Effect of methylmercury on some neurotransmitters and oxidative damage of rats

In order to study the molecular mechanism of injury in rat organs induced by methylmercury, and the relationship between neurotransmitter and oxidative damage in the toxicity process of rat injury by methylmercury was studied. The control group was physiological saline of 0.9%, the concentration of exposure groups were 5 mg/(kg5d) and 10 mg/(kg5d) respectively. The content of AChE, ACh, NOS, NO, MDA, SOD, GSH-Px and GSH in different organs of rats were determined with conventional methods. The results showed that after exposure to methylmercury for 7 d, the mercury content in brain of exposure groups increased clearly and had significant difference compared with the control group(P<0.01). In rat's brain, serum, liver and kidney, the content of ACh and AChE were all decreased; the content of NOS and NO were all increased; the content of MDA was increased compared with the control group, the exposure groups had significant difference (P<0.01); the content of SOD, GSH and GSH-Px was decreased compared with the control group, the exposure groups had significant difference(P<0.01). It could be concluded that methylmercury did effect the change of neurotransmitter and free radical. They participated in the toxicity process of injury by methylmercury. The damage of neurotransmitter maybe cause the chaos of free radical and the chaos of free radical may also do more damage to neurotransmitter vice versa.

Distribution characteristics of total mercury and methylmercury in the topsoil and dust of Xiamen, China

The levels and distribution of mercury （Hg） species, including total mercury （THg） and methylmercury （MeHg） in the topsoil and dust collected from twenty sampling stations located in different land function areas of Xiamen, China, were investigated. The THg concentrations in topsoil ranged from 0.071 to 1.2 mg/kg, and in dust ranged from of 0.034 to 1.4 mg/kg. For stations where the THg of dust was less than 0.31 mg/kg, THg concentrations in the topsoil were significantly correlated to those in the corresponding dust （r = 0.597, n = 16, P = 0.014）. The MeHg concentrations in topsoil were varied between 0.14 and 5.7 μg/kg. The ratios of MeHg/THg in the topsoil ranged from 0.069% to 0.74%. The range of MeHg concentration in the dust were 0.092-2.3 μg/kg. The ratios of MeHg/THg in the dust were at the same level as those in the topsoil. The MeHg concentrations in both topsoil and dust were linked to corresponding THg concentrations and soil organic matter. Neither THg nor MeHg concentration in the topsoil and dust was obviously linked to the land function.

Effect of methylmercury on LPO levels, SH groups and activities of GSH-Px, SOD, XOD in liver of rats

In recent years, lipid peroxidation has been considered as the initial step for foreign toxic substances to damage cells. In this paper, the effects of methylmercury (MeHg) on LPO (lipid peroxide) levels, SH (sulfhydryl) groups and activities of GSH\|Px (glutathione peroxidase), SOD (superoxide dismutase), XOD (xanthine oxidase) in liver of rats treated with doses of MeHg at different intervals were studied by TBA, Ellman Reagent, NBT colorimetric methods and chemilluminescence. Meanwhile, the contents of FR (free radical)and MeHg in the liver of female rats were measured by ESR and GC. Results showed that the LPO levels in the experimental group increased significantly over those of the control group ( p<0.05— p<0.001) , reaching maximum point on the first poisoning day. Both male and female rats showed marked positive dose\|effect relations (Male: Y=261.4±49.4X, r=0.94, p<0.02; Female : Y=255.0±73.0X, r=0.99, p<0.001 ). N-SH (nonprotein sulfhydryl), P\|SH (protein sulfhydryl), T-SH (total sulfhydryl) contents and GSH\|Px activities decreased significantly (p<0.05-p<0.001). For GSH\|Px, both groups reached minimum value on the first poisoning day. In female rats, activities of SOD and XOD increased markedly ( p<0.02-p<0.01 ) although the contents of FR showed no significant changes. The contents of MeHg was determined by GC, and it ranged from 0.0081—0.0191 ppm.

