Average THg Concentrations Research Articles

Mercury distribution in organisms, litter, and soils of the Middle Araguaia floodplain in Brazil.

Mercury (Hg) is a chemical element that, depending on its concentration, may become toxic to living organisms due to the ability of Hg to bioaccumulate in food chains. In this study, we collected samples of soil, litter, and organisms in the Middle Araguaia floodplain, Brazil. Total mercury (THg) concentrations in litter were significantly higher (p < 0.0001) than that in soil, ranging from 10.68 ± 0.55 to 48.94 ± 0.13 and 20.80 ± 1.07 to 55 .19 ± 1.59 ng g-1, respectively. Total mercury concentration levels in soil showed a linear, inversely proportional relationship with soil organic matter (SOM) contents and soil pH, consistent with the geochemical behavior of chemical elements in flooded environments. Ten orders of organisms were identified, and the average THg concentrations determined in their bodies were up to 20 times higher than those in soil and litter. We found a significant linear relationship between the levels of THg in litter and those found in soil organisms, thereby allowing the prediction of THg concentration levels in soil organisms through the analysis of litter at the sample units. The different dynamics and feeding habits of soil organisms and the concentration of THg in these organisms may be influenced by the river's course. This study provides evidence of the bioaccumulation of THg in soil organisms in the floodplain of the Middle Araguaia River, an important river basin in the Brazilian savanna.

Mercury contamination in the water and sediments of a typical inland river – Lake basin in China: Occurrence, sources, migration and risk assessment

In the area affected by non-ferrous metal mining activities, mercury (Hg) contamination in the water and sediments posed potential risks to ecology and human health. In this study, river water and sediment samples were collected in the Zijiang river - South Dongting Lake basin to analyze Hg residues, identify potential Hg sources and evaluate the ecological and health risks posed by Hg contamination. In this study, the average concentrations of THg, PHg, DHg and DMeHg in river water were 38.05 ± 27.13 ng/L, 25.18 ± 26.83 ng/L, 12.88 ± 9.64 ng/L and 0.29 ± 0.07 ng/L, respectively. The THg and MeHg contents in sediments were 234.24 ± 152.93 µg/kg and 0.48 ± 0.16 µg/kg, respectively. The more enrichment of Hg in sediments was observed in the Zijiang River than in the South Dongting Lake, especially in the upstream and midstream regions. Two potential Hg sources in the basin were identified by correlation matrix, principal component analysis (PCA) and positive matrix factorization (PMF) model. The comparable Hg flux with other rivers worldwide was found in the Zijiang River (0.53 Mg/y). Furthermore, it was found by the delayed geochemical hazard (DGH) model that the ecological risk of Hg was more significant in the Zijiang River with more frequent transformation pathways. For different populations, the health risk values caused by Hg were all lower than the USEPA’s guideline value. This study provided sound evidence for further control of Hg contamination.

Microbial mercury methylation potential in a large-scale municipal solid waste landfill, China

Landfills harbor ideal conditions for microbial mercury methylation. However, the levels and distribution of mercury (Hg) and methylmercury (MeHg), potential microbial Hg methylation, and their linkage within landfills are largely unknown. In the present study, total mercury (THg), MeHg, the Hg methylation gene (hgcA) and mer operon were quantified in 30 waste samples from different depths (0–30 m) at 5 locations within a large-scale landfill in China. The average concentrations of THg and MeHg in the solid waste samples were 1422.91 ng/g and 3.15 ng/g, respectively. THg (up to 14405.29 ng/g) and MeHg (up to 10.42 ng/g) have high concentrations in the middle part (10–15 m) along the depth profiles. The concentration of THg was strongly positively (both p < 0.05) correlated with the MeHg concentration and the relative abundance of hgcA, indicating that the THg concentration can play an important role in microbial Hg methylation. The hgcA genes were detected in most samples and mer operon were detected in all samples. Combined hgcA qPCR and metagenomics data showed that Archaea Methanofollis may mainly account for Hg methylation within landfills. These findings provide fundamental knowledge on Hg cycles in landfills.

