Cadmium and lead contamination of soils near plastic stabilizing materials producing plants in Northern Taiwan

Atmospheric mobilization and exchange at the air-water interface are significant features of biogeochemical cycling of Hg at the Earth's surface. Our marine studies of Hg have been extended to terrestrial aquatic systems, where we are investigating the tropospheric cycling, deposition and air-water exchange of Hg in the mid-continental lacustrine environs of northcentral Wisconsin. This program is part of a multidisciplinary examination into the processes regulating the aquatic biogeochemistry of Hg in temperate regions. Trace-metal-free methodologies are employed to determine Hg and alkylated Hg species at the picomolar level in air, water and precipitation. We have found Hg concentrations and atmospheric fluxes in these fresh water systems to be similar to open ocean regions of the Northern Hemisphere. A well constrained mass balance for Hg has been developed for one of the lakes, Little Rock Lake, which is an extensively studied clear water seepage lake that has been divided with a sea curtain into two basins, one of which is untreated (reference pH: 6.1) while the other is being experimentally acidified (current pH: 4.7). This budget shows that the measured total atmospheric Hg deposition (ca. 10 μg m⁻² yr⁻¹) readily accounts for the total mass of Hg in fish, water and accumulating in the sediments of Little Rock Lake. This analysis demonstrates the importance of atmospheric Hg depositional fluxes to the geochemical cycling and bioaccumulation of Hg in temperate lakes. It further suggests that modest increases in atmospheric Hg loading could lead directly to enhanced levels of Hg in biota. Analogous modeling for monomethylmercury (MMHg) is as yet limited. Nevertheless, preliminary data for the atmospheric deposition of MMHg indicate that this flux is insufficient. to account for the amounts of MMHg observed in biota. An in-lake synthesis of MMHg is implicated. The importance of volatile Hg which is principally in the elemental form, and its evasion to the atmosphere is also illustrated. We suggest that the in-lake production of Hg° can reduce the Hg (II) substrate used in the in-lake microbiological synthesis of MMHg.     

Bioaccumulation of mercury and methylmercury

The factors controlling the accumulation of mercury in fish are poorly understood. The oft invoked lipid solubility of MMHg is an inadequate explanation because inorganic Hg complexes, which are not bioaccumulated, are as lipid soluble as their MMHg analogs and, unlike other hydrophobic compounds, MMHg in fish resides in protein rather than fat tissue. We show that passive uptake of the lipophilic complexes (primarily HgCl₂ and CH₃HgCl) results in high concentrations of both inorganic and MMHg in phytoplankton. However, differences in partitioning within phytoplankton cells between inorganic mercury — which is principally membrane bound — and MMHg — which accumulates in the cytoplasm — lead to a greater assimilation of MMHg during Zooplankton grazing. Most of the discrimination between inorganic and MMHg thus occurs during trophic transfer while the major enrichment factor is between water and phytoplankton. As a result, MMHg concentrations in fish are ultimately determined by water chemistry which controls MMHg speciation and uptake at the base of the food chain.     

Biogeochemical Cycle of Mercury and Methylmercury in Two Highly Contaminated Areas of Tagus Estuary (Portugal)

Mercury (Hg) dynamics was evaluated in contaminated sediments and overlying waters from Tagus estuary, in two sites with different Hg anthropogenic sources: Cala Norte (CNOR) and Barreiro (BRR). Environmental factors affecting methylmercury (MMHg) production and Hg and MMHg fluxes across sediment/water interface were reported. [THg] and [MMHg] in solids (0.31–125 μg g^?1 and 0.76–201 ng g^?1, respectively) showed high variability with higher values in BRR. Porewater [MMHg] (0.1–63 ng L^?1, 0.5–86% of THg) varied local and seasonally; higher contents were observed in the summer campaign, thus increasing sediment toxicity affecting the sediment/water Hg (and MMHg) fluxes. In CNOR and BRR sediments, Hg availability and organic carbon were the main factors controlling MMHg production. Noteworthy, an upward MMHg diffusive flux was observed in winter that was inverted in summer. Although MMHg production increases in warmer month, the MMHg concentrations in overlying water increase in a higher proportion compared to the levels in porewaters. This opposite trend could be explained by different extension of MMHg demethylation in the water column. The high concentrations of Hg and MMHg and their dynamics in sediments are of major concern since they can cause an exportation of Hg from the contaminated areas up to ca. 14,600 mg year^?1 and an MMHg deposition of up to ca. 6000 mg year^?1. The results suggest that sediments from contaminated areas of Tagus estuary should be considered as a primary source of Hg for the water column and a sink of MMHg to the sedimentary column.     

