Heavy Metals in the Tissues of Commercially Important Fish of Amurskii Bay,Sea of Japan

The concentrations of iron, copper, zinc, manganese, cadmium, and mercury in tissues and organs of Pacific herring, Far Eastern navaga, and spotted flounder from Amurskii Bay, Sea of Japan, were determined using an atom-absorption method. The distribution of these elements has been studied in organisms of the fish. The greatest concentration of iron, copper, cadmium, and mercury is found in the liver of the fish, manganese is mostly accumulated in the bone tissue, and zinc is found in the skin. Some specific features of metal accumulation in the fish of Amurskii Bay have been revealed. For example, the concentration of iron in the liver of herring and flounder significantly increased the mean concentration known from other areas. A sanitary–hygienic evaluation is provided for the recent levels of metal concentrations in these three species of commercially important fish.     

The effect of mercury accumulation on the intestinal glycosidase activity in perch <Emphasis Type="Italic">Perca fluviatilis</Emphasis> L. from aquatic bodies of European Russia with different pH

The intestinal glycosidase activities and kinetic characteristics of carbohydrate hydrolysis change in different ways with mercury accumulation in the muscles of perch from aquatic bodies of European Russia. Amylolytic activity decreases in fish from aquatic bodies with a neutral pH with a growth in Hg content (0.05–0.30 mg per 1 kg fresh weight), whereas sucrase increases. A decrease in the Michaelis constant for carbohydrate hydrolysis reflects an adaptive increase in enzyme-substrate affinity. In fish from acid lakes, the muscle Hg accumulation amounts to 0.18–0.86 mg per 1 kg fresh weight. With a growth in Hg content, the glycosidase activities and enzyme-substrate affinity decrease in most cases, having a negative effect on the assimilation rate of the carbohydrate components of food.     

The accumulation of inorganic mercury from sea water by the plaice, Pleuronectes platessa L

The accumulation of inorganic mercury from sea water by plaice eggs, larvae, and adult fish has been studied using ²⁰³HgCl₂ as a tracer. The isotope was rapidly accumulated and the levels of accumulation have been related to stable element concentrations. High concentration factors were attained by many organs, but the distribution of the ²⁰³Hg was markedly different from that of the stable element. Whereas the largest fraction of the body burden of mercury is contained by muscle, only a slow rate of accumulation into this tissue was observed. In addition, the mercury in fish muscle is of the methyl form: no evidence for the methylation of the tracer was obtained.     

An in situ study of rock bass (Ambloplites rupestris) physiology: effect of season and mercury contamination

Selected physiological and biochemical variables were examined in rock bass, Ambloplites rupestris, which were collected on five different sampling dates from an area of chronic mercury contamination and a reference site on the South River, Virginia.The onset of spawning represented the most significant seasonal influence in the physiological profile of the fish, with elevations in hematocrit, hemoglobin, plasma protein, and plasma glucose. Sex-related differences in plasma calcium, liver glycogen and liver ascorbic acid were also unique to the period. Female rock bass had significantly higher levels of liver glutathione than did males on all but one of the sampling dates, although the cause of this difference is not clear.Rock bass from the mercury contaminated site had an average muscle mercury concentration of 1.37 mg Hg g^–1, and an average liver mercury concentration of 2.86 mg Hg g^–1. These levels were approximately an order of magnitude greater than those found in the tissues of the reference fish which averaged 0.165 and 0.101 mg Hg g^–1 in muscle and liver respectively. In July 1987, mercury concentrations in the liver of both reference and contaminated fish increased significantly, possibly the result of greater uptake of the metal through increased feeding or changes in the mercury level of selected prey items. Rock bass collected from the two sites in July also had significantly different levels of liver glutathione: reference fish exhibited an elevation and contaminated fish a depression. When fish from the two sampling stations received a 96-hr exposure to 150 µg HgCl₂ in the laboratory, both groups exhibited elevated liver mercury and decreased liver glutathione. Mercury levels in the gall bladders of the exposed fish were also elevated, suggesting that glutathione may have been lost through excretion with the metal in the bile.On the whole, physiological differences between the two groups of rock bass were limited, indicating that exposure to the mercury is not having a significant impact on the rock bass from the contaminated area. This is further supported by field examination of the fish and comparison of condition indices from rock bass previously taken from the same two stations.Those factors which significantly altered the physiology of the rock bass were unique to certain times of the year, indicating that the most appropriate sampling approach in future studies is one which examines a number of variables over a range of environmental conditions.     

