury vapor analyzer using a Tekran ® Model 1110 two port synchronized sampler. DF soil Hg0 emissions ranged from -2.5 ng m-2 hr-1 to 27.2 ng m-2 hr-1 and CF soil Hg0 emissions ranged from -3.2 ng m-2 hr-1 to 4.2 ng m-2 hr-1. Both DF and CF soil emissions were positively correlated with ground temperature and solar radiation, and negatively correlated with relative humidity. Emission fluxes were highest in the spring and summer months and lowest in the fall. Average Hg emission fluxes from soils under the CF canopy during the summer (0.67±0.76 ng m-2 hr-1), fall (-1.10±0.46 ng m-2 hr-1), and spring (-0.14±1.11 ng m-2 hr-1) were found to be significantly less than those of soils under the DF canopy (1.46±1.06 ng m-2 hr-1, 0.82±0.97 ng m-2 hr-1, & 1.55±2.98 ng m-2 hr-1 respectively). During leaf-on periods, the DF Hg0 emission flux was constant due to canopy shading and reduced exposure to solar radiation. The Hg0 emission flux was not significantly affected by precipitation events. Two empirical models were developed using the DF and U.S. EPA’s CASTNET meteorological data, to estimate yearly Hg0 emissions during both leaf-on and leaf-off periods. The cumulative estimated emission flux was 6.3 µg Hg0 m-2 year-1. New models are being developed to incorporate the CF emissions data to better estimate the total Hg0 flux in the Adirondack Park.

TG3-P12 — 11:00-12:00 and 17:30-18:30
A MULTI-MEDIA EVALUATION OF MERCURY LEVELS IN ENVIRONMENTAL SAMPLES NEAR A 2,600 MW COAL-FIRED POWER PLANT IN SOUTHEASTERN OHIO, USA
Author: REASH, Robin1
(1) American Electric Power, rjreash@aep.com

The James M. Gavin coal-fired power plant (Gallia County, OH) has two 1,300 MW generating units. Advanced air pollution control equipment installed at the facility consists of a Selective Catalytic Reaction (SCR) system for NOx control, and a magnesium-lime wet flue gas desulfurization (FGD) system for SO2 control. The facility’s waste streams discharge to the Ohio River and to Kyger Creek, a tributary of the Ohio River. Annual Hg emissions (air stacks) typically range between 170 – 350 kg/yr. A high Hg removal rate (coal to air stack) is typically observed (average = 90%), largely due to high conversion efficiency of elemental to oxidized/particulate Hg due to SCR operation. During 2004 – 2010, environmental samples were collected to evaluate the potential contribution of plant operations on near-field Hg enrichment. Lichen, fish, water, and sediment samples were collected at proximal locations and compared to reference site data. Composite samples of a lichen species (Flavoparmelia caperata) were collected at reference locations and sites near the power plant. The median concentration of Hg in samples collected near the plant site (0.142 mg/kg dry wt.) was somewhat lower than the median concentration for samples collected at upwind reference sites (0.158 mg/kg). For analysis of total Hg and MeHg in skin-off fillet samples, fish from two trophic levels were collected in lower Kyger Creek and the Ohio River during 2008 – 2010. A total of seven fish species were collected, and the mean trophic level MeHg concentrations were 0.097 mg/kg wet wt. (trophic level 3) and 0.121 mg/kg (trophic level 4). None of the samples approached U.S. EPA’s MeHg human health fish tissue criterion of 0.3 mg/kg wet wt. Median total and MeHg water concentrations were 2.9 ng/L and 0.042 ng/L (Ohio River) and 3.02 ng/L and 0.028 ng/L (Kyger Creek), similar to reference sites. Sediment samples from Kyger Creek downstream of the wastewater outfalls were moderately elevated. Overall, there was no consistent signal of elevated Hg levels in environmental samples collected proximal to the power plant site.

