Mercury Loading Research Articles

Mercury advisories and household health trade-offs

The conventional economic wisdom is that improving consumer information will enhance welfare. Yet, some scientists speculate that the Food and Drug Administration's prominent mercury in fish advisory may have harmed public health. Lower mercury intakes reduce neurological toxicity risks. However, since seafood is the predominant dietary source of healthful omega-3 fatty acids, reduced fish consumption may have significant offsetting health impacts. We explore this risk trade-off using a rich panel of household-level seafood consumption data. To control for confounding factors, we use a non-parametric changes-in-changes approach. We find strong evidence that while the advisory reduced mercury loadings, it did so at the expense of substantial reductions in healthful omega-3s. We find this response pattern even for consumers with low fish consumption. Using advisory response patterns as inputs into a prominent risk assessment model, the central estimate is that net benefits from the advisory were negative.

Potential Ecological Risk Assessment of Heavy Metals in Sediments from Hongfeng Lake, China

Hongfeng Lake, a man-made reservoir, is one of the five key drinking-water sources for Guiyang City, the capital of Guizhou Province in southwestern China. In the present research, the distribution and accumulation characteristics of seven heavy metals (Pb, Cd, As, Hg, Cu, Cr and Zn) in the sediment of this lake were analyzed by examining fourteen sediment samples. A method based on toxic-response factor was used to assess the potential ecological risk of these heavy metals to this lake. For comparison, the two sets of reference data representing the pre-industrial and the local baseline pollution levels of interested heavy metals were employed to derive their accumulating coefficients and potential ecological risk indices. The calculated potential ecological risk indices indicate that the lake was polluted by heavy metals, and both mercury and cadmium loadings were critical factors responsible for the ecological hazards posed to Hongfeng Lake among these seven elements.

Dynamic accumulation and redistribution of methylmercury in the lens of developing zebrafish embryos and larvae

Neurotoxic methylmercury compounds are widespread in the environment and human exposure worries many communities worldwide. Despite numerous studies addressing methylmercury toxicity, the detailed mechanisms underlying its transport and accumulation, especially during early developmental stages, remain unclear. Zebrafish larvae are increasingly used as a model system for studies of vertebrate development and toxicology. Previously, we have identified the lens epithelium as the primary site for cellular mercury accumulation in developing zebrafish larvae (Korbas et al. in Proc Natl Acad Sci USA 105:12108-12112, 2008). Here we present a study on the dynamics of methylmercury accumulation and redistribution in the lens following embryonic and larval exposure to methylmercury L-cysteineate using synchrotron X-ray fluorescence imaging. We observed highly specific accumulation of mercury in the lens that continues well after removal of fish from treatment solutions, thus significantly increasing the post-exposure loading of mercury in the lens. The results indicate that mercury is redistributed from the original target tissue to the eye lens, identifying the developing lens as a major sink for methylmercury in early embryonic and larval stages.

The importance of size and growth rate in determining mercury concentrations in European minnow (Phoxinus phoxinus) and brown trout (Salmo trutta) in the subalpine lake, Øvre Heimdalsvatn

The alien fish species, European minnow (Phoxinus phoxinus), was recorded in the mountain lake, Ovre Heimdalsvatn, southern Norway, for the first time in 1969. After some years minnows were observed in the diet of brown trout (Salmo trutta). In 2006, brown trout had significantly higher δ15N values than European minnow, indicating that brown trout holds the top trophic position in the lake food web. The δ15N signatures of brown trout were significantly correlated to fish size, age and mercury concentration, while δ15N signatures in minnows did not show any change with fish size, age and mercury concentrations, indicating that European minnow remain at the same trophic level throughout the life history. The mercury concentrations (mg kg−1 w.w.) in brown trout and minnows were in the range 0.014–0.093 and 0.014–0.16, respectively. For both species, positive relationships between total mercury concentrations and fish length, weight and age were found. Although European minnow was found as prey in brown trout stomachs, minnow had significantly higher mercury concentrations than brown trout. It is most likely that the higher mercury concentrations in the European minnow are due to the high metabolic rate, with more energy spent on maintenance than on growth as a consequence of its small size and very low annual growth rate compared to brown trout. Changes in population densities of both brown trout and European minnow may influence their habitat use, feeding preferences and metabolism, and may thus potentially lead to changes in the mercury loads of both species.

