Mercury distribution in medium-size rivers and reservoirs of the Sao Paulo state (southeast Brazil)

The aim of this work was to investigate mercury (Hg) levels in six meso-scale watersheds (Upper Paranapanema, Aguapeí, Peixe, S?o José dos Dourados, Mogi-Gua?u, and Piracicaba) of the S?o Paulo state to contribute to a more comprehensive understanding of Hg contamination in Brazil. Water, sediment, bivalves, and fish samples were collected during 2001 at 11 sites. Fish were also collected in the Jurumirim and Salto Grande Reservoirs which are 39 and 52 yr old since impoundment, respectively. Results showed that Hg concentrations were low in almost all samples, except fish from Jurumirim Reservoir (total mercury [T-Hg] = 1.14 +/- 0.55 mg kg(-1) wet wt.). In spite of industrialization and high population, the results showed that there was no important source of Hg contamination in the investigated areas. The higher concentrations found in fish from Jurumirim seem to be the result of processes that favor Hg mobilization and methylation as a consequence of the impoundment of the reservoir area. The same levels were not observed in the Salto Grande Reservoir, probably because these are no longer significant due to the long time since the impoundment. To understand the dynamics of methylmercury (MeHg) production and its accumulation in fish, further studies are needed in the Jurumirim Reservoir. The results show that even at low T-Hg concentrations in sediment and water, concentrations in fish can reach values that pose concerns for consumption. This emphasizes the importance of designing an optimized biomonitoring program that can provide warning of biogeochemical conditions that promote formation of MeHg.     

Environmental assessment of mercury dispersion, transformation and bioavailability in the Lake Victoria Goldfields, Tanzania

Environmental dispersion and transformation of mercury discharged from gold mining operations has been investigated in field and laboratory studies in order to provide better understanding of the degree of mercury (Hg) pollution and bioavailability in the Lake Victoria goldfields (LVGF) ecosystems. This paper reviews results already published elsewhere and presents additional data on Hg dynamics in the LVGF. Studies conducted at the Mugusu and Rwamagaza artisanal mines indicated different degrees of Hg contamination and dispersion in environmental matrices. Mercury concentration in contaminated river sediments near the Mugusu mine varied from 6.0 to 0.5 mg/kg on a dry weight basis. The highest Hg contamination levels (165-232 mg/kg) were associated with mine tailings at the Rwamagaza mine. Mercury concentrations in fish representing different dietary habits on the southwestern shore of Lake Victoria at the Nungwe Bay were very low (2-35 microg/kg) and thought to represent background levels. These and other results suggested that the use of Hg in gold extraction in the LVGF has not caused high Hg levels in lake fish. The study of Hg in lichens showed Parmelia lichen to be an effective bioindicator for atmospheric Hg contamination due to Hg emissions from gold-amalgam firing and purification operations. The Hg levels in the lichens around the Mugusu mine ranged from 3.1 to 0.1 microg/g; the highest levels were recorded in the lichens sampled close to gold-amalgam processing sites. The regional background level in the Parmelia lichen was 0.05-0.10 microg/g, with a mean level of 0.07 microg/g. Studies of Hg transformation in the mine tailings revealed unexpectedly high methylmercury (MeHg) levels in the tailings (629-710 ng/g), which indicated that oxidation and methylation of metallic Hg in the tailings occurred at significant levels under tropical conditions. Re-equilibration of the tailings with freshwater (FW) indicated the MeHg was firmly bound in the tailings and therefore very little MeHg was released to the water column (0.2-1.5 ng/L). The methylation of Hg in tropical loamy clay soil contaminated with HgCl(2) (5 mg Hg/kg) yielded MeHg concentrations of 11 and 14 ng/g when inundated with seawater and FW, respectively, for 4 weeks. Little MeHg was transferred from the soil to the equilibrated water (< or = 0.4 ng/L). Atmospheric exposure of the soil pre-inundated with FW resulted in net degradation of MeHg during the 1st week of exposure, followed by net production and accumulation of MeHg in the soil (up to 15.5 ng/g) during atmospheric desiccation. Mercury uptake by fish from the Hg(0)-contaminated aquatic sediment-tailings system in the aquarium experiment was found to be low, suggesting the low availability of MeHg for bioaccumulation in the system. These and other results provide useful insights into Hg transformation, mobility and bioavailability in tropical aquatic systems affected by Hg pollution from gold mining operations.     

