Decrease In Mercury Concentration Research Articles

Exploring Drivers of Historic Mercury Trends in Beluga Whales Using an Ecosystem Modeling Approach.

While mercury occurs naturally in the environment, human activity has significantly disturbed its biogeochemical cycle. Inorganic mercury entering aquatic systems can be transformed into methylmercury, a strong neurotoxicant that builds up in organisms and affects ecosystem and public health. In the Arctic, top predators such as beluga whales, an ecologically and culturally significant species for many Inuit communities, can contain high concentrations of methylmercury. Historical mercury concentrations in beluga in the western Canadian Arctic's Beaufort Sea cannot be explained by mercury emission trends alone; in addition, they could potentially be driven by climate change impacts, such as rising temperatures and sea ice melt. These changes can affect mercury bioaccumulation through different pathways, including ecological and mercury transport processes. In this study, we explore key drivers of mercury bioaccumulation in the Beaufort Sea beluga population using Ecopath with Ecosim, an ecosystem modeling approach, and scenarios of environmental change informed by Western Science and Inuvialuit Knowledge. Comparing the effect of historical sea ice cover, sea surface temperature, and freshwater discharge time series, modeling suggests that the timing of historical increases and decreases in beluga methylmercury concentrations can be better explained by the resulting changes to ecosystem productivity rather than by those to mercury inputs and that all three environmental drivers could partially explain the decrease in mercury concentrations in beluga after the mid-1990s. This work highlights the value of multiple knowledge systems and exploratory modeling methods in understanding environmental change and contaminant cycling. Future work building on this research could inform climate change adaptation efforts and inform management decisions in the region.

Effect on reclamation on mercury concentration in groundwater: a case study of Lubo\u0144 Chemical Plant (Pozna\u0144, Poland)

Luboń Chemical Plant (Poland), founded in 1914, is the place where many products such as superphosphate, hydrofluoric acid, sulfuric acid, aluminum fluoride, potassium fluoroborate, vanadium catalyst and other chemicals and post-production waste have been produced and stored. The main products manufactured by Luboń Chemical Plant are powdered superphosphate (obtained from apatite) and sulfuric acid (obtained from pyrite) The aim of the study was to determine the impact of the former post-crystallization leachate disposal site located in the area of Luboń Chemical Plant on groundwater contamination with mercury. Groundwater samples were collected from 12 piezometers in the area of the plant or in close vicinity to the plant, and from one piezometer located 2.5 km north of the study area, i.e., from Poznań-Dębina groundwater intake, in the years 2007–2014. Total mercury concentration in groundwater from Luboń was high in all samples, and ranged from 10.9 to 2818 ng L− 1 (average 335 ± 509 ng L− 1, median = 158 ng L− 1). The highest mercury concentration values were measured in piezometer no. 7, located in close proximity to the production facilities of the chemical plant, and they equaled 2604 ng L− 1 in 2007 and 2818 ng L− 1 in 2008. The lowest concentration of mercury (10.9 ng L− 1) was determined in 2014, in a sample taken from piezometer no. 13 located at the water intake for the agglomeration of Poznań (Poznań-Dębina). Based on the obtained results, two sources of groundwater pollution were found: (1) Luboń Chemical Plant, and (2) former post-crystallization leachate disposal site. A decrease in mercury concentrations with increasing distance of piezometers from the pollution sources was reported. Moreover, a reduction in mercury concentration over the years has been observed, especially after completion of reclamation and remediation works in the area of Luboń Chemical Plant in 2008. Despite the negative impact of the plant on groundwater quality measured in the piezometer located at the water intake Poznań-Dębina, the drinking water quality guidelines (1000 ng L− 1) was not exceeded.

Four years (2011–2015) of total gaseous mercury measurements from the Cape Verde Atmospheric Observatory