Response of a Macrotidal Estuary to Changes in Anthropogenic Mercury Loading between 1850 and 2000

Methylmercury (MeHg) bioaccumulation in marine food webs poses risks to fish-consuming populations and wildlife. Here we develop and test an estuarine mercury cycling model for a coastal embayment of the Bay of Fundy, Canada. Mass budget calculations reveal that MeHg fluxes into sediments from settling solids exceed losses from sediment-to-water diffusion and resuspension. Although measured methylation rates in benthic sediments are high, rapid demethylation results in negligible net in situ production of MeHg. These results suggest that inflowing fluvial and tidal waters, rather than coastal sediments, are the dominant MeHg sources for pelagic marine food webs in this region. Model simulations show water column MeHg concentrations peaked in the 1960s and declined by almost 40% by the year 2000. Water column MeHg concentrations respond rapidly to changes in mercury inputs, reaching 95% of steady state in approximately 2 months. Thus, MeHg concentrations in pelagic organisms can be expected to respond rapidly to mercury loading reductions achieved through regulatory controls. In contrast, MeHg concentrations in sediments have steadily increased since the onset of industrialization despite recent decreases in total mercury loading. Benthic food web MeHg concentrations are likely to continue to increase over the next several decades at present-day mercury emissions levels because the deep active sediment layer in this system contains a large amount of legacy mercury and requires hundreds of years to reach steady state with inputs.

Protocol to Reconstruct Historical Contaminant Loading to Large Lakes: The Lake Michigan Sediment Record of Mercury

Samples of opportunity from Pb-210 dated sediment cores collected from Lake Michigan between 1994 and 1996 were analyzed for mercury. The storage of anthropogenic and total (post-1850) mercury in the lake is calculated to be 186 and 228 t, respectively. By setting the sum of mercury stored in a representative core equal to the mercury storage within the entire lake, the time variation of annual mercury loading to the lake is calculated. The modern (1980-2002) mercury flux to the lake represented by the surface of the core at the time of collection in 1994 was 21.4 microg/m(2)/y. The preindustrial flux (< or =1850) was 3.09 microg/m(2)/y, and the peak flux in 1946 was 53.3 microg/m(2)/y. These yield modern and peak enrichment factors of 6.92 and 17.2, respectively. Modern fluxes exceed published atmospheric deposition estimates and, therefore, include terrestrial point sources, atmospheric deposition to watersheds, and atmospheric deposition to the lake. The modern net mercury load to the lake's sediments was 1157 kg/y in 1994. The atmosphere is estimated to contribute 91% of this load directly to the lake.

The Effects of Forest Harvest Operations on Mercury and Methylmercury in Two Boreal Streams: Relatively Small Changes in the First Two Years prior to Site Preparation

Forest harvest is hypothesized to increase the mercury (Hg) load in aquatic ecosystems. The Balsjö paired catchment study examined the outputs of methylmercury (MeHg) and total mercury (Hg(tot)) from two boreal catchments during the 2 y following forest harvest but prior to site preparation. This enabled us to separate the effect of the two operations that followed best management practices. Hg(tot) concentrations increased by approximately 15%, and fluxes by 20-30%. The MeHg concentrations and fluxes either declined or increased by up to 60%, depending on whether annual MeHg peaks during summer low flows were considered to have been influenced by forest harvest. The lack of a severalfold increase in Hg outputs after forest harvest, as reported from other sites, may be the result of minimal soil disturbance during the winter forest harvest operations. If so, there may be a greater Hg response after soil scarification to prepare for planting.