Nitrate controls methyl mercury production in a streambed bioreactor

Organic carbon bioreactors provide low-cost, passive treatment of a variety of environmental contaminants but can have undesirable side effects in some cases. This study examines the production of methyl mercury (MeHg) in a streambed bioreactor consisting of 40 m3 of wood chips and designed to treat nitrate (NO?) in an agricultural drainage ditch in southern Ontario (Avon site). The reactor provides 30 to 100% removal of NO?-N concentrations of 0.6 to 4.4 mg L(-1), but sulfate (SO?(2-)) reducing conditions develop when NO? removal is complete. Sulfate reducing conditions are known to stimulation the production of MeHg in natural wetlands. Over one seasonal cycle, effluent MeHg ranged from 0.01 to 0.76 ng L(-1) and total Hg ranged from 1.3 to 3.4 ng L(-1). During all sampling events when reducing conditions were only sufficient to promote NO?(-) reduction (or denitrification) ( = 5, late fall 2009, winter 2010), MeHg concentrations decreased in the reactor and it was a net sink for MeHg (mean flux of -5.1 μg m(-2) yr(-1)). During all sampling events when SO?(2-) reducing conditions were present ( = 6, early fall 2009, spring 2010), MeHg concentrations increased in the reactor and it was a strong source of MeHg to the stream (mean flux of 15.2 μg m(-2) yr(-1)). Total Hg was consistently removed in the reactor (10 of 11 sampling events) and was correlated to the total suspended sediment load ( r2 = 0.69), which was removed in the reactor by physical filtration. This study shows that organic carbon bioreactors can be a strong source of MeHg production when SO?(2-) reducing conditions develop; however, maintaining NO?-N concentrations > 0.5 mg L suppresses the production of MeHg.     

Are methylmercury concentrations in the wetlands of Kejimkujik National Park, Nova Scotia, Canada, dependent on geology?

In the relatively pristine ecosystem in Kejimkujik Park, Nova Scotia, methylmercury (MeHg) concentrations in loons, Gavia immer, are among the highest recorded anywhere in the world. This study investigated the influence of bedrock lithology on MeHg concentrations in wetlands. Twenty-five different wetland field sites were sampled over four different bedrock lithologies; Kejimkujik monzogranite, black sulfidic slate, gray slate, and greywacke. Soil samples were analyzed for ethylmercury (EtHg), MeHg, total Hg, acid-volatile sulfides (AVS), organic matter, and water content as well as the biological parameters, mercury methyltransferase (HgMT) activity, sulfate reduction rates, fatty acid methyl ester (FAME) composition, and acidity. Methylmercury concentrations in the wetlands were highly dependent (P < 0.08) on lithology with no significant difference between bogs, fens, and swamps. Methylmercury concentrations in wetland soils developed on Kejimkujik monzogranite averaged 900 ng kg(-1) compared with only 300 ng kg(-1) in wetland soils developed on black sulfidic slate. Fatty acid methyl ester composition was also lithologically dependent (P < 0.001) with biomarkers for Desulfobulbus spp. discriminating between sites containing high and low MeHg concentrations. Levels of MeHg in wetlands were predicted mainly (41% of the sum of squares) by HgMT activity that differed (P < 0.009) between wetlands, with activity in bogs almost three times that present in swamps. Wetland MeHg concentrations are highly dependent on the lithology on which they have developed for largely biological reasons.     

