Efficiency of white lupin in the removal of mercury from contaminated soils: soil and hydroponic experiments

Emilia fosbergii Nicolson, a novel and effective accumulator for phytoremediation of mercury-contaminated soils

Soil contamination by toxic metals threatens global public health, highlighting the need for cost-effective and ecologically sound site remediation. In this study, we assessed phytoremediation of Hg-contaminated soils by Emilia fosbergii Nicolson (Asteraceae). Pot experiment was conducted using a substrate of sand and vermiculite (1:1 volume ratio), treatments consisted of five Hg concentrations (0, 1, 3, 5, and 7 mg kg-1). Metal transfer rates were calculated, including accumulation (BAF), translocation (TF) and bioconcentration (BCF) factors. E. fosbergii roots exhibited greater Hg accumulation than other tissues, but biomass production and plant health were not significantly affected at the concentrations tested, as indicated by elongation factors and tolerance index. The results revealed BAF values between 2.18 and 7.14, TF values ranged between 0.15 and 0.52, and the BCF index varied between 8.97 and 26.58. Treatments with Hg content of 5 mg kg-1 and 7 mg kg-1 recorded the highest total Hg concentrations of 66 mg kg-1 and 65.53 mg kg-1 (roots), and 9.18 mg kg-1 and 33.88 mg kg-1 (aerial), respectively. E. fosbergii demonstrated promise for Hg phytoremediation due to its high accumulation capacity, indicated by regular TF and high BCF and BAF indexes, thus classifying it as a high Hg accumulator.

Oxidative stress protection and growth promotion activity of Pseudomonas mercuritolerans sp. nov., in forage plants under mercury abiotic stress conditions

SAICEUPSMT strain was isolated from soils in the mining district of Almadén (Ciudad Real, Spain), subjected to a high concentration of mercury. Using the plant model of lupinus, the strain was inoculated into the rhizosphere of the plant in a soil characterized by a high concentration of mercury (1,710 ppm) from an abandoned dump in the mining district of Almadén (Ciudad Real, Spain). As a control, a soil with a minimum natural concentration of mercury, from a surrounding area, was used. Under greenhouse conditions, the effect that the inoculum of the SAICEUPSMT strain had on the antioxidant capacity of the plant was studied, through the quantification of the enzymatic activity catalase (CAT), ascorbate peroxidase (APX), superoxide dismutase (SOD), and glutathione reductase (GR). Likewise, the capacity of the plant to bioaccumulate mercury in the presence of the inoculum was studied, as well as the effect on the biometric parameters total weight (g), shoot weight (g), root weight (g), shoot length (cm), root length (cm), total number of leaves (N), and total number of secondary roots (No). Finally, in view of the results, the SAICEUPSMT strain was identified from the phenotypic and genotypic point of view (housekeeping genes and complete genome sequencing). The inoculum with the SAICEUPSMT strain in the presence of mercury produced a significant reduction in the enzymatic response to oxidative stress (CAT, APX, and SOD). It can be considered that the strain exerts a phytoprotective effect on the plant. This led to a significant increase in the biometric parameters total plant weight, root weight and the number of leaves under mercury stress, compared to the control without abiotic stress. When analyzing the mercury content of the plant with and without bacterial inoculum, it was found that the incorporation of the SAICEUPSMT strain significantly reduced the uptake of mercury by the plant, while favoring its development in terms of biomass. Given the positive impact of the SAICEUPSMT strain on the integral development of the plant, it was identified, proving to be a Gram negative bacillus, in vitro producer of siderophores, auxins and molecules that inhibit stress precursors. The most represented fatty acids were C16:0 (33.29%), characteristic aggregate 3 (22.80%) comprising C16:1 ω7c and C16: 1ω6c, characteristic aggregate 8 (13.66%) comprising C18:1 ω7c, and C18: 1 cycle ω6c and C 17:0 (11.42%). From the genotypic point of view, the initial identification of the strain based on the 16S rRNA gene sequence classified it as Pseudomonas iranensis. However, genome-wide analysis showed that average nucleotide identity (ANI, 95.47%), DNA-DNA in silico hybridization (dDDH, 61.9%), average amino acid identity (AAI, 97.13%), TETRA (0.99%) and intergenic distance (0.04) values were below the established thresholds for differentiation. The results of the genomic analysis together with the differences in the phenotypic characteristics and the phylogenetic and chemotaxonomic analysis support the proposal of the SAICEUPSMT strain as the type strain of a new species for which the name Pseudomonas mercuritolerans sp. is proposed. No virulence genes or transmissible resistance mechanisms have been identified, which reveals its safety for agronomic uses, under mercury stress conditions.

