Total Mercury In Sediments Research Articles

Mercury in aquatic ecosystems of two indigenous communities in the Piedmont Ecuadorian Amazon: evidence from fish, water, and sediments

Mercury is a highly toxic element present in water, soil, air, and biota. Anthropogenic activities, such as burning fossil fuels, mining, and deforestation, contribute to the presence and mobilization of mercury between environmental compartments. Although current research on mercury pathways has advanced our understanding of the risks associated with human exposure, limited information exists for remote areas with high diversity of fauna, flora, and indigenous communities. This study aims to deepen our understanding of the presence of total mercury in water, sediments, and fish, within aquatic ecosystems of two indigenous territories: Gomataon (Waorani Nationality) and Sinangoé (Ai´Cofán Nationality) in the Ecuadorian Amazon. Our findings indicate that, for most fish (91.5%), sediment (100%) and water (95.3%) samples, mercury levels fall under international limits. For fish, no significant differences in mercury levels were detected between the two communities. However, eight species exceeded recommended global limits, and one surpassed the threshold according to Ecuadorian legislation. Piscivore and omnivore fish exhibited the highest concentrations of total mercury among trophic guilds. Only one water sample from each community’s territory exceeded these limits. Total mercury in sediments exhibited greater concentrations in Gomataon than Sinangoé. Greater levels of mercury in sediments were associated with the occurrence of total organic carbon. Considering that members of the communities consume the analyzed fish, an interdisciplinary approach, including isotopic analysis, methylmercury sampling in humans, and mercury monitoring over time, is imperative for a detailed risk assessment of mercury exposure in Amazonian communities.

Broad-Scale Assessment of Methylmercury in Adult Amphibians.

Mercury (Hg) is a toxic contaminant that has been mobilized and distributed worldwide and is a threat to many wildlife species. Amphibians are facing unprecedented global declines due to many threats including contaminants. While the biphasic life history of many amphibians creates a potential nexus for methylmercury (MeHg) exposure in aquatic habitats and subsequent health effects, the broad-scale distribution of MeHg exposure in amphibians remains unknown. We used nonlethal sampling to assess MeHg bioaccumulation in 3,241 juvenile and adult amphibians during 2017-2021. We sampled 26 populations (14 species) across 11 states in the United States, including several imperiled species that could not have been sampled by traditional lethal methods. We examined whether life history traits of species and whether the concentration of total mercury in sediment or dragonflies could be used as indicators of MeHg bioaccumulation in amphibians. Methylmercury contamination was widespread, with a 33-fold difference in concentrations across sites. Variation among years and clustered subsites was less than variation across sites. Life history characteristics such as size, sex, and whether the amphibian was a frog, toad, newt, or other salamander were the factors most strongly associated with bioaccumulation. Total Hg in dragonflies was a reliable indicator of bioaccumulation of MeHg in amphibians (R2 ≥ 0.67), whereas total Hg in sediment was not (R2 ≤ 0.04). Our study, the largest broad-scale assessment of MeHg bioaccumulation in amphibians, highlights methodological advances that allow for nonlethal sampling of rare species and reveals immense variation among species, life histories, and sites. Our findings can help identify sensitive populations and provide environmentally relevant concentrations for future studies to better quantify the potential threats of MeHg to amphibians.

Determination and evaluation of the ecological risk of mercury in different granulometric fractions of sediments from a public supply river in Brazil

This work reports the quantification of total mercury in sediments collected in periods with and without rain from the Joanes River, Bahia, Brazil. Determinations were made using Direct Mercury Analysis (DMA), the accuracy of which was confirmed with two certified reference materials. The highest total mercury concentrations were found at the sampling point close to commercial areas and large residential condominiums. On the other hand, the lowest levels were found in the site close to a mangrove region. The geoaccumulation index was applied to the total mercury results, evidencing low contamination in the region studied. The contamination factor showed that of the seven stations investigated, four samples collected in the rainy season showed moderate contamination. The results of the ecological risk assessment were utterly consistent with the contamination factor data. This study showed that the smaller sediment particles concentrate more mercury, corroborating what has been predicted by the adsorption processes.