Influence of eutrophication on the distribution of total mercury and methylmercury in hydroelectric reservoirs

The distribution of mercury (Hg) and the characteristics of its methylation were investigated in Wujiangdu (WJD) and Yinzidu (YZD) reservoirs in Guizhou province, China. The two reservoirs are characterized by high and low levels of primary productivity, respectively. Mercury species in water samples from depth profiles in both reservoirs and from interface water in the WJD were analyzed each season during 2007. The concentrations of total Hg (HgT(unf)) and methylmercury (MeHgT(unf)) in unfiltered water samples from the WJD varied from 3.0 to 18 pmol dm(-3) and from 0.17 to 15 pmol dm(-3), respectively; ranges were 2.0 to 9.5 pmol dm(-3) for HgT(unf) and 0.14 to 2.2 pmol dm(-3) for MeHgT(unf) in the YZD. Elevated methylmercury concentrations in water samples from the bottom water and water-sediment interface demonstrated an active net Hg methylation in the downstream reach of the WJD. There was no discernable Hg methylation occurring in the YZD, nor in the upstream and middle reaches of the WJD. The results suggest that high primary productivity resulting from cage aquaculture activities in the WJD is an important control on Hg methylation in the reservoir, increasing the concentrations of MeHg in water in the Wujiang River basin Southwestern China.     

Mercury sequestration in forests and peatlands: a review

Nearly all Hg in vegetation is derived directly from the atmosphere. Mass of Hg in forest vegetation (roughly 0.1 mg m(-2)) is about an order of magnitude smaller than that in the forest floor (1 mg m(-2)) and two orders of magnitude smaller than that in the mineral soil (10 mg m(-2)). Mass of Hg in peat (20 mg m(-2)) is greater than the sum of that in mineral soil and the forest floor; wetlands usually sequester more Hg than associated uplands. The strong relationship of Hg to organic matter, associated with binding by reduced S groups, is fundamental to understanding Hg distribution and behavior in terrestrial systems. The stoichiometry of the Hg-C relationship varies; Hg-S relationships, though less variable, are not constant. Because of the Hg-organic matter link, landscape conditions that lead to differential soil organic matter accumulation are likely to lead to differential Hg accumulation. The ratio of methylmercury (MeHg) to total Hg is generally low in both vegetation (near 1.5%) and soil (<1%), but areas of poorly drained soils and wetlands are sites of MeHg production. The annual emission of anthropic Hg from the 48 contiguous states of the USA (144 Mg) is two orders of magnitude less than the pool of Hg in forests of those states (30,300 Mg). Peatlands, less than 2% of total land area, sequester more than 20 times annual emissions (2930 Mg). If global climate change affects C storage it will indirectly affect Hg storage, having a major effect on the balance between emissions and sequestration and on the global Hg cycle.     

Mercury Accumulation in Periphyton of Eight River Ecosystems1

Abstract: In 2003, the U.S. Geological Survey (USGS) National Water‐Quality Assessment (NAWQA) program and U.S. Environmental Protection Agency studied total mercury (THg) and methylmercury (MeHg) concentrations in periphyton at eight rivers in the United States in coordination with a larger USGS study on mercury cycling in rivers. Periphyton samples were collected using trace element clean techniques and NAWQA sampling protocols in spring and fall from targeted habitats (streambed surface‐sediment, cobble, or woody snags) at each river site. A positive correlation was observed between concentrations of THg and MeHg in periphyton (r² = 0.88, in log‐log space). Mean MeHg and THg concentrations in surface‐sediment periphyton were significantly higher (1,333 ng/m² for MeHg and 53,980 ng/m² for THg) than cobble (64 ng/m² for MeHg and 1,192 ng/m² for THg) or woody snag (71 ng/m² for MeHg and 1,089 ng/m² for THg) periphyton. Concentrations of THg in surface‐sediment periphyton had a strong positive correlation with concentrations of THg in sediment (dry weight). The ratio of MeHg:THg in surface‐sediment periphyton increased with the ratio of MeHg:THg in sediment. These data suggest periphyton may play a key role in mercury bioaccumulation in river ecosystems.     

