The contribution of sulfate to rainfall pH around Kilauea Volcano,Hawaii

Between December 1986 and June 1987, the mean pH of rainfall downwind of the Kilauea main vent was found to be 4.5 (range 4.0 to 5.6), 1.2 units higher than the year before (1985-86), although 84% of the 12 sequential samples fell below pH 5.0. The SO₄ content, however, was 34% higher, averaging 18.5 mg L^?1. Upwind, in open forest the mean pH 4.7 was little changed from that measured before. Mean SO₄, however, has fallen to a low of 2.5 mg L^?1, but, more significantly, in 9 out of 12 sequential samples S04 was not detectable at all (i.e. < 0.5 mg L^?1). The calculated pH, assuming 100% H₂SO₄ would be 5.3 yet 58% of these samples fell below pH 5.0, the lowest being 4.0. Disparities between pH measured and calculated on the basis of SO₄ content indicated that other acid species were present in the precipitation. Oxidation of rain samples with H₂O₂ greatly increased SO₄ content and lowered pH downwind, but failed in most samples to alter either parameter in the upwind collections. These observations, together with the elimination of HCl and N03 by others, suggested that SO₂ contributes significantly to acidity downwind, but that in most upwind samples a source of H⁺ other than mineral acids, presumably organic compounds, must be of major importance.     

Lidar measurements of atmospheric mercury

Mercury is the only atmospheric pollutant that is present in the atmosphere in atomic form. The optical resonance line at 254 nm can be used for absorption measurements using different optical remote sensing techniques. Range-resolved Hg mapping can be performed using the differential absorption lidar (DIAL) technique. We have used the lidar technique both for mapping of industrial plumes and for background concentration measurements. Our studies also include Hg of geophysical origin.     

Reduction of mercury pollution in the vicinity of a caustic soda plant in Thailand

Fish samples collected near the caustic soda factory of TACSCO in Thailand during November and December 1978 were found to contain 0.10 to 1.38 ppm Hg in flesh (on wet weight basis), whereas those of the control areas contained 0.01 to 0.30 ppm. The Hg content of the fish in the TACSCO area had decreased by more than half from the first investigation which took place during 1975–76. This decrease is obviously a result of the functioning of the waste-water-treatment system built by the factory in 1974. The bottom mud collected near the factory in 1978 contained 8.39 to 57.95 ppm Hg (on dry weight basis) as compared with the mean of 0.03 ppm in samples taken from the control area. The Hg content in fish-eating birds were low, 0.04 to 0.44 ppm in the muscles and 0.05 to 1.32 ppm in the livers (on wet weight basis).     

An update of the mercury inventory and atmospheric mercury fluxes to and from Finland

Finland, the northern-most agricultural/industrial country in the world, has been for some time steadily improving environmental mercury (Hg) research. This paper focuses upon Hg recovery during zinc production, uses of Hg, updating of information on Hg emissions and atmospheric transport of Hg to and from Finland. The recovery of Hg as a by-product of zinc production began in 1970. The highest amount of recovered Hg was noted to be 160 t in 1989. Total uses of Hg in different sectors were about 7.4 t in 1992, which had decreased by 50% since the year 1987. In 1992, the estimated Hg emission to air was 2 t yr^?1, whereas to water and land the emission was about 0.20 and 3.67 t yr^?1, respectively. Natural Hg emission in Finland was estimated to be about 0.4 t yr^?1 (range: 0.3 to 0.5 t yr^?1). In addition, an initial attempt was made to estimate the atmospheric Hg flux to and from Finland; these values were noted to be 2.7 and 2.1 t yr^?1, respectively.     

Occurrence and turnover of atmospheric mercury over the nordic countries

A seasonal variation of both particle and gaseous Hg concentrations in the atmosphere is present in south-western Sweden. An average gaseous Hg level of 3.7 ng m^?3 is found in winter, compared to 2.8 ng m^?3 in summer. A weak decreasing south-north gradient for gaseous Hg in air over the Nordic countries is also present, with yearly average values from 3.2 to 2.8 ng m^?3. A gradient for particulate Hg is less clear. An air parcel trajectory sector classification of gaseous Hg levels in air, and to some extent the particulate associated Hg, clearly demonstrates the increased concentrations in the southern sectors, especially in south-western Sweden where the gaseous Hg increase is about I ng m^?3. These observations are consistent with an influence from the European continent. The average concentrations of Hg in precipitation at the various stations show a pronounced decreasing south-north gradient. A major portion of the total Hg present in precipitation is associated with particles. For the southern stations, a strong correlation between Hg and sulfate, or pH, is present suggesting a connection between Hg in precipitation and anthropogenic activities.     

