Absorption Of Hg Research Articles

Enrichment characteristics of Cd and Hg and regulation of heavy metal transporter signaling in Pleurotus ostreatus

Currently, heavy metal pollution has emerged as a global issue. Compared with green plants, edible fungi, significant crops cultivated worldwide, present a greater capacity to accumulate heavy metals (HMs). However, the enrichment characteristics and functions of heavy metal transporters (HMATs) in the accumulation of HMs in edible fungi are still unclear. Cadmium (Cd) and mercury (Hg) are the primary HMs enriched in edible fungi. This study focused on Pleurotus ostreatus, the second largest edible mushroom worldwide, to examine the enrichment process. In this study, a series of different concentrations of CdCl2 and HgCl2 (0, 0.01, 0.05, 0.5, 2, 5, 10, and 20 mg/L) were used to mimic HMs pollution. HMs in the experimental concentration range did not affect the mycelial growth rate or fruiting body yield of P. ostreatus. However, in the 20 mg/L treatment group, the HMs were mainly concentrated in the cap, with about 4.4 mg/kg Cd and 2.7 mg/kg Hg, and were predominantly present in the most toxic ion exchange state. Thirteen HMATs were identified in the genome database of P. ostreatus. Using RT-qPCR, seven HMATs (24093, 1066001, 1106787, 1066344, 1079972, 1095088, and 1104877) whose expression levels were more than twice that of the control under most concentrations of HMs were selected for further investigation of their transport functions and their involvement in signal regulation. Among them, gene 24093 was involved in the absorption of Cd and Hg. These transporters are regulated by ROS, Ca2+, and NO signals under HM stress. This study provides target genes for reducing the risk of HM accumulation through molecular means, and serves as a reference for HM remediation using edible fungi.

Evaluating the Potential of Modified Mango Leaves as a Biosorbent for the Removal of Mercury (II) Ion and Congo Red from Wastewater

The discharge of harmful metallic elements from industrial byproducts has resulted in notable environmental and public health risks. The aim of this study was to investigate the effectiveness of mango leaves as a cost-effective adsorbent in eliminating Hg (II) ions from industrial effluents. Experimental procedures were carried out under controlled conditions at ambient temperature to evaluate the influence of pH, contact duration, initial metal levels, adsorbent quantity, and temperature on the adsorption mechanism. The most favorable pH for optimal Hg (II) ions adsorption was identified at pH 7. The adsorption process displayed swift kinetics in the initial 30 minutes of contact, leading to a removal rate exceeding 90%, with equilibrium achieved after 70 minutes of stirring. Analysis of kinetics revealed a significant correlation coefficient for a pseudo-second-order kinetic equation. The absorption of Hg (II) ions escalated with increased stirring intensity and decreased adsorbent amount. The interaction between Hg (II) ions, Congo red, and mango leaves was analyzed employing Langmuir, Freundlich, and BET isotherm models. The equilibrium data was best fitted by the Langmuir model, presenting a correlation coefficient of 0.98 and a maximum adsorption capacity of 28.40 mg/g. These results underscore the potential of mango leaves as an affordable bio adsorbent for addressing heavy metal pollution in wastewater.

Algal-derived dissolved organic matter accelerates mercury methylation under cyanobacterial blooms in the sediment of eutrophic lakes

Mercury (Hg), especially in the form of methylmercury (MeHg), poses a significant threat to both organisms and the environment due to its extreme toxicity. While methylation process of Hg in sediments has been extensively studied, recognition of its associated risks and mechanisms during cyanobacterial blooms remains limited. This study investigated the distribution characteristics of Hg and MeHg in sediments of Taihu Lake, China. The concentration of Hg and MeHg varied within the range of 96.0–212.0 ng g−1 and 0.1–0.5 ng g−1, respectively. Higher ecological risks of Hg were found in algal-dominated regions compared to macrophyte areas. The significant correlations observed between Hg, MeHg, and algal-derived dissolved organic matter (ADOM) components C1 and C2 in algal-dominated regions indicate a close association between ADOM components and the Hg methylation process. These components are involved in the absorption or complexation of Hg, participate in redox reactions, and modulate microbial activity. The dsrB gene in sulfate-reducing bacteria (SRB) was found to accelerate the metabolic pathways of Hg methylation. These findings indicate that ADOM could enhance the methylation process of Hg during cyanobacterial blooms, which warrants attention.