Distribution and mobility of mercury in soils of a gold mining region, Cuyuni river basin, Venezuela

An extensive and remote gold mining region located in the East of Venezuela has been studied with the aim of assessing the distribution and mobility of mercury in soil and the level of Hg pollution at artisanal gold mining sites. To do so, soils and pond sediments were sampled at sites not subject to anthropological influence, as well as in areas affected by gold mining activities. Total Hg in regionally distributed soils ranged between 0.02 mg kg(-1) and 0.40 mg kg(-1), with a median value of 0.11 mg kg(-1), which is slightly higher than soil Hg worldwide, possibly indicating long-term atmospheric input or more recent local atmospheric input, in addition to minor lithogenic sources. A reference Hg concentration of 0.33 mg kg(-1) is proposed for the detection of mining affected soils in this region. Critical total Hg concentrations were found in the surrounding soils of pollutant sources, such as milling-amalgamation sites, where soil Hg contents ranged from 0.16 mg kg(-1) to 542 mg kg(-1) with an average of 26.89 mg kg(-1), which also showed high levels of elemental Hg, but quite low soluble+exchangeable Hg fraction (0.02-4.90 mg kg(-1)), suggesting low Hg soil mobility and bioavailability, as confirmed by soil column leaching tests. The vertical distribution of Hg through the soil profiles, as well as variations in soil Hg contents with distance from the pollution source, and Hg in pond mining sediments were also analysed.     

Non-point source mercury emission from the Idrija Hg-mine region: GIS mercury emission model

A mercury emission model was developed to estimate non-point source mercury (Hg) emissions occurring over the year from the Idrijca River catchment, draining the area of the world's second largest Hg mine in Idrija, Slovenia. Site-specific empirical correlations between the measured Hg emission fluxes and the parameters controlling the emission (comprising substrate Hg content, soil temperature, solar radiation and soil moisture) were incorporated into the mercury emission model developed using Geographic Information System technology. In this way, the spatial distribution and significance of the most polluted sites that need to be properly managed was assessed. The modelling results revealed that annually approximately 51 kg of mercury are emitted from contaminated surfaces in the catchment (640 km(2)), highlighting that emission from contaminated surfaces contributes significantly to the elevated Hg concentrations in the ambient air of the region. Very variable meteorological conditions in the modelling domain throughout the year resulted in the high seasonal and spatial variations of mercury emission fluxes observed. Moreover, it was found that mercury emission fluxes from surfaces in the Idrija region are 3-4 fold higher than the values commonly used in models representing emissions from global mercuriferous belts. Sensitivity and model uncertainty analysis indicated the importance of knowing not only the amount but also the type of mercury species and their binding in soils in future model development.     

Fish mercury increase in Lago Manso, a new hydroelectric reservoir in tropical Brazil

It has been frequently demonstrated that mercury (Hg) concentrations in fish rise in newly constructed hydroelectric reservoirs in the Northern Hemisphere. In the present work, we studied whether similar effects take place also in a tropical upland reservoir during impoundment and discuss possible causes and implications. Total Hg concentrations in fish and several soil and water parameters were determined before and after flooding at Rio Manso hydroelectric power plant in western Brazil. The Hg concentrations in soil and sediment were within the background levels in the region (22-35 ng g(-1) dry weight). There was a strong positive correlation between Hg and carbon and sulphur in sediment. Predatory fish had total Hg concentrations ranging between 70 and 210 ng g(-1) f.w. 7 years before flooding and between 72 and 755 ng g(-1) f.w. during flooding, but increased to between 216 and 938 ng g(-1) f.w. in the piscivorous and carnivorous species Pseudoplatystoma fasciatum, cachara, and Salminus brasiliensis, dourado, 3 years after flooding. At the same time, concentrations of organic carbon in the water increased and oxygen concentrations decreased, indicating increased decomposition and anoxia as contributing to the increased Hg concentrations in fish. The present fish Hg concentrations in commonly consumed piscivorous species are a threat to the health of the population dependent on fishing in the dam and downstream river for sustenance. Mercury exposure can be reduced by following fish consumption recommendations until fish Hg concentrations decrease to a safe level.     