Exposure of aboriginal people to methylmercury due to gold mining in the Amazon, Brazil

This paper outlines the results of our study aiming at evaluating the actual extent of human exposure to Hg mainly in Tapajos River Basin in central Amazonia, which is considered to be the oldest and most productive gold mining area in the Amazon. Human hair and blood as well as fish samples were collected from gold mining areas and various fishing villages located at different distances from main gold mining areas, and analyzed for total mercury(T Hg) and methylmercury (MeHg) with new methods recently being developed in our laboratory. The results to date showed the inhabitants of fishing villages particularly in the upstream Tapajos areas were constantly exposed to MeHg at abnormally high levels, with little confounding exposure to inorganic Hg. A highly significant correlation between Hg in hair and blood was observed in fishing villages, and the ratios of hair Hg to blood Hg were very close to 250g, generally established for MeHg. While, the levels of MeHg in hair and blood of gold miners and goldshop workers were low, indicating that they were mainly exposed to Hg in inorganic form. From these data, together with the levels of MeHg in fish, Hg contamination mechanisms are discussed.

Methylmercury chloride damage to the adult rat hippocampus cannot be detected by proton magnetic resonance spectroscopy

Previous studies have found that methylmercury can damage hippocampal neurons and accord- ingly cause cognitive dysfunction. However, a non-invasive, safe and accurate detection method for detecting hippocampal injury has yet to be developed. This study aimed to detect methylmercury-induced damage on hippocampal tissue using proton magnetic resonance spectroscopy. Rats were given a subcutaneous injection of 4 and 2 mg/kg methylmercury into the neck for 50 consecutive days. Water maze and pathology tests confirmed that cognitive function had been impaired and that the ultrastructure of hippocampal tissue was altered after injection. The results of proton magnetic resonance spectroscopy revealed that the nitrogen-acetyl aspartate/ creatine, choline complex/creatine and myoinositol/creatine ratio in rat hippocampal tissue were unchanged. Therefore, proton magnetic resonance spectroscopy can not be used to determine structural damage in the adult rat hippocampus caused by methylmercury chloride.

Distribution Characteristics of Methylmercury in Eriocheir sinensis Produced in Zhejiang Province and the Risk of Eating It

Based the detection of content of methylmercury in the meat and butter of Eriocheir sinensis cultured in Zhejiang Province by liquid chromatography-atomic fluorescence spectroscopy,the distribution characteristics of methylmercury were analyzed,and the exposure risk of methylmercury to consumers was evaluated. The results showed that the content of methylmercury in the crab meat was higher than that of the crab butter. According to China＇s national standard and industry standard,the content of methylmercury in the crab meat was lower than the limit and accorded with relevant regulations. According to the reference intake of methylmercury recommended by the World Health Organization（ WHO） and the United States Environmental Protection Agency（ US EPA）,the weekly intake of E. sinensis meat should not exceed 3.2 kg,and the daily intake should not exceed 200g.

Fluorimetric determination of methylmercury with 2, 3-dimercaptonaphthalene

Methylmercury is the most toxic one among the mercury species. Many methods including atomic absorption spectrometry, atomic emission spectrometry, atomic fluorescence spectrometry, gas chromatography, high\|performance liquid chromatography, ion chromatography, and capillary electrophoresis, have been published for the determination of methylmercury. These methods have been reviewed (Li, 1997; 1993; Niu, 1991). These methods require expensive equipment and highly qualified analysts. Although fluorimetric method is sensitive, inexpensive, easy to operate, no data about determination of methylmercury by fluorimetry can be found in the literature. In order to obtain a better method for the determination of methylmercury by fluorimetry, several reagents such as 8\| hydroxyquinoline, 8\|aminoquinoline, 8\|mercaptoquinoline, 2,3\| diaminonaphthalene, 2, 3\|dimercaptonaphthalene were tested. The 2, 3\|dimercaptonaphthalene gave better result than the other reagents. Under the optimal conditions, the concentration of 2, 3\| dimercaptonaphthalene was 5.6×10 -5 mol/L and the pH value of the solution was adjusted to 4.0 with acetate buffer solution. The excitation and emission fluorescence wavelengths of 2,3\| dimercaptonaphthalene-methylmercury complex were 512.5 nm and 500 nm(antistokes), respectively. The linear range was 0.3—80 ng/ml and the detection limit was 0.02 ng/ml. The relative standard deviation was 2.6%. The method may be applied to determine methylmercury in environmental samples, and detailed investigation is in progress.