Mercury concentrations and loads in a large river system tributary to San Francisco Bay, California, USA

In order to estimate total mercury (HgT) loads entering San Francisco Bay, U.S.A., via the Sacramento-San Joaquin River system, unfiltered water samples were collected between January 2002 and January 2006 during high flow events and analyzed for HgT. Unfiltered HgT concentrations ranged from 3.2 to 75 ng/L and showed a strong correlation (r2 = 0.8, p < 0.001, n=78) to suspended sediment concentrations (SSC). During infrequent large floods, HgT concentrations relative to SSC were approximately twice as high as observed during smaller floods. This difference indicates the transport of more Hg-contaminated particles during high discharge events. Daily HgT loads in the Sacramento-San Joaquin River at Mallard Island ranged from below the limit of detection to 35 kg. Annual HgT loads varied from 61 +/- 22 kg (n=5) in water year (WY) 2002 to 470 +/- 170 kg (n=25) in WY 2006. The data collected will assist in understanding the long-term recovery of San Francisco Bay from Hg contamination and in implementing the Hg total maximum daily load, the long-term cleanup plan for Hg in the Bay.

Growing season total gaseous mercury (TGM) flux measurements over an Acer rubrum L. stand

Relaxed eddy accumulation (REA) measurements of the total gaseous mercury (TGM) flux measurements were taken over a deciduous forest predominantly composed of Red Maple ( Acer rubrum L.) during the growing season of 2004 and the second half of the growing season of 2005. The magnitudes of the flux estimates were in the range of published results from other micrometeorological mercury fluxes taken above a tall canopy and larger than estimates from flux chambers. The magnitude and direction of the flux were not static during the growing season. There was a significant trend ( p < 0.001), from net deposition of TGM in early summer to net evasion in the late summer and early fall before complete senescence. A growing season atmosphere-canopy total mercury (TGM) compensation point during unstable daytime conditions was estimated at background ambient concentrations (1.41 ng m −3). The trend in the seasonal net TGM flux indicates that long term dry deposition monitoring is needed to accurately estimate mercury loading over a forest ecosystem.

Estimation of Mercury Bioaccumulation Potential from Wastewater Treatment Plants in Receiving Waters: Phase 2

This project was initiated in response to the establishment of mercury TMDLs around the country and issues raised by this process, specifically concerning the issue of mercury bioavailability. While many of these studies recognize that point sources constitute a small fraction of the mercury load to a water body, a question has been raised concerning the relative bioavailability of mercury coming from various sources. For instance, is the mercury discharged from a wastewater treatment plant more or less bioavailable than mercury in precipitation, mercury in urban stormwater, or mercury in sediments? This project seeks to address this question by developing a reliable definition and approach to estimating bioavailability, by profiling various sources of mercury in a watershed with regard to the species of mercury present and by profiling those factors or conditions in either the effluent or the receiving water that enhance or mitigate the bioavailability of those forms. There were several important objectives relevant to the estimation of bioavailability and potential bioaccumulation of mercury from wastewater treatment plants and other sources in receiving waters. The first was to develop a working definition of bioavailability. For purposes of this project, this definition includes not only methylmercury, the form of mercury that readily bioaccumulates in aquatic food chains, but also bioavailable and potentially bioavailable inorganic mercury species that can be converted to methylmercury within a reasonable time frame. It is concluded that the strength of binding to solids and mercury-sulfur-organic matter associations are major factors in determining the bioavailability of inorganic Hg. A second major objective was to identify those factors or conditions in both the effluent and the receiving waters that enhance or mitigate the transformation of inorganic mercury to methylmercury and its subsequent bioaccumulation. Profiles were developed for various sources of mercury in watersheds, including wastewater treatment plants, with regard to bioavailable and potentially bioavailable mercury, and key factors in effluents and receiving waters that enhance or mitigate it. A procedure to assess the relative bioavailability of mercury from various watershed sources, including wastewater treatment plants was developed and tested using data from a US location. The project also features a literature review of conventional and emerging technologies for the removal of mercury from effluent streams and their effects on mercury bioavailability. A review of the salient aspects of mercury TMDLs completed by EPA and the states is also included. This project concludes that, based on available data and bioavailability as defined in this report, wastewater effluent is one of the lowest among the sources evaluated with respect to mercury bioavailability, along with urban runoff and mining runoff. Atmospheric deposition and contaminated sediments tend to be among the highest sources with respect to mercury bioavailability. This title belongs to WERF Research Report Series . ISBN: 9781843393573 (Print) ISBN: 9781780403601 (eBook)