The potential of cost-effective coconut husk for the removal of toxic metal ions for environmental protection

Coconut (Cocos nucifera) husk, an agricultural waste, has been thoroughly investigated for the removal of toxic Cd(II), Cr(III) and Hg(II) ions from aqueous media. The parameters like nature and composition of electrolyte, concentration of toxic ions, dosage of coconut husk, and equilibration time between the two phases were optimized for their maximum accumulation onto the solid surface. The effect of common ions on the uptake of metal ions has been monitored under optimal conditions. The variation of retention of each metal ion with temperature was used to compute the thermodynamic quantities DeltaH, DeltaS and DeltaG. The values 18.1+/-0.6 kJmol(-1), 74+/-2 Jmol(-1)K(-1), and -3.8+/-0.04 kJmol(-1) at 298 K; 10.8+/-0.8 kJmol(-1), 48.8+/-2.7 Jmol(-1)K(-1), and -4.6+/-0.3 kJmol(-1) at 298 K; and -37.4+/-2k Jmol(-1), 105+/-7 Jmol(-1)K(-1) and -2.58+/-0.5 kJmol(-1) at 298 K were obtained for Cd(II), Cr(III) and Hg(II) ions, respectively. The sorption data were analysed by applying different sorption isotherms. The sorption capacity and energy were evaluated for each metal ion. The values of the Freundlich constants 1/n and C(m) were 0.92+/-0.04 and 52.6+/-22.2 mmolg(-1); 0.85+/-0.05 and 56.0+/-0.03 mmolg(-1); and 0.88+/-0.03 and 6.84+/-0.45 mmolg(-1) for Cd(II) Cr(III) and Hg(II) ions, respectively. Similarly, the Dubinin-Radushkevich (D-R) constants beta, X(m,) and E were evaluated for the three metal ions. To check the selectivity of the sorbent, sorption of a number of elements was measured under similar conditions. Separation of Zn(II) from Cd(II); Cr(III) from I(I), Zr(IV), Se(IV), and Hg(II) from Se(IV) and Zn(II) can be achieved using this sorbent. This cheap material has potential applications in analytical chemistry, water decontamination, industrial effluent treatment and in pollution abatement.     

SIMULATING SEDIMENT TRANSPORT IN THE CARSON RIVER AND LAHONTAN RESERVOIR,NEVADA, USA1

ABSTRACT: The discovery of the Comstock Lode in western Nevada in 1859 initiated the use of liquid mercury (Hg) or “quicksilver” to remove gold (Au) and silver (Ag) from crushed ore. Today, Hg is present in historic mill tailings piles, in alluvial deposits adjacent to the Carson River, and in Lahontan Reservoir. Mercury concentrations in Carson River water have been reported as high as 61 μg/L by the U.S. Geological Survey. Fish from Lahontan Reservoir have methylmorcury (MeHg) concentrations as much as four times the 1.0 μg/g limit for human consumption. Since more than 95 percent of total Hg in water can be associated with particulates, the transport of sediment must be quantified to understand the fate of Hg in the system. By linking the RIVMOD hydrodynamic model with the WASP5 water quality model, and using suspended sediment rating curves along with bedload transport equations, reliable predictions of sediment transport can be made. Measured suspended sediment data from the Carson River, and an estimate of annual sediment loading to Lahontan Reservoir, were used to create a calibrated sediment transport model. Model simulations predicted the long term transport of sediment into Lahontan Reservoir, the transport of sediment into Lahontan Reservoir during a flood year (1986 water year), and concentrations of total Hg in the Carson River using an estimate of sediment Hg concentrations. This research will eventually be used with an Hg model to predict the fate of Hg in the river and reservoir system.     

Clonal differences in mercury tolerance, accumulation, and distribution in willow

This study was performed to investigate mercury (Hg) tolerance, accumulation, and translocation within the genus Salix for the potential use of this plant to remediate Hg-contaminated sites. Six clones of willow (Salix spp.) were tested on tolerance to Hg by treating plants grown in solution culture with 0 to 15 microM HgCl(2). Results showed that willow had a large variation in its sensitivity to Hg. However, the accumulation and translocation of Hg to shoots was similar in the eight tested willow clones as shown by cold vapor atomic absorption spectrometry analysis when plants were treated with 0.5 microM HgCl(2) in a nutrient solution. The majority of total Hg accumulated was localized to the roots, whereas only 0.45 to 0.62% of the total Hg accumulated via roots was translocated to the shoots. Thus, the root system is the main tissue of willow that accumulates Hg and the majority of the Hg in the root system (80%) was bound in the cell wall.     