Elevated methylmercury production in mercury-contaminated soil and its bioaccumulation in rice:key roles of algal decomposition

Algal-derived organic matter(AOM)regulates methylmercury(MeHg)fate in aquatic ecosystems,whereas its role in MeHg production and bioaccumulation in Hg-contaminated paddies is unclear.Pot and microcosm experiments were thus performed to understand the response characteristics of MeHg concentrations in soil and rice in different rice-growing periods to algal decomposition.Compared to the control,algal decomposition significantly increased soil water-soluble cysteine concentrations during the rice-tillering and grain-filling periods(P<0.05).It also significantly lowered the molecular weight of soil-dissolved organic matter(SDOM)during the rice-tillering period(P<0.05)and SDOM humification/aromaticity during the grain-filling period.Compared to the control,AOM input increased the abundance of potential Hg and non-Hg methylators in soil.Furthermore,it also greatly increased soil MeHg concentrations by 25.6%-80.2%and 12.6%-66.1%during the rice-tillering and grain-filling periods,with an average of 42.25%and 38.42%,respectively,which were significantly related to the elevated cysteine in soil and the decrease in SDOM molecular weight(P<0.01).In the early stage(within 10 days of microcosm experiments),the MeHg concentrations in decayed algal particles showed a great decrease(P<0.01),suggesting a potential MeHg source in soil.Ultimately,algal decomposition greatly increased the MeHg concentrations and bioaccumulation factors in rice grains,by 72.30%and 16.77%,respectively.Overall,algal decomposition in Hg-contaminated paddies is a non-negligible factor promoting MeHg accumulation in soil-rice systems.

Methylmercury and sulfate-reducing bacteria in mangrove sediments from Jiulong River Estuary,China

Estuaries are important sites for mercury （Hg） methylation, with sulfate-reducing bacteria （SRB） thought to be the main Hg methylators. Distributions of total mercury （THg） and methylmercury （MeHg） in mangrove sediment and sediment core from Jiulong River Estuary Provincial Mangrove Reserve, China were determined and the possible mechanisms of Hg methylation and their controlling factors in mangrove sediments were investigated. Microbiological and geochemical parameters were also determined. Results showed that SRB constitute a small fraction of total bacteria （TB） in both surface sediments and the profile of sediments. The content of THg, MeHg, TB, and SRB were （350 ± 150） ng/g, （0.47 ± 0.11） ng/g, （1.4× 10^011 ± 4.1 × 10^9） cfu/g dry weight （dw）, and （5.0× 10^6 d： 2.7 × 10^6） cfu/g dw in surficial sediments, respectively, and （240 ± 24） ng/g, （0.30 ± 0.15） ng/g, （1.9 × 10^11 ± 4.2 × 10^9） cfu/g dw, and （1.3 × 10^6 ± 2.0 × 10^6） cfu/g dw in sediment core, respectively. Results showed that THg, MeHg, TB, MeHg/THg, salinity and total sulfur （TS） increased with depth, but total organic matter （TOM）, SRB, and pH decreased with depth. Concentrations of MeHg in sediments showed significant positive correlation with THg, salinity, TS, and MeHg/THg, and significant negative correlation with SRB, TOM, and pH. It was concluded that other microbes, rather than SRB, may also act as main Hg methylators in mangrove sediments.