Genome-Wide Association Study of Blood Mercury in European Pregnant Women and Children.

Mercury has high industrial utility and is present in many products, and environmental contamination and occupational exposure are widespread. There are numerous biological systems involved in the absorption, metabolism, and excretion of Hg, and it is possible that some systems may be impacted by genetic variation. If so, genotype may affect tissue concentrations of Hg and subsequent toxic effects. Genome-wide association testing was performed on blood Hg samples from pregnant women of the Avon Longitudinal Study of Parents and Children (n = 2893) and children of the Human Early Life Exposome (n = 1042). Directly-genotyped single-nucleotide polymorphisms (SNPs) were imputed to the Haplotype Reference Consortium r1.1 panel of whole genotypes and modelled againstlog-transformed Hg. Heritability was estimated using linkage disequilibrium score regression. The heritability of Hg was estimated as 24.0% (95% CI: 16.9% to 46.4%) in pregnant women, but could not be determined in children. There were 16 SNPs associated with Hg in pregnant women above a suggestive p-value threshold (p < 1 × 10-5), and 21 for children. However, no SNP passed this threshold in both studies, and none were genome-wide significant (p < 5 × 10-8). SNP-Hg associations were highly discordant between women and children, and this may reflect differences in metabolism, a gene-age interaction, or dose-response effects. Several suggestive variants had plausible links to Hg metabolism, such as rs146099921 in metal transporter SLC39A14, and two variants (rs28618224, rs7154700) in potassium voltage-gated channel genes. The findings would benefit from external validation, as suggestive results may contain both true associations and false positives.

Distribution characteristics of mercury concentration and estimation of mercury pools in different age groups of Larix gmelinii forests of Daxing'an Mountain

Forests are important sinks of atmospheric mercury. Quantifying mercury pools in forest ecosystem tissues are essential for understanding the global mercury cycle. To reveal the characteristics of Hg concentration and Hg pool distribution in natural forests at different ages, samples from the vegetation layer, organic horizons, coarse wood debris, and mineral soil layers were collected in young forest, middle forest, near-mature forest, and mature forest of Larix gmelinii forests at the Daxing'an Mountain. The results showed that there were differences in the absorption and accumulation of Hg by different tree species and tissues. In Larix gmelinii, the concentration of Hg followed the order of bark > branch > leaf > root > core, whereas in Betula platyphylla, the order was bark > leaf > branch > root > core. The mercury concentration in the organic horizons increased gradually with the decomposition process. There were no obvious regular patterns in the mercury concentrations of each tissue in different age groups Larix gmelinii forests. Furthermore, total biomass mercury pools (overstory, shrub layer, herb layer, moss layer, and coarse woody debris （CWD）) in the young, middle, near-mature, and mature forests of Larix gmelinii forests at Daxing'an Mountain were estimated to be 99.0 μg m-2，207 μg m-2，207 μg m−2 and 194 μg m−2, respectively. On ecosystem scale, total mercury pools were 16.9 mg m−2 (young), 27.5 mg m−2 (middle), 17.0 mg m−2 (near-mature), and 11.8 mg m−2(mature). The mineral soil mercury pool accounts for 94.0%–98.1% of the total ecosystem mercury pool, and its mercury pool proportion gradually decreased with the increase in forest age. These obtained results are quite valuable for further assessing the role of forest ecosystems in the atmospheric mercury cycle and estimating potential mercury emissions from biomass burning during forest wildfires.