Estimation of Mercury Bioaccumulation Potential from Wastewater Treatment Plants in Receiving Waters: Phase 1

This project was initiated in response to the establishment of mercury TMDLs around the country and issues raised by this process, specifically concerning the issue of mercury bioavailability. While many TMDLs recognize that point sources constitute a small fraction of the mercury load to a water body, a question has been raised concerning the relative bioavailability of mercury coming from various sources. For instance, is the mercury discharged from a wastewater treatment plant more or less bioavailable than mercury in precipitation, mercury in urban stormwater, or mercury in sediments? This project seeks to address this question by developing a reliable definition and approach to estimating bioavailability, by profiling various sources of mercury in a watershed with regard to the species of mercury present and by profiling those factors or conditions in either the effluent or the receiving water that enhance or mitigate the bioavailability of those forms. The report consists of two volumes. Volume I is a background document for evaluating the biovailability of mercury in wastewater effluents and receiving waters and establishes relevant project objectives. Volume II is a guidance document for wastewater treatment professionals interested in assessing the bioavailability of mercury in their wastewater, comparing it to other sources, and assessing changes in bioavailability in their effluent when it is mixed in a receiving water body. The project concludes that, based on available data and bioavailability as defined in this report, wastewater effluent is one of the lowest among the sources evaluated with respect to mercury bioavailability due to its typically low levels of methylmercury. Due to their typically low levels of suspended solids, wastewater treatment plants employing post-secondary treatment should not contribute appreciably to local sediment mercury burdens. This title belongs to WERF Research Report Series . ISBN: 9781843393566 (Print) ISBN: 9781780403618 (eBook)

Spatial and temporal variation of mercury load in surface water and sediments around an integrated steel plant in India

Coal burning in the steel industry is the chief source of mercury presence in surrounding environment. About 20 water-storage ponds and three natural water streams are located in adjoining areas of an integrated steel plant in Bhilai, India. Hundreds of hospital admissions with chronic ailments due to hazardous emissions from the steel industry are frequently reported. Many of these ailments are related to reported mercury-poisoning diseases. Measurements of mercury levels in various environmental matrices around this industrial area was started early in the 1990s. From 1990–1995, few environmental samples were analyzed for mercury content but from 1995 onwards, comprehensive assessment of mercury load along with other toxic metals in various environmental matrices were begun. This work synthesizes and compares data of mercury in the surface water from three major field programs, in 1997, 2002, and 2006. The focus is on both spatial and temporal variation. In the present survey (2006), mercury levels are significantly higher compared to subsequent surveys and have shown 10–18 times higher values compared to 2001 and 1997 surveys. The differences in Hg levels between downwind and other sites in three survey programs are found to be in order: 1997 > 2001 > 2006. Regression between water and sediment mercury levels has shown variation in correlation values and higher in winter season.

Mercury in the Mackenzie River delta and estuary: Concentrations and fluxes during open-water conditions

