Low-Temperature Thermal Desorption Effectively Mitigates Accumulation of Total Mercury and Methylmercury in Rice (Oryza sativa L.).

For maximally reserving soil fertility, two critical parameters (i.e. time and temperature) of low-temperature thermal desorption (LTTD) were initially optimized to remediate the mercury-contaminated soil from a mercury mining area. The effect of LTTD on soil properties was investigated, and the bioaccumulation of total mercury (THg) and methylmercury (MeHg) in rice (Oryza sativa L.) were researched via a pot experiment. Results indicated that the physicochemical properties and fertility of the soil after LTTD still meet the requirements of rice growth. Moreover, the concentrations of THg and MeHg in the remediated soil were decreased by 94.1% and 98.8%, respectively. Further, the bioavailability of Hg in soil was significantly reduced. More importantly, the concentrations of THg and MeHg in the seed of rice plant cultivated on the remediated soil were decreased by 57.6% and 80.2%, respectively. Overall, LTTD technology could efficiently remediate Hg-contaminated soil and be a promise remediation strategy.

Low-thermal remediation of mercury-contaminated soil and cultivation of treated soil.

In this study, low-thermal technology was used to treat the mercury contaminated farmland soil from a chemical plant in Guizhou Province, China. A series of field planting experiments were also aimed at determining the content of total and methyl-Hg in crop plants after thermal treatment. The results showed that the mercury concentration in soils was reduced about 70% from 255.74 mg/kg to 80.63 mg/kg when treated at 350 °C for 30 min in engineering-scale experiments, and the treated soil retained most of its original soil. Organic-bound and residual mercury in treated soil were reduced by 64.1 and 56.4% by means of a sequential extraction procedure, respectively. The total and methyl-mercury concentrations in crops decreased significantly, and the degree of soil mercury accumulation to crop roots has been reduced significantly. The total Hg concentrations in potato and corn were lower than the mercury tolerance limits for food in China, and the Hg concentration of radish was close to the limit. The technology provides a more sustainable remediation method for treating mercury-contaminated farmland soil in future engineering applications.

Organic selenium supplementation increases mercury excretion and decreases oxidative damage in long-term mercury-exposed residents from Wanshan, China.

Due to a long history of extensive mercury mining and smelting activities, local residents in Wanshan, China, are suffering from elevated mercury exposure. The objective of the present study was to study the effects of oral supplementation with selenium-enriched yeast in these long-term mercury-exposed populations. One hundred and three volunteers from Wanshan area were recruited and 53 of them were supplemented with 100 µg of organic selenium daily as selenium-enriched yeast while 50 of them were supplemented with the nonselenium-enriched yeast for 3 months. The effects of selenium supplementation on urinary mercury, selenium, and oxidative stress-related biomarkers including malondialdehyde and 8-hydroxy-2-deoxyguanosine were assessed. This 3-month selenium supplementation trial indicated that organic selenium supplementation could increase mercury excretion and decrease urinary malondialdehyde and 8-hydroxy-2-deoxyguanosine levels in local residents.

Mercury in human hair and blood samples from people living in Wanshan mercury mine area, Guizhou, China: an XAS study.

Human hair and blood samples from persons living in the town of Wanshan, a mercury mine area in Guizhou Province of China, were collected and the quantitative speciation and structural information of Hg and S in hair samples and of Hg in erythrocyte and serum samples were studied using X-ray absorption spectroscopy. Least-squares fitting of the X-ray absorption near-edge spectra found that inorganic mercury is the major mercury species in hair samples (91.74%), while inorganic and methyl mercury are both about 50% of total mercury in RBC and serum samples, which is in agreement with the data obtained by acidic extraction, fractionation of Hg(2+) and CH(3)Hg(+) and quantification by ICP-MS. Curve-fitting analysis revealed that the Hg-S bond length and coordination number in hair were 0.248+/-0.002 nm and 3.10, respectively, while the S-Hg bond length and coordination number in hair were 0.236+/-0.002 nm and 4.05. The Hg-S bond length and coordination number in RBC were 0.251+/-0.003 nm and 4.09, respectively, while they were 0.228+/-0.002 nm and 4.08 in serum, respectively. The techniques for speciation, structural and binding information described in this study will find the potential application in similar studies of other elements.

