Toxicity testing of heavy metals with theRhizobium-legume symbiosis: High sensitivity to cadmium and arsenic compounds

Legume root nodules are the site of biological nitrogen fixation in theRhizobium-legame symbiosis. Nodules are structures unique to this symbiosis and they are morphologically as well as physiologically distinct from other plant organs. Organic substances affecting the macro- or microsymbionts vitality, such as PAHs (Wetzel et al., 1991), reduce nodulation even before visible damage to the plant can be detected. We present data that the formation of nodules (nodulation) may also serve for ecotoxicological evaluation of heavy metals in different binding states. Tests were performed in petri dishes with alfalfa (lucerne) seedlings inoculated withRhizobium meliloti. Cultivation took place in growth cabinets with carefully standardized and documented growth conditions. Data from stressed plants was recorded after 14 days of cultivation on contaminated substrate. A dose responsive decrease in nodulation was found after application of cadmium acetate, cadmium iodide, cadmium chloride, sodium salts of arsenate and arsenite, arsenic pentoxide, and lead nitrate, whereas lead acetate showed no effect up to a concentration of 3 μM. The dose response curves were used to calculate EC10, EC50 and EC90 values. EC50 values for cadmium compounds range from 1.5 to9.5 pM. Testing different arsenic compounds results in EC50 from 2.6 to 20.1 μM. EC50 of lead nitrate is 2.2 μM. The sensitivity, reproducibility and reliability of this test system is discussed compared to established biotests.     

Toxic effects of low concentrations of Cu on nodulation of cowpea (Vigna unguiculata)

Although Cu is phytotoxic at Cu(2+) activities as low as 1-2 microM, the effect of Cu(2+) on the nodulation of legumes has received little attention. The effect of Cu(2+) on nodulation of cowpea (Vigna unguiculata (L.) Walp. cv. Caloona) was examined in a dilute solution culture system utilising a cation exchange resin to buffer solution Cu(2+). The nodulation process was more sensitive to increasing Cu(2+) activities than both shoot and root growth; whilst a Cu(2+) activity of 1.0 microM corresponded to a 10% reduction in the relative yield of the shoots and roots, a Cu(2+) activity of 0.2 microM corresponded to a 10% reduction in nodulation. This reduction in nodulation with increasing Cu(2+) activity was associated with an inhibition of root hair formation in treatments containing > or =0.77 microM Cu(2+), rather than to a reduction in the size of the Rhizobium population.     

Interactions of arsenic and phenanthrene on their uptake and antioxidative response in Pteris vittata L

The interactions of arsenic and phenanthrene on plant uptake and antioxidative response of Pteris vitatta L. were studied hydroponically. The combination of arsenic and phenanthrene decreased arsenic contents in fronds by 30-51%, whereas increased arsenic concentrations 1.2-1.6 times in roots, demonstrating the suppression of arsenic translocation compared to the corresponding treatment without phenanthrene. Under the co-exposure, As(III) concentrations in fronds deceased by 12-73%, and at higher arsenic exposure level (≥10 mg/L), As(V) in fronds and As(III) in roots increased compared to the single arsenic treatment. Arsenic exposure elevated phenanthrene concentrations in root by 39-164%. The co-existence of arsenic and phenanthrene had little impact on plant arsenic accumulation, although synergistic effect on antioxidants was observed, suggesting the special physiological process of P. vitatta in the co-exposure and application potential of P. vitatta in phytoremediation of arsenic and PAHs co-contamination.     

Two bacterial strains isolated from a Zn-polluted soil enhance plant growth and mycorrhizal efficiency under Zn-toxicity

In this study we investigated the interactions among plant, rhizosphere microorganisms and Zn pollution. We tested the influence of two bacterial strains isolated from a Zn-polluted soil on plant growth and on the symbiotic efficiency of native arbuscular mycorrhizal fungi (AMF) under Zn toxicity. The two bacterial strains exhibited Zn tolerance when cultivated under increasing Zn levels in the medium. However, strain B-I showed a higher Zn tolerance than strain B-II at the two highest Zn levels in the medium (75 and 100 mg l(-1) Zn). Molecular identification placed the strain B-I within the genus Brevibacillus. Our results showed that bacterial strain B-I consistently enhanced plant growth, N and P accumulation, as well as nodule number and mycorrhizal infection which demonstrated its plant-growth promoting (PGP) activity. This strain B-I has been shown to produce IAA (3.95 microg ml) and to accumulate 5.6% of Zn from the growing medium. The enhanced growth and nutrition of plants dually inoculated with the AMF and bacterium B-I was observed at three Zn levels assayed. This effect can be related to the stimulation of symbiotic structures (nodules and AMF colonization) and a decreased Zn concentration in plant tissues. The amount of Zn acquired per root weight unit was reduced by each one of these bacterial strains or AMF and particularly by the mixed bacterium-AMF inocula. These mechanisms explain the alleviation of Zn toxicity by selected microorganisms and indicate that metal-adapted bacteria and AMF play a key role enhancing plant growth under soil Zn contamination.     