Use of Genus Cistus in Phytotechnologies: Application in a Closed Mercury Mine

The Almadén mining district is known to be one of the richest mercury areas in the world. Despite the high concentrations of this metal, this territory has well-established vegetation that provides a wide range of mercury-tolerant plants that can be used as ecosystem services. This is the case of some species of Cistus that grow wild and spontaneously as part of the natural flora of Almadén. The objective of this study was to evaluate if there were differences between the absorption and distribution of Hg of five species of the genus Cistus in spontaneous growth and to evaluate their potential application in phytotechnologies. The work has been carried out with plant samples collected under field conditions in the “Fuente del Jardinillo” located in the old mining area of Almadén (Ciudad Real). The experimental plot was divided into three previously characterised subplots to ensure that all the sampled plants had grown in similar soil conditions (pH, organic matter content, EC, CEC, total Hg and available Hg). Additionally, the experiment was carried out in triplicate. The results showed that despite the homogeneity of the soil, the absorption of Hg in the aerial part of the plants showed significant differences related to Cistus species. The values in the bioaccumulation of mercury in the aerial part were also different. Based on the uptake of mercury by the plants sampled in this study, its potential use in phytotechnologies was established, classifying them as phytoextractors (Cistus albidus, C. ladanifer and C. monspeliensis) and phytostabilisers (C. crispus and C. salviifolius).

Influence of arbuscular mycorrhizal fungi on mercury accumulation in rice (Oryza sativa L.): From enriched isotope tracing perspective

The microorganisms that co-exist between soil and rice systems in heavy metal-contaminated soil environments play important roles in the heavy metal pollution states of rice, as well as in the growth of the rice itself. In this study, in order to further examine the effects of soil microorganisms on the mercury (Hg) uptake of rice plants and determine potential soil phytoremediation agents, an enriched 199Hg isotope was spiked in a series of pot experiments to trace the absorption and migration of Hg and rice growth in the presence of arbuscular mycorrhizal fungi (AMF). It was observed that the AMF inoculations significantly reduced the Hg concentration in the rice. The Hg concentration in rice in the AMF inoculation group was between 52.82% and 96.42% lower than that in the AMF non-inoculation group. It was also interesting to note that the presence of AMF tended to cause Hg (especially methyl-Hg (Me199Hg)) to migrate and accumulate in the non-edible parts of the rice, such as the stems and leaves. Under the experimental conditions selected in this study, the proportion of Me199Hg in rice grains decreased from 9.91% to 27.88%. For example, when the exogenous Hg concentration was 0.1 mg/kg, the accumulated methyl-Hg content in the grains of the rice in the AMF inoculation group accounted for only 20.19% of the Me199Hg content in the rice plants, which was significantly lower than that observed in the AMF non-inoculated group (48.07%). AMF also inhibited the absorption of Hg by rice plants, and the decrease in the Hg concentration levels in rice resulted in significant improvements in growth indices, including biomass and micro-indexes, such as antioxidant enzyme activities. The improvements occurred mainly because the AMF formed symbiotic structures with the roots of rice plants, which fixed Hg in the soil. AMF also reduce the bioavailability of Hg by secreting a series of substances and changing the physicochemical properties of the rhizosphere soil. These findings suggest the possibility of using typical co-existing microorganisms for the remediation of soil heavy metal contamination and provide valuable insights into reducing human Hg exposure through rice consumption.

Mercury Content and Amelioration of Its Toxicity by Nitric Oxide in Lichens.

Mercury (Hg) content measured in five epiphytic lichen species collected in Slovakia mountain forests ranged from 30 to 100 ng/g DW and was species-specific, decreasing in the order Hypogymnia > Pseudevernia > Usnea > Xanthoria > Evernia prunastri (but polluted sites had no impact on Hg amount in Xanthoria). Evernia was therefore used to study the impact of short-term exogenous Hg (100 µM, 24 h) and possible amelioration of Hg toxicity by nitric oxide (NO) donor sodium nitroprusside (SNP). NO was efficiently released from SNP as detected by two staining reagents and fluorescence microscopy and reduced Hg-induced ROS signal and absorption of Hg by thalli of Evernia prunastri. At the same time, NO ameliorated Hg-induced depletion of metabolites such as ascorbic acid and non-protein thiols, but not of free amino acids. The amount of metabolites, including soluble phenols, was reduced by excess Hg per se. On the contrary, NO was unable to restore Hg-stimulated depletion of chlorophyll autofluorescence but mitigated the decline of some macronutrients (K and Ca). Data confirm that accumulation of Hg in the epiphytic lichens is species-specific and that NO is a vital molecule in Evernia prunastri that provides protection against Hg-induced toxicity with considerable positive impact on metabolic changes.