Simultaneous radioassays of bacterial production and mercury methylation in the periphyton of a tropical and a temperate wetland

Laboratory radioassays were made to study mercury (Hg) methylation together with bacterial production in the periphyton of two aquatic macrophytes, the submerged Myriophyllum spicatum, from a constructed wetland in Sweden and the floating Eichhornia crassipes, from a eutrophied tropical lake in Brazil. Time course incubations were made by addition of (203)HgCl(2) and the methylmercury formed was extracted at pre-defined time intervals. Bacterial production ((14)C-leucine incorporation) was measured at the same time intervals, with plants removed from parallel incubations made with and without addition of cold HgCl(2). For E. crassipes, higher methylmercury production was observed at elevated bacterial production, whereas for M. spicatum, the bacterial production was significantly lower, and Hg methylation was below the detection limit. The combined results confirm the importance of microbial processes for Hg methylation, although other factors are known to influence this process in complex ways. The addition of Hg did not significantly influence bacterial production, while the incubation temperatures used (25 and 35 degrees C) resulted in different methylation rates. Radiotracer techniques for measurements of bacterial production such as (14)C-leucine uptake can provide useful insights into the Hg cycle in aquatic environments, and our data suggest that they may be used as a proxy of mercury methylation potentials.     

Fish Mercury and Surface Water Sulfate Relationships in the Everglades Protection Area

Few published studies present data on relationships between fish mercury and surface or pore water sulfate concentrations, particularly on an ecosystem-wide basis. Resource managers can use these relationships to identify the sulfate conditions that contain fish with health-concerning total mercury (THg) levels and to evaluate the role of sulfate in methyl-mercury (MeHg) production. In this study, we derived relationships between THg in three fish trophic levels (mosquitofish, sunfish, and age-1 largemouth bass) and surface water sulfate from 1998 to 2009 for multiple stations across the Everglades Protection Area (EPA). Results show the relationship between sulfate and fish THg in each fish type is nonlinear and largely skewed, similar to the relationship between MeHg production and sulfate concentration in peatland sediment pore water identified by other researchers. Peak fish THg levels occurred in ~1 to 12 mg/L sulfate conditions. There was significant variability in the fish THg data, and there were several instances of high-fish THg levels in high-sulfate conditions (>30 mg/L). Health-concerning fish THg levels were present in all surface water sulfate conditions; however, most of these levels occurred in 1–20 mg/L sulfate. The data in this study, including recent studies, show consistent and identifiable areas of high- and low-fish THg across the spectrum of surface water sulfate concentration, therefore, applying an ecosystem-wide sulfur strategy may be an effective management approach as it would significantly reduce MeHg risk in the EPA.     

Mercury speciation in highly contaminated soils from chlor-alkali plants using chemical extractions

A four-step novel sequential extraction procedure (SEP) was developed to assess Hg fractionation and mobility in three highly contaminated soils from chlor-alkali plants (CAPs). The SEP was validated using a certified reference material (CRM) and pure Hg compounds. Total, volatile, and methyl Hg concentrations were also determined using single extractions. Mercury was separated into four fractions defined as water-soluble (F1), exchangeable (F2) (0.5 M NH4Ac-EDTA and 1 M CaCl2 were tested), organic (F3) (successive extractions with 0.2 M NaOH and CH3COOH 4% [v/v]), and residual (F4) (HNO3 + H2SO4 + HClO4). The soil characterization revealed extremely contaminated (295 +/- 18 to 11 500 +/- 500 mg Hg kg(-1)) coarse-grained sandy soils having an alkaline pH (7.9-9.1), high chloride concentrations (5-35 mg kg(-1)), and very low organic carbon content (0.00-18.2 g kg(-1)). Methyl Hg concentrations were low (0.2-19.3 microg kg(-1)) in all soils. Sequential extractions indicated that the majority of the Hg was associated with the residual fraction (F4). In Soils 1 and 3, however, high percentages (88-98%) of the total Hg were present as volatile Hg. Therefore, in these two soils, a high proportion of volatile Hg was present in the residual fraction. The nonresidual fraction (F1 + F2 + F3) was most abundant in Soil 1 (14-42%), suggesting a higher availability of Hg in this soil. The developed and validated SEP was reproducible and efficient for highly contaminated samples. Recovery ranged between 93 and 98% for the CRM and 70 and 130% for the CAP-contaminated soils.     