Mercury speciation and mercury stable isotope composition in sediments from the Canadian Arctic Archipelago

Total mercury (THg) and monomethylmercury (MMHg) concentrations as well as mercury (Hg) isotope ratios were determined in sediment cores sampled from six locations from the Canadian Arctic Archipelago (CAA). At most sites, THg concentrations showed a decreasing trend with depth, ranging from 5 to 61 ng/g, implicating possible increased Hg deposition and/or riverine inputs in top sediment layers. MMHg values showed large oscillations within the top 10 cm of the cores. This variability decreased at the bottom of the cores with MMHg concentrations ranging from less than12 to up to 1073 pg/g. Average concentrations of THg and MMHg in the top 10 cm were linearly correlated, whereas no correlation was observed with organic matter (loss on ignition). Mercury isotope ratios showed negative values for both δ202Hg (−1.59 to −0.55‰) and Δ199Hg (−0.62 to −0.01‰). δ202Hg values became more negative with depth, while the opposite was observed for Δ199Hg. The former is consistent with predicted historical atmospheric Hg trends as a result of increased coal burning worldwide. Hg isotope ratio measurements in CAA sediments offer additional opportunities to trace Hg processes and sources in the Arctic.

Mercury speciation, bioavailability and risk assessment on soil–rice systems from a watershed impacted by abandoned Hg mine-waste tailings

Mercury (Hg) is a global pollutant and can be accumulated in the food chain, posing exposure risks to humans. In this study, rice plants and corresponding rhizosphere soil samples were collected from a watershed of the Wawu River Basin that is heavily impacted by historic Hg mining and retorting activities. Total mercury (THg) and methylmercury (MeHg) in rice grains, as well as other tissues and soil samples, were measured. Five soil Hg fractions, as well as soil parameters, were also determined. The results show that the average concentrations of THg and MeHg in rice grains were 14 ± 7.0 μg kg−1 and 7.2 ± 4.0 μg kg−1. Soil organic-bound (Hg-o) and strong complex-bound (Hg-s) were the main Hg fractions, accounting for 44% of the total. To estimate the Hg–ligand interaction in the soils, soil -N/Hg (R = 0.451, p < 0.05), -S/Hg (R = 0.372, p < 0.1), and -OM/Hg ratio (R = 0.320, p < 0.5) with MeHgsoil were observed with significant positive correlations, indicating that the formation of Hg–OM, Hg–N–OM or Hg–S–OM complexes could prevent Hg(II) from methylation in soils. The significant positive correlations of the -N/Hg ratio, -S/Hg ratio and -OM/Hg ratio with MeHg in rice tissues suggested that Hg methylation and MeHg demethylation occurred throughout the rice paddy ecosystem. The estimated MeHg daily intake (EDI) was 0.075 ± 0.041 μg kg−1 bw d−1 and was lower than the RfD level of 0.1 μg kg−1 bw d−1 recommended by the US EPA. However, approximately 29% of the hazardous index (HI) of MeHg in grain exceeded 1, posing a potential threat to local populations, particularly pregnant women and children.

Freshwater shrimps (Macrobrachium depressimanum and Macrobrachium jelskii) as biomonitors of Hg availability in the Madeira River Basin, Western Amazon.

Total mercury (THg) concentrations measured in two freshwater shrimp species (Macrobrachium depressimanum and Macrobrachium jelskii) showed a relationship with the location of artisanal and small-scale gold mining (ASGM) from the Madeira River Basin, Western Amazon. Between August 2009 and May 2010, 212 shrimp samples were collected in the confluence of the Madeira River with three of its tributaries (Western Amazon). THg concentration was quantified in the exoskeleton, hepatopancreas and muscle tissue of the shrimps by cold vapor atomic absorption spectrophotometry. There were no significant differences between the two shrimp species when samples came from the Madeira River, but Hg concentrations were significantly lower in a tributary outside the influence of the gold mining area. Average THg concentrations were higher in the hepatopancreas (up to 160.0ngg-1) and lower in the exoskeleton and muscle tissue (10.0-35.0ngg-1 and < 0.9-42.0ngg-1, respectively). Freshwater shrimps from the Madeira River respond to local environmental levels of Hg and can be considered as biomonitors for environmental Hg at this spatial scale. These organisms are important for moving Hg up food webs including those that harbor economic significant fish species and thus enhancing human exposure.

Comparison of mercury and methylmercury bioaccumulation in earthworms (Bimastus parvus) native to landfill-leachate-contaminated forest soil.