Evaluation of the oxidative stress alleviation in Lupinus albus var. orden Dorado by the inoculation of four plant growth-promoting bacteria and their mixtures in mercury-polluted soils

Mercury (Hg) pollution is a serious environmental and public health problem. Hg has the ability to biomagnify through the trophic chain and generate various pathologies in humans. The exposure of plants to Hg affects normal plant growth and its stress levels, producing oxidative cell damage. Root inoculation with plant growth-promoting bacteria (PGPB) can help reduce the absorption of Hg, minimizing the harmful effects of this metal in the plant. This study evaluates the phytoprotective capacity of four bacterial strains selected for their PGPB capabilities, quantified by the calculation of the biomercuroremediator suitability index (IIBMR), and their consortia, in the Lupinus albus var. orden Dorado. The oxidative stress modulating capacity in the inoculated plant was analyzed by measuring the activity of the enzymes catalase (CAT), superoxide dismutase (SOD), ascorbate peroxidase (APX), and glutathione reductase (GR). In turn, the phytoprotective capacity of these PGPBs against the bioaccumulation of Hg was studied in plants grown in soils highly contaminated by Hg vs. soils in the absence of Hg contamination. The results of the oxidative stress alleviation and Hg bioaccumulation were compared with the biometric data of Lupinus albus var. orden Dorado previously obtained under the same soil conditions of Hg concentration. The results show that the biological behavior of plants (biometrics, bioaccumulation of Hg, and activity of regulatory enzymes of reactive oxygen species [ROS]) is significantly improved by the inoculation of strains B1 (Pseudomonas moraviensis) and B2 (Pseudomonas baetica), as well as their corresponding consortium (CS5). In light of the conclusions of this work, the use of these strains, as well as their consortium, is postulated as good candidates for their subsequent use in phytostimulation and phytoprotection processes in areas contaminated with Hg.

A review on phytoremediation of mercury contaminated soils

Mercury (Hg) and its compounds are one of the most dangerous environmental pollutants and Hg pollution exists in soils in different degrees over the world. Phytoremediation of Hg-contaminated soils has attracted increasing attention for the advantages of low investment, in-situ remediation, potential economic benefits and so on. Searching for the hyperaccumulator of Hg and its application in practice become a research hotspot. In this context, we review the current literatures that introduce various experimental plant species for accumulating Hg and aided techniques improving the phytoremediation of Hg-contaminated soils. Experimental plant species for accumulating Hg and accumulation or translocation factor of Hg are listed in detail. The translocation factor (TF) is greater than 1.0 for some plant species, however, the bioaccumulation factor (BAF) is greater than 1.0 for Axonopus compressus only. Plant species, soil properties, weather condition, and the bioavailability and heterogeneity of Hg in soils are the main factors affecting the phytoremediation of Hg-contaminated soils. Chemical accelerator kinds and promoting effect of chemical accelerators for accumulating and transferring Hg by various plant species are also discussed. Potassium iodide, compost, ammonium sulphate, ammonium thiosulfate, sodium sulfite, sodium thiosulfate, hydrochloric acid and sulfur fertilizer may be selected to promote the absorption of Hg by plants. The review introduces transgenic gene kinds and promoting effect of transgenic plants for accumulating and transferring Hg in detail. Some transgenic plants can accumulate more Hg than non-transgenic plants. The composition of rhizosphere microorganisms of remediation plants and the effect of rhizosphere microorganisms on the phytoremediation of Hg-contaminated soils are also introduced. Some rhizosphere microorganisms can increase the mobility of Hg in soils and are beneficial for the phytoremediation.