Abstract. Mercury is a chemical with widespread anthropogenic emissions that is known to be highly toxic to humans, ecosystems and wildlife. Global anthropogenic emissions are around 20 % higher than natural emissions and the amount of mercury released into the atmosphere has increased since the industrial revolution. In 2005 the European Union and the United States adopted measures to reduce mercury use, in part to offset the impacts of increasing emissions in industrialising countries. The changing regional emissions of mercury have impacts on a range of spatial scales. Here we report 4 years (December 2011–December 2015) of total gaseous mercury (TGM) measurements at the Cape Verde Observatory (CVO), a global WMO-GAW station located in the subtropical remote marine boundary layer. Observed total gaseous mercury concentrations were between 1.03 and 1.33 ng m−3 (10th, 90th percentiles), close to expectations based on previous interhemispheric gradient measurements. We observe a decreasing trend in TGM (−0.05 ± 0.04 ng m−3 yr−1, −4.2 % ± 3.3 % yr−1) over the 4 years consistent with the reported decrease of mercury concentrations in North Atlantic surface waters and reductions in anthropogenic emissions. The decrease was more visible in the summer (July–September) than in the winter (December–February), when measurements were impacted by air from the African continent and Sahara/Sahel regions. African air masses were also associated with the highest and most variable TGM concentrations. We suggest that the less pronounced downward trend inclination in African air may be attributed to poorly controlled anthropogenic sources such as artisanal and small-scale gold mining (ASGM) in West Africa.

Mercury in Feathers and Blood of Gulls from the Southern Baltic Coast, Poland

Gulls were assessed as sentinels of contamination in the coastal zone of the Southern Baltic, research material being obtained from dead birds collected on Polish beaches and near fishing ports in 2009–2012. In feathers and blood of four gull species: herring gull (Larus argentatus), common gull (Larus canus), black-headed gull (Chroicocephalus ridibundus), and great black-backed gull (Larus marinus), concentration of total mercury (HgT) was assayed, taking into account the type of feathers, sex, and age. Stable isotopes (δ15N, δ13C) were used as tracers of trophic position in the food web. In the study, feathers and blood were compared as non-invasive indicators of alimentary exposure introducing mercury into the system. In order to do that, the correlations between mercury concentrations in the blood, feathers, and the birds’ internal tissues were examined. The strongest relations were observed in the liver for each species R2Common Gull = 0.94, p = 0.001; R2Black-headed Gull = 0.89, p = 0.001; R2Great Black-backed Gull = 0.53, p = 0.001; R2Herring Gull = 0.78, p = 0.001. While no correlation was found with feathers, only developing feathers of juvenile herring gulls were found to be a good indicator immediate of exposure through food (R2muscle = 0.71, p = 0.001; R2kidneys = 0.73, p = 0.001; R2heart = 0.89, p = 0.001; R2lungs = 0.86, p = 0.001; R2brain = 0.83, p = 0.001). Additionally, based on studies of herring gull primary feathers, decrease of mercury concentration in the diet of birds over the last two decades is also discussed.

Long-term (∼57 ka) controls on mercury accumulation in the Southern Hemisphere reconstructed using a peat record from Pinheiro mire (Minas Gerais, Brazil).

Natural archives have been used to reconstruct mercury atmospheric deposition at different spatial and temporal scales during the Holocene in the Northern Hemisphere. In this study, we present the results from a Brazilian mountain mire (Pinheiro mire, Minas Gerais, SE Brazil), extending back to ∼57 ka. The core was analyzed for mercury concentration, organic matter content, organic carbon isotopic composition, and tracers of mineral matter flux. Principal components analysis followed by principal components regression enabled us to determine the evolution of the weight of the latent processes governing the accumulation of mercury through time. We show that climate change was the main driver for the variations of mercury concentrations, either indirectly by (i) enhancing soil erosion in the mire's catchment, which led to a decrease in mercury concentration due to dilution by low mercury-containing mineral matter, (ii) increasing regional dust deposition, which resulted in increased concentrations, or directly, by long-term changes in atmospheric wet deposition (arid vs humid periods). Internal peat processes (i.e., decomposition and mass loss) had a minor influence at the time scale represented by the core.

Analysis and interpretation of 18 years of mercury observations since 1996 at Mace Head, Ireland

Observations of atmospheric mercury at the Mace Head Atmospheric Research Station on the Atlantic coast of Ireland made from February 1996 to December 2013 are analyzed. Using meteorological analysis and a sophisticated Lagrangian dispersion model, the hourly averaged mercury concentrations were attributed to four different air mass types: baseline, local, European polluted, and sub-tropical maritime. Monthly median Hg concentrations of all types decreased over the analyzed period but the trend for sub-tropical maritime air masses was with −0.016 ± 0.002 ng m−3 yr−1 in absolute terms significantly smaller than the trends for all other classes which varied between −0.021 and −0.023 ng m−3 yr−1. The seasonal variation for sub-tropical maritime air masses is also shallower than for all other classes. This is most likely due to shallower seasonal variation of oxidant concentrations at lower latitudes. The north-south gradient of the trend is qualitatively consistent with the GEOS-Chem model predictions based on decrease of mercury concentrations in surface waters of the North Atlantic but the trends are smaller than predicted. Tests for temporal change of the trends indicate that the decreasing trends of mercury concentrations are leveling off for all air masses with possible exception of the sub-tropical maritime air mass. Quantitative assessment of the trend changes, however, will require a longer time series of the mercury measurements at Mace Head.