Effects of soil properties on production and bioaccumulation of methylmercury in rice paddies at a mercury mining area,China

Rice paddy soil is recognized as the hotspot of mercury（Hg） methylation, which is mainly a biotic process mediated by many abiotic factors. In this study, effects of key soil properties on the production and bioaccumulation of Hg and methylmercury（MeHg） in Hg-contaminated rice paddies were investigated. Rice and soil samples were collected from the active Hg smelting site and abandoned Hg mining sites（a total of 124 paddy fields） in the Wanshan Mercury Mine, China. Total Hg（THg） and MeHg in soils and rice grains, together with sulfur（S）,selenium（Se）, organic matter（OM）, nitrogen（N）, phosphorus（P）, mineral compositions（e.g., SiO2, Al2O3 and Fe2O3） and pH in soils were quantified. The results showed that long-term Hg mining activities had resulted in THg and MeHg contaminations in soil-rice system. The newly-deposited atmospheric Hg was more readily methylated relative to the native Hg already in soils, which could be responsible for the elevated MeHg levels in soils and rice grains around the active artificial Hg smelting site. The MeHg concentrations in soils and rice grains showed a significantly negative relationship with soil N/Hg, S/Hg and OM/Hg ratio possibly due to the formation of low-bioavailability Hg–S（N）–OM complexes in rhizosphere. The Hg–Se antagonism undoubtedly occurred in soil-rice system, while its role in bioaccumulation of MeHg in the MeHg-contaminated rice paddies was minor. However, other soil properties showed less influence on the production and bioaccumulation of MeHg in rice paddies located at the Wanshan Mercury Mine zone.

Assessing pre/post-weaning neurobehavioral development for perinatal exposure to low doses of methylmercury

Fetuses and neonates are known to be high-risk groups for Methylmercury（MeHg）exposure.MeHg can be transferred to the fetus through the placenta and to newborn offspring through breast milk.The aim of the present study was to investigate the neurotoxic effects of low doses of MeHg（1 and 5 μg/m L in drinking water） administration,from gestational day 1 to postnatal day（PND） 21,on the neurobehavioral development of rats.The results showed that the no-observed-effect level of MeHg is somewhere in the range of 1-4 μg/mL.Neurobehavioral development analysis revealed a delayed appearance of cliff drop and negative geotaxis reflexes in the 5 μg/mL MeHg exposure group.Developmental exposure to MeHg affected locomotor activity functions for the females,but not for the males,implying that the female pups were more vulnerable than the male pups.All pups exposed to 5 μg/mL of MeHg showed a significant deficit in motor coordination in the rotarod test compared with controls,and the highest accumulated concentrations of Hg were found in the cerebellum,followed by the hippocampus and cerebral cortex,indicating that the cerebellum is a possible target for MeHg toxicity.We demonstrated adverse effects of developmental exposure to MeHg associated with tissue concentrations very close to the current human body burden of this persistent and bioaccumulative compound.

Role of the floodplain lakes in the methylmercury distribution and exchanges with the Amazon River,Brazil

Seasonal variability of dissolved and particulate methylmercury（F-MeHg, P-MeHg） concentrations was studied in the waters of the Amazon River and its associated Curuai floodplain during hydrological year 2005–2006, to understand the MeHg exchanges between these aquatic systems. In the oxic white water lakes, with neutral pH, high F-MeHg and P-MeHg concentrations were measured during the rising water stage（0.70 ± 0.37 pmol/L, n = 26） and flood peak（14.19 ± 9.32 pmol/g, n = 7） respectively, when the Amazon River water discharge into the lakes was at its maximum. The lowest mean values were reported during the dry season（0.18 ± 0.07 pmol/L F-MeHg, n = 10 and 1.35 ± 1.24 pmol/g P-MeHg, n = 8）, when water and suspended sediments were outflowing from the lakes into the River. In these lakes,the MeHg concentrations were associated to the aluminium and organic carbon/nitrogen changes. In the black water lakes, with acidic pH and reducing conditions, elevated MeHg concentrations were recorded（0.58 ± 0.32 pmol/L F-MeHg, n = 16 and 19.82 ± 15.13 pmol/g PMeHg, n = 6）, and correlated with the organic carbon and manganese concentrations. Elevated values of MeHg partition coefficient（4.87 〈 Kd〈 5.08 log（L/kg） indicate that MeHg is mainly transported associated with the particulate phase. The P-MeHg enrichment detected in all lakes suggests autochthonous MeHg inputs from the sediments into the water column. The MeHg mass balance showed that the Curuai floodplain is not the source of P-MeHg for the Amazon River.