TG3-P13 — 11:00-12:00 and 17:30-18:30
HG DISTRIBUTION CHARACTERISTICS IN COAL FROM XINJIANG AND NEI MONGOL, NORTH OF CHINA
Authors: ZHENG, Na1, WANG, Qichao1, LIU, Jingshuang1, LIANG, Zhongzhu2
(1)Northeast Institute of Geography and Agricultural Ecology, Chinese Academy of Sciences, zhengnalzz@neigae.ac.cn; (2) National Key Laboratory of Applied Optics, Changchun Institute of Optics, Fine Mechanics and Physics, Chinese Academy of Sciences.

Hg is released into the atmosphere from both natural and anthropogenic sources, especially coal and transported globally, even to regions without significant mercury emission sources. There are abundant reserves of coal which have become China’s most important source of primary energy. In past reports, coal used to estimate mercury emission was sampled from the main provinces, such as Shanxi. The details on mercury in coal from Xinjiang and Nei Mongol provinces were very limited due to wide area and difficulties to sampling. The prospective reserve of coal in Xinjiang amounted to 182-219 million tons, and the proven recoverable coal in Nei Mongol reached 70 million tons. More than 200 coal samples from 45 mine in Xinjiang and more than 150 samples from 40 mines were collected and analyzed for total mercury. The average Hg content in coal from Xinjiang and Nei Mongol were 47.88 and 80.54µg kg-1, and the maximal Hg content was 170.4 and 268 µg kg-1. Hg contents in coal from different regions in Xinjiang followed in the order of Qitai > Urumchi > Hetian, Kuche and Baicheng >Yining and Hami > Aletai >Wucai >Taicheng. Hg contents in coal from different regions in Nei Mongol was in the order of Eerduosi > Huolinhe >Dayan > Chifeng. Hg content in coal of Xinjiang from this study was higher than the datum from USGS, and it in Nei Mongol was lower than USGS. Mercury emission decreased with the use of coal from Xinjiang, and mercury emission from coal combustion in China was recalculated.

TG3-P14 — 11:00-12:00 and 17:30-18:30
COMPARISON BETWEEN ATMOSPHERIC MERCURY MEASUREMENTS AND MODEL AROUND A CHLOR-ALKALI PLANT IN FLIX (SPAIN)
Authors: BASELGA, Leticia1, ESBRÍ, José M2, LLANOS, Wiilians R2, MARTÍNEZ-CORONADO, Alba2, HIGUERAS, Pablo L2, DÍEZ, Sergi3
(1) Ecologistas en Acción, España., residuos@ecologistasenaccion.org; (2) Instituto de Geología Aplicada, Universidad de Castilla-La Mancha. 13400 Almadén (Ciudad Rea), Spain; (3) Department of Environmental Chemistry, Institute of Environmental Assessment and Water Research (IDÆA), Spanish National Research Council (CSIC). 08034 Barcelona, Spain.

Since 1980 chlor-alkali industry is the main mercury consumer in industrialized countries, being responsible for 90% of its use. In Spain, this industry declares 2.54 tons per year of mercury emissions to the atmosphere, figures what may be underestimated. The aim of the present work is to evaluate the distribution of mercury vapours in the atmosphere in the vicinity of one of these plants; it is located near Flix (Tarragona, NE Spain), and it is in activity since 1897, with a production capacity of 150,000 tonnes of chlorine per year. The plant is located 1 km away from the town, and a residential area is located besides the perimeter of the plant.

We have monitored this chlor-alkali facility and its surroundings using a Lumex RA-915+ analyzer (ZAAS-HFM) for continuous Hg measurements, with a wide measurement range (2 – 25,000 ng m-3), GPS technology to georeferenciate data and a geostatistical treatment by kriging. Mercury dispersion patterns were modelized using ISC-Aermod software and annual emissions declared by the chlor-alkali plant (65.7 kg per year in 2009).