Using empirical methods to assess the risks of mercury accumulation in fish from lakes receiving acid rain

It has been hypothesized that concentrations of mercury ([Hg]) in fish increase with increasing acidic deposition. Our investigation suggests that this hypothesis is false for three species of fish from Ontario lakes. Across Ontario, Canada, slightly lower average [Hg] in Lake Trout, Walleye and Northern Pike (controlled for fish length) were associated with regions receiving progressively greater rates of sulphate deposition. We also observed that lake concentration of dissolved organic carbon ([DOC]), not pH, alkalinity or sulphate ion concentration, was the strongest correlate of this residual fish Hg contamination. Path analysis also determined a net reduction in fish [Hg] at higher rates of sulphate deposition. However, this analysis indicated a far more complex web of interactions between sulphate deposition, water chemistry and fish [Hg] than simple correlation analysis could define. Path analysis provided empirical evidence in support of several previously described mechanisms interacting simultaneously to influence fish Hg accumulation. Based on these empirical observations, an alternate hypothesis is proposed whereby increasing sulphate deposition results in lower [DOC] levels in lakes which, in turn, cause a decline in fish Hg contamination.     

Pilot plant for bioremediation of mercury-containing industrial wastewater

Mercury is an extremely toxic pollutant that is currently being emitted mainly by low level industrial sources. It is distributed globally through the atmosphere, from where it precipitates onto the surface of the Earth, enters aquatic organisms, accumulates in fish and finally affects the health of human populations. Microbes have evolved a mechanism for mercury detoxification [mercury resistance operon ( mer)] based on intracellular reduction of Hg(2+) to non-toxic Hg(0) by the mercuric reductase enzyme and subsequent diffusional loss of Hg(0) from the cell. It was shown that Hg(0) produced by microbial detoxification can be retained quantitatively in packed bed bioreactors, in which biofilms of mercury-resistant bacteria are grown on porous carrier material. This review describes operation of this system on a technical, fully automated, scale, and its operation at a chloralkali electrolysis factory. It was shown to work with high efficiency under fluctuating mercury concentrations and to be robust against transiently toxic conditions. The gradient of mercury concentration in the technical scale system exerted a strong selective pressure on the microbial community, which resulted in a succession of mercury-resistant strains at high mercury concentrations and an increase in phylogenetic and functional diversity at low mercury concentrations. Clean-up of mercury-containing wastewater by mercury-resistant microbes is a simple, environmentally friendly and cost-effective alternative to current treatment technologies.     

Factors influencing changes in mercury concentrations in lake water and yellow perch (<Emphasis Type="Italic">Perca flavescens</Emphasis>) in Adirondack lakes

Over the past 20+ years, fish with elevated concentrations of mercury (Hg) have been observed in remote lake districts, including the Adirondack region of New York. Across eastern North America studies have also reported a negative correlation between fish Hg concentration and lake pH. Recent controls in emissions of sulfur dioxide (SO₂) have resulted in some improvement in the acid–base status of acid-impacted surface waters including Adirondack lakes. In addition, there has been an apparent decrease in atmospheric Hg deposition. A synoptic survey of 25 lakes in the Adirondacks was conducted in 1992–1993 to analyze spatial patterns of Hg in the water column and yellow perch (Perca flavescens). The same cluster of 25 lakes was resurveyed in 2005–2006 to evaluate if changes in lake concentrations of Hg species or fish Hg have occurred. We observed a varied response of changes in water chemistry and fish Hg concentrations. In twelve of the resurveyed lakes the yellow perch had lower Hg concentrations, six lakes had yellow perch with higher Hg concentrations, and in seven lakes yellow perch Hg concentrations did not change significantly (α = 0.05). Four variables appear to influence the change in yellow perch Hg concentrations in the Adirondacks: watershed area, elevation, change in pH, and change in fish body condition. We hypothesize that as the acidity in lakes is attenuated, the lakes may become more productive and/or water quality conditions less stressful to fish leading to increasing fish body condition. As fish body condition improves, fish exhibit “growth dilution” of tissue contaminants leading to lower fish Hg concentrations.     