Total mercury (THg) and methylmercury (MeHg) bioaccumulation was explored in the Bimastus parvus species of earthworm (B. parvus) native to the leachate-contaminated forest soils around a Hg-polluted traditional landfill in Japan. General soil properties and concentrations of THg and MeHg in forest soils and in B. parvus were determined. The results indicated that the average THg concentrations in B. parvus and in forest soils in the leachate-contaminated sites were 10.21 and 14.90 times higher than those in the reference sites, respectively, whereas similar average MeHg concentrations were observed in forest soils (< 0.01 mg kg-1) and in B. parvus (0.100-0.114 mg kg-1) across all sampled sites. The average bioaccumulation factors of THg in B. parvus (BAFTHg) in forest soil were similar between the leachate-contaminated sites and the reference sites. Cluster and regression analyses demonstrated that the B. parvus Hg (THg and MeHg) and soil THg were positively correlated with each other and with soil organic matter (SOM) and clays, but were negatively correlated with sand and hardly correlated with silts and pH in leachate-contaminated forest soils. From these results, it was proposed that Hg exposure to food chains is possible through B. parvus, because B. parvus showed a high ability to accumulate THg and MeHg in both leachate-contaminated and reference forest soils. Together, these findings indicated that the role of B. parvus in MeHg production is not clear, and it is possible that the MeHg in B. parvus was firstly formed within forest soils and then accumulated in their tissues.

Spatial and temporal variation of total mercury and methylmercury in lacustrine wetland in Korea.

The spatial and temporal variations of total mercury (THg) and methylmercury (MeHg) concentrations (n = 120, respectively) in water and sediments of the Yangsuri lacustrine wetland in Korea were measured. The average concentrations of THg and MeHg in surface water were 2.04 ± 1.97 and 0.05 ± 0.05 ng L(-1), respectively. The concentrations of THg and MeHg in sediments ranged from 1.28 to 85.83 and ≤0.01 to 0.35 ng g(-1), respectively, and varied depending on the location. In the vegetated zone located near residential areas, the highest concentrations of THg and MeHg in both surface water and sediments were obtained near the residential areas, especially during the fall season. This result might be due to increased methylation rate of Hg by water turnover in the fall season. While THg and MeHg concentrations in water were not correlated, they were significantly correlated in sediment (r = 0.75; P < 0.01). Log-transformed Hg concentrations in sediments were highly correlated with log-transformed organic matter (OM) and acid volatile sulfide (AVS) concentrations (P < 0.01). We also collected five species of fish near the output point of the wetland, and MeHg concentrations in fish tissue varied from 21.30 to 154.66 μg kg(-1) w/w, which was significantly dependent on fish species (P < 0.05). This is the first reported study which measured the levels of mercury, especially MeHg in the wetlands, and freshwater fish species in Korea.

Mercury pollution in fish from South China Sea: Levels, species-specific accumulation, and possible sources

Both total mercury (THg) and methylmercury (MeHg) levels in fish collected from South China Sea (SCS) were studied to understand Hg pollution in Chinese tropical marine ecosystems. The average THg concentrations in fish species ranged from 39.6μg/kg for rabbitfish (Siganus fuscessens) to 417μg/kg for thornfish (Terapon jarbua), while those of MeHg varied from 13μg/kg (rabbitfish) to 176μg/kg (thornfish). The median values of MeHg/THg ratios in different fish species ranged from 36 to 85%. Significant inter-species differences of THg and MeHg in fish were observed due to feeding habits and fish sizes. Overall, carnivorous fish had higher levels of THg, MeHg and MeHg/THg ratios than omnivorous and herbivorous fish. High Hg levels in fish of the SCS were probably related to Hg input from atmospheric deposition and anthropogenic activities.

Environmental impact factors and mercury speciation in the sediment along Fujian and eastern Guangdong coasts

Concentrations of total mercury (THg) and methyl mercury (MeHg) were determined for 32 surface sediments collected along the coastal line of Fujian Province and eastern Guangdong Province. The spatial distributions of THg and MeHg and their environmental impact factors were investigated. The average concentrations of THg and MeHg in the sediments were 31.5 ng/g and 0.096 ng/g, respectively. Both sediment THg and MeHg concentrations showed relatively high value in the Minjiang Estuary and the coastal areas of Quanzhou and Putian. The concentrations overall decreased as the distance to the shoreline increased. The correlations among environmental impact factors and THg, MeHg were analyzed. The sediment THg concentration was highly correlated to the concentrations of organic matter, copper, total nitrogen (TN) and total phosphorus (TP), and significantly correlated to pH value of the bottom seawater and concentration of sediment sulfide. The sediment MeHg concentration was highly correlated to the concentrations of organic matter and copper, and significant correlated to the concentrations of sulfide, TN, TP and pH value of the bottom seawater.