Consumption of mercury-contaminated rice induces oxidative stress and free radical aggravation in rats.

OBJECTIVE: To study the oxidative stress induced by consumption of mercury-contaminated rice in rats, and to assess the possible public health risk of mercury contamination in Wanshan mining area. METHODS: Sprague Dawley rats were fed the mercury-contaminated rice produced from Wanshan area for 90 days. The antioxidant status and the free radicals in rat serum were evaluated. RESULTS: High mercury accumulation in organs of rats fed the mercury-contaminated rice confirmed the server pollution of mercury in Wanshan mining area. The intensity of electron spin resonance (ESR) signal increased by 87.38% in rats fed the rice from Wanshan compared with that in the control rats fed the rice from Shanghai, suggesting that chronic dietary consumption of rice from mercury mining area could induce an aggravation of free radicals. Feeding the mercury-contaminated rice was associated with significant decreases in the antioxidant enzymatic activities of superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) and concentration of serum nitric oxide (NO), but it had no effect on serum nitric oxide synthase (NOS) activity. Feeding the mercury-contaminated rice raised the level of serum malonyldialdehyde (MDA), indicating the occurrence of oxidative stress. CONCLUSION: The long-term dietary consumption of mercury-contaminated rice induces the aggravation of free radicals and exerts oxidative stress.

Comparison of electrokinetic soil remediation methods using one fixed anode and approaching anodes.

During the cation exchange membrane (CEM) enhanced electrokinetic (EK) soil remediation, the nearer to the anode, the higher are the H+ concentrations and the redox potentials. As both low pH and high redox potential are helpful to speed-up Cd electro-migration, soils near the anode can be quickly remedied. Usually EK process is operated with one fixed anode (FA). A novel CEM enhanced EK method with approaching anodes (AAs) is proposed to accelerate electro-migration effect. Several mesh Ti/Ru anodes were inserted as AAs in the treated soil. They were switched in turn from the anode towards the cathode. Thus high H+ ions concentrations and high redox potentials quickly migrate to the cathode. Consequently, soil remediation is accelerated and nearly 44% of energy and 40% of time can be saved. The mechanism of Cd electro-migration behavior in soils during CEM enhanced EK is described as the elution in an electrokinetically driven chromatogram.

Mercury pollution in two typical areas in Guizhou province, China and its neurotoxic effects in the brains of rats fed with local polluted rice.

Guizhou province, which located in southwestern of China, is an important mercury (Hg) production center. This study was to investigate the environmental levels and ecological effects of mercury in two typical Hg polluted areas in Guizhou province. In addition, to improve the understanding of the neurotoxic effects of Hg, a rats based laboratory study was also carried out in this study. Samples of water, soil, plants, crops and animals collected from Wanshan mercury mine area, Guzhou province, were analyzed by mercury analyzer. The effects of Hg contaminated rice on the expression of c-jun mRNA in rat's brain and the expression of c-JUN protein in cortex, hippocampus were observed using reverse transcription polymerase chain reaction (RT-PCR) and immunocytochemical methods. The results showed that the mercury contents in most environmental samples of aquatics, soil, atmosphere and the biomass of corn, plant and animals, were higher than the national standard and the corresponding data from unpolluted area. It was found mercury pollutions were significant in soil and air. In the laboratory study, the expression of c-jun mRNA and its protein was significantly induced by Hg polluted rice collected from local area. Selenium could reduce the Hg accumulation in the body and had antagonist effect on Hg in terms of the expression of c-jun mRNA and c-JUN protein. The environmental data and Hg levels in different creatures collected in this study will facilitate the environmental and ecological risk assessment of Hg in the polluted areas. It was urged to be alert of mental health problem in human beings when any kind of Hg-polluted food was taken. More efforts should be performed to protect the local ecosystem and human health in the mercury polluted area of Wanshan, Guizhou province of China.