Effect of soil mercury pollution on ginger (Zingiber officinale Roscoe): Growth, product quality, health risks and silicon mitigation

The mercury residue in soil not only poisons plants, but also bioaccumulates and biomagnifies through the food chain, causing a significant risk to human health. As an essential condiment on the table, the food safety of ginger should be focused on. Using soil culture experiments, this study aimed to identify the response of ginger growth to mercury pollution, assess the transmission and residue of mercury in different product organs and explore the mitigation mechanism of silicon on mercury toxicity. Effects of soil mercury pollution on ginger growth showed hormesis and time effect. Long-term mercury pollution led to growth inhibition and quality degradation of ginger, eventually reducing its yield by 25.96% (mercury = 9 mg kg-1). Contents of mercury and silicon in different organs both were the highest in root, followed by rhizome, less in stem and leaf, especially the mercury residue in rhizome manifested as Mother-ginger > Son-ginger > Grandson-ginger. At 6 mg kg-1 soil mercury level, the mercury residue of Mother-ginger exceeds the edible pollutant limit standard (China) by 10.7 times, which makes no obvious risk after being consumed by adults, but poses a potential health threat to children. Notably, it is safer to consume the newly sprouted and inflated tender ginger. Application of silicon fertilizer could alleviate mercury toxicity, mainly by promoting ginger root growth and leaf pigment synthesis, stimulating water-gas exchange system, fluorescence system and antioxidant system to make an anti-stress response. 2 mg kg-1 silicon fertilizer had the most significant mitigation effect on mercury stress, which increased the yield of ginger by 24.85% and reduced the mercury residue of ginger block by 44.44%-60.17%.

Screening of Heavy Metal-Immobilizing Bacteria and Its Effect on Reducing Cd2+ and Pb2+ Concentrations in Water Spinach (Ipomoea aquatic Forsk.)

Microbial immobilization is considered as a novel and environmentally friendly technology that uses microbes to reduce heavy metals accumulation in plants. To explore microbial resources which are useful in these applications, three water spinach rhizosphere soils polluted by different levels of heavy metals (heavy pollution (CQ), medium pollution (JZ), and relative clean (NF)) were collected. The community composition of heavy metal-immobilizing bacteria in rhizosphere soils and its effects on reducing the Cd²⁺ and Pb²⁺ concentrations in water spinach were evaluated. Four hundred strains were isolated from the CQ (belonging to 3 phyla and 14 genera), JZ (belonging to 4 phyla and 25 genera) and NF (belonged to 6 phyla and 34 genera) samples, respectively. In the CQ sample, 137 strains showed a strong ability to immobilize Cd²⁺ and Pb²⁺, giving Cd²⁺ and Pb²⁺ removal rates of greater than 80% in solution; Brevundimonas, Serratia, and Pseudoarthrobacter were the main genera. In total, 62 strains showed a strong ability to immobilize Cd²⁺ and Pb²⁺ in the JZ sample and Bacillus and Serratia were the main genera. A total of 22 strains showed a strong ability to immobilize Cd²⁺ and Pb²⁺ in the NF sample, and Bacillus was the main genus. Compared to the control, Enterobacter bugandensis CQ-7, Bacillus thuringensis CQ-33, and Klebsiella michiganensis CQ-169 significantly increased the dry weight (17.16-148%) of water spinach and reduced the contents of Cd²⁺ (59.78-72.41%) and Pb²⁺ (43.36-74.21%) in water spinach. Moreover, the soluble protein and Vc contents in the shoots of water spinach were also significantly increased (72.1-193%) in the presence of strains CQ-7, CQ-33 and CQ-169 compared to the control. In addition, the contents of Cd and Pb in the shoots of water spinach meet the standard for limit of Cd²⁺ and Pb²⁺ in vegetables in the presence of strains CQ-7, CQ-33 and CQ-169. Thus, the results provide strains as resources and a theoretical basis for the remediation of Cd- and Pb-contaminated farmlands for the safe production of vegetables.

Rhodobacter xinxiangensis sp. nov., isolated from pakchoi-cultivated soil contaminated with heavy metal and its potential to reduce Cd and Pb accumulation in pakchoi (Brassica campestris L.)