Antioxidant activity of curcumine as protector on methylmercury inducedpancreas damage in mice

Curcumin has been reported to have a strong antioxidant activity. In recent years, use of antioxidant in reducing heavy metal toxicities has been increased worldwide. In this study, we investigated the protective effects of curcumin on methylmercury-induced pancreas damage in mice. Briefly, 50 male mice were divided into five groups as follows: negative control(mice were given daily with aquadest); positive control(mice were orally given 2 mg/kg BW methylmercury daily for 35 d); and the treatment groups(mice were orally adminstered with curcumin 100 mg; 200 mg; 400 mg/kg BW daily for 35 d, and from 5th day, animals were given 2 mg/kg BW methylmercury daily 1 h after curcumin administration for 30 d). On day 35, levels of glucose, insulin, MDA, SOD and GPx were measured. Pancreas also was fixed in 10% neutral buffered formalin solution for histopathological examination. The results revealed that methylmercury toxicity induced a significant increase in the levels of glucose and MDA. Moreover, a significant decrease in insulin, SOD and GPx levels was observed, and pancreas tissues showed degeneration and necrotic changes in the islets of Langerhans. Treatment with curcumin(400 mg/kg BW but not 200 mg/kg BW and 100 mg/kg BW) significantly(P<0.05) decreased glucose and MDA levels in pancreas in mercury-induced mice. Treatment with curcumin 400 mg/kg BW also significantly increased insulin, SOD and GPx levels and reversed the histopathological damage in methylmercury-induced mice. Taken together, curcumin could be a potent natural herbal product, which had pancreas protective effect against methylmercury-induced pancreas damage in mice.

Assessing the utility of dissolved organic matter photoreactivity as a predictor of in situ methylmercury concentration

Methylmercury（MeHg） bioaccumulation is a growing concern in ecosystems worldwide. The absorption of solar radiation by dissolved organic matter（DOM） and other photoreactive ligands can convert MeHg into less toxic forms of mercury through photodemethylation. In this study, spectral changes and photoreactivity of DOM were measured to assess the potential to control photoreactions and predict in situ MeHg concentration. Water samples collected from a series of lakes in southwestern Nova Scotia in June, August, and September were exposed to controlled ultraviolet-A（UV-A） radiation for up to 24 hr. Dissolved organic matter photoreactivity, measured as the loss of absorbance at 350 nm at constant UV-A irradiation, was positively dependent on the initial DOM concentration in lake waters（r^2=0.94）. This relationship was consistent over time with both DOM concentration and photoreactivity increasing from summer into fall across lakes. Lake in situ MeHg concentration was positively correlated with DOM concentration and likely catchment transport in June（r = 0.77） but not the other sampling months. Despite a consistent seasonal variation in both DOM and Fe, and their respective correlations with MeHg, no discernable seasonal trend in MeHg was observed. However, a 3-year dataset from the 6 study lakes revealed a positive correlation between DOM concentration and both Fe（r = 0.91） and MeHg concentrations（r = 0.51） suggesting a more dominant landscape mobility control on MeHg.The DOM-MeHg relationships observed in these lakes highlights the need to examine DOM photoreactivity controls on MeHg transport and availability in natural waters particularly given future climate perturbations.