Estimates of mercury (Hg) loadings to the Arctic Ocean from circumpolar rivers have not considered biogeochemical changes that occur when river water is temporarily stored in large deltas (delta effect). There are also few data describing Hg changes across the freshwater–saltwater transition zone (FSTZ) of these rivers. We assessed temporal changes in unfiltered total mercury (THg) and methylmercury (MeHg) concentrations during open-water 2004 in the Mackenzie River upstream of the Mackenzie River delta, and in 6 floodplain lakes across an elevation gradient. These data were used to calculate Hg fluxes from the Mackenzie River and to evaluate a delta effect on Hg using an estimate of delta river water storage and a mixing analysis. Mean THg concentrations were highest in river water (9.17 ± 5.51 ng/L) and decreased up the lake elevation gradient. Mean MeHg concentrations were highest in lakes periodically connected to the river (0.213 ± 0.122 ng/L) and MeHg concentrations in elevated lakes showed a mid-summer peak. Results from the mixing analysis showed that the delta effect may be large enough to affect Hg loadings to the Arctic Ocean. THg concentrations exiting the delta (10.2 ng/L) were 16% lower than those entering (12.1 ng/L), whereas MeHg showed little change. We calculated 2.5-month (open-water) THg and MeHg fluxes from the Mackenzie River of 1208 and 8.4 kg. These fluxes are similar in magnitude to previous annual estimates in the arctic literature suggesting that previously published annual Hg fluxes from the Mackenzie River may be large underestimates. We also assessed changes in Mackenzie River water THg and MeHg concentrations as it crossed the FSTZ during an open-water cruise. THg decreased non-conservatively across the estuary from 3.8–0.6 ng/L, possibly due to mixing and particle settling. MeHg concentrations were variable and near detection. Our results show that the Mackenzie River estuary is a dynamic environment and may have important controls on Hg delivered to the Arctic Ocean.

Legacy sources of mercury in an urbanised watershed

Environmental context. Mercury is a neurotoxin that bioaccumulates and is associated with global contamination and often with regional atmospheric sources. However, in Connecticut, USA, in watersheds characterised by a gradient of forested to urban land uses we found that the predominant source of elevated Hg is local. This study uses a novel nested sampling method to pinpoint hot spots of mercury and presents inorganic mercury concentrations in water, sediment, soil, and aquatic organisms. The results indicate that mercury contamination is an environmental legacy associated with the silver plating industry and that local sources are critical to the biogeochemical mercury cycle here. Abstract. Mercury levels were measured in various environmental compartments of the Quinnipiac River system (CT, USA). In streams, dissolved mercury reached a maximum of 6.3 ng L–1 during baseflow and 30 ng L–1 during stormflow, whereas surficial impoundment sediments had a maximum mercury concentration of 420 μg kg–1. A sediment core collected from the Quinnipiac River indicates that peak loading of mercury occurred before 1940. Wharton Brook tributary of the Quinnipiac River represents 30% of the mercury loading to the river and the likely source of mercury to the sediment is a past silver manufacturing plant. Analysis of soil samples from the riparian zone of Wharton Brook, a tributary of concern because it empties into a popular fishing location, revealed mercury concentrations as high as 20 000 μg kg–1. It appears that the soil surrounding the former factory is acting as the current source of mercury to the water column and aquatic communities. Removal of contaminated soil will probably be necessary to reduce mercury levels and the threat to humans in downstream environments.

Factors Controlling the Spatial Variability of Mercury Distribution in Spanish Topsoil

This study characterized the sources and scales of mercury variability in agricultural soils of the river Ebro (9.5 million ha) using geostatistical methods and data from 624 samples. The Ebro basin (20% of Spanish land mass) is an important agricultural area that is industrialized. Spatial analysis was done on a local scale (20 km) and indicated that high Hg concentrations were related to mining and specific agronomic practices, such as sewage effluents from irrigation. The intermediate scale (100 km) was associated with mercury from atmospheric deposition (mining, smelting, and industrial activities). The regional scale (220 km) corresponded to mineralogical structure and bedrock influence. The analysis demostrates that while geographical and geochemical processes and anthropogenic influences, such as industrialization and agricultural practices, can influence the content and distribution of mercury in the valley, the calcareous nature of the soils (alkaline pH and low organic matter) minimize the effect of the mercury load.