A Gram-stain-negative, aerobic, and motile strain, TJ48^T, was isolated from pakchoi-cultivated soil contaminated with Cd and Pb in Xinxiang (China). Cells of the strain were rod-shaped and colonies on LB agar were faint yellow. Strain TJ48^T was positive for catalase and oxidase and the optimal condition for growth was 28 °C, with 1% (w/v) NaCl and at pH 7.0. Phylogenetic analysis based on the 16S rRNA gene sequences showed that strain TJ48^T was closely related to the genus Rhodobacter and the closest relatives were Rhodobacter ovatus JA234^T (97.4%, 16S rRNA gene sequence similarity) and Rhodobacter azotoformans KA25^T (96.5%). The DNA G + C content of strain TJ48^T was 64.7 mol%. Genome-to-genome distance calculations (GGDC) and ANIb values from genomic comparison between the genomes of strain TJ48^T and the related reference species were less than 70% and 95%, respectively. The major cellular fatty acids were summed feature 8 (C_18:1ω7c and/or C_18:1ω6c) and C_17:0. The only isoprenoid quinone detected was Ubiquinone-10 (Q-10). The polar lipid profile contains diphosphatidylglycerol, phosphatidylglycerol, phosphatidylethanolamine, one unidentified aminophospholipid, one unidentified phospholipids, and three unidentified lipids. Strain TJ48^T significantly increased the dry weight of roots (26.2-66.3%) and shoots (16.7-37.8%) of pakchoi and reduced the Cd (50.2-60.1%) and Pb (55.6-60.9%) contents in pakchoi shoots and roots. On the basis of the physiological, genotypic and genomic characteristics, the strain TJ48^T represent a novel species of the genus Rhodobacter, and the name Rhodobacter xinxiangensis sp. nov. is proposed (type strain TJ48^T = CCTCC AB2019120^T = KCTC 72510^T).

Isolation of urease-producing bacteria and their effects on reducing Cd and Pb accumulation in lettuce (Lactuca sativa L.)

Excess Cd and Pb in agricultural soils enter the food chain and adversely affect all organisms. Therefore, it is important to find an eco-friendly way to reduce heavy metal accumulation in vegetables. We used urea agar plates to isolate urease-producing bacteria from the rhizosphere soil of lettuce in Cd- and Pb-contaminated farmland and investigated their ability to produce urease and immobilize heavy metals. The effects of these strains on the biomass, quality, and Cd and Pb accumulation of lettuce were also studied. The results showed that two urease-producing bacteria, Enterobacter bugandensis TJ6 and Bacillus megaterium HD8, were screened from the rhizosphere soil of lettuce. They had a high ability to produce urease (44.5 mS cm-1 min-1 OD600-1 and 54.2 mS cm-1 min-1 OD600-1, respectively) and IAA (303 mg L-1 and 387 mg L-1, respectively). Compared with the control, inoculation with strains TJ6 and HD8 reduced the Cd (75.3-85.8%) and Pb (74.8-87.2%) concentrations and increased the pH (from 6.92 to 8.13-8.53) in solution. A hydroponic experiment showed that the two strains increased the biomass (31.3-55.2%), improved the quality (28.6-52.6% for the soluble protein content and 34.8-88.4% for the vitamin C (Vc) content), and reduced the Cd (25.6-68.9%) and Pb (48.7-78.8%) contents of lettuce shoots (edible tissue). In addition, strain HD8 had a greater ability than strain TJ6 to reduce lettuce Cd and Pb uptake and water-soluble Cd and Pb levels in solution. These data show that the urease-producing bacteria protect lettuce against Cd and Pb toxicity by extracellular adsorption, Cd and Pb immobilization, and increased pH. The effects of heavy metal immobilization by the two strains can guarantee vegetable safety in situ for the bioremediation of heavy metal-polluted farmland.