Photodegradation of methylmercury in Jialing River of Chongqing, China

Photodegradation（PD） of methylmercury（MMHg） is a key process of mercury（Hg） cycling i water systems, maintaining MMHg at a low level in water systems. However, we posses little knowledge of this important process in the Jialing River of Chongqing, China. In sit incubation experiments were thus performed to measure temporal patterns and influencin factors of MMHg PD in this river. The results showed that MMHg underwent a ne demethylation process under solar radiation in the water column, which predominantl occurred in surface waters. For surface water, the highest PD rate constants were observed i spring（12 × 10^-3± 1.5 × 10^-3m2/E）, followed by summer（9.0 × 10^-3）± 1.2 × 10^-3 m^2/E）, autum（1.4 × 10^-3± 0.12 × 10^-3m^2/E）, and winter（0.78 × 10^-3± 0.11 × 10^-3m^2/E）. UV-A radiatio（320-400 nm）, UV-B radiation（280-320 nm）, and photosynthetically active radiation（PAR400-700 nm） accounted for 43%-64%, 14%-31%, and 16%-45% of MMHg PD, respectively. PD rat constants varied substantially with the treatments that filtered the river water and amended with chemicals（i.e., Cl^-, NO3^-, dissolved organic matter（DOM）, Fe（III））, which reveals tha suspended particulate matter and water components are important factors in affecting the PD process. For the entire water column, the PD rate constant determined for each wavelengt range decreased rapidly with water depth. UV-A, UV-B, and PAR contributed 27%-46%, 6.2%12%, and 42%-65% to the PD process, respectively. PD flux was estimated to be 4.7 μg/（m^2·yea in the study site. Our results are very important to understand the cycling characteristics o MMHg in the Jialing River of Chongqing, China.

Understanding the excretion rates of methylmercury and inorganic mercury from human body via hair and fingernails

Effective biomarkers are necessary to better understand the human mercury(Hg) exposure levels. However, mismatched biomarker sampling method causes extra uncertainty in assessing the risk of Hg exposure. To compare the differences between hair and fingernail, and further understand the excretion rates of methylmercury(MeHg) and inorganic mercury(IHg) via hair and fingernails, the total mercury(THg), Me Hg, and IHg concentrations in paired hair and fingernail samples were investigated through paired samples collected from two typical mining areas, Wanshan mercury mine area(WMMA) and Hezhang zinc smelting area(HZSA). The positive correlation in THg, MeHg, and IHg concentrations( p < 0.01) between hair and fingernail samples indicated that those two biomarkers can be corrected in application of assessing human Hg exposure. Compared to fingernails, the hair was suggested to be a more sensitive biomarker as the concentration of THg, MeHg and IHg were 2~4 times higher than those in fingernails. Furthermore, the amounts of THg, MeHg, and IHg excreted via hair were 70~226 times higher than that excreted via fingernails, and the hair plays a more important role than fingernails in the excretion of Hg from human bodies. Present study therefore provides some new insights to better understand the fate of human assimilated Hg.

Trophic transfer of mercury and methylmercury in an aquatic ecosystem impacted by municipal sewage effluents in Beijing, China

Gaobeidian Lake, located in Beijing, China, serves as a recipient lake for efluents from a large municipal sewage treatment plant （MSTP）. In order to evaluate the effects of discharging MSTP efluent on the mercury contamination of the local aquatic ecosystem, sediment cores, water, plankton, fish, and turtle samples were collected from Gaobeidian Lake for mercury speciation analysis. High concentrations of total mercury （T-Hg） were detected in sediment cores （5.24–17.0 μg/g dry weight （dw）, average： 10.1 μg/g）. The ratio of methylmercury （MeHg） to T-Hg was less than 0.3% in sediments and ranged from 35% to 76% in biota samples. The highest level of T-Hg and MeHg were found in aquatic bryophyte and crucian carp （3673 and 437 ng/g dw, respectively）. The relative contents of MeHg were significantly correlated with trophic levels （R2 = 0.5506, p 0.001）, which confirmed that MeHg can be bio-transferred and biomagnified via food chain in this aquatic ecosystem.