Gut-on-a-chip for exploring the transport mechanism of Hg(II)

Animal models and static cultures of intestinal epithelial cells are commonly used platforms for exploring mercury ion (Hg(II)) transport. However, they cannot reliably simulate the human intestinal microenvironment and monitor cellular physiology in situ; thus, the mechanism of Hg(II) transport in the human intestine is still unclear. Here, a gut-on-a-chip integrated with transepithelial electrical resistance (TEER) sensors and electrochemical sensors is proposed for dynamically simulating the formation of the physical intestinal barrier and monitoring the transport and absorption of Hg(II) in situ. The cellular microenvironment was recreated by applying fluid shear stress (0.02 dyne/cm2) and cyclic mechanical strain (1%, 0.15 Hz). Hg(II) absorption and physical damage to cells were simultaneously monitored by electrochemical and TEER sensors when intestinal epithelial cells were exposed to different concentrations of Hg(II) mixed in culture medium. Hg(II) absorption increased by 23.59% when tensile strain increased from 1% to 5%, and the corresponding expression of Piezo1 and DMT1 on the cell surface was upregulated.

COMPARISON OF REMAINING COAL-BURNING ASH-BASED ON CD, PB, AND HG CONCENTRATION AT DIFFERENT TEMPERATURES: A CASE STUDY IN ACEH PROVINCE

This study aims to investigate the efficiency level of absorption of heavy metals Cd, Pb, and Hg. Combustion is carried out using coal with the addition of absorbent ratios of 2%, 4%, 6%, 8%, and 10%. The adsorbent used is natural zeolite which is widely available and inexpensive. This study provides practical implications for the easy and inexpensive removal of heavy metal emissions during combustion. The results show that the maximum efficiency level for Cd metal reached 22.96% which was recorded at a temperature of 600 °C for an adsorbent ratio of 10%. The maximum efficiency level of Pb metal from the experimental results was obtained at a temperature of 600 °C with an adsorbent ratio of 10% to 10.83%. Meanwhile, the efficiency level for Hg metal produced was 0.05% which was recorded at the adsorbent ratio of 10% at 800 °C. The maximum total capacity of Pb metal for each tested combustion temperature was 600 °C 39.85 mg/kg, 700 °C 25.43 mg/kg, and 800 °C 7.21 mg/kg. On the other words, the higher the combustion temperature tested, the lower the absorption efficiency rate obtained.

Development of sulfurized Polythiophene-Silver Iodide-Diethyldithiocarbamate nanoflakes toward Record-High and selective absorption and detection of mercury derivatives in aquatic substrates

Large-scale disposal of mercury derivatives via industries into the ecosystem created ever-lasting pollution in nature that could lead to bioaccumulation and put living species' lives in danger; hence, it is vital to remove these hazardous pollutants using practical approaches. Herein, this requirement is addressed by developing a 2D absorber with active sulfur domains composed of polythiophene (PT), AgxIx, and sodium diethyldithiocarbamate (PT-AgI-D). The developed configuration exhibited record-high absorption capacity and Femto molar-level sensitivity toward absorption and detection of mercury derivatives, viz., Hg metallic (Hg (m)), HgCl2, and HgO. Accordingly, the PT-AgI-D showed a superior removal capacity of 733.7, 186.6, and 299.4 mg g−1 toward the absorption of Hg (m), HgCl2, and HgO from aquatic media, respectively, with a yield of 99% at optimum conditions. More importantly, the absorber exhibited a detection limit (DL)/sensitivity of 11.86/79.57, 20.04/44.62, and 32.83/35.11 fM/(µA/fM) cm−2 toward Hg (m), HgCl2, and HgO, respectively. Furthermore, precise assessments revealed favorable reproducibility, selectivity, stability, and reusability of the absorber even after 20 adsorption–desorption cycles, highlighting its superior performance in removing mercury derivatives from aquatic media.