Brassica juncea (L.) Czern. (Indian mustard): a putative plant species to facilitate the phytoremediation of mercury contaminated soils

A Phytoremediation experimental set up was established by spiking the soil with varying concentrations of mercury (Hg) (Treatment: T1:10; T2:50; T3:100; T4:500 and T5:1,000 mg Hg/kg soil). Hg removal ability of the Indian mustard plant was determined after 30, 60 and 90 days of exposure. Hg accumulation trend in second and third month of exposure was root > leaf > stem, while for the 1st month it was root > stem > leaf. The highest percentage of Hg accumulation (81%) and glutathione (14 mg/kg) was observed in the plants of T4 and T5 treatment, respectively at 90 days of exposure indicating a high level of Hg stress tolerance. At 90 days of exposure the chlorophyll a content in leaves grown on Hg-free soil (control soil) was 1.8, 2.4, 2.8, 3.6 and 4.4 fold higher than T1, T2, T3, T4 and T5 treatment respectively. With increase in exposure duration, translocation factor decreased whereas bioconcentration factor increased signifying Hg is mainly accumulated in the roots. The study suggests that Brassica juncea can withstand under high Hg contamination and can show great potential to phytostabilize Hg when grown under 100 mg/kg of soil Hg without showing any significant detrimental effect on the plant.

Effects of mercury on the germination and growth of Quercus ilex L. seedlings

While it is well-known that the toxicity of mercury for plants is related to its bioavailability in the environment in which the plant lives, few studies have addressed Hg effects under controlled conditions of life-limiting available Hg concentrations. This study examines the effects of Hg on the holm oak (Quercus ilex L.) exposed to medium-high available Hg concentrations. Holm oak seeds were sown in a perlite substrate and grown in the presence of a nutrient solution containing 0, 5, 25, or 50 μM Hg. The variables determined as outcome measures were impacts on germination, growth, and nutrient accumulation along with Hg concentration in leaves, stems, and roots at different growth stages. Our findings suggest no overall detrimental effects of the metal on germination, nutrient accumulation, and plant growth, although root morphology was clearly modified. Mercury accumulation in the plant varied according to time, organ, Hg treatment dose, and plant growth stage. When comparing Hg build-up in the different organs, highest concentrations of the metal were detected in the roots, followed by the leaves and stems. The Hg accumulation pattern was positively correlated with time and Hg dose, whereas negative correlation was observed with growth stage. The impacts of all these factors on Hg accumulation were not additive pointing to interesting interaction effects that should be explored in future work.

Mercury accumulation plant Cyrtomium macrophyllum and its potential for phytoremediation of mercury polluted sites

Cyrtomium macrophyllum naturally grown in 225.73 mg kg^-1 of soil mercury in mining area was found to be a potential mercury accumulator plant with the translocation factor of 2.62 and the high mercury concentration of 36.44 mg kg^-1 accumulated in its aerial parts. Pot experiments indicated that Cyrtomium macrophyllum could even grow in 500 mg kg^-1 of soil mercury with observed inhibition on growth but no obvious toxic effects, and showed excellent mercury accumulation and translocation abilities with both translocation and bioconcentration factors greater than 1 when exposed to 200 mg kg^-1 and lower soil mercury, indicating that it could be considered as a great mercury accumulating species. Furthermore, the leaf tissue of Cyrtomium macrophyllum showed high resistance to mercury stress because of both the increased superoxide dismutase activity and the accumulation of glutathione and proline induced by mercury stress, which favorited mercury translocation from the roots to the aerial parts, revealing the possible reason for Cyrtomium macrophyllum to tolerate high concentration of soil mercury. In sum, due to its excellent mercury accumulation and translocation abilities as well as its high resistance to mercury stress, the use of Cyrtomium macrophyllum should be a promising approach to remediating mercury polluted soils.

Low-molecular-weight organic acids correlate with cultivar variation in ciprofloxacin accumulation in Brassica parachinensis L