Mercury speciation in open ocean waters

Vital to our understanding of the biogeochemical cycling of Hg and the origin of the enhanced monomethylmercury (MMHg) concentrations in biota is knowledge of the sources, behavior and fate of methylated Hg species in natural waters. Methylated Hg species, dissolved gaseous and reactive mercury were measured in the equatorial Pacific Ocean in early 1990. Both dimethylmercury (DMHg) and MMHg were found in the subthermocline waters of the equatorial Pacific Ocean. Maxima in alkylmercury species in the O₂ minimum region coincided with a decrease in reactive mercury. A significant inverse correlation between DMHg, and MMHg, concentration and O₂ content was observed. A maximum in reactive mercury was observed in the region of the thermocline, with similar concentrations in the surface and deeper waters. Atmospheric deposition is not a significant source of MMHg to this region. The data suggest formation of alkylmercury species in the low oxygen zone, with Hg(II) being the most likely substrate. A model for the cycling of Hg species in the equatorial Pacific Ocean is presented. These results are the first direct evidence of a significant open ocean source of methylated Hg species and suggest a pathway for mercury accumulation in pelagic fish.     

Distribution of Mercury and Monomethylmercury in Sediments of Vigo Ria, NW Iberian Peninsula

Fifty four samples of surface sediments (1-cm of thickness) and a gravity core of 154-cm long were collected in the Vigo Ria, NW of Iberian Peninsula. In the laboratory the sediments were oven dried at 40°C, desegregated, homogenised and analyzed for total Hg, monomethylmercury (MMHg), Al, and particulate organic carbon (POC). Mercury in sediments varied within a broad range: 0.09 to 8.9 nmol g^?1 the higher concentrations being found in the shipyards and docks areas of Vigo port (southern–middle Ria zone). No correlation was found between Hg and POC. The good exponential correlation between total Hg and Al levels suggests that Hg is closely associated with the fine fraction of sediments. Monomethylmercury concentrations in surface sediments ranged between <1.4 (DL) and 8.5 pmol g^?1 being the spatial distribution similar to that observed for total Hg. The lack of correlations MMHg–Al and MMHg–POC suggests that in situ processes of methylation/demethylation are responsible for MMHg distribution rather than the sediment characteristics. Additionally, these processes appear mercury-dependent only for Hg concentrations above 2.5 nmol g^?1. On the basis of these results it was estimated that 155 kg of Hg (0.1% MMHg) are present in the surface sediments of Vigo Ria, being 61% of anthropogenic origin.     

Speciation and Concentrations of Mercury in Certain Coastal Marine Sediments

Concentrations of total mercury (Hg), methyl Hg and Hg(II) were determined in coastal marine sediments collected from the Baltic, South China and the Bering Seas. Methyl Hg concentrations in sediments were between 0.01 and 2 ng g-¹ on a dry weight basis, accounting for only <1% of the total Hg concentrations. The percentage of Hg(II) (i.e. available Hg) in total Hg was between 5 and 13 suggesting that most of the Hg in sediments was bound as HgS and/or Hg-humic complexes. Relatively larger proportion of methyl Hg was found in less polluted freshwater sediments than in marine sediments. Methyl Hg concentrations in marine sediments were not found to be correlated with total Hg and/or Hg (II) concentrations.     