During the surveys, mercury contents (up to 25,000 ng·m-3) surpassed the WHO maximum recommended level (1000 ng·m-3) in the vicinity of the plant; at the residential area we have found areas with concentrations above WHO and USEPA reference concentration for chronic mercury exposure (200 and 300 ng·m-3, respectively).

The mercury dispersion model confirms the affection to the residential area close to the facility, in particular in summer, when expected atmospheric mercury concentrations exceed the above mentioned thresholds. Besides, values estimated by the model on the basis of declared emissions are much lower than real data measured during our surveys, confirming the underestimation of emissions.

TG3-P15 — 11:00-12:00 and 17:30-18:30
INFLUENCE OF SUBMARINE FUMAROLES ON THE DISTRIBUTION OF MERCURY IN WATER AND SEDIMENT OF KAGOSHIMA BAY, JAPAN
Authors: TOMIYASU, Takashi1, MATSUOKA, Hiroyuki1, KODAMATANI, Hitoshi1, KONO, Yuriko1, MATSUYAMA, Akito2, HIDAKA, Masayasu1, OKI, Kimihiko1
(1) Kagoshima University, tomy@sci.kagoshima-u.ac.jp; (2) National Institute for Minamata Disease;

Submarine fumaroles were located in the 200-m deep basin of the northern part of bay head area of Kagoshima Bay. To estimate the influence of mercury emitted from the fumaroles, the distributions of mercury in water and sediment were studied.

The samples had been taken in the bay head area in February and June, 2010. The sediment samples were taken from the bottom using a gravity core sampler. Total mercury (T-Hg) concentration in the samples was measured by CVAAS after acid digestion. The sea water samples were collected every 50 m from the surface to 10 m above the sea bottom with Niskin sampling bottle. For Hg2+ and T-Hg measurement the water samples were filtered with 0.45 µm membrane filter. Hg2+ was measured by CVAAS using SnCl2 as a reducing agent. T-Hg was measured by the CVAAS after BrCl oxidation under UV radiation. For Hg0 measurement, unfiltered water samples were bubbled with nitrogen without reducing agent and Hg0 swept from the water was measured by CVAAS.

In February, the water samples were collected at 3 locations in the 200 m deep area. T-Hg of the seawater columns were 0.49±0.43 ng/l and the values showed no association with depth. In June, water samples were collected at the 200-m deep basin, and 4 and 8 km away from the basin. The depths of them were 130 and 140 m, respectively. In this season, thermocline was observed about 0-120 m deep and pH decreased sharply at 120 m deep, which may be caused by the fumarolic activity. Significant higher concentrations, 2.5 and 3.1 ng/l of T-Hg and 0.69 and 0.90 of Hg0, were observed at 150 and 190 m deep. Surface to 100 m deep layers showed no tendency in the vertical and horizontal variations of mercury with lower concentrations of 0.43±0.19 ng/l for T-Hg and 0.05±0.02 ng/l for Hg0. In the distribution of T-Hg in surface sediment, 0.73±0.18 mg/kg was observed near the fumaroles and the value decreased with distance from there. These observations suggested that the fumaroles are main sources of mercury in the study area. The formation of seasonal thermocline may be a important factor for the dispersion of the mercury.

TG3-P16 — 11:00-12:00 and 17:30-18:30
MERCURY CONCENTRATION IN DEWATERED SLUDGE FROM SEWAGE AND WASTEWATER TREATMENT PLANTS AND ITS EMISSION ASSESSMENT
Author: ZOH, Kyung-Duk1
(1) Seoul National University, zohkd@snu.ac.kr