To understand the mechanism controlling cultivar differences in the accumulation of ciprofloxacin (CIP) in Chinese flowering cabbage (Brassica parachinensis L.), low-molecular-weight organic acids (LMWOAs) secreted from the roots of high- and low-CIP cultivars (Sijiu and Cutai, respectively) and their effects on the bioavailability of CIP in soil were investigated. Significant differences in the content of LMWOAs (especially maleic acid) between the two cultivars played a key role in the variation in CIP accumulation. Based on the Freundlich sorption coefficient (K_f) and distribution coefficient (K_d), the presence of LMWOAs reduced the CIP sorption onto soil particles, and higher concentrations of LMWOAs led to less CIP sorption onto soil. On the other hand, LMWOAs enhanced CIP desorption by lowering the solution pH, which changed the surface charge of soil particles and the degree of CIP ionization. LMWOAs promoted CIP desorption from soil by breaking cation bridges and dissolving metal cations, particularly Cu²⁺. These results implied that the LMWOAs (mainly maleic acid) secreted from Sijiu inhibited CIP sorption onto soil and improved CIP desorption from soil to a greater extent than those secreted from Cutai, resulting in higher bioavailability of CIP and more uptake and accumulation of CIP in the former.

Comparison of extractants used for the assessment of mercury availability in a soil from the Almadén mining district (Spain)

Single extraction methods have been extensively used to assess the availability of metals in polluted soils. This work focused on checking the feasibility of several chemicals, i.e. CaCl₂, EDTA, diethylenetriaminepentaacetic acid (DTPA) and a low-molecular-weight organic acid mixture (rhizosphere-based method), to be used as extractants for mercury (Hg) in a soil from the Almadén mining district (Spain). Moreover, the effect of several experimental parameters, i.e. extraction time (0.5, 1, 2, 5, 16 and 24 h), concentration of extractant (0.01, 0.05, 0.1 and 1 M) and soil/extractant ratio (1:2, 1:5 and 1:10), on the amount of Hg extracted was investigated. The Hg extraction ability followed the descending order EDTA > rhizosphere-based method > DTPA ≈ CaCl₂. This ranking was attributed to the higher complexation power of EDTA and organic acids. It was also found that extraction times between 2 and 5 h are required to avoid underestimation of mobile Hg and re-adsorption of the Hg previously extracted. Although some exceptions were found, Hg extraction efficiency was generally enhanced with higher extractant concentrations. Finally, the amount of Hg extracted by the four extractants increased with decreasing soil/extractant ratios.

EDTA and hydrochloric acid effects on mercury accumulation by Lupinus albus

The efficiency of white lupine (Lupinus albus) to uptake and accumulate mercury from a soil polluted by mining activities was assessed in a pot experiment with chemically assisted phytoextraction. The mobilizing agents tested were ethylenediaminetetracetic acid (EDTA) and hydrochloric acid (HCl). Two doses of each amendment were used (0.5 and 1.0 g of amendment per kg of soil), and unamended pots were used as a control. Addition of HCl to the soil did not negatively affect plant biomass, while the use of EDTA led to a significant decrease in plant growth when compared to that found for non-treated pots, with plants visually showing symptoms of toxicity. The addition of hydrochloric acid increased root, shoot and total plant Hg uptake of white lupine by 3.7 times, 3.1 times and 3.5 times, respectively, in relation to non-amended plants. The greatest efficiency was obtained for the highest HCl dose. EDTA led to higher concentrations of total plant Hg than that found with the control, but, due to the aforementioned decrease in plant biomass, the Hg phytoextraction yield was not significantly increased. These results were attributed to the capability of both amendments to form stable Hg complexes. The concentration of Hg in the water of the soil pores after the phytoextraction experiment was very low for all treatments, showing that risks derived from metal leaching could be partially avoided by using doses and chemicals suitable to the concentration of metal in the soil and plant performance.

Mercury uptake and effects on growth in Jatropha curcas

The use of metal-accumulating plants for the phytoremediation of contaminated soils is gaining more attention. Mercury (Hg)-contaminated soils from historical gold mines represent a potential risk to human health and the environment. Therefore, Jatropha curcas plant, that has shown its tolerance to these environments, is a species of particular interest to implement phytoremediation techniques in gold mining sites. In this work, the behavior of J. curcas was assessed in different hydroponic cultures fortified with Hg at concentrations of 5, 10, 20, 40, and 80μgHg/mL (T5, T10, T20, T40 and T80, respectively). After exposure, plant growth, net photosynthesis, leaf area, and Hg accumulation were determined and variables such as net Hg uptake, effective Hg accumulation, translocation and bioaccumulation factors were calculated. Accumulation of Hg in root and leaf tissues increased with respect to the Hg concentrations in the hydroponic culture, with statistically significant differences (p<0.05) among treatments. Moreover, Hg concentration in roots was 7 and 12-fold higher in average than in plant leaves and shoots, respectively. Many effects were found in the development of plants, especially related with loss of biomass and leaf area, with significant growth inhibition related to control values (>50% with treatment T5). Moreover, percentage of inhibition was even higher (>60%) with same treatment for net photosynthesis. Finally, it should be highlighted that for T40 and T80 treatments, plant growth and photosynthesis were almost completely depleted (88%-95%).