Evaluation of Total Mercury in Sediments of the Descoberto River Environmental Protection Area-Brazil.

To evaluate the total mercury accumulation (THg) in the Descoberto river basin environmental protection area (DREPA), nine sediment and water samples were collected from the Descoberto reservoir (lentic environment), and 23 in its tributaries (lotic environment), which are located in a densely urbanized area within the Descoberto river watershed, Brazil. The following physicochemical parameters of water were determined: dissolved oxygen (DO); hydrogen potential (pH); total dissolved solids (TDS); nitrate (NO3−); chloride (Cl−); temperature (T); sulfate (SO42−), and in sediment, the concentration of total mercury (THg) and volatile material (VM) was determined. THg concentrations in sediments showed a significant difference (p = 0.002) between tributaries (0.03 µg g−1 ± 0.02) and reservoir (0.08 µg g−1 ± 0.04), indicating accumulation in the lentic environment. Most of the results evaluated for ecotoxicological risks presented values below the concentration, at which adverse effects would rarely be observed, ERL (effects range low). However, in relation to the enrichment factor (EF), applied to identify the anthropogenic contribution, the results indicate that most of the samples are moderately polluted through atmospheric deposition due to vehicular traffic and agriculture. These results show that the likelihood of methylation in the lentic environment is higher than in the lotic environment.

The spatial distribution of total mercury in sediments in the Yatsushiro Sea, Japan.

The Yatsushiro Sea in Japan is contaminated with mercury in wastewater discharge from the Chisso Company, which produced acetaldehyde from 1932 onwards. In this study, we investigated the current spatial distribution of total mercury (T-Hg) in sediments, both at the surface and at different depths, using 43 sediment cores and 22 surface sediment samples collected from the Yatsushiro Sea in August 2017. Altogether, 821 surface and core samples were analyzed for their T-Hg concentrations. Most of the mercury that was discharged from Chisso remained either in, or around the exit of, Minamata Bay, but some had been transported from Minamata Bay to the Nagashima Sea. We estimated that almost 51 and 6 tons of mercury had accumulated in the Yatsushiro and the Amakusa Sea areas, respectively. The amount of acetaldehyde produced in Chisso over time was correlated with the T-Hg concentrations in the sediments from the Yatsushiro Sea.

Mercury Distribution of Benthonic Animals and Response to Mercury in Sediments in Caohai Wetland, Guizhou Province

Caohai wetland is a National Nature Reserve. Benthic animals were collected from the deep-water area in the middle of Caohai Lake and the shallow-water area in the surrounding marshes, and mercury and methyl mercury distributions in the benthic animals were analyzed and discussed. The risk of mercury pollution was evaluated. The concentrations of total mercury and methyl mercury in the benthonic animals were in the range of 0.51-46.55 ng·g-1 with an average of 7.82 ng·g-1 and 0.04-27.71 ng·g-1 with an average of 4.31 ng·g-1, respectively. This was lower than reports from other natural reserves. By contrast, the total mercury and methyl mercury in the benthic animals in summer were higher than in other seasons, which was consistent with the characteristics of methyl mercury distribution in sediments but opposite to the spatial distribution characteristics of total mercury in sediments. The methyl mercury contents in Cipangopaludina cathayensis were positively correlated with the content of methyl mercury in the sediments (r=0.52, P<0.05). The results showed methylation and the bioavailability of mercury in sediments from the shallow-water area were obviously higher than those from the deep-water area in the middle of Caohai Lake. The difference in organic matter content of the sediment or the wet-dry alternation (flooding-receding-flooding) in the surrounding shallow marshes was suspected to be associated with the obvious difference. The high enrichment coefficient of total mercury and methyl mercury in benthic animals were sufficient to raise the risk of mercury contamination in the aquatic food chain in the wetland.

