Hg Deposition Rates Research Articles

Comparison of Hg concentrations in ombrotrophic peat and corresponding humic acids, and implications for the use of bogs as archives of atmospheric Hg deposition

An ombrotrophic peat core was collected from Etang de la Gruère (Swiss Jura Mountains) and divided into 3 cm slices ( n = 26). Humic acids (HA) were extracted and the yield of HA was employed as an index of humification. Mercury concentrations were measured in both the peat samples and the corresponding HA. The highest Hg concentrations were found in the top half of the peat core, corresponding to the least humified peats, indicating that the changing rates of atmospheric Hg deposition during the past decades, not the degree of humification, is the single most important factor determining the distribution of this trace element in peat cores. Up to 89% of the total Hg in the peat samples, with an average of ca. 66%, is found in the HA fraction, which explains why the distribution of Hg in peat and the corresponding HA is similar. Because of the physico-chemical and biological stability of HA with time, the preservation of most of the Hg in this fraction suggests that peat cores from ombrotrophic bogs may provide reliable records of the atmospheric Hg deposition. The correlation between Hg and Br in HA isolated from these same peat samples suggests that the two elements may behave similarly during humification.

Experimental Evidence of a Linear Relationship between Inorganic Mercury Loading and Methylmercury Accumulation by Aquatic Biota

Developing effective regulations on mercury (Hg) emissions requires a better understanding of how atmospheric Hg deposition affects methylmercury (MeHg) levels in aquatic biota. This study tested the hypothesis that MeHg accumulation in aquatic food webs is related to atmospheric Hg deposition. We simulated a range of inorganic Hg deposition rates by adding isotopically enriched Hg(II) (90.9% 202Hg) to 10-m diameter mesocosms in a boreal lake. Concentrations of experimentally added ("spike") Hg were monitored in zooplankton, benthic invertebrates, and fish. Some Hg(II) added to the mesocosms was methylated and incorporated into the food web within weeks, demonstrating that Hg(II) deposited directly to aquatic ecosystems can become quickly available to biota. Relationships between Hg(II) loading rates and spike MeHg concentrations in zooplankton, benthic invertebrates, and fish were linear and significant. Furthermore, spike MeHg concentrations in the food web were directly proportional to Hg(II) loading rates (i.e., a percent change in Hg(II) loading rate resulted in, statistically, the same percent change in MeHg concentration). This is the first experimental determination of the relationship between Hg(II) loading and MeHg bioaccumulation in aquatic biota. We conclude that changes in atmospheric Hg deposition caused by increases or decreases in Hg emissions will ultimately affect MeHg levels in aquatic food webs.

Effects of Environmental Methylmercury on the Health of Wild Birds, Mammals, and Fish

Wild piscivorous fish, mammals, and birds may be at risk for elevated dietary methylmercury intake and toxicity. In controlled feeding studies, the consumption of diets that contained Hg (as methylmercury) at environmentally realistic concentrations resulted in a range of toxic effects in fish, birds, and mammals, including behavioral, neurochemical, hormonal, and reproductive changes. Limited field-based studies, especially with certain wild piscivorous bird species, e.g., the common loon, corroborated laboratory-based results, demonstrating significant relations between methylmercury exposure and various indicators of methylmercury toxicity, including reproductive impairment. Potential population effects in fish and wildlife resulting from dietary methylmercury exposure are expected to vary as a function of species life history, as well as regional differences in fish-Hg concentrations, which, in turn, are influenced by differences in Hg deposition and environmental methylation rates. However, population modeling suggests that reductions in Hg emissions could have substantial benefits for some common loon populations that are currently experiencing elevated methylmercury exposure. Predicted benefits would be mediated primarily through improved hatching success and development of hatchlings to maturity as Hg concentrations in prey fish decline. Other piscivorous species may also benefit from decreased Hg exposure but have not been as extensively studied as the common loon.