[Effect of chronic exposure by mercury contaminated rice on neurotransmitter level changes in rat brain].

In order to survey the potential health risk of environmental exposure by mercury, Sprague-Dawley rats were reared by mercury contaminated rice from mercury mining area. The changes of neurotransmitter acetylcholine (ACh) and acetylcholinesterase (AChE) in rat brain were examined at different times. The results show that the mercury-contaminated rice significantly increase the content of ACh in rat brain after exposure for 7 days. ACh maintained at a high level even after exposure for 30 days, but decreased significantly after exposure for 90 days. The changes of AChE represented an inverse trend compared with that of ACh. The coexisting selenium in rice exhibited antagonistic effects on both mercury accumulation and toxicity. The findings suggested that neurotoxic effects of environmental mercury contamination had been significantly represented after chronically dietary exposure. Further studies are needed to examine the relationship between the neurotransmitter level changes and the Alzheimer's Disease (AD).

Accumulation of mercury, selenium and their binding proteins in porcine kidney and liver from mercury-exposed areas with the investigation of their redox responses.

The subcellular localization of Se and Hg and their cytosolic binding proteins, including cellular oxidative status, in porcine liver and kidney have been studied by using samples from a chronic Hg-contaminated area and a non-Hg-contaminated area. Coaccumulation and redistribution of Se and Hg in subcellular fractions due to mercury exposure were found. The Hg and Se concentrations in tissues from Hg-exposed porcine were 80 fold and 5-20 fold higher than controls, respectively. Interestingly, the retention of both Se and Hg increased 10% in mitochondria, while decreased 10% in cytosol of Hg-exposed pig liver. Mercury was mainly in the form of MTs in the cytosol of the non-Hg-exposed porcine kidney. MT binds Hg in the cytosol with limited capacity, and the rest Hg was redistributed to the high molecular weight (MW) proteins (80-100 kDa) in the Hg-exposed group. The coaccumulation of Hg and Se was also found in high MW proteins, where their molar ratio tended to be 1:1. Moreover, the Se-containing polypeptides (3-6 kDa) increased significantly both in hepatic and renal cytosol of the Hg-exposed pigs. Se-dependent GSH-Px and SOD activity were increased to cope with Hg-induced oxidative stress. In previous studies, the roles of Se and MTs were generally taken into account separately; we discussed their combining roles in the case of high Hg exposure. The present results were beneficial to understand the existing states of Hg in vivo and evaluate the interaction of toxic and essential elements.

The roles of serum selenium and selenoproteins on mercury toxicity in environmental and occupational exposure.

Many studies have found that mercury (Hg) exposure is associated with selenium (Se) accumulation in vivo. However, human studies are limited. To study the interaction between Se and Hg, we investigated the total Se and Hg concentrations in body fluids and serum Se-containing proteins in individuals exposed to high concentrations of Hg. Our objective was to elucidate the possible roles of serum Se and selenoproteins in transporting and binding Hg in human populations. We collected data from 72 subjects: 35 had very low Hg exposure as evidenced by mean Hg concentrations of 0.91 and 1.25 ng/mL measured in serum and urine, respectively; 37 had high exposure (mean Hg concentrations of 38.5 and 86.8 ng/mL measured in serum and urine, respectively). An association between Se and Hg was found in urine (r = 0.625; p < 0.001) but not in serum. Hg exposure may affect Se concentrations and selenoprotein distribution in human serum. Expression of both selenoprotein P and glutathione peroxidase (GSH-Px) was greatly increased in Hg miners. These increases were accompanied by elevated Se concentrations in serum. In addition, selenoprotein P bound more Hg at higher Hg exposure concentrations. Biochemical observations revealed that both GSH-Px activity and malondialdehyde concentrations increased in serum of the Hg-exposed group. This study aids in the understanding of the interaction between Se and Hg. Selenoproteins play two important roles in protecting against Hg toxicity. First, they may bind more Hg through their highly reactive selenol group, and second, their antioxidative properties help eliminate the reactive oxygen species induced by Hg in vivo.