Metamorphosis in Chironomids, More than Mercury Supply, Controls Methylmercury Transfer to Fish in High Arctic Lakes

Lake-dwelling Arctic char (Salvelinus alpinus) are monitored internationally as a sentinel species for effects of atmospheric mercury deposition on Arctic fresh waters. We investigated the control of mercury supply and biological processes on the methylmercury (MeHg) content of their main food, aquatic chironomids, in 22 lakes and ponds in the Canadian High Arctic. Total mercury (THg) concentrations in sediment (corrected for organic matter content) increased with drainage basin size, suggesting a gradient in mercury loading among study sites. MeHg concentrations in sediment and water were low and relatively uniform along this THg supply gradient suggesting MeHg production in High Arctic lakes is weakly coupled to inorganic mercury supply. Metamorphosis was a key biological process that concentrated MeHg in adult chironomids 1.7-2.9 times more than in immature stages. Drainage basin size, environmental mercury levels, and habitat characteristics were also significant factors but they explained less variation in chironomid MeHg concentration than their degree of maturity. Chironomid larvae, pupae, and adults are distinct mercury sources for fish, and we provide evidence from nitrogen stable isotopes and published feeding studies that suggest differential consumption of these stages may affect MeHg uptake by Arctic char. We conclude that biological and food web processes have a greater impact on MeHg transfer to fish than atmospheric mercury deposition in High Arctic lakes.

Quantifying bank erosion on the South River from 1937 to 2005, and its importance in assessing Hg contamination

Bank sediments along a 40 km reach of the South River, downstream of Waynesboro, VA, store mercury from historical contamination as a result of textile manufacturing. Knowledge of the rate at which contaminated sediment is released to the stream channel through bank erosion is required to implement restoration programs designed, for example, to minimize its ecological impact and to reduce risk to human health. Digitized stream channel boundaries based on visual interpretations of georeferenced aerial imagery from 1937 and 2005 were compared to calculate a minimum estimate of the total area of bank sediment eroded between Waynesboro and Port Republic, Virginia. Estimates of riverbank height were extracted from aerial LIDAR data, allowing areal estimates of bank retreat to be converted to volumes. Nominal annual rates of bank retreat, averaged over the 68-year period, for several example locales along the study reach are very low, ranging from 3 to 15 cm per year. Bank erosion occurs at the outside banks of bends, through the development of islands, where deposition on confluence bars pushes the main flow into the opposite bank, and in small areas along the channel that are difficult to classify or explain. A minimum estimate of the total volume eroded for the study reach is approximately 161,000 m 3; the corresponding annual mass of mercury supplied to the channel by bank erosion is 109.6 kg/year. Our work demonstrates that a careful analysis of aerial imagery and LIDAR data can provide detailed, spatially explicit estimates of mercury loading from bank erosion, even when rates of riverbank erosion are unusually low.

Long-Term Wet and Dry Deposition of Total and Methyl Mercury in the Remote Boreal Ecoregion of Canada

Although a positive relationship between atmospheric loadings of inorganic mercury (Hg(II)) to watersheds and concentrations of methyl mercury (MeHg) in fish has now been established, net wet and dry deposition of Hg(II) and MeHg to watersheds remains challenging to quantify. In this study, concentrations and loadings of total mercury (THg; all forms of Hg in a sample) and MeHg in open area wet deposition, throughfall, and litterfall were quantified atthe remote Experimental Lakes Area in the boreal ecoregion, NW Ontario, Canada. Between 1992 and 2006, mean annual THg and MeHg loadings in the open were 36 +/- 17 and 0.5 +/- 0.2 mg ha(-1), respectively. Throughfall THg and MeHg loadings were generally 2-4 times and 0.8-2 times higher, respectively, than loadings in the open. Loadings of both THg and MeHg were highest under an old growth spruce/fir canopy and lowest under a deciduous maple canopy, whereas loadings under young jack pine and wetland spruce/pine/alder canopies were intermediate. Litterfall generally represented the largest input of THg (86-105 mg ha(-1)) and MeHg (0.7-0.8 mg ha(-1)) to the landscape on an annual basis. Using the "direct" method of estimating dry deposition (thoughfall + litterfall - open loadings), we calculated that annual dry deposition of THg and MeHg under forest canopies ranged from 105 to 201 mg ha(-1), whereas dry deposition of MeHg ranged from 0.7 to 1.2 mg ha(-1). Photoreduction and emission of wet-deposited Hg(ll) from canopy foliage were accounted for, resulting in 3-5% (5-6 mg ha(-1)) higher annual estimates of dry deposition than via the direct method alone. NetTHg and MeHg loadings to this remote landscape were lower than at any other previously studied forested site globally. This study shows that THg and MeHg loading can be extremely variable within a heterogeneous boreal landscape and that processes such as Hg photoreduction and emission from foliage should be considered when estimating dry deposition of Hg.