The role of dissolved organic carbon in the chemistry and bioavailability of mercury in remote Adirondack lakes

A number of recent studies have documented elevated concentrations of mercury (Hg) in fish caught in remote lakes and a pattern of increased concentrations of Hg in fish tissue with decreasing water column pH. Because of the potential linkage between fish Hg and surface water acidification, factors regulating water column concentrations and bioavailability of Hg were investigated in Adirondack lakes through a field study and application of the Mercury Cycling Model (MCM). Concentrations of total Hg and total MeHg were highly variable, with concentrations of total MeHg about 10% of total Hg in lakes which did not show anoxic conditions. In lakes exhibiting anoxic conditions in the hypolimnion during summer stratification, concentrations of total MeHg were elevated. Concentrations of total Hg and total MeHg increased with decreasing pH in remote Adirondack lakes. However, more importantly, concentrations of total Hg and total MeHg increased with increasing concentrations of dissolved organic carbon (DOC) and percent near-shore wetlands in the drainage basin. Mercury concentrations in muscle tissue of yellow perch from Adirondack lakes were elevated above the U.S. FDA action level (1 μg/g Hg) in 7% of the fish sampled or in one or more individual fish from 9 of the 16 lakes sampled. Fish Hg concentrations generally increased with increasing fish length, weight and age. Patterns of increasing Hg concentration with age likely reflect shifts in prey of yellow perch and the bioconcentration of Hg along the food chain. For age 3 to 5 perch, concentrations of Hg increased with increasing concentrations of DOC and percent near-shore wetlands in the drainage basin. However, for a lake with very high DOC concentrations, fish concentrations of Hg declined. Calculations with the MCM also show that concentrations of Hg species increase with increasing DOC due to complexation reactions. Increases in DOC result in increasing concentrations of Hg in biota but decreases in the bioconcentration factor of Hg in fish tissue. This research suggests that DOC is important in the transport of Hg to lake systems. High concentrations of DOC may complex MeHg, diminishing its bioavailability. At high concentrations of monomeric Al, the complexation of MeHg with DOC apparently decreases, enhancing the bioavailability of MeHg.     

Application of the Regional Mercury Cycling Model (RMCM) to Predict the Fate and Remediation of Mercury in Onondaga Lake,New York

Onondaga Lake exhibits elevated concentrations of total mercury (HgT) and methyl-mercury (MeHg) in the water column, sediments and fish tissue due to industrial inputs, wastewater discharge and urban runoff. The steady-state Regional Mercury Cycling Model (RMCM) was calibrated to Onondaga Lake and applied to evaluate various remediation scenarios. Because of detailed data available for Onondaga Lake, the RMCM was effectively calibrated. Model predictions of water column and fish concentrations of Hg generally agreed with measured values. The model underestimated concentrations of Hg in sediments. Mass balance calculations show that inputs of HgT largely originate from tributary and wastewater inflows to the lake. In contrast, MeHg is largely derived from internal production. Model calculations suggest that elimination of Hg inputs from wastewater effluent and of drainage from a former chlor-alkali facility could greatly decrease Hg concentrations in fish tissue.     

Mercury in vegetation and lake sediments from the U. S. arctic

Global atmospheric concentrations of mercury (Hg) appear to be increasing and with it the potential for ecosystem exposure and ecological effects. From 1990 to 1993 we examined U. S. arctic ecosystems over a broad spatial scale to develop baseline information on current concentrations of trace elements, heavy metals (including Hg), persistent organic compounds, and radionuclides in various components of the terrestrial and freshwater biosphere. Matrices reported here include, vegetation (lichens and mosses) and lake sediments. Total Hg in two lichen and two moss species from Alaska were generally low (0.02–0.112 μg/g dw), compared to reported values from other arctic locations and showed a statistically significant negative relationship between total Hg content and distance from the marine coastline.²¹⁰Pb dated sediment cores indicated that average preindustrial total Hg accumulation rates were over four times greater in arctic Schrader lake than in subarctic Wonder Lake. Both lakes indicated a small increase (5–8%) in total Hg flux to the sediments during the last 145 years, much smaller than similar increases in total mercury for lakes in the north central U. S. The likely source of recent increases in Hg in these Alaskan ecosystems is long range atmospheric transport. While we can detect increases in mercury in lake sediments likely due to anthropogenic activities, values are low and there appears to be no immediate threat to terrestrial environments and inland freshwaters of arctic Alaska from long range atmospheric transport and deposition of Hg.     