Oxidative stress on domestic ducks (Shaoxing duck) chronically exposed in a Mercury-Selenium coexisting mining area in China.

The Wanshan mercury mine is the largest mercury deposit in Guizhou Province, China. Few attempts have been made to study the toxic effects of mercury on biota in this mining area. This study was the first to investigate the oxidative stress on domestic ducks (Shaoxing duck) chronically exposed to mercury in the Wanshan mining area. Chemical analyses revealed higher concentrations of both, mercury and selenium in samples from the Wanshan area. Total mercury and selenium concentrations in duck tissues varied from 0.073 to 4.465 mg/kg and from 1.073 to 6.35 mg/kg, respectively. Analysis of covariance revealed that there were significant effects of zone on accumulation of mercury and selenium in all duck tissues (P<0.01). Moreover, analysis of covariance indicated that mercury content significantly affected the accumulation of selenium in duck muscle, brain, and liver (P<0.01). Mercury and selenium were also highly correlated in Wanshan duck liver, muscle, brain, and lung. The statistical analysis suggested that selenium might be an interactive factor in mercury toxicity. As for the biochemical analyses, it was observed that selenium-dependent glutathione peroxidase and superoxide dismutase activities and glutathione (GSH) content were significantly increased in the livers and brains of Wanshan ducks (P<0.01, 0.05). However, no significant changes were observed in malondialdehyde content (P>0.05). Although the results indicated that adaptive responses of the redox-defense system are associated with the increased enzyme activities and GSH content, the most likely explanation is that selenium plays a critical role. Therefore, the effects of the interaction environmentally occurring selenium and mercury on public health in the Wanshan area should be examined in further studies.

Free radicals and antioxidant status in rat liver after dietary exposure of environmental mercury.

Potential health effect of dietary exposure to environmental mercury was examined in this study. Dietary exposure significantly increased content of reduced glutathione (GSH) and activity of glutathione peroxidase (GSH-Px) in rat liver at 7 or 20 days (P<0.05; P<0.01), but parameters droped to normal levels after 90 days of exposure. The early increases of the two antioxidants were partly associated with the co-accumulated selenium. However, activity of superoxide dismutase (SOD) was observed significantly decreased after 30 and 90 days of exposure (P<0.05, P<0.05). Changes of antioxidants were paralleled by the induction and aggravation of free radicals in rat liver at 30 and 90 days (P<0.01, P<0.01), increased nitric oxide (NO) content at 90 days (P<0.01). The excess availability of free radicals and the decreased levels of antioxidants resulted in a significant increase of malonyldialdehyde (MDA) after 90 days of exposure, indicating the aggravation of hepatic oxidative status. A number of biomarkers were required to monitor and minimize the health risk for the local population.

[Induction of free radicals after dietary exposure by mercury contaminated rice and protective effect of coexisting selenium].

Sprague-Dawley rats were reared by environmental mercury contaminated rice to survey the potential health risk of Wanshan mercury mining area. Electron spin resonance (ESR) was introduced to detect the species and the intensities of free radicals, using spin trap 5,5-dimethyl-1-pyrroline-N-oxide (DMPO). The results showed that the mercury-contaminated rice significantly increased the levels of free radicals and MDA in rat brain at 7 days (p < 0.05). ESR spectrums showed that the principal spin adducts resulted from the trapping of alkyl free radical (alphaH = 22.7 x 10(-4)T +/- 1.6 x 10(-4)T, alphaN = 15.5 x 10(-4)T +/- 0.5 x 10(-4)T), and hydroxyl radical. Levels of free radicals and MDA increased slowly until after 90-day exposure period (83%, 100%). Element correlation analysis showed high correlations of mercury and selenium in the brain of rat fed with Wanshan rice, suggesting that the coexisting selenium in rice exhibited antagonistic effects on both mercury accumulation and toxicity. The slight increases of free radicals in rat brain at 7, 20 and 30-day exposure periods should be related with the scavenger effect of Se.