Biochar affects methylmercury production and bioaccumulation in paddy soils: Insights from soil-derived dissolved organic matter

Biochar has been used increasingly as a soil additive to control mercury(Hg) pollution in paddy rice fields. As the most active component of soil organic matter, soil dissolved organic matter(DOM) plays a vital role in the environmental fate of contaminants. However, there are very few studies to determine the impact of biochar on the Hg cycle in rice paddies using insights from DOM. This study used original and modified biochar to investigate their effect on DOM dynamics and their potential impact on methylmercury(MeHg) production and bioaccumulation in rice plants. Porewater DOM was collected to analyze the variations in soil-derived DOM in paddy soils. The results showed that the addition of biochar, whether in original or modified form, significantly reduced the bioaccumulation of MeHg in rice plants, especially in hulls and grains( p < 0.05). However, MeHg production in soils was only inhibited by the modified biochar. Biochar addition induced a significant increase in DOM’s aromaticity and molecular weight( p < 0.05), which decreased Hg bioavailability. Furthermore, enhanced microbial activity was also observed in DOM( p < 0.05), further increasing MeHg production in the soil. Thus, the effect of biochar on the fate of Hg cycle involves competition between the two different roles of DOM. This study identified a specific mechanism by which biochar affects Hg behavior in rice paddy soil and contributes to understanding the more general influence of biochar in agriculture and contaminant remediation.

Ant colonization increased total mercury but reduced methylmercury contents in boreal mires, Northeast China

Soil macroinvertebrates as ecosystem engineers play significant, but largely ignored, roles in affecting mercury(Hg) cycle by altering soil physical-chemical properties. Ant is likely expanded into boreal mires with climate warming, however, its impacts on Hg cycle remained poorly understood. We compared total Hg(THg) and methylmercury(Me Hg) contents in soils from antmounds( Lasius flavus) and the nearby ambient in a boreal mire in Northeast China. The present work seeks to unravel factors that controlling Me Hg levels in case of ant appearance or absence. The average THg was 179 μg/kg in the ant mound and was 106.1 μg/kg in nearby soils, respectively. The average Me Hg was 10.9 μg/kg in the ant mound and was 12.9 μg/kg in nearby soils, respectively. The ratios of Me Hg to THg(%Me Hg) were 7.61% in ant mounds and 16.75% in nearby soils, respectively. Ant colonization caused THg enrichment and Me Hg depletion, and this change was obvious in the 10-20 cm depth soil layer where ants mainly inhabited. Spectrometry characteristics of soil dissolved organic matter(DOM) exert a stronger control than microorganisms on Me Hg variation in soils. A structural equation model revealed that the molecular weight of DOM inhibited Me Hg irrespective of ant presence or absence, while humification conducive to Me Hg significantly in ant mound soils. Microorganisms mainly affected Hg methylation by altering the molecular weight and humification of DOM. We propose that the effects of ant colonization on Me Hg rested on DOM feature variations caused by microorganisms in boreal mires.

Influence of dissolved organic matter on methylmercury transformation during aerobic composting of municipal sewage sludge under different C/N ratios

Current knowledge about the transformation of total mercury and methylmercury(Me Hg) in aerobic composting process is limited. In this study, the composition and transformation of mercury and dissovled organic matter(DOM) in aerobic composting process of municipal sewage sludge were were comprehensively characterized, and the differences among the three C/N ratio(20, 26 and 30) were investigated. The main form of mercury in C/N 20 and 26 was organo-chelated Hg(F3, 46%-60%);while the main form of mercury in C/N 30 was mercuric sulfide(F5, 64%-70%). The main component of DOM in C/N 20 and 26 were tyrosine-like substance(C1, 53%-76%) while the main fractions in C/N 30 were tyrosine-like substance(C1, 28%-37%) and fulvic-like substance(C2, 17%-39%). The mercury and DOM varied significantly during the 9 days composting process. Compared to C/N 20 and 26, C/N 30 produced the less Me Hg after aerobic composting process, with values of 658%(C/N 20), 1400%(C/N 26) and 139%(C/N 30) of the initial, respectively. Meanwhile, C/N 30 produced the best compost showed greater degree of DOM molecular condensation and humification. Hg fraction had been altered by DOM, as indicated by a significant correlation between mercury species and DOM components. Notably, C/N 30 should be used as an appropriate C/N ratio to control the methylation processes of mercury and degration of DOM.