微波消解-原子荧光光谱法同时测定土壤中痕量砷和汞

建立了微波消解—原子荧光光谱法同时测定土壤中痕量砷和汞的方法。通过对消解体系以及灯电流、载气流量、屏蔽气流量等仪器参数进行优化,确定了最佳实验条件。在优化的实验条件下,采用原子荧光光谱法同时测定砷和汞的检出限分别为0.02μg/L和0.01μg/L,线性范围分别为0～40μg/L和0～4μg/L,两元素的加标回收率在92%～102%之间,相对标准偏差砷为0.9%～3.1%,汞为1.5%～3.4%,完全适用于土壤环境样品的检测。     

Adsorption-desorption characteristics of mercury in paddy soils of China

Mercury (Hg) has received considerable attention because of its association with various human health problems. Adsorption-desorption behavior of Hg at contaminated levels in two paddy soils was investigated. The two representative soils for rice production in China, locally referred to as a yellowish red soil (YRS) and silty loam soil (SLS) and classified as Gleyi-Stagnic Anthrosols in FAO/UNESCO nomenclature, were respectively collected from Jiaxin County and Xiasha District of Hangzhou City, Zhejiang Province. The YRS adsorbed more Hg(2+) than the SLS. The characteristics of Hg adsorption could be described by the simple Langmuir adsorption equation (r2 = 0.999 and 0.999, P < 0.01, respectively, for the SLS and YRS). The maximum adsorption values (Xm) that were obtained from the simple Langmuir model were 111 and 213 mg Hg(2+) kg(-1) soil, respectively, for the SLS and YRS. Adsorption of Hg(2+) decreased soil pH by 0.75 unit for the SLS soil and 0.91 unit for the YRS soil at the highest loading. The distribution coefficient (kd) of Hg in the soil decreased exponentially with increasing Hg(2+) loading. After five successive desorptions with 0.01 mol L(-1) KCl solution (pH 5.4), 0 to 24.4% of the total adsorbed Hg(2+) in the SLS soil was desorbed and the corresponding value of the YRS soil was 0 to 14.4%, indicating that the SLS soil had a lower affinity for Hg(2+) than the YRS soil at the same Hg(2+) loading. Different mechanisms are likely involved in Hg(2+) adsorption-desorption at different levels of Hg(2+) loading and between the two soils.     

Removal of mercury from aqueous solutions using activated carbon prepared from agricultural by-product/waste

Removal of mercury from aqueous solutions using activated carbon prepared from Ceiba pentandra hulls, Phaseolus aureus hulls and Cicer arietinum waste was investigated. The influence of various parameters such as effect of pH, contact time, initial metal ion concentration and adsorbent dose for the removal of mercury was studied using a batch process. The experiments demonstrated that the adsorption process corresponds to the pseudo-second-order-kinetic models and the equilibrium adsorption data fit the Freundlich isotherm model well. The prepared adsorbents ACCPH, ACPAH and ACCAW had removal capacities of 25.88 mg/g, 23.66 mg/g and 22.88 mg/g, respectively, at an initial Hg(II) concentration of 40 mg/L. The order of Hg(II) removal capacities of these three adsorbents was ACCPH > ACPAH > ACCAW. The adsorption behavior of the activated carbon is explained on the basis of its chemical nature. The feasibility of regeneration of spent activated carbon adsorbents for recovery of Hg(II) and reuse of the adsorbent was determined using HCl solution.     