Neurotransmitter level changes in domestic ducks (Shaoxing duck) growing up in typical mercury contaminated area in China.

The neurotransmitter level changes of ducks exposed 8-month in a mercury-polluted site (Wanshan, China) and a reference site (Shanghai, China) were examined. Chemical analyses showed both higher mercury and selenium concentrations in the organ of Wanshan ducks. An increased content of acetylcholine (ACh) in brain and blood and a decreased activity of acetylcholinesterase (AChE) in blood were observed. Moreover, there was an increasing trend for nitric oxide synthase (NOS) activity and nitric oxide(NO) production in duck brain, but a reduction of NOS activity in duck serum. The possible explanations were due to the interactive effect of selenium accumulation and the sublethal exposure level of mercury in Wanshan area. The present study showed that AChE and NOS were sensitive to mercury contamination of real circumstance, suggesting that these two indexes have the potential to be biomarkers in assessment of health effects by mercury contamination.

[Antagonistic effects of selenium on the expression of c-fos in central nerval system of rat included by mercury contaminated rice].

The objective of this paper is to study the antagonisms between selenium and mercury and the effect of different species mercury on the brain injury. The expression of c-fos mRNA and c-FOS protein in rat brain induced by Hg-contaminated rice was observed by using reverse transcriptions polymerase chain reaction (RT-PCR) and immunocytochemical methods. The results show the Hg-contaminated rice induced significantly the expression of c-fos mRNA and c-FOS protein; selenium could antagonize mercury accumulative level in brain. Antagonistic effects of selenium on the expression of c-fos included by mercury and the molecule mechanism of the antagonisms between selenium and mercury was probed, too.

Rice from mercury contaminated areas in Guizhou Province induces c-jun expression in rat brain.

OBJECTIVE: Mercury (Hg), as one of the priority pollutants and also a hot topic of frontier environmental research in many countries, has been paid higher attention in the world since the middle of the last century. Guizhou Province (at N24 degrees 30'-29 degrees 13', E103 degrees 1'-109 degrees 30', 1 100 m above the sea level, with subtropical humid climate) in southwest China is an important mercury production center. It has been found that the mercury content in most media of aquatics, soil, atmosphere and in biomass of corns, plants and animals, is higher than the national standard. The present study aims to explore the influence of mercury pollution on the health of local citizens. METHODS: The effect of rice from two mercury polluted experimental plots of Guizhou Province on the expression of c-jun mRNA in rat brain and c-jun protein in cortex, hippocampus and ependyma was observed using reverse transcription polymerase chain reaction (RT-PCR) and immunocytochemical methods. RESULTS: The results showed that the mercury polluted rice induced expression of c-jun mRNA and its protein significantly. Selenium can reduce Hg uptake, an antagonism between selenium and mercury on the expression of c-jun mRNA and c-jun protein. CONCLUSION: c-jun participates in the toxicity process of brain injury by mercury polluted rice, the expression of c-jun mRNA in brain, and c-jun protein in rat cortex and hippocampus can predict neurotoxicity of mercury polluted rice. People should be advised to be cautious in eating any kind of Hg-polluted foods. To reveal the relationship between c-jun induction and apoptosis, further examinations are required.

[Expression of c-FOS protein in rat hippocampus by inducing of mercury contaminated rice].

In order to probe into the biological effects of mercury in typical mercury contaminated area and try to apply the expression of immediately early gene c-fos in brain to early predict the neurotoxicity of mercury in typical polluted areas, the expression of c-FOS protein in rat hippocampus is observed using immunocytochemical methods. The results show the mercury pollutes rice induced significantly the expression of c-FOS protein in hippccampus;the antagonisis between selenium and mercury on the exposure process. It is suggested that c-fos can be used as an effective index of detecting and assessing neurotoxicology of mercury polluted areas.