Atmospheric mercury in northern Wisconsin: Sources and species

The atmospheric chemistry, deposition and transport of mercury (Hg) in the Upper Great Lakes region is being investigated at a near-remote sampling location in northern Wisconsin. Intensive sampling over two years and various seasons has been completed. A multi-phase collection strategy (gas-, particle- and precipitation-phases) was employed to gain insight into the processes controlling concentrations and chemical/physical speciation of atmospheric Hg. Additional chemical and physical atmospheric determinations (e.g. ozone, particulate constituents, meteorology) were also made during these periods to aid in the interpretation of the Hg determinations. For example, correlations of Hg with ozone, sulfur dioxide and synopticscale meteorological features suggest a regionally discernible signal in Hg. Comparison to isosigma backward air parcel trajectories confirms this regionality and implicates the areas south, southeast and northwest of the site to be sources for Hg. Particle-phase Hg (Hg_p) was found to be approximately 40% in an oxidized form, or operationally defined as “reactive”. However, this was quite variable from year-to-year. Hg_p and other particle constituents (esp. sulfate) show significant correlation and similarity in behavior (concentration ratios in precipitation and in particles). These observations are part of the growing evidence to support the hypothesis that precipitation-phase Hg arises in large part from the scavenging of atmospheric particulates bearing Hg. Observed concentrations of rain and particle-Hg fit broadly the theoretical expectations for nucleation and below-cloud scavenging. Significant increases in the Hg/aerosol mass ratio appear to take place during transport. Enrichment of aerosols is taken as evidence of gas/particle conversion which could represent the step linking gas-phase Hg with rain. The refined budget indicates ca. 24% of total deposition is from summer particle dry deposition, and that this deposition also contributes ca. 24% of all reactive Hg deposition. Additionally, almost all (86%) deposition (wet and dry) occurs during the summer months.     

Environmental biogeochemistry of mercury in Antarctic ecosystems

Polar regions are recognized as important sinks for long-range transport and deposition of Hg derived from natural and anthropogenic sources at lower latitudes. In previous studies we found enhanced Hg accumulation in soils, mosses and lichens from ice-free areas of Victoria Land facing the Terra Nova Bay coastal polynya. This study extends research to the distribution of organic C, total N, S, Hg, Al and Fe in surface soils, cyanobacterial mats and short sediment cores from four lacustrine ecosystems, each with different environmental characteristics and varying distances from the polynya. Results show that planktonic and benthic mats from lakes, along with mosses in the watershed, are the main sinks for Hg in summer meltwater. The C-normalized Hg concentrations in short sediment cores were higher in samples from lakes more exposed to marine aerosols from the coastal polynya. Reactive halogens in the aerosol promote the oxidation and deposition of atmospheric Hg in coastal ecosystems. The analysis of sediment cores did not reveal increasing Hg concentrations in recent sediments, except in the Lake 14 at Edmonson Point. The latter ice-free area is unaffected by the polynya and the increase in Hg concentrations in surface sediments could be due to local changes in lake water level and S biogeochemistry. Although change in sea ice coverage may enhance the role of Antarctic coastal ecosystems as sink in the global Hg cycle, our results seem to exclude possible risks for Antarctic terrestrial and freshwater organisms.     

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.     

An assessment of adult risks of paresthesia due to mercury from coal combustion

This paper presents a probabilistic assessment of the risks of transient adult paresthesia (tingling of the extremities) resulting from ingestion of methylmercury (MeHg) in fish and shellfish. Two scenarios are evaluated: the “baseline,” in which the MeHg dose results from the combined effects of eating canned tuna fish, various marine seafoods, and freshwater sportfish, and an “impact” scenario in which the Hg content of the freshwater sportfish is increased due to local deposition from a hypothetical 1000 MW_e coal-fired power plant. Measurements from the literature are used to establish the parameters of the baseline, including atmospheric rates of Hg deposition and the distributions of MeHg in fish. The Hg intake for the impact scenario is then based on linear scaling of the additional annual Hg deposition as estimated from a Gaussian plume dispersion model. Human health responses are based on a logistic fit to the frequencies of paresthesia observed during a grain poisoning incident in Iraq, 1971–2. Based on a background prevalence rate of 2.2% for adult paresthesia, the assessment predicts a 5% chance that the increase in paresthesia prevalence due to either baseline or incremental MeHg doses might approach about 1% of the background prevalence rate.     