Seasonal changes of mercury speciation in the coastal sediments

PurposeMercury speciation in sediments is linked to environmental conditions and processes. Domination of particular mercury species depends on its source, displays considerable seasonal behavior, and may be further modified due to oxygen levels, icing conditions, or the input of fresh organic matter. The purpose of this study was to examine the coastal area of the Gulf of Gdańsk in terms of mercury contamination and the influence of seasonal environmental changes on its speciation.Materials and methodsIn three highly dynamic coastal sites, mercury speciation in sediments was studied in relation to other environmental parameters (redox conditions, organic matter concentration, bacteria abundance, etc.). Sediment and water samples were collected monthly during a 3-year study. Sequential extraction of sediments was used for identification of four inorganic mercury species: dissolved, bound with fulvic and humic acids, mercury sulfide, and residual fraction. Cold vapor atomic fluorescence spectrometry (CV-AFS) was used for extracts and liquid sample analysis. Total mercury in sediments was measured with atomic absorption spectrometry (AAS). Changes in salinity were analyzed by measurements of chloride and sulfate ion concentrations using ion chromatography. Bacteria number and biomass were measured by direct counting using epifluorescence microscopy.Results and discussionSeasonal changes in mercury speciation were observed at all sites and attributed to different processes. Labile mercury fraction contribution varied from 0 to 80%. The speciation patterns varied locally as the stations selected for the study are diversified in terms of anthropogenic impact, water dynamics, and output from land. Mercury concentrations at all stations fluctuated during phytoplankton blooms, icing of marine waters, precipitation, or increased surface runoff from the land. In this local scale, the global climate changes are visible already as environmental conditions in studied area changed in comparison to elder research.ConclusionsObtained results suggest that although mercury emissions to the environment have decreased in recent years, local weather conditions, which may be intensified by climate change, seriously affect the bioavailability of past mercury deposits in coastal sediments.

An Ecological and Human Biomonitoring Investigation of Mercury Contamination at the Aamjiwnaang First Nation

The Aamjiwnaang First Nations community is located in Canada's 'Chemical Valley' situated in southwest Ontario near Sarnia. Mercury pollution in the region has been known since the 1940s but little is known about levels in the environment and area residents. The current study, using ecological and human exposure assessment methods, was conducted at the community's request to help fill these gaps. First, Canada's National Pollutant Release Inventory and the U.S. Toxics Release Inventory were queried to investigate mercury releases from area facilities. In 2010, 700 pounds of mercury were emitted into the air, 25 pounds were released into water bodies, and 93 thousand pounds were disposed of on-site via underground injections or into landfills, and together these show continued releases into the region. Second, mercury levels were measured in stream sediment and nearby soil from sites at Aamjiwnaang (n=4) and off Reserve (n=19) in Canada and the U.S. during three seasons that spanned 2010-2011. Total mercury in sediment across all sites and sampling seasons ranged from 5.0 to 398.7µg/kg, and in soils ranged from 1.2 to 696.2µg/kg. Sediment and soil mercury levels at Aamjiwnaang were higher than the reference community, and Aamjiwnaang's Talfourd Creek site had the highest mercury levels. Third, a biomonitoring study was performed with 43 mother-child pairs. Hair (mean±SD of all participants: 0.18±0.16µg/g) and blood (1.6±2.0µg/L) mercury levels did not differ between participants studied on- and off-Reserve, likely because of limited seafood intake (<1 serving/week). Urine mercury levels (0.5±0.8µg/L) were significantly higher (1.5-2.5 times) in mother-child pairs living on-Reserve versus those living off-Reserve. In general, the study links evidence of mercury sources, environmental fate, and human exposures, and in doing so it shows that mercury levels in ecological and human samples are similar to values found in other areas, though there are some trends and evidence of contamination at Aamjiwnaang that warrant attention.