汞在新建水库食物网中生物累积与风险评价研究进展

汞是唯一参与全球循环的液态重金属。1974年,自美国学者Smith首次报道水库中鱼类总汞含量高于邻近自然湖泊以来,水库中鱼类汞升高的风险成为新建水库环境影响评价中的重要内容之一。汞在水库生态系统生物组分和非生物组分中含量升高的现象先后在世界各国报道,包括加拿大、美国、芬兰、泰国和巴西等。通过对系列的野外研究进行回顾,表明了水库形成后生态系统中汞的甲基化过程发生了变化。水库形成对汞在食物网中的鱼类、底栖生物、浮游生物的累积产生影响。水库中汞的生物累积、迁移转化主要与被淹没土壤和植物腐解过程有着直接或间接的关系。水库形成后,总汞、甲基汞和甲基汞比例在生态系统食物网各组分中的变化并不一致。蓄水后,水体中总汞变化较小,甲基汞和甲基汞比例上升明显;浮游生物尤其是浮游动物中总汞升高,但甲基汞和甲基汞比例升高更为明显;与浮游动物类似,底栖水生昆虫中总汞升高,甲基汞和甲基汞比例升高也更为明显;鱼类作为食物网顶级消费者,甲基汞比例一般在80%以上,在水库形成后鱼类总汞和甲基汞均明显升高,但甲基汞比例变化已经不大。这些变化揭示了水库形成后甲基汞在食物网传递的两个主要可能途径,一是微型生物食物网。通过悬浮颗粒物、浮游植物、浮游动物这一环节,甲基汞和甲基汞比例有明显的增加。第二个途径是底层生物食物网。通过悬浮颗粒物、细菌、碎屑食性底栖水生昆虫、肉食型底栖水生昆虫环节,甲基汞和甲基汞比例明显增加。这两种途径均能导致以水生昆虫、小鱼、甲壳类等为食的肉食性鱼类汞含量增加。水库形成后,生态系统中汞的甲基化发生了明显的"加速"过程。这种"加速"过程最直接的因素是成库后大量土壤淹没使得汞的甲基化平衡被打破。这个过程主要有两方面的影响。一方面是直接影响,被淹没土壤和植被在腐解过程中主动或被动地将甲基汞释放到水库生态系统中;另一方面是间接影响,被淹没土壤和植被的腐解使水库底部形成厌氧环境,有利于无机汞从被淹没土壤和植被中溶出,为甲基化反应提供充裕的、可供甲基化的无机汞,同时腐解产生的大量营养物质为微生物提供丰富食物来源,使硫酸盐还原菌大量繁殖,促进无机汞的甲基化。在我国,有关汞在新建水库食物网中生物累积和风险评价的研究有待进一步加强。     

Mercury and selenium interaction in vivo: effects on thioredoxin reductase and glutathione peroxidase

Mercury compounds exert toxic effects via interaction with many vital enzymes involved in antioxidant regulation, such as selenoenzymes thioredoxin reductase (TrxR) and glutathione peroxidase (GPx). Selenium supplementation can reactivate the mercury-inhibited TrxR and recover the cell viability in vitro. To gain an insight on how selenium supplementation affects mercury toxicity in vertebrates, we investigated the effects of selenium on the mercury accumulation and TrxR and GPx activities in a fish model. Juvenile zebra-seabreams were exposed either to methylmercury (MeHg) or inorganic mercury (Hg(2+)) in the presence or absence of sodium selenite (Se) for 28 days followed by 14 days of depuration. Mercury accumulation was found to be 10-fold higher under MeHg exposure than under Hg(2+) exposure. Selenium supplementation caused a half decrease of the accumulation of MeHg but did not influence Hg(2+) accumulation. Exposure to both mercurials led to a decrease of the activity of TrxR (<50% of control) in all organs. Se supplementation coincident with Hg(2+) exposure protected the thioredoxin system in fish liver. However, supplementation of Se during the depuration phase had no effects. The activity of GPx was only affected in the brain of fishes upon the exposure to MeHg and coexposure to MeHg and Se. Selenium supplementation has a limited capacity to prevent mercury effects in brain and kidney. These results demonstrate that Se supplementation plays a protective role in a tissue-specific manner and also highlight the importance of TrxR as a main target for mercurials in vivo.     