International field intercomparison of atmospheric mercury measurement methods

To determine the extent of comparability of sampling and analytical procedures for atmospheric mercury (Hg) being used by different scientific groups around the world and hence the compatibility of measurement results, the Atmospheric Environment Service (AES) co-ordinated a field intercomparison study in Windsor, Ontario, over a period of 5 days- during Sept./Oct.,1993. This study brought together 2 groups (University of Michigan Air Quality Laboratory; Chemistry Institute of GKSS) which performed conventional (manual) sample collection procedures for total gaseous mercury (TGM) and for particulate-phase mercury (PPM), followed by cold-vapor atomic fluorescence spectrophotometric (CVAFS) analysis in the respective laboratories. Two other groups (Ontario Hydro, and the Ontario Ministry of Environment & Energy) each operated a novel mercury vapor analyzer produced by Tekran Inc. of Toronto. As is the case for the manual methods, this analyzer also uses gold amalgamation and CVAFS. During the intercomparison, meteorological parameters (air temperature, barometric pressure, wind speed/direction and relative humidity) were obtained at the study site.     

An intensive multi-site pilot study investigating atmospheric mercury in Broward County,Florida

An intensive multi-site pilot study of atmospheric Hg was conducted in Broward County, Florida in August and September of 1993. Broward County, which contains the city of Fort Lauderdale, is located in southeastern Florida. The county borders the Florida Everglades on the west and the Atlantic Ocean on the east. A network of four sampling sites was set up for 20 days throughout Broward County to measure Hg in both the vapor phase and the particle phase as well as Hg in precipitation. The mean concentrations of total vapor phase Hg measured at two inland sites were found to be significantly higher (3.3 and 2.8 ng/m³) than that measured at a site located on the Atlantic shore (1.8 ng/m³). The mean concentrations of particle phase Hg collected at the two inland sites (51 and 49 pg/m³) were found to be 50% greater than that measured at the coastal site (34 pg/m³). In addition, event precipitation samples were collected at four sampling sites over the 20 day study period and were analyzed for both reactive and total Hg. The mean concentration of total Hg in the precipitation samples was found to be 44 ng/L, with a range of 14 to 130 ng/L. It was determined that further meteorological analysis and a more complete characterization of the aerosol and precipitation composition are needed to identify the probable source(s) contributing to the increased deposition of Hg.     

Is mercury increasing in the atmosphere? The need for an atmospheric mercury network (AMNET)

Mercury uses in human endeavors will lead to a general, though variable, volatilization of Hg. Current estimates for anthropogenic interferences range from about 50 to 75% of the total annual Hg emissions to the atmosphere. Recent modeling suggests that the present atmospheric Hg burden has increased by a factor of 3 during the last 100 years with a current rate of increase of about 0.6% yr^?1 (ca. 0.01ng m^?3yr^?1). This impact, which is significant, can be examined and assessed empirically. To date, however, atmospheric Hg programs have not employed an experimental design sufficient to account for short time scale atmospheric Hg variations of natural and anthropogenic origin, and to resolve the long term temporal pattern. I am proposing an international research program, AMNET, or Atmospheric Hg Network, to address the important question, “Is Hg increasing in the atmosphere?” AMNET would examine temporal and spatial variations in atmospheric Hg and assess the influence of natural and anthropogenic sources on the global atmospheric Hg cycle. This program requires international support and cooperation. The experimental design of AMNET would follow the successful Atmospheric Lifetime Experiment Program (ALE), which examined the contemporary temporal changes in the atmospheric concentrations of the freons, methyl chloroform, carbon tetrachloride, and nitrous oxide. Following the ALE design, AMNET sampling stations would be maintained in both hemispheres and at sites free from strong local pollution sources of Hg (e.g., remote islands). Measurements would be made for a period of three to five years. The precision and accuracy of the Hg⁰ determinations must be ≥ 1%. The accurate resolution of the variability and secular trends in the atmospheric Hg burden can provide: (1) a direct quantitative assessment of the scale to which anthropogenic processes are affecting the natural biogeochemical cycling of Hg; (2) an essential refinement and constraint currently lacking in mass balance models; (3) an enhanced knowledge of the behavior of Hg in the atmosphere, and (4) an accurate data base required for global circulation atmospheric chemical Hg models.     