Biogeochemical factors affecting the distribution, speciation, and transport of Hg species in the Deûle and Lys Rivers (Northern France).

The Deûle River is a highly polluted River by heavy metals caused by the historical discharges of ore minerals from the former ore smelter "Metaleurop." The potential mercury (Hg) pollution in the Deûle River implicates the importance of Hg distribution study in the river. As well as to configure the different biogeochemical factors that control the distribution and the potential transport of Hg to distant places. Four different sites were studied as follows: D-A (Deûle River, a site located upstream the river), D-B (Deûle River, a site located near a Zn, Pb, Cu, and Ni smelter that closed in 2003), L-C (Lys River, a site located upstream the confluence of the Deûle River with Lys River), and L-D (downstream the rivers confluence). Different Hg analyses were performed including total mercury in sediment (HgTS), methylmercury (MeHg) in sediment, total mercury in pore water (HgTPW), total mercury in surface water (HgTD), and total suspended particulate Hg in water (HgTP). HgTS decreases downstream from the Deûle River sites with a mean value of 11 ± 0.34 mg/kg to Lys River site (L-D) with a mean value of 0.53 ± 0.02 mg/kg at the confluence. The unaffected side of the Lys River, localized before the confluence (L-C), is characterized by low HgTS of an average value of 0.042 ± 0.003 mg/kg and high % MeHg reaching 4.2 %. Whereas, the highly contaminated Deûle sites are designated by low % MeHg with an average value of 0.053 %. Low pristine environments like that found in L-C site with more favorable biogeochemical conditions of lower concentrations of HgTS, sulfides, and Corg host more active biotic methylation than that of the highly polluted Deûle sites with high concentrations of HgTS and sulfides concentrations. Methylation in D-B (the closet site to Metaleurop smelter) is an old and recent methylation activity that has contributed to MeHg accumulation in the sediments as opposed to the exclusive recent events of methylation in Lys sites. MeHg in all sites is produced in situ rather than exported from other potential sources confirmed by significant relations of % MeHg with %Corg and AVS. Hg pollution is transported from the Deûle River to the Lys River (L-C and L-D) through suspended particles leached or remobilized from the River catchment. The dominance of reducing conditions in the Deûle River attributed to higher sulfide concentration has contributed to higher HgTPW than the Lys sites. Diffusive fluxes of HgT from sediment to water column for the Deûle and Lys River sites (L-C and L-D) were estimated to be 224, 53, and 2 ng/cm(2) year, respectively.

Total mercury in sediments, macrophytes, and fish from a shallow steppe lake in eastern Austria.

During summer 2011, samples of sediment, macrophytes, and fish tissues from the shallow, slightly alkaline Lake Neusiedl, Austria, were evaluated for their total Hg content. This is the first report of Hg levels from this lake. Sediments displayed Hg contents between 0.025 and 0.113 μg g(-1) dw (dry weight), significantly correlating with the proportion of organic components pointing to a small anthropogenic impact on the lake's Hg content. Hg Levels in plants and fish were unexpectedly high: both investigated submerged plant species, Potamogeton pectinatus and Myriophyllum spicatum, showed mean values of 0.245 ± 0.152 and 0.298 ± 0.115 μg g(-1) dw, respectively. Biomagnification was evident when comparing muscle samples of the planktivorous fish species rudd Scardinus erythrophthalmus (n = 10, mean = 0.084 μg g(-1) ww (wet weight)) with the piscivorous perch Perca fluviatilis (n = 21, mean = 0.184 μg g(-1) ww) or pike-perch Sander lucioperca (n = 9, mean = 0.205 μg g(-1) ww). Significantly lower values were found in the muscle of the piscivorous pike Esox lucius (n = 25, mean = 0.135 μg g(-1) ww), pointing to a specific Hg metabolism of this fish, presumably under the particular physicochemical properties of the lake. Hg Concentrations in fish could pose a risk to piscivorous birds in this protected wetland system.