Mercury levels in road dust and household TSP/PM2.5 related to concentrations in hair in Guangzhou, China

Road dust, household total suspended particulate matters (TSP) and PM2.5 were collected in urban area of Guangzhou, south of China, to investigate the concentrations of total mercury (THg) and methyl mercury (MeHg). The household PM2.5 concentrations varied between 16.2 and 623μg/m3. The average PM2.5 level (174μg/m3) from all of the locations exceeded 24-h concentration from WHO air quality guideline The average concentrations of THg and MeHg were: 235μg/kg and 0.392μg/kg in road dust, 600μg/kg and 1.49μg/kg in TSP; 1006μg/kg (104pg/m3) and 1.40μg/kg (0.134pg/m3) in PM2.5. Risk assessment showed that the Hazardous quotients (HQs) of exposure to Hg and MeHg via road dust and TSP were less than 1, indicating that no adverse risk was manifested. Ingestion of dust was found to constitute a relatively minor pathway of Guangzhou residents′ exposure to Hg. Furthermore, human hair samples from 88 Guangzhou citizens were also analyzed to investigate the mercury accumulation in human body in Guangzhou. The average concentrations of THg and MeHg in human hair samples were 869±831μg/kg and 104±108μg/kg respectively. However, no significant correlations of the mercury species were noted between human hair and road dust, TSP and PM2.5.

Mercury distribution and bioaccumulation up the soil-plant-grasshopper-spider food chain in Huludao City, China

The purpose of this study is to investigate total mercury (THg) distribution and its bioaccumulation up the soil-plant-grasshopper-spider in the Huludao City, which is polluted seriously by chlor-alkali and zinc smelting industry in Northeast of China. Results indicated that average THg concentrations in soil, plant leaves, grasshopper Locusta migratoria manilensis and Acrida chinensis, and spider were 0.151, 0.119, 0.167 and 0.134 mg/kg, respectively. THg spatial distribution suggested that most of mercury came from the chlor-alkali plant and the two zinc smelteries. The highest mercury concentration was found in the wings among different grasshoppers' organs. Although spiders are the predatory, THg concentrations in their bodies were not high, and only on the same level as in grasshoppers, which might be due to spiders' special living habits. In the light of the mercury transportation at every stage of the soil-plant-grasshopper-spider food chain, the bioaccumulation factors were 0.03, 0.79-1.11 and 0.80-1.13 respectively. It suggested that mercury biomagnification up terrestrial food chains was not so large and obvious as it was in the aquatic food chain.

The variations of mercury in sediment profiles from a historically mercury-contaminated reservoir, Guizhou province, China

Baihua Reservoir in Guizhou Province, China, experienced serious Hg contamination from Guizhou Organic Chemical Plant (GOCP) between 1971 and 1997. However, the biogeochemical cycling of Hg in this reservoir is not well studied. Sediment cores were collected in fall 2002, spring 2003 and in spring and fall 2004. THg and MeHg concentrations in all sediment profiles ranged from 0.26 to 38.9 mg/kg and from 0.5 to 27.5 μg/kg (d.w.), respectively. The distribution of THg in sediment cores was characterized by a few peaks, which may correspond to the Hg-containing wastewater discharge history of the GOCP. The average THg concentrations in sediments cores decreased from upstream to downstream due to the deposition of particulate Hg, which is the major form of Hg in water. THg and MeHg concentrations in pore water varied from 6.1 to 5860 ng/L and from 0.3 to 15.4 ng/L, respectively, which were significantly higher than levels in the overlying water column. Average diffusive flux from sediment to water is 1642 and 36 ng/m 2/day for THg and MeHg. The spatial distribution of THg in pore water from upstream to downstream showed the same trend as the sediment, but MeHg in pore water did not show a declining pattern with distance from the GOCP. These results suggested that sediments experienced serious contamination of Hg, and the contaminated sediment is an important Hg contamination source to the overlying water.

A comparison of total mercury and methylmercury export from various Minnesota watersheds

Methylmercury (MeHg) bioaccumulates in aquatic food webs and can pose health risks to animals at higher trophic levels. Characterization of MeHg production in and export from watersheds can help clarify exposure scenarios for aquatic life downstream. A number of studies have demonstrated that anoxic conditions in the saturated soils of wetlands can promote the production of MeHg, and these wetlands may be major sources of MeHg to connected water bodies. Here, we report in-stream loadings of total mercury (THg) and MeHg for five rivers in Minnesota (USA). The watersheds of these rivers differ widely in the proportion of land area made up by wetlands and in other land use, drainage, and soil characteristics. Export of THg from these rivers varied widely, with much higher loadings and annual average concentrations of THg in streams of the Minnesota River basin compared to streams in the headwater Mississippi River basin. In contrast and despite the apparent differences in the makeup of these watersheds, yields and annual average concentrations of MeHg were remarkably similar for the rivers studied here. Differences in land use/land cover, drainage, soils, and other characteristics of these watersheds influence the export of both THg and MeHg in these rivers, but overall MeHg yields vary less than THg yields.