Oxidation Absorption of Hg0 in the Gas Phase Using a Double Catalyzers–Double Oxidants Coactivation Technology

Oxidation Absorption of Hg⁰ in the Gas Phase Using a Double Catalyzers–Double Oxidants Coactivation Technology

The effectivity of Biduri combined with indigenous bacteria in mercury absorption

Heavy metals pollution, especially Mercury (Hg), is one of the most serious environmental problems. The presence of excessive Hg will cause soil degradation and threaten the life of the ecosystem, for that remediation is necessary. Biduri is known to be able to absorb heavy metals, but there is no research on the ability of Biduri in absorb Hg. The use of indigenous bacteria is expected to increase the absorption of Mercury by Biduri. The purpose of this study was to determine the potential of Biduri combined with indigenous bacteria and Agrobacterium sp I37 in absorbing of Hg in the soil. The experimental was designed as factorial with completely randomized design, consisting of 2 factors namely Bioremediation agent (A0: without bioremediation agent, A1: indigenous bacteria, A3: Agrobacterium sp I37) and Hg dosage (D0: without Hg, D1: Hg 0.3 µg.g-1, D2: Hg 0.51 µg.g-1). The results showed that the combination of Biduri with indigenous bacteria + 0.3 µg.g-1 Hg shows highest absorption of Hg at 57.19 µg (99.24% higher than control) and reduce soil Hg levels by 0.09 µg.g-1. Biduri is a hyperaccumulator plant because it is able to absorb more than 10 µg.g-1 of mercury.

A 16.2-kyr lacustrine sediment record of mercury deposition in Dahu Swamp, eastern Nanling Mountains, southern China: Analysis of implications for climatic changes

This study provides a 16.2-kyr record of mercury (Hg) deposition derived from a lacustrine sedimentary sequence in Dahu Swamp, eastern Nanling Mountains. Results indicate that changes in climatic conditions had a significant effect on Hg concentrations (Hg–C) and accumulation rates (Hg-AR). Multi-proxy records including dry density, grain size, geochemical elements, organic matter and pollen indicators were compared with Hg accumulation. The results revealed that the contributions of detrital input and atmospheric deposition were minor, and Hg accumulation in the sediments was closely related to changes in climatic conditions: relatively drier and colder climate would result in shrinkage of the lake water body thus favoring increased formation of organic-rich peat or gyttja and leading to enhanced absorption of Hg by organic matter and result in increases of Hg–C and Hg-AR in sediments, and vice versa. Our results indicate that variations of Hg accumulation in Dahu Swamp were greatly impacted by climate under the influences of solar insolation changes and shrinkage or expansion of ice sheets in high latitudes to the north. The results of this study provide an insight into the response of Hg accumulation to low latitude climate processes in the East Asian summer monsoon region.

Heavy metal contamination risk assessment and correlation analysis of heavy metal contents in soil and crops.