Great tits breeding performance and mercury contamination from the paper and pulp industry in the west coast of Portugal

Passerine species have been increasingly used as monitors of metal pollution, especially by making use of non-destructive indicators of bird exposure, such as collecting feathers, faeces or blood. During this study, mercury concentrations were determined in feathers, faeces and blood of nestling great tits (Parus major) in industrial (a paper mill) and rural sites on the west coast of Portugal. The aim of this study was to compare the level of mercury in both areas over the study period, as indicated by nestlings’ mercury levels, while assessing possible contamination effects on the breeding performance and health status of great tits. Over the years, feathers showed a significant annual decrease in mercury contamination in the study area. Blood analyses also revealed a significant annual decrease in mercury concentrations, but no significant differences were detected between areas. Faeces data showed no significant difference between years or areas. We found no direct influence of mercury levels on nestling health status or great tit breeding performance.

Potential Use of Aspergillus Flavus Strain KRP1 in Utilization of Mercury Contaminant

Aspergillus flavus strain KRP1 isolated from tropical forest soil was examined for its potential use in degradation of mercury contaminant in soil. This fungal strain has shown its capability to grow best in 25ppm mercury which contaminated Potato Dextrose Agar (PDA) plate media compared with other strains. The preference pH for fungal growth was ranged from 5-7 and reached optimum on pH 6. The optimum temperature was found to be 27.5-35°C. The growth expression of fungi to the presence of mercury contaminant in media was by showing the inhibitory on growth diameter compared to non-contaminated media. The minimum inhibitory concentration (MIC) of this fungal strain to mercury was at 100ppm when there was no growth on the plate media while the growth on non-contaminated media reached maximum (5 day old). The fungal strain was also evaluated in vitro for the potential use in bioremediation of soil contaminated by mercury through observation of the growth profile and the mercury concentration in culture medium. The growth profiles of Aspergillus flavus strain KRP1 showed considerable growth in culture medium containing mercury. This result was supported by the decrease of mercury concentration which indicates a utilization process for mercury and might have mechanism for degradation. This indicates that this fungal strain has a potential use for areas where mercury contaminant is exist.

Mercury in Perch (Perca fluviatilis) from Sweden and Finland

High mercury concentrations in freshwater fish from the Nordic region have been of concern for a long time. Ongoing monitoring of key ecological species occurs in these countries to follow the situation. Here, we investigated spatial and temporal trends in mercury concentrations in European perch (Perca fluviatilis) within the Swedish and Finnish aquatic environments, collated from national monitoring programmes collected between 1974 and 2005 (n = 5,172). Data were length and weight adjusted to remove perch size as a confounding factor. Temporal trend analyses and t tests comparing pre- and post-1996 mercury concentrations for each country (1974–1995; 1996–2005; perch adjusted to 200 g/25 cm), showed a significant decrease in mercury concentration in perch from Sweden (p < 0.001) and a possible increase in mercury concentration in perch from Finland (p < 0.001). No statistically significant geographical trends were seen. Average mercury concentrations exceeded both the current environmental quality standard (EQS) of 20 ng/g wet weight (ww) and a discussed EQS for the Nordic region of 200–250 ng/g ww. Despite large reductions in mercury use and production in these countries, concentrations in perch continue to be higher here than in other European areas, posing a continued environmental risk.

Environmental geochemistry studies in the area of Idrija mercury mine, Slovenia

Five centuries of mining and processing of mercury ore in the Idrija area have resulted in widespread contamination of different environmental compartments. Environmental impacts on a regional and local scale, caused by atmospheric emissions from the Idrija ore roasting plant, were established in the investigations of mercury spatial distribution in soil and attic dust in 160 km(2) area. Very high values were determined in the Idrijca River valley, and they decrease exponentially with the distance from Idrija. Mercury concentrations in attic dust are higher than in surrounding soils and the attic dust/soil ratio changes with distance. Measurements of mercury in the air confirmed widespread dispersion of mercury and showed highly elevated mercury concentrations around roasting plant and mine ventilation shaft. Beside, systematic monitoring of mercury contents in the stream sediments has demonstrated that huge amounts of mercury are stored in areas where ancient overbank sediments were deposited, and there was no decrease in mercury concentration in active sediments during the last 15 years. Recently, interesting and extremely polluted locations of historical small-scale roasting sites in the Idrija surroundings were discovered. Ongoing geochemical study aims to determine the extreme pollution and significance of these sites for wider contamination of soils and aquatic systems. Presented studies have shown that Hg mining in Idrija caused intense pollution of local and regional environment including the aquatic systems in the Gulf of Trieste, which is seen as the final sink of a major part of the Hg stored in soils and river sediments in the Idrija area.