The distribution of dissolved and particulate mercury in three Siberian estuaries and adjacent Arctic coastal waters

Dissolved and particulate mercury distributions were determined in the three largest Siberian rivers and in adjacent Arctic coastal waters during two cruises. Water samples were collected in the Lena River and its mixing zone in the Laptev Sea in September 1991, and in the Ob and Yenisei Rivers and the adjacent Kara Sea in September 1993. Average total dissolved Hg concentration was 5.0 pM in the Lena River, 2.8 pM in the Ob River and 1.5 pM in the Yenisei River. Mercury content of suspended particulate matter was low, averaging 0.17 mg kg^?1 in the Lena and 0.05 mg kg^?1 in the Ob and Yenisei Rivers. These concentrations are lower than those observed in other world rivers affected by local input of man-made origin. In the estuarine mixing zones, higher concentrations of dissolved and particulate Hg which may originate from the spring flood were found. The carbon cycle is apparently a driving mechanism for Hg distribution in Arctic coastal waters. Particulate Hg content was positively correlated with the content of organic matter of the particles. In the Kara Sea, uptake by phytoplankton is suspected to be responsible for the increase in particulate Hg levels. Mercury fluxes from the three rivers to the Arctic Shelf are estimated and compared to direct atmospheric inputs.     

Nutrient Removal from Simulated Wastewater Using Canna indica and Schoenoplectus validus in Mono- and Mixed-Culture in Wetland Microcosms

In order to understand the bioaccumulation of mercury in fish in the Iranian coastal waters of the Caspian Sea and the Persian Gulf, different fish species were sampled from both regions in January 2002. Mullet fishes were sampled from the Caspian Sea and six other species from the Persian Gulf: Largetooth flounder, Spotfin flathead, Japanese threadfin bream, Greater lizardfish, Elongate sole and Giant seacatfish. In the Persian Gulf, total Hg concentrations in fish ranged from 0.0123 to 0.0867 mg kg^?1 w.w. (0.0614 to 0.433 mg kg^?1 d.w.). Methylmercury accounts for 64–100% of the total mercury. Highest mercury concentrations were observed in the predatory fish: Giant seacatfish, Threadfin bream and the larger Greater lizardfish caught near Mogham Port. In these species the methylmercury fraction is always higher than 90%. A low methylmercury fraction was only observed in the smallest specimen of flounder and Elongate sole. In the Caspian Sea Hg concentrations in Mullet ranged from 0.0102 to 0.108 mg kg^?1 w.w. The observed concentrations are comparable to those found in other areas of the Persian Gulf as well as in other marine environments and are much lower then the WHO guideline of 0.5 mg kg^?1 w.w.     

Mercury in the Swedish environment — Recent research on causes,consequences and corrective methods