Dewatered sludge cake which is solidified waste produced from sewage and wastewater treatment plants, contains high concentration of various toxic trace metals including mercury (Hg). In spite of its chemical characteristics, a great part of the dewatered sludge goes into the landfill, incinerate or dispose into the ocean in many countries including Korea. Therefore the sludges containing toxic metals can affect the environment. This study measured the distribution of total mercury (THg) concentration in dewatered sludge. Dewatered sludge cakes were obtained in total 15 sewage and wastewater treatment plants in Korea for three seasons (spring, summer, and fall) in 2010. Note that there are three types treatment plants in Korea; treating sewage only (STP), wastewater only (WWTP), and both sewage and wastewater (SWWTP). Distribution of THg concentrations in dewatered sludge cakes ranged 0.464~2.247 mg/Kg for STP as dry weight basis (d.w.), 0.147~10.249mg/kg d.w. for WWTP and 0.010~36.71mg/kg d.w. for SWWTP. Using THg concentrations in sludge and daily amount of sludge production, the mercury emission from dewatered sludge cake were estimated, and calculated emission estimates ranged 16.635~198.81 g/day in STP, 1.563~78.829 g/day for WWTP, 0.282~177.11 g/day for SWWTP. These results imply that considerable amounts of mercury are emitted into the environment by dewatered sludge.

TG3-P17 — 11:00-12:00 and 17:30-18:30
IMPACT OF ENVIRONMENTAL FACTORS ON HG EMISSION FLUX FROM SOIL SURFACES
Authors: PARK, Sang-Young1, HAN, Young-Ji 1
(1) Kangwon National University, beleth302@Gmail.com

Atmospheric mercury (Hg) plays an important role for approximately 50-70% of total Hg emissions (Nriagu, 1990; Mason et al., 1994). However since natural sources are widely distributed and difficult to pinpoint (Kim and Lindberg, 1995; Cobos et al., 2002) the uncertainty of natural Hg emission rate is rather large. Among natural sources , soil becomes the largest source, as well as the ocean. Like water surfaces soil has the potential to act as a source and a sink in global mercury cycle, depending on the Hg concentration gradient and/or both meteorological and soil conditions.

In this study we measured Hg emission flux from soil surfaces using dynamic flux chamber (DFC) in both field and laboratory conditions. Inlet and outlet lines of DFC were connected to the Tekran 2537B instrument through the Tekran 1110 synchronized two-port sampling unit in order to continuously measure Hg0 concentration. In field study Hg emission flux was measured at two different sites including lawn and forest soil floors in campus of Kangwon National University in Korea. Between October 2010 and November 2010 the average of Hg emission flux was 0.05 ± 1.96 ng m-2 hr-1 and 0.15 ± 1.14 ng m-2 hr-1 at lawn and forest sites, respectively. In previous research, the Hg emission flux was positively correlated with ambient air temperature, soil surface temperature, and solar radiation, and negatively correlated with relative humidity and soil wetness (Gabriel et al., 2006; Wallschlager et al., 2000; Wang et al., 2005). However the variation of Hg emission flux was tended to be opposite to the results of previous investigations, showing that Hg emission flux was negatively correlated with soil surface temperature, ambient air temperature, and solar radiation in this study. Laboratory experiments measuring variation of Hg emission flux from soil surfaces by changing influence factors will also produce the interesting results in this presentation.

TG3-P18 — 11:00-12:00 and 17:30-18:30
VARIATION OF DISSOLVED GASEOUS MERCURY (DGM) CONCENTRATION AFFECTED BY ENVIRONMENTAL FACTORS IN REAL AND LABORATORY CONDITIONS
Authors: YANG, Ji Hae1, HAN, Young ji2
(1)Kangwon national University, sohyanglove@hanmail.net; (2).

It is noted that dissolved gaseous mercury undergoes volatilization process from water surfaces including lake and ocean. In aquatic system Hg experiences oxidation and reduction mechanisms, and Hg0 (which is mostly regarded as DGM) is often produced by biotic and abiotic processes. For abiotic process solar radiation has been suggested to be the most important factor and other parameters including pH, DO, and DOC also affected to Hg reduction in previous researches. However how these factors quantitatively affect to Hg reactions (and resulting DGM concentration) has not been identified. Reduction mechanism by solar radiation can be expressed as the following.