Diversity of Epiphytic Lichens and Hg Contents of Xanthoria parietina Thalli as Monitors of Geothermal Air Pollution in the Mt. Amiata Area (Central Italy)

The diversity of epiphytic lichens and mercury concentrations in lichen samples were measured to monitor the release of airborne pollutants from the industrial exploitation of geothermal resources in the Mt. Amiata area (Italy). The lichen biodiversity showed a general condition of moderate environmental alteration around the geothermal power plants, contrasting with the low environmental alteration of the remaining sites investigated. According to the accumulated Hg in lichen thalli, it was possible to estimate mean Hg and H2S concentrations in the air, which resulted in very good agreement with values measured instrumentally. Based on these data and the correlation between lichen diversity values and Hg concentrations in lichens, it was possible to calculate the threshold of 8 μg/m3 H2S as responsible for the worsening from low to moderate environmental alteration according to the biodiversity of epiphytic lichens, and to infer that around geothermal power plants, although not toxic to humans, H2S concentrations are such to alter the nasal quality of the air. Based on the growth rate of X. parietina, it was possible to convert Hg concentrations into estimates of average Hg deposition rates, which showed fluxes of the order of 65–100 mg/ha/y, indicating a dispersions factor of about 104 for the Hg emitted from the geothermal power plants.

Changes in lead and mercury atmospheric deposition due to industrial emissions in Southeastern Brazil

Este estudo apresenta uma primeira estimativa de emissoes de Pb e Hg para a Regiao Sudeste do Brasil, a regiao mais industrializada da America do Sul, durante o seculo XX, baseada na analise de perfis de sedimentos datados, coletados em lago ombrotrofico da Serra do Itatiaia, na regiao do vale do Rio Paraiba do Sul, Estado do Rio de Janeiro. As concentracoes medias de Pb ao longo dos perfis variaram de 40 a 180 µg g-1, enquanto que para Hg as concentracoes variaram de 30 a 420 ng g-1. As concentracoes de Hg se correlacionaram significativamente com as de Pb ate os anos 80. A taxa de acumulacao de Pb no periodo pre-industrial foi de cerca de 8,0 ± 2,0 mg m-2 ano-1, com um maximo observado na superficie dos perfis variando de 40 a 80 mg m-2 ano-1. Por outro lado, a taxa de acumulacao de Hg foi de 36 ± 4 µg m-2 ano-1, entre 1910 e 1940, apresentando um maximo nos anos 60 de cerca de 120 µg m-2 ano-1, e decrescendo novamente apos os anos 70 para 20 µg m-2 ano-1. O padrao de distribuicao temporal da acumulacao de Hg e similar aqueles relatados para diferentes regioes do hemisferio norte. Entretanto, as taxas de acumulacao pre-industrial de Pb e Hg sao de 3 a 6 vezes maiores que os valores relatados para o periodo pre-industrial no hemisferio norte. Emissoes originadas na industrializacao mais antiga no hemisferio norte podem ter influenciado a magnitude da acumulacao pre-industrial na regiao em estudo, que se iniciou pelo menos 100 anos depois. No caso do Hg, a mineracao de ouro e prata nos tres seculos anteriores, pode tambem ter influenciado as taxas de acumulacao pre-industrial estimadas neste estudo.

Comparison of mercury in atmospheric deposition and in Illinois and USA soils

Abstract. It has been reported that most mercury (Hg) in USA soils is from atmospheric Hg deposition, mostly from anthropogenic sources. This paper compares the rates of atmospheric Hg deposition to amounts of Hg in Illinois and USA soils. The amounts of Hg in these soils are too great to be attributed mainly to anthropogenic atmospheric Hg deposition. Keywords: mercury, atmospheric deposition, soil, geology, Illinois, USA

500 years of mercury production: global annual inventory by region until 2000 and associated emissions

Since pre-industrial times, anthropogenic emissions of Hg have at least doubled global atmospheric Hg deposition rates. In order to minimize environmental and human health effects, efforts have been made to reduce Hg emissions from industries and power plants, while less attention has been paid to Hg mining. This paper is a compilation of available data on primary Hg production and associated emissions with regional and annual resolution since colonial times. Globally, approximately one million tons of metallic Hg has been extracted from cinnabar and other ores during the past five centuries, half already before 1925. Roughly half has been used for mining of gold and silver, but the annual Hg production peaked during a short period of recent industrial uses. Comparison with total historic Hg deposition from global anthropogenic emissions (0.1–0.2 Mtons) suggests that only a few percent of all mined Hg have escaped to the atmosphere thus far. While production of primary Hg has changed dramatically over time and among mines, the global production has always been dominant in the region of the mercuriferous belt between the western Mediterranean and central Asia, but appears to be shifting to the east. Roughly half of the registered Hg has been extracted in Europe, where Spanish mines alone have contributed one third of the world's mined Hg. Approximately one fourth has been mined in the Americas, and most of the remaining registered Hg in Asia. However, the Asian figures may be largely underestimated. Presently, the dominant Hg mines are in Almadén in Spain (236 t of Hg produced in 2000), Khaydarkan in Kyrgyzstan (550 t), Algeria (estimated 240 t) and China (ca. 200 t). Mercury by-production from mining of other metals (e.g. copper, zinc, gold, silver) in 2000 includes 48 t from Peru, 45 t from Finland and at least 15 t from the USA. Since 1970, the recorded production of primary Hg has been reduced by almost an order of magnitude to approximately 2000 t in the year 2000. Mining is thus still of similar magnitude as all current anthropogenic Hg emissions to the atmosphere, and mined Hg may account for more than one third of these emissions. Also before use, mercury is emitted from Hg mines locally during the mining and refining processes and from mining waste. Global direct emissions to the atmosphere amount to 10–30 t per year currently (up to 10 at Almadén alone), and probably exceed 10 000 t historically. Termination of Hg mining will reduce associated local emissions to the atmosphere and biosphere. Since several economically viable Hg-free alternatives exist for practically all applications of Hg, the production and use of Hg can be further reduced and all primary production of Hg other than by-production terminated.