A dynamic integrated model for mercury bioaccumulation in marine organisms

A novel integrated dynamic model, the Integrated Fish Model (INTFISH), incorporating mercury (Hg) dynamics at non-steady state in marine organisms, is presented and is applied to the benthic food web in a polluted area. The integrated Fish model represents the dynamics of inorganic mercury (Hg^II) and methyl‑mercury (MeHg) in a real marine ecosystem including environmental (seawater and sediments) and biota compartments. Mercury concentration in fish is estimated using the INTFISH model coupled, in real-time, with results from i) the seawater and sediments modules computed using the HR3DHG model, ii) a dedicated Phytoplankton model and iii) six modules for Hg fluxes within the invertebrate compartment, incorporating the main organisms included in fish diet preferences, whose variations during the whole life cycle are also taken into account to verify the sensitivity of the integrated model to the core set of parameters. The simulated total mercury concentrations (Hg^TOT) in specimens of red mullet (Mullus barbatus), selected as target species for the Fish model, are in excellent agreement with field observations reported from the investigated area. The intrinsic modularity of the model offers the opportunity to extend simulations to other fish species (which are part of the diet of human populations of interest) and predict Hg concentration in food. A natural extension of the model will allow to evaluate the health risks related to human consumption of contaminated fish.     

Concomitant Antibiotic and Mercury Resistance Among Gastrointestinal Microflora of Feral Brook Trout, Salvelinus fontinalis

Twenty-nine bacterial isolates representing eight genera from the gastrointestinal tracts of feral brook trout Salvelinus fontinalis (Mitchell) demonstrated multiple maximal antibiotic resistances and concomitant broad-spectrum mercury (Hg) resistance. Equivalent viable plate counts on tryptic soy agar supplemented with either 0 or 25?μM HgCl₂ verified the ubiquity of mercury resistance in this microbial environment. Mercury levels in lake water samples measured 1.5?ng?L^?1; mercury concentrations in fish filets ranged from 81.8 to 1,080?ng?g^?1 and correlated with fish length. The presence of similar antibiotic and Hg resistance patterns in multiple genera of gastrointestinal microflora supports a growing body of research that multiple selective genes can be transferred horizontally in the presence of an unrelated individual selective pressure. We present data that bioaccumulation of non-point source Hg pollution could be a selective pressure to accumulate both antibiotic and Hg resistant bacteria.     

Stoichiometry and kinetics of mercury uptake by photosynthetic bacteria

Mercury adsorption on the cell surface and intracellular uptake by bacteria represent the key first step in the production and accumulation of highly toxic mercury in living organisms. In this work, the biophysical characteristics of mercury bioaccumulation are studied in intact cells of photosynthetic bacteria by use of analytical (dithizone) assay and physiological photosynthetic markers (pigment content, fluorescence induction, and membrane potential) to determine the amount of mercury ions bound to the cell surface and taken up by the cell. It is shown that the Hg(II) uptake mechanism (1) has two kinetically distinguishable components, (2) includes co-opted influx through heavy metal transporters since the slow component is inhibited by Ca²⁺ channel blockers, (3) shows complex pH dependence demonstrating the competition of ligand binding of Hg(II) ions with H⁺ ions (low pH) and high tendency of complex formation of Hg(II) with hydroxyl ions (high pH), and (4) is not a passive but an energy-dependent process as evidenced by light activation and inhibition by protonophore. Photosynthetic bacteria can accumulate Hg(II) in amounts much (about 10⁵) greater than their own masses by well-defined strong and weak binding sites with equilibrium binding constants in the range of 1 (μM)^?1 and 1 (mM)^?1, respectively. The strong binding sites are attributed to sulfhydryl groups as the uptake is blocked by use of sulfhydryl modifying agents and their number is much (two orders of magnitude) smaller than the number of weak binding sites. Biofilms developed by some bacteria (e.g., Rvx. gelatinosus) increase the mercury binding capacity further by a factor of about five. Photosynthetic bacteria in the light act as a sponge of Hg(II) and can be potentially used for biomonitoring and bioremediation of mercury-contaminated aqueous cultures.     

Sexual dimorphism in inorganic mercury toxicokinetics and the attendant lipotoxic and non-lipotoxic dyslipidemia in the rat