Influence of a wastewater treatment plant on mercury contamination and sediment characteristics in Vidy Bay (Lake Geneva, Switzerland)

Previous direct observations of the sediment surface in Vidy Bay, Lake Geneva (Switzerland), revealed a range of sediment characteristics in terms of colour, texture and morphology. Dives with the MIR submersibles during the éLEMO project permitted the exploration of a large portion of Vidy Bay. It is the most contaminated part of Lake Geneva, due to inputs of treated and untreated waters from a large wastewater treatment plant (WWTP). To evaluate the influence of WWTP effluent on mercury contamination and sediment characteristics, 14 sediment cores were retrieved in the vicinity of the wastewater treatment plant effluent. Total mercury concentrations in sediments ranged between 0.32 and 10.1 mg/kg. Inorganic mercury and monomethylmercury concentrations in overlying and pore waters were also measured. The total partition coefficients of mercury (logK d) ranged from 3.6 to 5.8. The monomethylmercury concentration in pore waters of surface sediments was a large proportion of the total mercury concentration (44 ± 25 %). A Spearman test showed a negative correlation between the distance to the wastewater treatment plant outlet and the concentrations of total mercury in sediments and pore waters. Visual observations from the submersible allowed recognizing six different types of sediment. The areal distribution of these different sediment types clearly showed the influence of the wastewater treatment plant outlet on the sediment surface patterns. However, no relationship with mercury concentrations could be established.

Environmental Impacts of the Tennessee Valley Authority Kingston Coal Ash Spill. 2. Effect of Coal Ash on Methylmercury in Historically Contaminated River Sediments

The Tennessee Valley Authority Kingston coal ash spill in December 2008 deposited approximately 4.1 million m(3) of fly ash and bottom ash into the Emory and Clinch River system (Harriman, Tennessee, U.S.A.). The objective of this study was to investigate the impact of the ash on surface water and sediment quality over an eighteen month period after the spill, with a specific focus on mercury and methylmercury in sediments. Our results indicated that surface water quality was not impaired with respect to total mercury concentrations. However, in the sediments of the Emory River near the coal ash spill, total mercury concentrations were 3- to 4-times greater than sediments several miles upstream of the ash spill. Similarly, methylmercury content in the Emory and Clinch River sediments near the ash spill were slightly elevated (up to a factor of 3) at certain locations compared to upstream sediments. Up to 2% of the total mercury in sediments containing coal ash was present as methylmercury. Mercury isotope composition and sediment geochemical data suggested that elevated methylmercury concentrations occurred in regions where native sediments were mixed with coal ash (e.g., less than 28% as coal ash in the Emory River). This coal ash may have provided substrates (such as sulfate) that stimulated biomethylation of mercury. The production of methylmercury in these areas is a concern because this neurotoxic organomercury compound can be highly bioaccumulative. Future risk assessments of coal ash spills should consider not only the leaching potential of mercury from the wastes but also the potential for methylmercury production in receiving waters.

Distribution of mercury in water, sediment and fish from the Volta lake and its major tributaries

Concentrations of total mercury and methyl mercury were determined in fish and sediment from the waters of the Volta Lake and its main tributaries to understand their distribution in the ecosystem. Total mercury concentrations in fish ranged from 2.11to 355.16 (mean: 75.64) ng/g wet wt. Methyl mercury concentration ranged from 1.77 to 319.48 (mean: 68.44) ng/g wet wt and accounted for, on the average 90% of the total mercury in the muscles of the fish. Methyl mercury concentrations in fish were directly proportional to total mercury concentrations with average correlation coefficient of r = 0.98. The relationship of total mercury and methyl mercury concentrations in fish to those of sediments from corresponding locations was fish-species dependent. Concentrations of total mercury in sediment ranged from 0.96 to 700.25 ng/g dry wt. which is lower than the IAEA threshold of 810ng/g. Water samples from the main tributaries of the Volta and the Volta Lake showed total mercury concentrations of 0.0027 to 0.0862 ng/L and methylmercury concentrations of 0.0004 to 0.0259 ng/L. The methylmercury concentrations accounted for 13.2 to 35.0% of total mercury in the water samples. The results of this study indicate that mean total mercury and methylmercury concentrations in fish increase with increase in trophic level of fish. All the fish samples obtained from the Volta and its major tributaries had mercury concentrations below the WHO/FAO recommended limit of 500 ng/g wet weight. The low levels of mercury in the fish analyzed in this study suggest a comparatively clean aquatic environment which has not yet been impacted by mercury contamination.