Wildfire induced changes in aquatic invertebrate communities and mercury bioaccumulation in the Okefenokee Swamp

Fire is an important natural disturbance in the Okefenokee Swamp. From April–June 2007, wildfire burned 75% of the wetland area. With the existence of extensive pre-fire data sets on community structure and total mercury of invertebrates, the fire presented an opportunity to assess impacts of wildfire on invertebrates. Post-fire collection of samples occurred in September, December, and May, 2007–2009. Sample sites included 13 burned and 8 non-burned (reference) sites. Comparisons of data among pre-fire, post-fire reference, and post-fire burned sites revealed that the major difference between pre-fire communities and post-fire communities was a decrease in the number of water mites. We also found a decrease in mercury concentrations in amphipods, odonates, and crayfish post-fire. The differences between pre-fire and post-fire samples may be confounded by drought conditions during the baseline study. NMDS ordinations and ANOSIM tests suggested that habitat was an important factor; communities in burned cypress differed from reference cypress. Unexpectedly, burned sites had lower mercury concentrations in odonates and crayfish, with variation again being greatest in cypress stands. These findings and others suggest mercury levels do not follow a predictable pattern but can vary with pre-fire concentrations, variation in water levels, and burn intensity. We found that wildfire in the Okefenokee had little impact on invertebrates in prairies and scrub-shrub thickets, but can affect indicator organisms (Oecetis, Ischnura, and Sigara) in cypress stands. Our study suggests that vegetation type and burn intensity may have impacts on the invertebrate communities and mercury concentrations of organisms.

A Simple Preconcentration-Storing Technique Based on Sulfide Precipitation for Multipoint Monitoring of Mercury in Rainwater and Snow by Cold Vapor Atomic Absorption Spectrometry

Abstract A preconcentration-storing technique that does not require any special or expensive apparatus and reagents was developed to monitor mercury in rainwater and snow at many points as simultaneously as possible. A commercially available sodium hypochlorite solution was added to the sample solution to prevent a decrease in mercury concentration after sampling. Mercury(II) ion (0.5–50 ng) in 500 mL of the sample solution was concentrated by adding zinc(II) ion and a small amount of sulfide ion and then coagulating/coprecipitating with Zn(OH)2 or ZnS after reduction of residual hypochlorite by addition of hydroxylammonium chloride. The supernatant solution was discarded by decantation, and the solution including the precipitates could be stored for at least 20 days without any loss of mercury. The recoveries of mercury(II) ion from the 500 mL of the sample solutions spiked with mercury(II) ions were 99–109%, with standard deviation ranges of 3–8%, although the recovery of methylmercury(II) ion was 68 ± 5%. Using this technique, the determination of mercury in rainwater and snow was demonstrated at Toyama Prefecture, Japan, from April 2004 to February 2005; mercury levels ranging from 2.7 to 33.7 ng L−1 were found.

Mercury levels and liver pathology in feral fish living in the vicinity of a mercury cell chlor-alkali factory

Twenty-three barbels ( Barbus graellsii), 30 bleaks ( Alburnus alburnus) and 4 sediment samples were collected from four areas of the Cinca River (NE Spain), upstream and downstream of a mercury cell chlor-alkali plant. Mercury concentration in sediments downstream of the plant was about 25 times higher than the concentration upstream. Mercury levels in the muscle and liver of barbels downstream of the chlor-alkali plant were 10 and 30 times higher than those upstream. The average mercury concentration in the muscle and liver of barbels downstream of the factory was 1.48 and 1.78 mg/kg w.w., with maximal concentrations of 2.43 and 3.64 mg/kg w.w, respectively. Liver/muscle ratio of mercury was significantly higher in barbels sampled downstream of the factory. Bleak showed a similar pattern, with a significantly higher whole-body mercury concentration downstream of the chlor-alkali plant. Nevertheless, a progressive decrease in mercury concentration downstream of the impact area was found in bleak, but not in barbel. Histopathological analysis showed that fish downstream of the factory had significantly higher prevalence of liver pathologies ( p < 0.05). Although there are no specific histopathological markers of mercury exposure, barbels with the highest Hg levels in the liver also showed the most severe pathologies, and the processes found in these barbels were consistent with the pro-oxidant effect of heavy metals.