During the last decade a new pattern of Hg pollution has been discerned, mostly in Scandinavia and North America. Fish from low productive lakes, even in remote areas, have been found to have a high Hg content. This pollution problem cannot be connected to single Hg discharges but is due to more widespread air pollution and long-range transport of pollutants. A large number of waters are affected and the problem is of a regional character. The national limits for Hg in fish are exceeded in a large number of lakes. In Sweden alone, it has been estimated that the total number of lakes exceeding the blacklisting limit of 1 mg Hg kg-1 in 1-kg pike is about 10 000. The content of Hg in fish has markedly increased in a large part of Sweden, exceeding the estimate background level by about a factor of 2 to 6. Only in the northernmost part of the country is the content in fish close to natural values. There is, however, a large variation of Hg content in fish within the same region, which is basically due to natural conditions such as the geological and hydrological properties of the drainage area. Higher concentrations in fish are mostly found in smaller lakes and in waters with a higher content of humic matter. Since only a small percentage of the total flow of Hg through a lake basin is transferred into the biological system, the bioavailability and the accumulation pattern of Hg in the food web is of importance for the Hg concentrations in top predators like pike. Especially, the transfer of Hg to low trophic levels seems to be a very important factor in determining the concentration in the food web. The fluxes of biomass through the fish community appear to be dominated by fluxes in the pelagic food web. The Hg in the lake water is therefore probably more important as a secondary source of Hg in pike than is the sediment via the benthic food chain. Different remedy actions to reduce Hg in fish have been tested. Improvements have been obtained by measures designed to reduce the transport of Hg to the lakes from the catchment area, eg. wetland liming and drainage area liming, to reduce the Hg flow via the pelagic nutrient chains, eg. intensive fishing, and to reduce the biologically available proportion of the total lake dose of Hg, eg. lake liming with different types of lime and additions of selenium. The length of time necessary before the remedy gives result is a central question, due to the long half-time of Hg in pike. In general it has been possible to reduce the Hg content in perch by 20 to 30% two years after treatments like lake liming, wetland liming, drainage area liming and intensive fishing. Selenium treatment is also effective, but before this method can be recommended, dosing problems and questions concerning the effects of selenium on other species must be evaluated. Regardless how essential these kind of remedial measures may be in a short-term perspective, the only satisfactory long-term alternative is to minimize the Hg contamination in air, soil and water. Internationally, the major sources of Hg emissions to the atmosphere are chlor-alkali factories, waste incineration plants, coal and peat combustion units and metal smelter industries. In the combustion processes without flue gas cleaning systems, probably about 20 to 60% of the Hg is emitted in divalent forms. In Sweden, large amounts of Hg were emitted to the atmosphere during the 50s and 60s, mainly from chlor-alkali plants and from metal production. In those years, the discharges from point sources were about 20 to 30 t yr 1. Since the end of the 60s, the emission of Hg has been reduced dramatically due to better emission control legislation, improved technology, and reduction of polluting industrial production. At present, the annual emissions of Hg to air are about 3.5 t from point sources in Sweden. In air, more than 95% of Hg is present as the elemental Hg form, HgO⁰. The remaining non-elemental (oxidized) form is partly associated to particles with a high wash-out ratio, and therefore more easily deposited to soils and surface waters by precipitation. The total Hg concentration in air is normally in the range 1 to 4 ng m-3. In oceanic regions in the southern hemisphere, the concentration is generally about 1 ng m^?3, while the corresponding figure for the northern hemisphere is about 2 ng m-3. In remote continental regions, the concentrations are mainly about 2 to 4 ng m^?3. In precipitation, Hg concentrations are generally found in the range 1 to 100 ng L^?1. In the Nordic countries, yearly mean values in rural areas are about 20 to 40 ng L^?1 in the southern and central parts, and about 10 ng L^?1 in the northern part. Accordingly, wet deposition is about 20 (10 to 35) g km^?2 yr^?1 in southern