The influence of variability in the biology of living organisms is poorly appreciated in toxicology. However, multiple lines of evidence indicate that sex-differences modulate toxicokinetics and toxicodynamics from cellular/molecular to whole animal levels resulting in different toxic responses of living organisms to xenobiotics exposure. In order to investigate the influence of sex in inorganic mercury (Hg) exposure, male and female Wistar rats were exposed to 0.5, 1.0 and 1.5 mg Hg/kg body weight orally as HgCl₂ twice a week for 12 weeks. Higher Hg levels in the females (except heart) as compared to males were observed in the animals. At the highest dose of inorganic Hg, female renal Hg content was 3.3 times higher than that of the males. Mixed sexual dimorphism characterised circulating-lipid- and organ-lipid lipotoxic and non-lipotoxic dyslipidemia. The highest dose of inorganic Hg, induced hypercholesterolemia in the males as opposed to hypocholesterolemia in the female. Plasma and erythrocyte free fatty acids increased in both sexes, although the increase was more pronounced in the male. Reverse cholesterol transport was inhibited in the male at the highest dose of Hg, whereas female HDL became enriched with cholesterol. Female erythrocytes had all their lipids increased, whereas only male erythrocyte triglyceride increased. Brain cholesterol and phospholipids, and splenic phospholipids were depleted in both sexes. Our findings indicate that inorganic Hg exposure appears to affect Hg and lipid kinetics differently in both sexes, thus underscoring the need to develop sex-tailored approaches in the treatment of metal toxicosis and its metabolic outcomes.     

汞在SPAC-人体系统中的转递及主要影响因素

汞（Hg）是环境中一种具有高度毒性的重金属元素,且具有较高挥发性,因而作为一种全球性的污染物而备受关注。汞在SPAC系统中的迁移转化,是全球汞循环的重要环节,与人类的建康密切相关。汞通过食物链进入人体并在体内蓄积受多种因素影响,主要包括3个方面：土壤性质（如土壤汞含量、pH、有机质、粘土矿物等）,植物特性（植物类型、种类和生育期等）,大气状况（如光照强度、气温和大气湿度等）。此外,锌、硒和抗氧化剂等的存在也有较大影响。综述了汞在SPAC-人体系统中的迁移积累及其调控机理。     

The phytochelatin transporters AtABCC1 and AtABCC2 mediate tolerance to cadmium and mercury

Heavy metals such as cadmium (Cd) and mercury (Hg) are toxic pollutants that are detrimental to living organisms. Plants employ a two-step mechanism to detoxify toxic ions. First, phytochelatins bind to the toxic ion, and then the metal-phytochelatin complex is sequestered in the vacuole. Two ABCC-type transporters, AtABCC1 and AtABCC2, that play a key role in arsenic detoxification, have recently been identified in Arabidopsis thaliana. However, it is unclear whether these transporters are also implicated in phytochelatin-dependent detoxification of other heavy metals such as Cd(II) and Hg(II). Here, we show that atabcc1 single or atabcc1 atabcc2 double knockout mutants exhibit a hypersensitive phenotype in the presence of Cd(II) and Hg(II). Microscopic analysis using a Cd-sensitive probe revealed that Cd is mostly located in the cytosol of protoplasts of the double mutant, whereas it occurs mainly in the vacuole of wild-type cells. This suggests that the two ABCC transporters are important for vacuolar sequestration of Cd. Heterologous expression of the transporters in Saccharomyces cerevisiae confirmed their role in heavy metal tolerance. Over-expression of AtABCC1 in Arabidopsis resulted in enhanced Cd(II) tolerance and accumulation. Together, these results demonstrate that AtABCC1 and AtABCC2 are important vacuolar transporters that confer tolerance to cadmium and mercury, in addition to their role in arsenic detoxification. These transporters provide useful tools for genetic engineering of plants with enhanced metal tolerance and accumulation, which are desirable characteristics for phytoremediation.     

Accumulation of Ag, Cd, Co, Cu, Hg, Ni and Pb in Pavlova viridis Tseng (Haptophyceae)

The flagellate alga Pavlova viridis Tseng was investigated in the laboratory for accumulation of the heavy metals, silver, cadmium, cobalt, copper, mercury, nickel and lead. The cultures were grown in an artificial seawater medium mixed with the individual metals at different concentrations. Based on data from the controls, the baseline metal concentrations in P. viridis were shown to be in an order of Cu > Pb > Co > Cd > Ni > Ag > Hg. In the experimental groups, the seven metals displayed different isotherm equilibrium patterns and the metal uptake capacity of the alga was Ni > Pb > Co > Hg > Cu > Cd > Ag at equilibrium. When assessed using the bioconcentration factors, metal accumulation by P. viridis was demonstrated to be the most efficient at a concentration of 0.001 mg L-1 for Ag, Cd and Co, and at 0.01 mg L-1 for Cu, Hg, Ni and Pb. This study suggests that P. viridis can be a source of mineral supplements in mariculture. The alga is not, however, recognized as an effective agent for removing heavy metals from wastewater. This revised version was published online in June 2006 with corrections to the Cover Date.     