Hg(II) + photo-reductants → DGM(Hg0) + photo-oxidants

Since solar radiation significantly influences on DGM production DGM concentration often shows diel pattern, increasing during daytime and decreasing during nighttime in previous studies.

In this presentation, we will report the relationship of DGM formation with controlling factors such as solar radiation, UV, pH, temperature, ionic substances and DOC (dissolved organic carbon) both for environmental field (including lakes and ocean) and in laboratory. We used semi-real time DGM analysis system consisting of Tekran 2537B (sample flow=1.5 L/min) and dual pump (CPKS 600) to continuously determine DGM concentrations in water. In this study DGM concentrations were measured to be 1.4 ± 1.1 pg/L in small pond( 2010.9.29~2010.10.5), 51.1 ± 34.5 pg/L in the large artificial reservoir (2006.5~2007.2), and 2.7 ± 2.3 pg/L in Yellow Sea ( 2010.5.27~28). In both pond and ocean surfaces DGM concentration and solar radiation showed very similar diurnal pattern (p-value<0.01), however in artificial reservoir DGM concentration followed the variation of solar radiation only during winter time. On the other hand there was no significant relationship between DGM and pH (r2=0.0007) or between DGM and water temperature (r2=0.0021) in pond and ocean surfaces. In laboratory chamber study we have analyzed DGM variation by changing UV radiation under controlled temperature, pH, and other parameters, after injecting 1 ppm Hg standard solution into distilled water bottle. When UVA and UVB lights were turned on DGM concentration showed dramatic increase. However DGM concentrations continuously decreased when UVC light was being turned on.

TG3-P19 — 11:00-12:00 and 17:30-18:30
EVALUATION OF NATURAL AND ANTHROPOGENIC POLLUTION SOURCES OF MERCURY IN NORTH WEST OF IRAN IN A GIS FRAMEWORK
Authors: TAVAKOLI MOHAMMADI, Mohammad Reza1, MARZBAN, Mehdi1, AHMADI, Mohammad1
(1)Tarbiat Modares University, Tehran, Iran, mr.tavakolimohammadi@modares.ac.ir

Environmental protection against various pollutants, such as heavy metals formed by industries, mines and modern technologies, is a concern for researchers and industry. Mercury is among the most important of such pollutants due to high toxicity, disrupting soil ecosystem and high probability of contaminating groundwater resources. In this study, present situation and environmental effects of this metal in the provinces of East and West Azerbaijan and Ardebil in north west of Iran have been assessed in Geographic Information Systems (GIS) environment. The results showed that the downstream river of the Pouya-Zarkan plant in Takab and waste water from Sadr leather manufacturing company and Tabriz oil refinery are mercury-contaminated areas in East and West Azerbaijan provinces, however, no mercury-contaminated site has been reported in Ardebil Province yet.

TG3-P20 — 11:00-12:00 and 17:30-18:30
AN ASSESSMENT OF THE POTENTIAL SOURCES OF MERCURY IN THE WESTERN CAPE PROVINCE, SOUTH AFRICA
Authors: WINGROVE, Heinrich1, LEANER, Joy2, CHETTY, Kamaseelan2, BAIJNATH-PILLAY, Nitasha2, MAKOALA, Millicent2, BILL, Catherine2, BARRANTES, Vera3, MASON, Robert4
(1) Department of Environmental Affairs and Development Planning, hwingrove@pgwc.gov.za; (2) D:EADP; (3) UNITAR; (4) University of Connecticut, USA.