Total mercury in sediments and in Brazilian Ariidae catfish from two estuaries under different anthropogenic influence

Santos-São Vicente estuary, located in São Paulo State, Brazil, has a history of contamination by inorganic chemicals such as mercury (Hg). In the 1980s the Cubatão was considered one of the most polluted sites in the world as a consequence of the intense industrial activities located in the city close to the estuary. To provide data and evaluate the local biota, total mercury (THg) contents were determined in sediments and in fish, Cathorops spixii, from different areas of the Santos-São Vicente estuary. For comparison, samples were also collected in a non-polluted system with similar hydrochemistry characteristics, the Cananeia estuary. The water characteristics and THg levels in sediment and fish samples confirmed a high human influence in the Santos-São Vicente estuary. The lowest THg values, observed in Cananeia, were evidence of low anthropogenic influence. High values observed in Santos-São Vicente show the necessity for a monitoring program.

소양호 다중매체 내 수은오염실태 조사

Abstract : In this study the seasonal and spatial pattern of mercury (Hg) concentrations in multimedia environments were investi-gated in Lake So-Yang. Total mercury (TM) in water column greatly enhanced as turbidity and particulate organic carbon (POC) increased due to the severe runoff, suggesting that most of Hg existed as particulate Hg in Lake Soyang. We also collected 22 species of fish in Lake Soyang and Han River, and the average total mercury in fish was 0.073 ppm, lower than both Korean (0.5ppm) and EPA criteria (0.3 ppm). However when considering the amount of fish intake for Korean the Hg criterion in fish must be more stringent than current value, and the advisory for fish consumption should be made. Hg in fish considerably varied with sampling sites, having the highest in the upper region (Yang-gu) and the lowest in downstream (Han River). This spatial variation was possibly derived by “bloom dilution” associated with high phosphorus loading or elevated DOC concentrations, or both. Total mercury in sediment varied from 69.9 to 98.3 µg/kg, which was relatively lower than those measured in Voyageurs National Park in Minnesota in USA (102~364 µg/kg).

Assessment of mercury contamination of the Svitava and Svratka rivers and muscle of chub (Leuciscus cephalus L.) in the urban agglomeration of Brno in the Czech Republic

This study focused on the total mercury and methylmercury content in the muscle of chub (Leuciscus cephalusL.), the total mercury in the river sediments and the evaluation of health risks associated with fish contamination. Chub were caught at seven localities on the Svratka and Svitava rivers in the agglomeration of Brno in 2008. The results were compared to those obtained from the same sites in 2007. Total mercury was determined by atomic absorption spectrophotometry using an AMA 245 analyzer, and methylmercury was determined by gas chromatography (using an electron-capture detector) after acid digestion and toluene extraction in chub muscle. The highest concentrations of total mercury and methylmercury (0.12 ± 0.14 and 0.07 ± 0.02 mg·kg-1fresh weight, respectively) were found in Svratka before junction (south of Brno), whereas the lowest concentration of mercury and methylmercury in chub (0.06 ± 0.01 and 0.04 ± 0.01 mg·kg-1) was detected in Svitava before junction with the Svratka River. Total mercury in sediments ranged from 0.01 to 1.05 mg·kg-1dry weight, the highest value was detected in the sediment from Rajhradice. The lowest content (0.01 mg·kg-1) was at Kníničky. Hazard indices calculated for the selected localities showed no health risk for either a standard consumer or a fishing family. Fish from the Svitava and Svratka rivers show very low mercury concentration and hazard index and their consumption poses no health risk from total mercury and methylmercury contamination.