Red-backed salamander (Plethodon cinereus) as a bioindicator of mercury in terrestrial forests of the northeastern United States

Despite concerns over the widespread deposition of mercury (Hg) in remote forested areas of the northeastern United States (U.S.), little information is available on the bioaccumulation of Hg in this region's terrestrial fauna. There is a strong need to develop baseline data on appropriate bioindicator species for this area, and here we report Hg concentrations in one of the most widely distributed vertebrates in forested areas, the red-backed salamander (Plethodon cinereus). To inform the use of this species as a bioindicator of Hg accumulation, we assessed ratios of bioavailable methylmercury (MeHg) to total Hg, and techniques for non-destructive sampling along an elevational gradient of increasing forest floor Hg concentrations. Total Hg in body samples was 70% MeHg, and Hg concentrations in tail-clips, which can be collected non-lethally, were positively correlated with body concentrations. Mercury concentrations in salamanders increased 2.4-fold along an increasing elevational gradient of Hg in soils. We conclude that Hg concentrations in P. cinereus can act as a biomonitoring tool for broad areas of remote terrestrial forests, and may help identify regions and landscape characteristics of particular concern for Hg bioaccumulation.     

Quantitative Trait Loci for Mercury Accumulation in Maize (Zea mays L.) Identified Using a RIL Population

To investigate the genetic mechanism of mercury accumulation in maize (Zea mays L.), a population of 194 recombinant inbred lines derived from an elite hybrid Yuyu 22, was used to identify quantitative trait loci (QTLs) for mercury accumulation at two locations. The results showed that the average Hg concentration in the different tissues of maize followed the order: leaves > bracts > stems > axis > kernels. Twenty-three QTLs for mercury accumulation in five tissues were detected on chromosomes 1, 4, 7, 8, 9 and 10, which explained 6.44% to 26.60% of the phenotype variance. The QTLs included five QTLs for Hg concentration in kernels, three QTLs for Hg concentration in the axis, six QTLs for Hg concentration in stems, four QTLs for Hg concentration in bracts and five QTLs for Hg concentration in leaves. Interestingly, three QTLs, qKHC9a, qKHC9b, and qBHC9 were in linkage with two QTLs for drought tolerance. In addition, qLHC1 was in linkage with two QTLs for arsenic accumulation. The study demonstrated the concentration of Hg in Hg-contaminated paddy soil could be reduced, and maize production maintained simultaneously by selecting and breeding maize Hg pollution-safe cultivars (PSCs).     

Operon mer: bacterial resistance to mercury and potential for bioremediation of contaminated environments

Mercury is present in the environment as a result of natural processes and from anthropogenic sources. The amount of mercury mobilized and released into the biosphere has increased since the beginning of the industrial age. Generally, mercury accumulates upwards through aquatic food chains, so that organisms at higher trophic levels have higher mercury concentrations. Some bacteria are able to resist heavy metal contamination through chemical transformation by reduction, oxidation, methylation and demethylation. One of the best understood biological systems for detoxifying organometallic or inorganic compounds involves the mer operon. The mer determinants, RTPCDAB, in these bacteria are often located in plasmids or transposons and can also be found in chromosomes. There are two classes of mercury resistance: narrow-spectrum specifies resistance to inorganic mercury, while broad-spectrum includes resistance to organomercurials, encoded by the gene merB. The regulatory gene merR is transcribed from a promoter that is divergently oriented from the promoter for the other mer genes. MerR regulates the expression of the structural genes of the operon in both a positive and a negative fashion. Resistance is due to Hg2+ being taken up into the cell and delivered to the NADPH-dependent flavoenzyme mercuric reductase, which catalyzes the two-electron reduction of Hg2+ to volatile, low-toxicity Hg0. The potential for bioremediation applications of the microbial mer operon has been long recognized; consequently, Escherichia coli and other wild and genetically engineered organisms for the bioremediation of Hg2+-contaminated environments have been assayed by several laboratories.     

Mercury in the muscle tissue of fish in the Central and South Vietnam

The content of mercury has been determined in the muscle tissue of 18 fish species in rivers, lakes, and reservoirs of Central and South Vietnam. The region is characterized by lower metal concentrations than those in water bodies in temperate and northern latitudes. In 76% of samples (n = 986), the content of Hg was ≤0.5 μg Hg/g of dry (≤0.1 μg/g of wet) tissue weight. In water bodies and watercourses of tropical latitudes, interspecific variations in fish can be one of the factors responsible for a wide range of Hg variation within the same species.