The 2003 UNEP Governing Council Decision and the 2006 Strategic Approach to International Chemicals Management (SAICM) aims at reducing risks to human health and the environment from the release of mercury and its compounds. In addition, the 2005 UNEP Governing Council Decision supports a Global Mercury Partnership, while the 2009 UNEP Governing Council Decision agreed to elaborate on the need to develop a legally binding instrument on Hg and for UNEP to convene an Intergovernmental Negotiating Committee (INC), with the mandate to prepare for a legally binding instrument. In terms of the above, the Department of Environmental Affairs and Development Planning (D:EADP) and UNITAR identified the gaps and needs (e.g. legal, financial, personnel needs etc.) in terms of establishing a Mercury Monitoring System within the Western Cape. In addition, a Hg Inventory for Western Cape, which integrates data within the Provincial Pollutant Release and Transfer Register Framework, was developed. The database contains information on the potential Hg sources, including the amount of Hg-containing products produced or combusted within the Province. The UNEP Toolkit was used to estimate the Hg emissions from the potential Hg sources. The results of the Hg emissions estimated are presented and recommendations are made in terms of Hg research to be undertaken, as well as the setting up of the Mercury Monitoring System in the Western Cape Province.

TG3-P21 — 11:00-12:00 and 17:30-18:30
MERCURY VOLATILIZATION FROM A SALT MARSH: EXAMINING SOLAR RADIATION AND TIDAL EFFECTS
Authors: MCARTHUR, Gordon1, O’DRISCOLL, Nelson2, RISK, David3, DALZIEL, John 4
(1) St Francis Xavier University, gmcarthu@stfx.ca; (2) Acadia University; (3) St Francix Xavier University; (4) Environment Canada.

Hg fluxes from soils and sediments have been measured in coastal regions including tidal mudflats and salt marshes. In some studies hystereses have been observed but are not apparent when flux measurements are represented as cumulative mercury flux. Hystereses can be caused by lags between drivers and flux, volatilization efficiency differences at different times throughout the day as well as methodological problems. While we know what causes hysteresis we do not understand why the lags and efficiency differences occur. Although findings to date have observed hystereses, their causes have not been thoroughly investigated. Such investigation could provide insights to the mechanisms of mercury oxidation, reduction and potential methodological artifacts in flux measurements.

This poster will provide background information on the significance of Hg fluxes from the Bay of Fundy and a summary of our investigation into the relationship between a variety of meteorological variables and Hg flux from a salt marsh on the shores of the Minas Basin, NS. Furthermore, the intermediary effect that soil moisture levels have on the efficiency of solar radiation to volatilize Hg is examined.

The objective of this study was to measure in-situ volatilization fluxes of gaseous elemental mercury from a salt marsh over 9 days in July 2009 using a Teflon dynamic flux chamber. Fluxes ranged from -0.5 to 5 ng m-2 s-1, peak daily fluxes occurred very close to solar noon and at night dropped to ~ 0 ng m-2 s-1. During the study, the site underwent a drying out period, followed by one rain event followed by another warm dry period; this allowed us to identify differing efficiencies of solar radiation to volatilize Hg for the pre and post rain periods (1.98 x greater for the pre-rain period). The resulting hystereses for pre and post rain periods were visibly different. From examining the hystereses we found response times of Hg flux to solar radiation also differed pre (immediate response) and post rain (40 min lagged response) and there was a consistent difference between morning and afternoon Hg volatilization efficiencies. Air temperature and tide height were identified by GLS regression to be of secondary importance to Hg fluxes. Overall, our results indicate that moisture regulated photochemical reactions were of primary importance for explaining Hg fluxes in this salt marsh ecosystem.

TG3-P22 — 11:00-12:00 and 17:30-18:30
PALEORECORDS DOCUMENT RISING MERCURY CONTAMINATION IN LAKE TANGANYIKA
Authors: CONAWAY, Christopher H.1, SWARZENSKI, Peter W.1, COHEN, Andrew S.2
(1) US Geological Survey, kitconaway@hotmail.com; (2) University of Arizona.