Heavy metal pollution is a notable threat to agricultural production. Soil heavy metal pollution can cause potential ecological risk (ERI), and crop heavy metal pollution can cause human health risk (HRI). However, most previous studies partially focused on heavy metal pollution in soil or crop but often neglected the relationship between them. Actually, soil heavy metal can pollute crops to some extent, while not all heavy metal pollution in crops comes from soil. The inner relationship of pollution risk in soil-crop system is worth attention. In this study, we selected Ningbo as the study region and used sample data to assess both soil and crop heavy metal risks, in order to explore the differences between heavy metal contamination risks in soil and crops as well as the relationships between heavy metal contents in soil and crops. Our results showed that Hg was the most polluted heavy metal in soil, which led to the highest ecological risk in Jiangbei (Comprehensive ERI=567) with the maximum ERI of Hg (430). However, As in crops contributed the most to health risk and caused the highest health risk in Fenghua (HRI=10) with the largest contribution of 64.5%. Such differences of pollution risk assessment indicated that the contents of the same heavy metal were inconsistent in soil and crops. Our results further showed that the heavy metals in soil had the greatest influence on Zn in crops. Pb and Cr in soil had synergistic effects on the crop absorption of Zn, whereas As, Hg and Cu played antagonistic roles in the crop absorption of Zn. Our study confirms that heavy metals in soil would variously influence heavy metals in crops and the interaction of heavy metals is very important for pollution risk control, which have been largely ignored yet.

Characterization of the mercury-binding proteins in tuna and salmon sashimi: Implications for health risk of mercury in food

Fish consumption is one of the major ways through which humans receive exposure to mercury (Hg). The existing forms of Hg in food, particularly Hg bound to proteins, may affect the absorption of Hg by humans and subsequently its potentially toxic effects. However, the knowledge regarding Hg-binding proteins in edible fish muscle is scarce. In the present study, salmon and tuna fish muscles, collected from seven different regions and countries, were analyzed using metallomics- and proteomics-based techniques. The concentration of Hg in sashimi samples ranged from 4.4 to 317.4 ng/g. Size exclusion chromatography (SEC) coupled with inductively coupled plasma mass spectrometer (ICP-MS) showed that beta-actin was a novel Hg-binding protein from the fish muscles, and this protein could also bind bismuth (Bi), silver (Ag), and copper (Cu). Hg bound to beta-actin accounted for approximately 30.2–37.6% of the total Hg in the tuna muscles and was significantly correlated to total Hg in the fish muscles (r = 0.98, p < 0.01) and in the fraction of soluble proteins (r = 0.94, p < 0.01). These findings suggest that proteins act as the main Hg accumulation sites in edible fish; thus, increasing human exposure to Hg following gastrointestinal digestion.

Removal of mercury (II) from aqueous solutions by multiwalled carbon nanotubes coated with manganese oxide

Background and aims: Water pollution by heavy metals is one of the most important environmental problems. Among the heavy metals, mercury (Hg) is a very toxic metal and its high concentration can lead to impaired pulmonary and renal dysfunction. The aim of this study was to determine the amount of Hg removal by carbon nanotubes coated with manganese (Mn) oxide from aqueous solutions. Methods: In this study, multi-walled carbon nanotubes coated with Mn oxide were prepared and used to remove Hg from aqueous environments. In addition, the physical and structural characteristics of the nanotubes were determined by the X-ray diffraction (XRD). The impact of diverse variables was further investigated, including the initial concentration of Hg, the initial pH of the solution, contact time, mixing rate, as well as the amount of nano-composite and the impacts of confounders (nitrate and chloride). Finally, optimum conditions for each of these parameters were obtained by the Taguchi statistical method. Results: The XRD analysis showed that the nanotubes were properly coated with Mn oxide. Furthermore, the results demonstrated that under pH 7, the rate of mixing of 150 rpm, the contact time of 60 minutes, the amount of nano-composite of 60 mg, and the initial density of Hg 80 mg/L can be achieved by removing 95% Hg. Moreover, the confounder factors of nitrate and chloride reduced the amount of Hg removal by 4 and 5%, respectively. Conclusion: Based on the results, the nanotubes coated with Mn oxide can be used as easy and strong absorbents for the rapid absorption of Hg from drinking water and industrial wastewater.

Comparative study of the effects of different chelating ligands on the absorption and transport of mercury in maize (Zea mays L.)