An Investigation of Total Mercury in Sediments and Interstitial Water in the North Fork Holston River below Saltville, Virginia, USA

ABSTRACT The North Fork Holston River (NFHR) is historically renowned for having one of the most diversity rich unionid populations (Unionidae) worldwide; however, in recent decades, drastic reductions in mussel diversity, abundance, and recruitment have been documented. Unionid declines have been blamed on anthropogenic influences, specifically mercury-contaminated wastewater from a now closed chlorine-alkali plant in Saltville, VA. The objective of this research was to evaluate total mercury (Hg) contamination of sediments and interstitial waters in the NFHR beginning below Saltville and downstream for approximately 50 river miles. Mercury contaminated sediments and interstitial water were found downstream of the closed plant with the highest sediment concentration of 2.82 mg/kg dry weight total Hg found at river mile (rm) 80 and the highest interstitial water value at rm 30.4 with 2.1 μg/l. After 60-d in situ testing, total Hg concentrations in Asian clam (Corbicula fluminea) tissues were found to range from 0.016 to 0.13 mg/kg, while resident clams had Hg concentrations of 0.094 and 0.11 mg/kg wet weight. Although chronic toxicity was not observed, based on Corbicula growth and survival tests, nor in testing with cladocerans, mercury contamination is still a persistent problem at sites in the NFHR below the closed plant with negative correlations between mean clam growth and sediment Hg concentrations.

Mercury cycling in surface water, pore water and sediments of Mugu Lagoon, CA, USA

Mugu Lagoon is an estuary in southern California, listed as impaired for mercury. In 2005, we examined mercury cycling at ten sites within at most four habitats. In surface water (unfiltered and filtered) and pore water, the concentration of total mercury was correlated with methylmercury levels ( R 2 = 0.29, 0.26, 0.27, respectively, p < 0.05), in contrast to sediments, where organic matter and reduced iron levels were most correlated with methylmercury content ( R 2 = 0.37, 0.26, respectively, p < 0.05). Interestingly, levels for percent methylmercury of total mercury in sediments were higher than typical values for estuarine sediments (average 5.4%, range 0.024–38%, n = 59), while pore water methylmercury K d values were also high (average 3.1, range 2.0–4.2 l kg −1, n = 39), and the estimated methylmercury flux from sediments was low (average 1.7, range 0.14–5.3 ng m −2 day −1, n = 19). Mercury levels in predatory fish tissue at Mugu are >0.3 ppm, suggesting biogeochemical controls on methylmercury mobility do not completely mitigate methylmercury uptake through the food web.