Synthesis and characterization of cubic thiol-functionalized periodic mesoporous organosilicas as effective mercury ion adsorbents

Well-ordered thiol-functionalized periodic mesoporous organosilicas (SH-PMO) with ethane bridging groups and cubic Pm3n symmetry for aqueous mercury removal have been synthesized via co-condensation of tetramethoxysilane (TMOS) with 1,2-bis(trimethoxysilyl)ethane (BTME) and 3-mercaptopropyltrimethoxysilane (MPTMS) in a highly acidic medium by using cetyltriethylammonium bromide (CTEABr) as the template. The SH-PMO materials thus obtained have been characterized by X-ray diffraction, nitrogen physical sorption, thermogravimetric analysis, and solid-state 29Si and 13C NMR spectroscopy. We have found that it is necessary to employ a controlled amount of BTME in order to preserve the cubic mesoporous structure in the resulting material when a high quantity of mercaptopropyl groups is incorporated. Direct evidence of the presence of chemically attached thiol and ethane moieties is provided by 29Si and 13C magic angle spinning (MAS) NMR spectroscopy. The maximum content of the attached thiol group (–SH) in the mesoporous framework is 2.40 mmol/g. The total access of the Hg 2+ ions to every complexation site, i.e., an Hg/S ratio close to 1, in the SH-PMO materials is also demonstrated, and a maximum mercury loading capacity of 464 mg/g is achieved. This makes its effectiveness for mercury ion trapping comparable to that of the highest capacity materials previously reported. 13C cross-polarization magic angle spinning (CPMAS) NMR demonstrates that the 13C chemical shift of the carbon atom adjacent to the –SH group is highly sensitive to the Hg 2+ ion binding.

Model Calculations of Total Maximum Daily Loads of Mercury for Drainage Lakes1

Abstract: The Watershed Analysis Risk Management Framework watershed model was enhanced to simulate the transport and fate of mercury and to calculate the fish mercury concentrations (FMC) attained by fish through the food web. The model was applied to Western Lake Superior Basin of Minnesota, which has many peat lands and lakes. Topographic, land use, and soil data were used to set up the model. Meteorology and precipitation chemistry data from nearby monitoring stations were compiled to drive the model. Simulated flow and mercury concentrations for several stream stations were comparable to available data. The model was used to perform mercury total maximum daily load calculations for two contrasting drainage lakes (Wild Rice Lake and Whiteface Reservoir). The model results for wet deposition, dry deposition, evasion, watershed yield, and soil sequestration of mercury were comparable with available actual data. The model predicted lake ice cover from November to April and weak stratification in summer, typical of shallow lakes in cold regions. The simulated sulfate decrease and methylmercury increase near the lake bottom in late summer are caused by sulfate reduction and mercury methylation that occur in the surficial sediment. Simulated FMC were within the range of observed values and the R2 of correlation between the simulated and observed FMC was 0.77. Under the 1989‐2004 base condition, the average simulated FMC of four‐year‐old walleye was 0.31 μg/g for Whiteface Reservoir and 0.15 μg/g for Wild Rice Lake. The FMC criterion in Minnesota is 0.2 μg/g. Wild Rice Lake already meets this criterion without any load reduction. The model showed that a 65% reduction in atmospheric mercury deposition will not, by itself, allow Whiteface Reservoir to meet the criterion in 15 years. Additional best management practices will be needed to reduce 50% of the watershed input.