Mercury (Hg) pollution seriously threatens food safety and has attracted global attention. Phytoextraction, due to its low cost, applicability, and environmental friendliness, is considered a new technology for clean-up of heavy metal contamination in the environment. However, the low bioavailability of Hg in polluted areas greatly limits the applicability of phytoextraction. Here, we compared the effects of six common chelating ligands on the absorption and transport of Hg in maize (Zea mays L.), which has a high biomass and short growth cycle. The results showed that the root length and biomass of maize seedlings of the groups treated with the six chelating ligands (EDTA, iodide, ammonium, thiosulfate, thiocyanate, and thiocarbamide) did not change compared with those of the non-treated groups. Co-exposure to Hg and each chelating ligand markedly alleviated the inhibitory effect induced by Hg. Iodide treatment resulted in the lowest root Hg content and highest translocation factor (TF) value, while ammonium treatment gave rise to the highest shoot Hg concentration and lowest TF. Compared with other chelating ligands, thiosulfate exhibited the maximum alleviation of Hg toxicity and achieved the highest concentration of Hg in the roots and aerial parts. Moreover, the TF and Hg accumulation in the thiosulfate and Hg co-exposed group were much higher than those in the group exposed to Hg alone. This finding suggests that, among these common chelating ligands, thiosulfate compounds have great potential for Hg phytoextraction, while the others can immobilize Hg in polluted areas.

Bioconcentration and translocation of Cd and Hg in a tomato (Solanum lycopersicum) from cultivated soils in southeastern Brazil.

Food is the main source of toxic metals like mercury (Hg) and cadmium (Cd) to humans. This study evaluated the accumulation and translocation of Cd and Hg in a soil-plant system in four tomato plantations and assessed the risk associated with ingestion of these metals. Ten soil samples (rhizosphere) and 10 samples of plant tissues (leaf, ripe fruit, green fruit, and roots) were collected in each plantation. Spatial variation in Cd and Hg concentrations was negligible. The Cd level in rhizosphere was lower in comparison with that of plant tissues. Hg levels in rhizosphere were similar to roots and higher than the value observed in aerial parts of plants. The Cd bioconcentration factor was approximately five times higher compared to that of Hg. Approximately 93% and 48.6% of Cd and Hg accumulated in roots reached aerial parts, respectively. Our results indicate that tomato readily absorbs Cd accumulated in soil, translocating it to aerial parts. Comparatively, the absorption of Hg is not efficient. Levels of Cd in tomatoes were over 17 times higher than the maximum residual levels in 57.5% of ripe fruits and in 27.5% of green tomatoes.

Effect of iron plaque and selenium on mercury uptake and translocation in rice seedlings grown in solution culture.

A hydroponics experiment was conducted to investigate the effect of iron plaque on root surfaces and selenium (Se) on the uptake and transfer of mercury (Hg) in rice seedlings by adding in the EDTA-Fe (0, 10, 30, 50, 70mg Fe l-1) into the solution to produce a different amount of iron plaque outside rice root. After 24h, the red-brown iron plaque was formed on the root surface, and the amount of iron plaques was positively correlated with the amount of Fe in the solution. The iron plaque deposited on the root surface has a strong adsorption effect on the inorganic Hg. The addition of Se could promote the adsorption of Hg2+ on the iron plaque of rice, and the introduction of Se could increase the adsorption capacity of Hg on iron plaque on average by 1.42 times. The Hg was extracted by DCB (Dithionite-citrate-bicarbonate) up to between 66.2 and 67.8% of the total Hg when the roots with iron plaque (Fe70) were incubated with the combination of 5μmolL-1 of HgCl2 and 5μmolL-1 of Na2SeO3 for an hour. After 3days, the content of Hg in the iron plaque decreased to 6.3-33.9%, indicating that part of the inorganic Hg adsorbed by the iron plaque could be reabsorbed and used. Besides that, the iron plaque allowed the Hg to stay longer in the iron plaque, which hindered the transfer of Hg to the shoot significantly. Hg adsorbed in the iron plaque can be desorbed by low-molecular-weight organic acids, which was equivalent to desorption of Hg from ferric hydroxide oxides. Hg adsorbed on the iron plaque can be moved back to the rest of the plant. These results suggest that the iron plaque and Se in the root surface might play a role as "physical buffer" in the absorption and transfer of Hg.