Environmental and human exposure assessment monitoring of communities near an abandoned mercury mine in the Philippines: a toxic legacy

Abandoned mines are an important global concern and continue to pose real or potential threats to human safety and health including environmental damage/s. Very few countries had government mine regulation and reclamation policies until the latter part of the century where legal, financial and technical procedures were required for existing mining operations. Major reasons for mine closure may be mainly due to poor economies of the commodity making mining unprofitable, technical difficulties and national security. If the mine is abandoned, more often than not it is the government that shoulders the burden of clean-up, monitoring and remediation. The topic of abandoned mines is complex because of the associated financial and legal liability implications. Abandoned mercury mines have been identified as one of the major concerns because of their significant long-term environmental problems. Primary mercury production is still ongoing in Spain, Kyrgzystan, China, Algeria, Russia and Slovakia while world production declined substantially in the late 1980s. In the Philippines, the mercury mine located southeast of Manila was in operation from 1955 to 1976, before ceasing operation because of the decline in world market price for the commodity. During this time, annual production of mercury was estimated to be about 140,000 kg of mercury yearly. Approximately 2,000,000 t of mine-waste calcines (retorted ore) were produced during mining and roughly 1,000,000 t of these calcines were dumped into nearby Honda Bay to construct a jetty to facilitate mine operations where about 2000 people reside in the nearby three barangays. In October, 1994 the Department of Health received a request from the Provincial Health Office for technical assistance relative to the investigation of increasing complaints of unusual symptoms (e.g. miscarriages, tooth loss, muscle weakness, paralysis, anemia, tremors, etc.) among residents of three barangays. Initial health reports revealed significant elevation of blood mercury levels exceeding the then recommended exposure level of 20ppb in 12 out of the 43 (27.9%) residents examined. The majority of the volunteers were former mine workers. In this study the abnormal findings included gingivitis, mercury lines, gum bleeding and pterydium. The most common neurologic complaints were numbness, weakness, tremors and incoordination. Anemia and elevated liver function tests were also seen in a majority of those examined. The assessment also revealed a probable association between blood mercury level and eosinophilia. The same association was also seen between high mercury levels and the presence of tremors and working in the mercury mine. To date, there are very limited environmental and health studies on the impact of both total and methylmercury that have been undertaken in the Philippines. Thus, this area of study was selected primarily because of its importance as an emerging issue in the country, especially regarding the combined effects of total and methylmercury low-dose and continuous uptake from environmental sources. At present the effects of total mercury exposure combined with MeHg consumption remain an important issue, especially those of low-dose and continuous uptake. Results of the study showed that four (4) species of fish, namely ibis, tabas, lapu-lapu and torsillo, had exceeded the recommended total mercury and methylmercury levels in fish (NV>0.5 microg/gf.w., NV>0.3 microg/gf.w., respectively). Saging and kanuping also exceeded the permissible levels for methylmercury. Total and methylmercury in canned fish, and total mercury in rice, ambient air and drinking water were within the recommended levels, however, additional mercury load from these sources may contribute to the over-all body burden of mercury among residents in the area. Surface water quality at the mining area, Honda Bay and during some monitoring periods at Palawan Bay exceeded total mercury standards (NV>0.002 ng/mL). Soil samples in two sites, namely Tagburos and Honda Bay, exceeded the EPA Region 9 Primary Remediation Goal recommended values for total mercury for residential purposes (NV>23 mg/kg). The hand to mouth activity among infants and children is another significant route for mercury exposure. Statistically significant results were obtained for infants when comparing the results after one year of monitoring for methylmercury levels in hair for both exposed and control sub-groups. Likewise, comparing the initial and final hair methylmercury levels among pregnant women/mothers in the exposed group showed statistically significant (p<0.05) results. Comparing the exposed and control sub-groups' mercury hair levels per sub-group showed statistically significant results among the following: (a) initial and final total mercury hair levels among children, (b) initial and final methylmercury hair levels among children, (c) final total mercury hair levels among pregnant women, (d) initial and final total mercury hair levels among mothers, and (e) initial and final methyl hair levels among mothers.