Lake Tanganyika is the largest (32,600 km2), deepest (1470 m), and oldest (>12 Ma) of the East African Rift Lakes. Therefore, sediment that has accumulated at the lake bottom likely contains some long, high-resolution, records of change. Previous studies using sediment cores manage to correlate sed change with climatic regimes and changes in inputs across Africa where Lake Tanganyika is situated. Lake Tanganyika mercury deposition records were derived using 14C and excess 210Pb geochronometers in sediment cores collected from two contrasting depositional environments: the Kalya Platform, located mid-lake and removed from watershed impacts, and the Nyasanga/Kahama River delta region, which drains relatively perturbed watersheds. At the Kalya Platform , pre-industrial mercury concentrations are 23±0.2 ng/g, increasing to 74 ng/g in modern surface sediment. Similarly, the mercury accumulation rate increases from 1.0 to 7.2 µg/m2/yr from pre-industrial to modern times. At the Nyasanga/Kahama delta region, pre-industrial mercury concentrations are 20±3 ng/g ng/g, increasing to 45 ng/g in surface sediment, and mercury accumulation rate increases from 30 to 70 µg/m2/yr. Mercury accumulation rates at the Kalya Platform area suggest the importance of atmospheric inputs and geochemical processes affecting deposition, whereas the mercury accumulation pattern at Nyasanga/Kahama delta suggests the relative importance of terrigenous inputs to the observed record. Despite differences in mercury accumulation rates, both cores show an increase in mercury contamination consistent with the onset of large-scale systematic production of gold in the region at that time that began in the 1930s and continued until the 1970s. The results document an increase of mercury flux to the highly-productive Lake Tanganyika ecosystem that is consistent with mercury contamination from gold mining in the region, but also reflects local mercury controls that are both terrestrial and lacustrine.

TG3-P23 — 11:00-12:00 and 17:30-18:30
ATMOSPHERIC EMISSIONS OF MERCURY FROM RESIDENTIAL COAL COMBUSTION IN SHAANXI PROVINCE, CHINA
Author: LI, Zhonggen1
(1) Institute of Geochemistry, Chinese Academy of Sciences, zhonggenli@gmail.com

Behaviors of mercury (Hg) in the small-scale coal combustion process, like cooking and heating for the residential purpose, are poorly understood compared with that for large and medium scale coal combustion. In this study, Hg concentrations in several kinds of coal and their bottom ashes from a range of residential houses in Shaanxi province, northwest China, were determined by CV-AAS technique. Results showed Hg in the bituminous coal from northern Shaanxi and the neighbourhood province (Ningxia autonomous region) were low (range: 5.4-43.5 ng/g, mean 18.6±14.8 ng/g, N=9), while Hg were much higher in stone coal (range: 219-1175 ng/g, mean 682.3±478.7 ng/g, N=3), a low rank anthracite produced in southern Shaanxi, and honeycomb briquette (range: 118.5-1655 ng/g, mean 548.5±560.9 ng/g, N=6) that made from stone coal. Hg in bottom ash were the lowest, with means 1.8, 3.7 and 11.3 ng/g for bituminous coal, stone coal and honeycomb briquette, respectively. Emission factors of Hg were estimated based on the mass balance method, that 99.12-99.68% Hg in the fuel were lost into air during the combustion process, leading to about 0.5 tonne Hg released into the ambient air through the residential use in Shaanxi province each year, with primarily (87%) from the stone coal and its products. The estimated average Hg concentrations in the indoor air ranged 1.3-48.7 µg/m3 for three different kinds of fuel under the condition without chimney or ventilation, and the highest Hg concentration could even reach to 118.2 µg/m3 , these are much higher than the national standard for Hg in the atmosphere in the residential area (0.3 µg/m3, TJ36-79), or the workshop (10 µg/m3, TJ36-79). Since stone coal burning has resulted in endemic arsenic poisoning and fluorosis among the local residents in Southern Shaanxi, Hg poisoning arising from this kind of coal buring could not be excluded. Preventive measures, such as change the high Hg fuel to low ones, enhanced ventilation, etc, would be the cost-effective solutions to reduce the health risk. And more detailed studies are needed.

Wednesday, 31 December, 1969