Multielement analysis and mercury speciation in atmospheric samples from the Toronto area

Inductively coupled plasma atomic emission spectrometry. (ICP-AES), graphite furnace atomic absorption (GFAAS) and gas chromatography with an atomic absorption detector (GC-AAS) were used for the analysis of atmospheric samples collected in the Toronto area of Southern Ontario. Airborne particulate matter and particulate and soluble fractions of snow were analyzed for S, Al, Fe, Ca, Mg, P, Pb, Zn, Cu, Cr, Cd, Ni, As, and Hg. Also, determinations of organic Hg compounds in filtered snow were performed. The element concentrations in airborne particulate matter from Toronto were similar in amount to those found in other major cities and were the highest in winter. Regional differences in the chemical composition of snow were shown to be related to industrial density. The majority of elements existed in the highest concentrations in the soluble fraction of snow, except for Al, Fe, and Pb, which were largely present in particulate matter. Differences in the distribution of elements in particulate matter in fresh and old snow were observed and depended on particle size and element. The results demonstrated the usefulness of snow as an indicator of atmospheric pollution.     

Long-term changes in concentration and deposition of atmospheric mercury over Scandinavia

Samples for measurements of total gaseous mercury (Hg) in air have been collected since 1980 in south-western part of Scandinavia. A collection program for precipitation samples used to determine changes in depositional fluxes of total Hg has been in operation since 1987. A comparison of today's total gaseous Hg levels in air and the total Hg concentrations in precipitation with the ones found earlier, shows a clear decrease with time. At the Swedish west-coast, yearly average air concentrations and median levels of 3.3 and 3.1 (1980–1984), 3.2 and 2.8 (1985–1989), and 2.7 and 2.6 ng Hg/m³ (1990–1992), respectively, were found. Increased average and median winter concentrations were always found, with levels at 3.7 and 3.4, 3.7 and 3.3, and 3.0 and 2.7 ng Hg/m³ for the respective time period. Higher winter values were expected due to increased anthropogenic emissions and changes in the mixing height of the atmosphere. The corresponding total wet deposition rates decreased from 27 (1987–1989) to 10 μg Hg/m² yr. (1990–1992). A finding of special interest was the decreased number of episodic events of high total gaseous Hg levels in air, from 1990 and further on. In addition, the frequency distribution of the concentrations of Hg in air seems to be different for these years compared to the other two time periods. A frequency distribution of air concentrations of Hg more resembling a normal distribution was found for the years 1990 to 1992. The decrease of the atmospheric burden of total gaseous Hg and deposition of total Hg are most probably connected to lower emissions in source areas on the European continent. It seems logical to state that the problem of high Hg depositional fluxes to Scandinavia, is best solved by abatement strategies on the regional scale.     

Cycling of methyl mercury and mercury — Responses in the forest roof catchment to three years of decreased atmospheric deposition

Studies of the biogeochemistry of total mercury (Hg) and methyl mercury (MeHg) in the Lake Gårdsjön watershed have shown that the atmosphere is the most important source of Hg and MeHg in the ecosystem. Soils are accumulating most of the deposited Hg and MeHg, but transport of Hg and MeHg from the forested catchments into the lake ecosystems is enough to explain elevated concentrations of MeHg in fish in more than 10 000 Swedish lakes. An experimental roof was constructed to study effects of decreased atmospheric input on an entire forested catchment. The experiment started in April 1991, and decreases in the output of both MeHg and Hg occurred during 1991, 1992 and 1993. Runoff fluxes from the control catchment during the pre-treatment period were related to the experimental catchment using regression analyses. Since April 1991, after three year experiment, predicted compared to measured fluxes showed that Hg output decreased by 32% and MeHg by 28%. The decrease in Hg was most obvious during high water flows in winter/spring while MeHg decreased during all seasons of the year. The decreased input of Hg and MeHg to the Forest Roof Catchment is the most probable explanation to the rapid decrease in output of Hg and MeHg by runoff from the catchment basin.     