Enhanced mobilization of arsenic and heavy metals from mine tailings by humic acid

Arsenic and heavy metal mobilization from mine tailings is an issue of concern as it might pose potential groundwater or ecological risks. Increasing attention recently has been focused on the effects of natural organic matter on the mobility behavior of the toxicants in the environment. Column experiments were carried out in this research study to evaluate the feasibility of using humic acid (HA) to mobilize arsenic and heavy metals (i.e., Cu, Pb and Zn) from an oxidized Pb-Zn mine tailings sample collected from Bathurst, New Brunswick, Canada. Capillary electrophoresis analyses indicated that arsenate [As(V)] was the only extractable arsenic species in the mine tailings and the addition of HA at pH 11 did not incur the oxidation-reduction or methylation reactions of arsenic. A 0.1% HA solution with an initial pH adjusted to 11 was selected as the flushing solution, while distilled water (initial pH adjusted to 11) was used as the control to account for the mobilization of arsenic and the heavy metals by physical mixing and the effect of pH. It was found that the HA could significantly enhance the mobilization of arsenic and heavy metals simultaneously from the mine tailings. After a 70-pore-volume-flushing, the mobilization of arsenic, copper, lead and zinc reached 97, 35, 838 and 224 mg kg(-1), respectively. The mobilization of arsenic and the heavy metals was found to be positively correlated with the mobilization of Fe in the presence of the HA. Moreover, the mobilization of arsenic was also correlated well with that of the heavy metals. The mobilization of co-existing metals to some extent might enhance arsenic mobilization in the presence of the HA by helping incorporate it into soluble aqueous organic complexes through metal-bridging mechanisms. Use of HA in arsenic and heavy metal remediation may be developed as an environmentally benign and possible effective remedial option to reduce and avoid further contamination.     

Effect of sulfide on the cytotoxicity of arsenite and arsenate in human hepatocytes (HepG2) and human urothelial cells (UROtsa)

Arsenic, a common poison, is known to react with sulfide in vivo, forming thioarsenates. The acute toxicity of the inorganic thioarsenates is currently unknown. Our experiments showed that a fourfold sulfide excess reduced acute arsenite cytotoxicity in human hepatocytes (HepG2) and urothelial cells (UROtsa) significantly, but had little effect on arsenate toxicity. Speciation analysis showed immediate formation of thioarsenates (up to 73 % of total arsenic) in case of arsenite, but no speciation changes for arsenate. Testing acute toxicity of mono- and trithioarsenate individually, both thioarsenates were found to be more toxic than their structural analogue arsenate, but less toxic than arsenite. Toxicity increased with the number of thio groups. The amount of cellular arsenic uptake after 24 h corresponded to the order of toxicity of the four compounds tested. The dominant to almost exclusive intracellular arsenic species was arsenite. The results imply that thiolation is a detoxification process for arsenite in sulfidic milieus. The mechanism could either be that thioarsenates regulate the amount of free arsenite available for cellular uptake without entering the cells themselves, or, based on their chemical similarity to arsenate, they could be taken up by similar transporters and reduced rapidly intracellularly to arsenite.     