Effect of peat decomposition and mass loss on historic mercury records in peat bogs from patagonia.

Ombrotrophic peat bogs have been widely used to evaluate long-term records of atmospheric mercury (Hg) deposition. One of the major aims of these investigations is the estimation of the increase in atmospheric Hg fluxes during the industrial age compared to preindustrial fluxes. Comparability of Hg accumulation rates calculated from density, peat accumulation rates, and Hg concentrations requires linearity between these parameters. Peat formation is a dynamic process accompanied by intense mass loss and alteration of the organic material. Our investigations on three peat cores from the Magellanic Moorlands, Chile, indicate that Hg concentrations in peat strongly depend on peat humification. Moreover, differences in mass accumulation rates during peat evolution are not compensated by linear changes in density, peat accumulation, or Hg concentrations. We suggest that Hg accumulation rates be normalized to carbon accumulation rates to achieve comparability of Hg accumulation rates derived from differently altered peat sections. Normalization to the carbon accumulation rates reduces Hg accumulation rates in less degraded peat sections in the upper peat layers by factors of more than 2. Our results suggest that the increase in Hg deposition rates during modern times derived from ombrotrophic peat bogs are potentially overestimated if Hg accumulation rates are not corrected for mass accumulation rates.

Distributions of mercury and phosphorous in everglades soils from water conservation area 3A, Florida, U.S.A.

Soils in the southern half of Water Conservation Area3A are mostly peats with some organic-rich marls. Mercury contents of 64 surface samples over a500 km2 area average 28.7 ng cc-1 (209 ppb drysediment), which is typical of organic-rich soils. High Hg contents in Everglades fish are therefore notcaused by anomalously high soil Hg. Hg contents showno systematic lateral variation, consistent withdeposition from well-mixed atmospheric sources ratherthan nearby point sources or runoff from canals.Cores from 9 sites contain more Hg and P at or nearthe surface than at 20–30 cm depth. Hg and P contentsof individual cores correlate well and define separatebackground and anomalous populations. The subsurfacedistribution of P is determined largely by uptake bysawgrass and other plants. The correlation between Pand Hg suggests that, although atmospheric Hgdeposition has undoubtedly increased in recentdecades, postdepositional mobilization of Hg may beimportant in Everglades soils. This finding, togetherwith recent direct measurements of atmospheric Hgdeposition, indicates that previous estimates of Hgdeposition rates based on Everglades peat cores, whichassumed that Hg is immobile in peat after deposition,have yielded large overestimates.

Mercury and major ions in rainfall, throughfall, and foliage from the Florida Everglades

The deposition of Hg to the Everglades has been investigated using monthly integrated bulk and wet-only tower based precipitation samples, tower based aerosol Hg samples, and ground based throughfall samples. A small set of foliage samples was collected and analyzed for `reactive' and total Hg. There are large differences in the major ion chemistry of the wet and throughfall samples. Dry deposition of seasalt aerosols (Na and Cl) and foliar leaching of Ca and K contribute significantly to the throughfall fluxes. The concentrations and fluxes of total Hg in bulk deposition, wet deposition, and throughfall are not significantly different. These data demonstrate that dry deposited Hg is not `washed off' of, or leached from foliage by rainfall. Results from the chemical reactivity experiments suggest that the leaves accumulate Hg as they mature. The calculated litterfall Hg fluxes are similar to the measured rates of rainfall Hg deposition.