Linkages between atmospheric mercury deposition and the methylmercury content of marine fish

Enhanced Hg deposition to productive marine systems may result in concurrent increases in monomethyl Hg (MMHg) concentrations of marine fish. Consequently, it is important to understand what effects an increasing Hg supply may have on the marine food chain. A simple ocean model is employed to estimate the fraction of total Hg inputs which is required to sustain “average” marine fish MMHg concentrations annually. Calculations show that upwelling zones require 20% of total annual Hg inputs, coastal zones 5%, and open-ocean regions only 0.02%. The value for coastal areas is similar to that calculated for the acidified basin of Little Rock Lake, Wisconsin, a small fresh water seepage lake. These calculations point to Hg source strength and rates of particle scavenging as being key factors in controlling the rate of transport to sites of methylation (and subsequent entry into the marine food chain). If biological variables (scavenging rates, primary productivity) remain constant while anthropogenically-derived Hg deposition increases, it is likely that concentrations in marine biota (including fish) will rise in accord.     

Relationships between the atmospheric deposition of trace elements,major ions,and mercury in florida: The FAMS project (1992–1993)

A multiple chemical tracer approach was used in an effort to account for the atmospheric Hg deposition measured throughout Florida as part of the Florida Atmospheric Mercury (FAMS) Study. Samples of bulk deposition and wet-only deposition were analyzed for a suite of major ions and trace elements in addition to Hg. Significant correlations were found between three groups of elements: Al, Mn, and Fe; Ni, Cu, Zn, and Cd; and As, V, and Pb. However, Hg did not correlate strongly with any of the other chemical tracers. Annual bulk deposition fluxes are attributed to sea-salt aerosols (Na, Cl), the delivery of Saharan dust (Al and Fe), the supply of anthropogenic pollutant aerosols (V, Ni, Cu, Zn, As, Cd, Pb), acidic aerosols (nitrate and nss-sulfate), and an unidentified source for Hg.     

Pre-industrial atmospheric deposition of mercury: Uncertain rates from lake sediment and peat cores

Lacustrine sediment cores from depositional areas have frequently been used to estimate pre-industrial rates of atmospheric Hg deposition. However, this approach tends to result in overestimates, partly because of Hg inputs from the catchment, partly because of a horizontal redistribution of sediments within lakes. Peat core studies may suffer from a vertical migration of Hg due to water table fluctuations. A natural Hg deposition rate around 2 μg m^?2 y^?1 is suggested to be more realistic than values of 3 to 12 μg m^?2 y^?1 reported from recent studies. The anthropogenic impact on the present Hg deposition may have been underestimated accordingly.     

Using Epiphytic Macrolichen Communities for Biomonitoring Ammonia in Forests of the Greater Sierra Nevada, California

Chronic, excessive nitrogen deposition is potentially an important ecological threat to forests of the greater Sierra Nevada in California. We developed a model for ammonia bioindication, a major nitrogen pollutant in the region, using epiphytic macrolichens. We used non-metric multidimensional scaling to extract gradients in lichen community composition from surveys at 115 forested sites. A strong ammonia deposition gradient was detected, as evidenced by a high linear correlation with an index of ammonia indicator species conventionally known as “nitrophytes” (r = 0.93). This gradient, however, was confounded by elevation (r = ?0.54). We evaluated three statistical techniques for controlling the influence of elevation on nitrophytes: simple linear regression, nonlinear regression, and nonparametric regression. We used the unstandardized residuals from nonlinear regression to estimate relative ammonia deposition at each plot, primarily because this model had the best fit (r ² = 0.33), desirable asymptotic properties, and it is easy to apply to new data. Other possible sources of noise in the nitrophyte-ammonia relationship, such as substrate pH and acidic deposition, are discussed. Lichen communities indicated relatively high deposition to forests of the southern Sierra Nevada, the Modoc Plateau, as well as in stands near urban areas. Evidence of elevated ammonia was also detected for popular recreation areas such as Sequoia and Yosemite National Parks. Lichen communities from forests in the Tahoe basin, northern Sierra Nevada, southern Cascades, and eastern Klamath Range appeared considerably less impacted. This model will be used for continual assessment of eutrophication risks to forest health in the region.     