Mercury in river sediments, floodplains and plants growing thereon in the drainage area of the Idrija mine, Slovenia

half a millennium of mercury production at Idrija is reflected in increased mercury contents in all of its environmental segments. Stream sediments have been monitored along the Idrijca and Soca rivers (70 km) every 5 years since 1991. It has been discovered that there was no decrease in mercury concentration in stream sediments during the last 15 years. upstream from the town of Idrija, mercury concentrations in active river sediments vary from 1 to 10 mg/kg dry weight (average 3.3 mg/kg). From Idrija to Spodnja Idrija mercury concentrations increase extremely and vary greatly. The average in this area amounts to 603 mg/kg with individual contents up to 4121 mg/kg. From Spodnja Idrija to the Idrijca-Soca confluence the average is 213 mg/kg, while the average in the Soca river sediments is 57 mg/kg. Floodplain soils and samples of averaged meadow forage and plantain (Plantago lanceolata) were collected on river terraces at two localities in the lower course of the Idrijca. It has been determined that floodplains along the Idrijca River are strongly enriched with mercury. The average concentration of hg in the upper 20 cm of the floodplain at IdB location is 157.7 and at TEm location it is 294.8 mg/kg. Samples of averaged meadow forage and plantain contain from 0.055 to 0.220 mg hg/kg. In comparison to the plant samples from Idrija in the 1970s, these contents are relatively low. however, regarding mercury contents in plants in non-polluted soils the contents on the Idrijca River terraces are considerably higher than the background.

Effect of point source removal on mercury bioaccumulation in an industrial pond.

A one hectare pond on the headwaters of a mercury-contaminated creek in Oak Ridge, Tennessee acted as a biochemical reactor for the production of methylmercury, increasing waterborne methylmercury concentrations in the stream below the pond discharge. The flow of the creek was diverted around the pond in order to eliminate this input. Waterborne total mercury, methylmercury, and mercury in fish, were monitored in the pond and stream before and after bypass. Waterborne methylmercury concentration in the creek downstream from the pond decreased over 800% following diversion of streamflow around the pond, but mercury in redbreast sunfish in the pond tailwater did not decline similarly. Within the pond, now isolated from fresh waterborne mercury inputs from the stream, methylmercury concentrations in the water column remained similar to levels present before bypass. However, mercury concentrations in sunfish in the pond decreased approximately 75% following bypass, despite the continued presence of highly contaminated sediments (approximately 50 mg Hg/kg dry weight). We concluded that a decrease in the fraction of 'dissolved methylmercury' in the isolated pond relative to pre-bypass conditions explained the decrease in mercury in fish within the pond. That observation also indicates that mercury associated with pond sediments was relatively unavailable for eventual bioaccumulation when compared to 'fresh' mercury contributed by upstream sources. The lack of a post-bypass decrease in mercury concentrations in tailwater fish was also likely to be associated with the particle-associated nature of waterborne methylmercury exported from the pond.

Lessons from Minamata mercury pollution, Japan - after a continuous 22 years of observation

One of the most visible tragedies by industrial water pollution is Minamata disease, methylmercury poisoning caused by eating contaminated fish, which has killed more than 100 people and paralyzed several thousand people around Minamata Bay, Japan and the adjacent Yatsushiro Sea since 1956. The cause of Minamata disease was confirmed, not by analyzing environmental samples such as sediments (containing more than 600 ppm of Hg) or fish (at least 20 ppm) at the bay, but by symptoms of Minamata disease patients that resembled previous mercury poisoning reported in a European medical journal. Mercury dispersion was traced for 22 years to collect mercury concentration measurements in Yatsushiro Sea surface sediments at 24 fixed stations. The analytical results of mercury revealed four trends of mercury movement from the bay: 1) a rapid increase in Hg concentrations up to 1984; 2) a dramatic decrease in mercury concentrations after an artificial mercury decontamination project began in 1984; 3) a strange drop in mercury contents due to an historical rainfall in the region in 1982 and; 4) natural decontamination, which has been underway since 1985. The tragedy at Minamata has provided many lessons which have shaped the scientific field in environmental research, especially in the area of water quality.