Mercury in mercury(II)-spiked soils is highly susceptible to plant bioaccumulation

Heavy metal phytotoxicity assessments usually use soluble metal compounds in spiked soils to evaluate metal bioaccumulation, growth inhibition and adverse effects on physiological parameters. However, exampling mercury phytotoxicity for barley (Hordeum vulgare) this paper highlights unsuitability of this experimental approach. Mercury(II) in spiked soils is extremely bioavailable, and there experimentally determined bioaccumulation is significantly higher compared to reported mercury bioaccumulation efficiency from soils collected from mercury-polluted areas. Our results indicate this is not affected by soil sorption capacity, thus soil ageing and formation of more stable mercuric complexes with soil fractions is necessary for reasonable metal phytotoxicity assessments.

Phytoremediation of mercury-contaminated soils by Jatropha curcas

Jatropha curcas plants species were tested to evaluate their phytoremediation capacity in soils contaminated by different levels of mercury. The experimental treatments consisted of four levels of mercury concentrations in the soil - T0, T1, T5, and T10 (0, 1, 5, and 10 μg Hg per g soil, respectively). The total mercury content absorbed by the different plant tissues (roots, stems and leaves) was determined during four months of exposure. The growth behavior, mercury accumulation, translocation (TF) and bioconcentration (BCF) factors were determined. The different tissues in J. curcas can be classified in order of decreasing accumulation Hg as follows: roots>leaves>stems. The highest cumulative absorption of the metal occurred between the second and third month of exposure. Maximum TF was detected during the second month and ranged from 0.79 to 1.04 for the different mercury concentrations. Values of BCF ranged from 0.21 to 1.43. Soils with T1 showed significantly higher BCF (1.43) followed by T10 (1.32) and T5 (0.91), all of them at the fourth month. On the other hand TFs were low (range 0.10-0.26) at the en of the experiment. The maximum reduction of biomass (16.3%) occurred for T10 (10 μg Hg g(-1)). In sum, J. curcas species showed high BCFs and low TFs, and their use could be a promising approach to remediating mercury-contaminated soils.

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).

Accumulation of total mercury and methylmercury in rice plants collected from different mining areas in China

A total of 155 rice plants were collected from ten mining areas in three provinces of China (Hunan, Guizhou and Guangdong), where most of mercury (Hg) mining takes place in China. During the harvest season, whole rice plants were sampled and divided into root, stalk & leaf, husk and seed (brown rice), together with soil from root zone. Although the degree of Hg contamination varied significantly among different mining areas, rice seed showed the highest ability for methylmercury (MeHg) accumulation. Both concentrations of total mercury (THg) and MeHg in rice plants were significantly correlated with Hg levels in soil, indicating soil is still an important source for both inorganic mercury (IHg) and MeHg in rice plants. The obvious discrepancy between the distribution patterns of THg and MeHg reflected different pathways of IHg and MeHg accumulation. Water soluble Hg may play more important role in MeHg accumulation in rice plants.

Could an abandoned mercury mine area be cropped?

The Almadén area (Spain) is known for its high natural mercury background as well as for the anthropogenic impact due to mining activities. After the end of these activities, appropriate alternative use of the soil has to be found, and agricultural activities stand out as an environmentally-friendly and potentially profitable alternative, giving to the soil a sustainable use without risks for human or animal health according to current legislation. Experiments performed at different scales (involving hydroponics, growth in pots and lysimeters) allow recommendations to be made regarding the adequacy of cultivation of different crops for animal or human consumption before they are sown in the field. Regarding crops for animal feeding, mercury accumulation in vegetative organs represents a higher potential risk for animals. Nevertheless, seeds and fruits can be used, both for human and animal consumption. Finally, this work will lead the way to obtain a scientific basis for elaborating a list of recommendations on sustainable and safe alternative land use, according to current international legislation.