Mercury accumulation in Devils Lake, North Dakota — Effects of environmental variation in closed-basin lakes on mercury chrologies

Sediment cores were collected from lakes in the Devils Lake Basin in North Dakota to determine if mercury (Hg) accumulation chronologies from sediment-core data are good indicators of variations in Hg accumulation rates in saline lakes. Sediment cores from Creel Bay and Main Bay, Devils Lake were selected for detailed analysis and interpretation. The maximum Hg concentration in the Creel Bay core was 0.15 micrograms per gram at 8 to 9 centimeters. The maximum Hg concentration in the Main Bay core was 0.07 micrograms per gram at 5 to 7 centimeters. The general decreases in Hg concentrations with depth are attributed to historic variations in atmospheric Hg deposition rate. Hg stratigraphies combined with210 Pb and 137Cs dating analyses yield Hg chronologies that indicate a general increase in Hg accumulation rates in Devils Lake since the middle of the 19th century.

Total Mercury and Methylmercury Contents of Insects from Boreal Lakes: Ecological, Spatial and Temporal Patterns

Abstract Mercury (Hg) and methylmercury (MeHg) concentrations in insects from 19 lakes in Quebec (Canada) and Sweden ranged from 550 ng Hgg−1 dry weight (dw). The mean proportion of MeHg to total Hg concentrations depended on the feeding behaviour of the animals, increasing from 35-50% in detritivores-grazers (dipterans, ephemeropterans, trichopterans) to 70–95% in predators (heteropterans, coleopterans, odonates). These differences were attributed to the biomagnification of MeHg in the food web since the MeHg/total Hg ratio in the organisms was not related to their body size. A large part of the overall variability of total Hg (r2=0.57, p=0.0001) and MeHg (r2=0.79, p=0.0001) concentrations in insects was explained by taxonomic differences, probably related to feeding behaviour, and the differences between lakes. MeHg concentrations in chironomids and in odonates were significantly correlated with sediment MeHg contents (r=0.78, p=0.005; r=0.62, p=0.001, respectively). However, our results suggest that animal feeding behaviour and the quality of ingested food are more important in determining MeHg accumulation in insects than either MeHg contents of sediment or atmospheric Hg deposition rates. Our data indicate that the bioavailability of Hg to the lower trophic levels of the food web is determined by abiotic factors and controls contamination of predators at the top of the food chain. Total Hg concentrations in insects increased from spring to fall, from 60–80 ng Hgg−1 dw to 125–175 ng Hgg−1 dw in the detritivore-grazer taxa, and from 88–120 ng Hgg−1 dw to 180–200 ng Hgg−1 dw in the predator taxa. MeHg/total Hg ratios showed little variability from spring to fall and the increase of Hg and MeHg concentrations in insects seemed to be related to enhanced methylation resulting from the rise of water temperature and to the variations in the nature of the food ingested.

Anthropogenic influences on the global mercury cycle: A model-based analysis

A model of the global Hg cycle is presented and applied to analyze modern Hg budgets and historical changes in deposition. Our modeling suggests that mixing into the ocean interior is a significant sink of Hg and likely has limited any anthropogenically-caused increase in surface ocean Hg concentrations to about 50% above natural levels rather than 200% as has recently been argued. Additionally, both the increase in air pollutants during the industrial era and their recent decrease in North America likely have affected atmospheric Hg scavenging and the resulting records of Hg deposition rates in lake and bog sediments.

Historical deposition rates of mercury in scandinavia estimated by dating and measurement of mercury in cores of peat bogs

Historical deposition rates of Hg were determined in 7 ombrotrophic bogs located far from direct sources in Sweden and Norway. The peat bog cores were dated using 210Pb. Based on the dating result 10 to 12 slices from each core were analyzed for Hg. In Southwestern Scandinavia (Rorvik) the deposition rate has increased from about 10 to about 30 μg Hg m−2 yr−1 since the beginning of this century. In Northwestern Norway (Overbygd) the deposition rate has increased from about 10 to about 35 μg Hg m−2 yr−1 since the 1960's. In Southeast Sweden (Aspvreten) the deposition rate decreased since the beginning of this century. There are no significant trends in the historical deposition rates at the two other stations in middle Scandinavia. A comparison between recent Hg deposition rates measured by peat bog analysis, wet precipitation and mosses shows good agreement at all stations except those in Northern Norway were local dry deposition of Hg may be an important source of Hg.