Scandinavia and 5 (2 to 7) in the northern part. Calculations of Hg deposition based on forest moss mapping techniques give similar values. The general pattern of atmospheric deposition of Hg with decreasing values from the southwest part of the country towards the north, strongly suggests that the deposition over Sweden is dominated by sources in other European countries. This conclusion is supported by analyses of air parcel back trajectories and findings of significant covariations between Hg and other long range transported pollutants in the precipitation. Apart from the long range transport of anthropogenic Hg, the deposition over Sweden may also be affected by an oxidation of elemental Hg in the atmosphere. Atmospheric Hg deposited on podzolic soils, the most common type of forest soil in Sweden, is effectively bound in the humus-rich upper parts of the forest soil. In the Tiveden area in southern Sweden, about 75 to 80% of the yearly deposition is retained in the humus layer, chemically bound to S or Se atoms in the humic structure. The amount of Hg found in the B horizon of the soils is probably only slightly influenced by anthropogenic emissions. In the deeper layers of the soil, hardly any accumulation of Hg takes place. The dominating horizontal flow in the soils takes place in the uppermost soil layers (0 to 20 cm) during periods of high precipitation and high groun water level in the soils. The yearly transport of Hg within the soils has been calculated to be about 5 to 6 g km^?2. The specific transport of total Hg from the soil system to running waters and lakes in Sweden is about 1 to 6 g km^?2 yr¹. The transport of Hg is closely related to the transport of humic matter in the water. The main factors influencing the Hg content and the transport of Hg in run-off waters from soils are therefore the Hg content in soils, the transport of humic matter from the soils and the humus content of the water. Other factors, for example acidification of soils and waters, are of secondary importance. Large peatlands and major lake basins in the catchment area reduce the out-transport of Hg from such areas. About 25 to 75% of the total load of Hg of lakes in southern and central Sweden originates from run-off from the catchment area. In lakes where the total load is high, the transport from run-off is the dominating pathway. The total Hg concentrations in soil solution are usually in the range 1 to 50, in ground water 0.5 to 15 and in run-off and lake water 2 to 12 ng L^?1, respectively. The variation is largely due to differences in the humus content of the waters. In deep ground water with a low content of humic substances, the Hg concentration is usually below 1 ng L^?1. The present amount and concentrations of Hg in the mor layer of forest soils are affected by the total anthropogenic emissions of Hg to the atmosphere, mainly during this century. Especially in the southern part of Sweden and in the central part along the Bothnian coast, the concentrations in the mor layer are markedly high. In southern areas the anthropogenic part of the total Hg content is about 70 to 90%. Here, the increased content in these soils is mainly caused by long-range transport and emissions from other European countries, while high level areas in the central parts are markedly affected by local historical emissions, mainly from the chlor-alkali industry. When comparing the input/output fluxes to watersheds it is evident that the present atmospheric deposition is much higher than the output via run-off waters, on average about 3 to 10 times higher, with the highest ration in the southern parts of Sweden. Obviously, Hg is accumulating in forest soils in Sweden at the present atmospheric deposition rate and, accordingly, the concentrations in forest soils are still increasing despite the fact that the emissions of Hg have drastically been reduced in Sweden during the last decades. The increased content of Hg in forest soils may have an effect on the organisms and the biological processes in the soils. Hg is by far the most toxic metal to microorganisms. In some regions in Sweden, the content of Hg in soils is already today at a level that has been proposed as a critical concentration. To obtain a general decrease in the Hg content in fish and in forest soils, the atmospheric deposition of Hg has to be reduced. The critical atmospheric load of Hg can be defined as the load where the input to the forest soils is less than the output and, consequently, where the Hg content in the top soil layers and the transport of Hg to the surface waters start to decrease. A reduction by about 80% of the present atmospheric wet deposition has to be obtained to reach the critical load for Scandinavia.     