Monitoring of the mercury mining site Almadén implementing remote sensing technologies

The Almadén area in Spain has a long history of mercury mining with prolonged human-induced activities that are related to mineral extraction and metallurgical processes before the closure of the mines and a more recent post period dominated by projects that reclaim the mine dumps and tailings and recuperating the entire mining area. Furthermore, socio-economic alternatives such as crop cultivation, livestock breeding and tourism are increasing in the area. Up till now, only scattered information on these activities is available from specific studies. However, improved acquisition systems using satellite borne data in the last decades opens up new possibilities to periodically study an area of interest. Therefore, comparing the influence of these activities on the environment and monitoring their impact on the ecosystem vastly improves decision making for the public policy makers to implement appropriate land management measures and control environmental degradation. The objective of this work is to monitor environmental changes affected by human-induced activities within the Almadén area occurring before, during and after the mine closure over a period of nearly three decades. To achieve this, data from numerous sources at different spatial scales and time periods are implemented into a methodology based on advanced remote sensing techniques. This includes field spectroradiometry measurements, laboratory analyses and satellite borne data of different surface covers to detect land cover and use changes throughout the mining area. Finally, monitoring results show that the distribution of areas affected by mercury mining is rapidly diminishing since activities ceased and that rehabilitated mining areas form a new landscape. This refers to mine tailings that have been sealed and revegetated as well as an open pit mine that has been converted to an "artificial" lake surface. Implementing a methodology based on remote sensing techniques that integrate data from several sources at different scales greatly improves the regional characterization and monitoring of an area dominated by mercury mining activities.

Impact of the lavender rhizosphere on the mercury uptake in field conditions

Lavender plants as well as their rhizosphere and bulk soil were sampled on a wide range of soils with different land use within the Almadén mercury mining district. The aim of this work is to evaluate the role of the rhizosphere on mercury behavior in soil-lavender plant system including chemometric analysis. The edaphic parameters that significantly differed between lavender rhizosphere and bulk soil were: total Hg; easily available Hg; electrical conductivity; organic matter; cation exchange capacity; soluble ions (Cl(-); SO(4)(2-); PO(4)(3-); NO(3)(-); Al(+); Mn(2+); Ca(2+) and Mg(2+)). The most important variable in the differentiation is electrical conductivity. Furthermore, both organic matter and Mn(2+) in rhizosphere soil seem to block Hg availability to plant. However, the presence of sulfates seems to favor it. Regarding other relationships, Hg seems to block Pb uptake by lavender plants and, on the other hand, the presence of Mn(2+) seems to favor it. Furthermore, Hg root uptake by lavender and its distribution throughout the plant have been studied. The more available Hg in rhizosphere soil, the more Hg is translocated to aerial part and less Hg is retained by root. In all cases, the Hg concentration in the root was higher than in the aerial part.

Potential cultivation of Hordeum vulgare L. in soils with high mercury background concentrations

Experimental work was carried out under close-to-real conditions to study mercury uptake by Hordeum vulgare L. cultivated in lysimeter experiments. The soil in the lysimeter experiment was obtained from a test plot located near Almadén (Spain) and had a mean mercury content of 22.9 mg kg(-1). A sequence of four crops was sown starting in autumn 2000 and repeated on a yearly basis until 2004. The first crop was grown in the field prior to the extraction of 5 one-cubic-meter lysimeters. The succeeding crops were sown in the lysimeter experiments at the CIEMAT Research Centre (Madrid, Spain). Samples of root and shoot were obtained during the four seasons. Concentrations of mercury at plant maturity in roots vary between I and 3 mg kg(-1) and in straw and grain the concentrations range from 72 to 480 microg kg(-1) and from 5 to 257 microg kg(-1), respectively. In order to assess the potential risk for human health and animal feed, an evaluation of the mercury content in the edible part of the crop has been carried out. According to legislation, there is no human health intoxication risk with a balanced consumption; otherwise, the forage use would have to be controlled.