Lessons from Minamata mercury pollution, Japan — After a continuous 22 years of observation

One of the most visible tragedies by industrial water pollution is Minamata disease, methylmercury poisoning caused by eating contaminated fish, which has killed more than 100 people and paralyzed several thousand people around Minamata Bay, Japan and the adjacent Yatsushiro Sea since 1956. The cause of Minamata disease was confirmed, not by analyzing environmental samples such as sediments (containing more than 600 ppm of Hg) or fish (at least 20 ppm) at the bay, but by symptoms of Minamata disease patients that resembled previous mercury poisoning reported in a European medical journal. Mercury dispersion was traced for 22 years to collect mercury concentration measurements in Yatsushiro Sea surface sediments at 24 fixed stations. The analytical results of mercury revealed four trends of mercury movement from the bay: 1) a rapid increase in Hg concentrations up to 1984; 2) a dramatic decrease in mercury concentrations after an artificial mercury decontamination project began in 1984; 3) a strange drop in mercury contents due to an historical rainfall in the region in 1982 and; 4) natural decontamination, which has been underway since 1985. The tragedy at Minamata has provided many lessons which have shaped the scientific field in environmental research, especially in the area of water quality.

Methyl mercury in the dutch rhine delta

Samples of yellow eel from various locations in the Dutch Rhine area have been analyzed for trend monitoring of mercury since 1977. In the western Rhine delta mercury levels in eels have hardly changed since the seventies, whereas in the eastern part of the Dutch Rhine area a considerable decrease of mercury concentrations in eel has occurred. Because of continuous sedimentation of contaminated suspended matter transported from upstream regions, accumulation rates and concentrations of mercury in eel in the western Rhine delta remained at a relatively high level. Analyses of methyl mercury in biota have been performed to elucidate the role of methyl mercury in the mercury contamination of the Dutch Rhine ecosystem. Low percentages of methyl mercury were observed in zooplankton (3 to 35%). In benthic organisms (mussels) percentages of methyl mercury ranged from 30 to 57%, while in fish species and liver of aquatic top predator birds almost all the mercury was present in the form of methyl mercury (&amp;gt; 80%). During the period 1970-1990 mercury concentrations of suspended matter in the eastern Rhine delta have drastically decreased. These concentrations seemed to be highly correlated with mercury concentrations of eel (R = 0.84). The consequences of this relation are discussed.

Human milk as a source of methylmercury exposure in infants.

As methylmercury is excreted in human milk and infants are particularly susceptible to toxicity due to this compound, the purpose of this study was to evaluate the possible transfer of methylmercury to infants via breast-feeding. In a community with a high intake of seafood, 583 children from a birth cohort were followed. The duration of nursing was recorded, and hair samples were obtained for mercury analysis at approximately 12 months of age. The hair mercury concentrations increased with the length of the nursing period, and those nursed throughout the first year showed the highest geometric mean (9.0 nmol/g or 1.8 microg/g). Human milk therefore seems to be an important source of methylmercury exposure in infants. An increasing time interval from weaning to hair sample collection was not associated with any detectable decrease in mercury concentrations. A slow or absent elimination of methylmercury during the first year after birth could explain this finding. In certain fishing communities, infants nursed for long periods may be at increased risk of developing methylmercury toxicity.

Decrease in mercury concentration in blood after long term exposure: a kinetic study of chloralkali workers.

The elimination of mercury (Hg) in blood was investigated in 14 chloralkali workers exposed to metallic Hg vapour for 1-24 (median 10) years. Blood and urine samples were collected on several (median eight) occasions during a period of 17-26 days. The initial Hg concentrations were about 80 nmol/l in whole blood (B-Hg) and 17 nmol/mmol creatinine in urine (U-Hg). The decrease in Hg in whole blood, plasma (P) and erythrocytes (Ery) was best characterised by a two compartment model. In a model with a common half life for all subjects, the best fit for B-Hg was obtained with half lives of 3.8 days for a fast phase and 45 days for a slow phase. The half life of the fast phase was shorter for P-Hg than for Ery-Hg, whereas the opposite was the case for the slow phase. The half lives of the slow phases in whole blood and plasma were longer, and the relative fractions of the slow phases were higher (about 50%) after long term exposure than those (about 20%) reported after brief exposure. Slower elimination indicates higher accumulation of Hg in organs with long half lives, and possibly the presence of at least one additional, even slower compartment. The U-Hg fluctuated substantially during the sampling period, and average concentrations decreased only slightly.