Mercury in the Diatoms of Various Ecological Formations

Mercury is a neurotoxin, its main source in the human organism being fish and seafood. The first level in the marine food web is formed of planktonic and benthic photosynthetic microorganisms, which form a biofilm on the surface of the hard bottom (epilithon) or plants (epiphyton). They are carriers of nutritional as well as toxic substances and pass these on to subsequent levels of the trophic web. Their biomass is often dominated by diatoms. This was the basis for the presented study into Hg accumulation in epilithic, epiphytic and planktonic diatoms, which was carried out in 2012–2013 in the coastal zone of the Puck Lagoon and the Gulf of Gdańsk (southern Baltic). In this coastal area, both micro- and macroorganisms develop particularly intensively. The collected results indicate an increase in Hg concentration in the biofilm during the warm season which, with the lengthening of the vegetative period due to global warming in recent years, is of great significance. As a consequence, the annual mercury load entering the trophic web is larger in comparison with a year in which there is a long, cold winter. An important parameter influencing the accumulation of Hg was the function of those organisms from the biofilm-forming communities. In this case, the highest concentrations of Hg were measured in organisms forming high-profile guilds.     

Factors affecting the bioaccessibility of methylmercury in several marine fish species

Bioaccessibility refers to the maximum bioavailability of pollutant ingested with food, and its measurements can lead to a more accurate risk assessment as compared to the measurements of total concentrations of pollutant in food. This study examined the factors affecting the bioaccessibility of methylmercury (MeHg) in nine species of marine fish with an aim to identify ways of reducing MeHg bioaccessibility. MeHg bioaccessibility without any treatment in the nine species of marine fish ranged from 16.0 to 67.7%. Steaming, grilling, and frying reduced MeHg bioaccessibility by 29.4-77.4% for rabbitfish and 74.6-95.8% for grouper. Co-consumption of phytochemical-rich foods such as green tea decreased the bioaccessibility of MeHg by 72.2% for rabbitfish and 74.0% for grouper, whereas meso-2,3-dimercaptosuccinic acid increased it by 39.2-108% for rabbitfish and 45.3-75.7% for grouper. The bioaccessibilities of both MeHg and inorganic mercury were independent of the total Hg concentration and the exposure route (dietary vs dissolved). In eight of the nine species studied, bioaccessibility was negatively correlated with the extent to which MeHg was partitioned into the metal-rich granule fraction and the trophically available fraction. It was positively correlated with partitioning into the cellular debris fraction. This study demonstrated the important control of subcellular distribution in MeHg bioaccessibility.     

Methylated and elemental mercury cycling in surface and deep ocean waters of the North Atlantic

Biogeochemical cycling of mercury (Hg) in the ocean and air-sea exchange are integral parts of the global Hg cycle. Ionic Hg (i.e. reactive Hg-Hg°) is converted in ocean surface waters to elemental Hg (Hg°) with the subsequent loss, via gas evasion, of the Hg° to the atmosphere. During a recent cruise in the North Atlantic Ocean, Hg° in surface waters was a substantial fraction of the reactive Hg (85%, on average) and there was a relationship between photosynthetic pigment concentration and Hg°. In addition, there was evidence of Hg bound to “collodial” material (of greater than 1,000 molecular weight). Ionic Hg concentrations were around 0.15 pM, similar to the average colloidal Hg concentration of 0.2 pM. Methylated Hg compounds, both dimethylHg (DMHg) and monomethylHg (MMHg), were found in the deeper waters with DMHg being the predominant methylated species. This contrasts with freshwater lakes where MMHg is the principal species and no DMHg has been found. Preliminary modelling, using estimated rate constants for the formation and decomposition of DMHg and MMHg, predicts an enhanced stability of DMHg in ocean waters relative to fresh water. Deep ocean waters, formed by sinking of surface waters, can preserve DMHg that was produced in the more productive surface regime.     

Determination of mercury methylation rates using A 203-HG radiotracer technique

A radiotracer method for the determination of mercury (Hg) methylation rates in bulk water and water overlying intact sediment cores has been developed. A sediment core with overlying water is collected in a core tube, the overlying water is spiked with high specific activity 203-Hg radiotracer, and the core is incubated at ambient temperature. Aliquots of the overlying water are removed, the Hg is extracted from the sample, and the activity in the extract is measured. A 10–25 fold sample preconcentration is achieved using a dithizone-chloroform extraction technique and a sodium nitrite back extraction step to separate inorganic Hg(II) from monomethylmercury (MMHg). The use of this technique, in conjunction with high specific activity 203-Hg, has allowed for spiking concentrations in the overlying water of approximately 1 ng Hg/L. This spiking level is about the same concentration as the ambient water overlying the core, thus not significantly perturbing the system. Our technique is a significant improvement over previous methodologies which used 203-Hg spike additions of 1 μg Hg/L or higher. The technique was used to measure Hg methylation rates at the Experimental Lakes Area (ELA) in Ontario, Canada during August of 1993 and at an extensively studied estuarine site in Gulf Breeze, Florida, USA during September, 1993 and June, 1994. Multiple cores were collected and spiked with a range of 1 to 11,800 ng Hg (as 203-Hg) into the overlying water. MMHg production at the ELA site indicated rates of 0.25 to 3.7 pg/cm²/day (0.08 to 2.5 % methylation/day). Results from Gulf Breeze were significantly higher at 1.5 to 425 pg/cm²/day or 0.06 to 18 % methylation/day. These rates are one to three orders of magnitude greater than previously measured “specific rates” in bulk water samples and sediments. A direct comparison of rates with previous sediment methylation assay techniques is not possible, however, because of the significant differences between our methodology and previous assay protocols.