Total mercury in sediments from mud volcanoes in Gulf of Cadiz

Mercury emissions into the environment have bothnatural and anthropogenic sources. Natural sourcesinclude volcanic activity, erosion of mineral deposits (theearth’s crust contains 0.5 parts per million of mercury)(Gochfeld, 2003; Gustin, 2003), association with hydrocar-bons (Miedaner et al., 2005; Wilhelm et al., 2006), and vol-atilization from the oceans, whereas man related sourcesinclude metal smelting, coal combustion, chemical synthe-sis/use, and waste incineration (SEC, 2005). Between2700 and 6000 tons of elemental mercury are released peryear via natural means to the biosphere through degassingfrom the earth’s crust and oceans (Tchounwou et al., 2003).Industrial wastes and the combustion of fossil fuels add upto an additional 2000–3000 tons of mercury to the environ-ment (ATSDR, 1999). Natural and anthropogenic sourcesled to a significant enhancement in environmental exposureand deposition, increasing the existing global Hg pool cre-ated by past releases (SEC, 2005).Mercury has high affinity for suspended particles, whichcan lead to its extraction from the water column and itsaccumulation in the sediments. Thus, sediments functionas a deposit and also as a source of mercury to porewatersand biota (Ramalhosa et al., 2001, 2006; Ram et al., 2003).It is also well known that methylation processes, mediatedby bacteria in sediments, convert mercury into methylmer-cury, the most toxic lipophilic form (Heyes et al., 2006;Kim et al., 2006). This organic mercury is readily bio-available, accumulating along food chains due to bio-concentration and biomagnification (Baeyens et al., 2003;Gochfeld, 2003; Tchounwou et al., 2003). Therefore, mer-cury is now acknowledged as a global, diffuse and chronicproblem (SEC, 2005) due to its high toxicity to humans,ecosystems and wildlife.Mud volcanism and fluid flow processes at active conti-nental margins with high sedimentation rates, and in accre-tionary wedges such as in the Gulf of Cadiz (GC), have animportant role in the hydrological budgets, biogeochemicalcycles and physical properties of sediments. Fluid flow andmud volcanism also make a potentially important contri-bution to the geochemical budget of metals in the oceanand in the atmosphere. Fluid advection through the sedi-ments provides an efficient mechanism for the upwardtransport of reactive components and trace gases, wheremethane is one of the most important, and has an impacton the mineralization within the shallow sediments andon the chemistry and benthic biota. The widespread occur-rence of fluid escape processes has been recognized in avariety of different marine settings and throughout the geo-logical record (Campbell et al., 2002; Peckmann and Thiel,2004). The nature and composition of the expelled fluidsand materials from the fluid escape structures and mud vol-canoes (MV) can give valuable information on the geologyand geochemistry of the deeper sediments.The Gulf of Cadiz, located south of Iberia is an areawith extensive evidence of hydrocarbon-rich gas seepage,manifested by the presence of mud volcanoes, pockmarks,diapiric ridges and the formation of methane-related authi-genic carbonates (Gardner, 2000, 2001; Mazurenko et al.,2002; Pinheiro et al., 2003; Somoza et al., 2003). The firstmud volcanoes were discovered in this area in 1999 (Gard-ner, 2000, 2001) and since then they have been extensivelyinvestigated in the framework of several national and inter-national projects (INGMAR; MVSEIS; HERMES). Mostof the geochemistry studies dealing with mud volcanoes inthis area have focused either on the characterization of thegas composition in gas hydrates and in interstitial fluids, or

Assessment of mercury mobility and bioavailability by fractionation method in sediments from coastal zone inundated by the 26 December 2004 tsunami in Thailand

The 26 December 2004 tsunami covered significant portion of a coastal zone with a blanket of potentially contaminated sediments. In this report are presented results on mercury concentrations in sediments deposited by the tsunami in a coastal zone of Thailand. Since the total mercury concentrations are insufficient to assess mercury mobility and bioavailability in sediment, its fractionation was applied. Sediments were sampled within 50 days after the event and analyzed by sequential extraction method. The procedure of sequential extraction involved five subsequent stages performed with solutions of chloroform, deionized water, 0.5 M HCl, 0.2 M NaOH, and aqua regia. The mean concentration of total mercury in sediments was 119 ± 50 ng g−1 dry mass (range 66–230). The fractionation revealed that mercury is mainly bound to the least bioavailable sulphides 75 ± 6% (range 62–86), organomercury compounds 14 ± 7% (range 4–26), and humic matter 9 ± 7% (range 1–27). The lowest contributions bring fractions of water-soluble mercury 0.8 ± 1.0% (range 0.1–3.6) and acid soluble mercury 0.9 ± 0.5% (range 0.2–2.1). Although, the total mercury content is similar in a reference sample and in the tsunami sediments, the highly toxic organomercury fraction contribution is higher in the latter. The results were compared with chemical and sedimentological properties of the sediments but no significant correlations were obtained between them.