Increased oxidative DNA damage, as assessed by urinary 8-hydroxy-2'-deoxyguanosine concentrations, and serum redox status in persons exposed to mercury.

BACKGROUND: Mercury is a ubiquitous and highly toxic environmental pollutant. In this study, we evaluated the relationship between mercury exposure and oxidative stress, serum and urinary mercury concentrations, oxidative DNA damage, and serum redox status in chronically mercury-exposed persons compared with healthy controls. METHODS: We measured urinary 8-hydroxy-2'-deoxyguanosine (8-OHdG), which we used as a biomarker of oxidative DNA damage in the mercury-exposed persons, by HPLC with electrochemical detection (ECD). We evaluated antioxidant status by measuring the activities of superoxide dismutase and glutathione peroxidase and the concentrations of total reduced glutathione and protein-bound thiols in serum. RESULTS: The significant increase in 8-OHdG concentrations in urine indicated that mercury-induced oxidative damage to DNA occurred in vivo. Differences in body mercury burden and antioxidant enzyme activities were statistically significant between the mercury-exposed persons and controls. Serum and urinary mercury concentrations in the mercury-exposed persons were more than 40-fold higher than in controls. CONCLUSIONS: Mercury exposure can induce oxidative DNA damage, whereas the antioxidative repair systems can be expected to minimize DNA lesions caused by mercury. Measurement of urinary 8-OHdG could be useful for evaluating in vivo oxidative DNA damage in mercury-exposed populations.

[Correlation of mercury, selenium and other elements in the tissues of fishes from the regions at different mercury exposure level].

The contents of selenium and other elements in fish liver and muscle tissues collected from mercury polluted area of Wanshan, Guizhou province of China and non-known mercury polluted one of Beijing were determined with instrumental neutron activation analysis, and that of mercury was determined with atomic fluorescence spectrometry. The correlation among the determined elements, especially between mercury and selenium, in the fish tissues were studied. For most of the elements significant difference of elemental content was found between tissues of liver and muscle, and mostly the content in liver was higher than that in muscle. It was interesting to note that the average content of mercury in Guizhou fish liver was 25-fold higher than that in Beijing one, and 5-fold higher in Guizhou fish muscle than that in Beijing one. For most of the elements no significant difference on the average content was found between the same tissues of the two areas. The molar ratio of Hg/Se increased with the increasing of Hg content at the low Hg level, but the alteration trend became gently and reached to a higher constant value (about 0.2) at the higher Hg level. Only the element of bromine and rubidium was found to have strong linear correlation between the two different tissues of liver and muscle. Though certain correlation existed among the different elements of fish tissues from the two areas, the most significant and the closest one existed between the mercury and selenium of muscle tissue of Guizhou fishes. A closer correlation was also found between them of liver tissue of Guizhou fishes. As for Beijing fish tissues, the correlation of mercury and selenium only existed in liver but no correlation of them was found in muscle. Our results confirm the fact that a certain interaction exists between mercury and selenium in organisms including fish, and it is more evident as the mercury-exposed level is higher. Some significant correlation was also observed between other elements, such as potassium and sodium, cesium and rubidium, iron and zinc, in fish tissues and it could be well explained by their similar chemical and physical properties or their different biological functions.

[Effect of methylmercury on expression of immediate early gene c-jun mRNA in rat brain].

In order to probe into the early prediction molecular index and the signal transduction molecular mechanism of methyl mercury chloride (MMC) neurotoxicity, the expression of c-jun mRNA in rat brains induced by different concentration MMC for different times were observed by using reverse transcription polymerase chain reaction (RT-PCR) methods (the control group was physiological saline of 0.9%, the concentrations of expose groups were 0.05, 0.5, 5 mg x kg(-1) respectively, the sampling times were 20, 60, 240, 1440 min). The result showed the expression of c-jun mRNA in rat brains was prior to the accumulation of mercury, and the expression of c-jun mRNA in rat brains could early predict the neurotoxicity of MMC. IEG (c-jun) participated in the toxicity process of injury by MMC.