Atmospheric mercury concentrations above mercury contaminated mill tailings in the Carson River Drainage Basin,NV

During processing of the historic Comstock Ore, Virginia City, NV, an estimated 5.5 × 10⁹ g of metallic mercury (Hg) were released into the Carson River Drainage Basin. The Bessels Mill site is one of at least 75 locations where Hg was used to amalgamate the gold and silver from the ore. Although the mill is no longer standing, Hg contaminated tailings attest to its past location. Mercury concentrations in samples of tailings from the Bessels Mill site are as high as 1570 μg/g. Mercury concentrations vary spatially over the site. Total Hg concentrations in air measured directly over the site are well above regional background levels (1 to 7.1 ng/m³). The highest average atmospheric Hg concentration measured at the site was 240 ng/m³ for October 1993. The estimated range of Hg flux to the atmosphere from the site was 37 to 500 ng/m² hr. Atmospheric Hg concentrations varied seasonally, diurnally and spatially. Atmospheric Hg concentrations varied as a function of Hg concentration, soil and air temperature, wind speed and surface morphology.     

Modeling the elemental mercury cycle in Pallette Lake,Wisconsin, USA

The spatial and temporal distribution of elemental Hg (Hg°) and reactive Hg (Hg_R) has been studied on Pallette Lake, Wisconsin during May – August, 1993 and May, 1994. In general, Hg° concentrations near the lake surface greatly exceeded saturation with respect to atmospheric Hg° indicating a flux out (?) of the lake. Evasional losses were estimated using a thin film model and averaged ?101 pmol m^?2 d^?1 during July and August, 1993. A large portion of atmospherically deposited Hg is re-emitted. Thus, in-lake Hg° production' and evasion to the atmosphere will significantly reduce the amount of Hg which is transported to the sediments, the principal site of methylation. Laboratory experiments were conducted to ascertain the rate of Hg° formation from Hg(II). Reduction was significantly lower in heat sterilized lakewater suggesting Hg° production was biologically mediated. The temporal distribution of epilimnetic Hg°, as measured at the lake center, was influenced by Hg° evasion, Hg° production and advective transport of water parcels of differing Hg content. Spatial gradients in Hg° and Hg_R were identified and a transport model was employed to estimate the advective flux of Hg°. The importance of atmospheric deposition and sediment-water interaction as sources of Hg_R to epilimnetic waters were examined. Porewater concentrations of Hg° and Hg_R were determined on several occasions. During May, 1994, the depletion of lakewater Hg_R following a input pulse due to rain was observed and the estimated removal rate (16–20% d^?1) agrees well with reduction rates obtained in the laboratory (23% d^?1).     

Human exposure to mercury due to goldmining in the Tapajos River basin,Amazon, Brazil: Speciation of mercury in human hair,blood and urine

To obtain the basic information on human exposure to mercury (Hg) due to gold mining activities in Amazon, total mercury (T-Hg) and methylmercury (MeI Ig) were determined for human hair, blood and/or urine samples collected from populations living in gold mining area and fishing villages upstream of the Tapajos River basin. Abnormally high levels of T-Hg were observed in hair and blood from all fishing villages investigated and more than 90% of T-Hg was in the form of MeHg in both samples, whereas in goldrnining area the value were much lower and the %MeHg values varied widely (20–100%) with individuals even in blood samples. Urine from gold shop workers contained Hg mostly in inorganic form at 165μg/g creatinine on the average, with the range of 20 to 450μg/g creatinine. A good correlation between Hg in hair and blood was found in fishing villages and the ratios of hair Hg to blood Hg were very close to 250, generally established for MeHg. T-Hg and inorganic Hg levels in urine from gold shop workers were also significantly correlated with inorganic Hg in blood.     

Sources of mercury in the Arctic

Global and regional emission inventories of mercury are reviewed with special emphasis on the source regions with potential impact on the Arctic environment. These sources are located mostly in Eurasia and North America and emit almost 1300 t of Hg to the air annually. Combustion of fossil fuels to produce electricity and heat is the major source of Hg. Major portion of the element emissions from this source is in a gaseous phase. A small portion of Hg emissions in Eurasia and North America is deposited in the Arctic region, perhaps 60 to 80 t annually. Additional amounts of Hg in the Arctic air originate from natural sources, although it is very difficult to quantify them. A small decrease of anthropogenic Hg emissions is observed in Europe at present. These emissions are expected to increase again in the near future.