Sex-specific differences in early renal impairment associated with arsenic,lead, and cadmium exposure among young adults in Taiwan

Exposure to a single metal has been reported to damage renal function in humans. However, information regarding the association between multiple-metal exposure and markers for early renal impairment in different sexes among the young adult Taiwanese population is scarce. We assessed the association between exposure to arsenic (As), cadmium (Cd), and lead (Pb), and early renal impairment markers using urinary microalbumin (MA), β2-microglobulin (β2MG), and N-acetyl-beta-D-glucosaminidase (NAG) by analyzing 157 young adults aged 20?29 years, in Taiwan. Inductively coupled plasma mass spectrometry was used to determine urinary As, Cd, and Pb levels. Regression models were applied to different sex groups. The results showed that after adjusting for potential confounding factors and each metal, urinary Cd levels were significantly positively associated with urinary MA (β?=?0.523, 95% CI: 0.147–0.899) and β2MG (β?=?1.502, 95% CI: 0.635–2.370) in males. However, the urinary Cd level was significantly positively associated with only urinary NAG (β?=?0.161, 95% CI: 0.027–0.296) in females. This study thus indicates that the effect of exposure to metals (especially Cd) on early renal impairment among young adults in Taiwan is sex-specific. Our study results could contribute toward developing early intervention programs for decreasing the incidence of renal dysfunction. Further studies are warranted to confirm our findings and clarify the potential mechanisms involved.

     

Arsenic speciation in plants growing in arsenic-contaminated sites

Concentrations of total arsenic and of arsenic species were determined by ICPMS and HPLC-ICPMS in terrestrial plant samples. The arsenic concentration in plant samples from the contaminated sites ranged from 1.14 to 98.5 mg kg(-1) (dry mass). However, a very high value, exceeding largely this range was found in a moss sample growing in the contaminated area (1750 mg kg(-1)). Plants growing in a non-contaminated area with similar geological characteristics contained 0.06-0.58 mg As kg(-1). Plant samples from different species were selected and extracted with water, water/methanol (9+1, v/v), and water/methanol (1+1, v/v). Water/methanol (9+1, v/v) was selected as extractant for the speciation analysis for all the plant samples. The extraction efficiencies ranged from 3.0% to 41.4%, with good agreement between samples from the same plant species. Arsenite and/or arsenate were found in all the plant samples. Additionally, methylarsonate (MA), dimethylarsinate (DMA), trimethylarsine oxide (TMAO) and tetramethylarsonium ion (TETRA) were also identified in several plants, and in some cases MA and DMA were the main species found. TMAO, which is usually found as a trace constituent in organisms, was also a significant arsenical in one of the studied samples, where it constituted 24% of the extracted arsenic. In the present study, the patterns of arsenic species varied with the plant species and much higher proportion of organoarsenicals was found in plants from the more contaminated sites.     

The effect of heavy metals on dinitrogen fixation by Rhizobium-white clover in a range of long-term sewage sludge amended and metal-contaminated soils

An investigation was conducted to determine whether effective strains of Rhizobium leguminosarum biovar. trifolii capable of symbiotic N2 fixation with white clover (Trifolium repens) were present in a range of metal-contaminated soils. A number of historically sewage-amended sites (including experimental, pasture grassland and arable sites) were selected and compared with highly contaminated samples from abandoned heavy metal mines. Many sites had metal concentrations above the limits established by the UK Government, based on those developed by the European Commission (EC) for sludge-amended soils. Acetylene reduction activity (ARA) was used to screen the samples for effective N2 fixation. When the host plant was indigenous to the sward, rhizobia were found in the nodules and in the soil rhizosphere at all the sites tested. They were shown to be capable of effective symbiosis and N2 fixation, even though metal concentrations greatly exceeded the soil metal limits in some cases. However, nodulation failed to occur in some cases where T. repens was not indigenous to metal-contaminated soils. This indicated either that an ineffective rhizobial population was present, or that effective cells were absent from the soil. The influence of individual metals on ARA could not be determined conclusively because of the confounding effects of soil physicochemical variability and the presence of different metals at high concentrations together in the soil. However, Cd concentrations appeared to be particularly important in determining the presence of effective ARA in soils with no indigenous clover. In contrast to previous studies, the results presented here suggest that heavy metals may have had a quantitative effect on the free-living population of rhizobia, rather than a genetic effect.     

A phospho-compost biological-based approach increases phosphate rock agronomic efficiency in faba bean as compared to chemical and physical treatments

Under arid and semi-arid conditions, direct application of phosphate rock (PR) as a source of phosphorus (P) for crop production is likely influenced by agricultural practices and soil properties. Different approaches could be used to improve the agronomic efficiency of low-grade PR over a wider range of soils and crops. In this study, biological, physical, and chemical treatments of low-grade Moroccan PR were investigated and compared through agronomic trials on faba bean grown under alkaline soil conditions. The physical treatment was based on blending PR with triple superphosphate (TSP) at 75:25 and 50:50 ratios, the biological treatments involved co-application of PR with compost at 50:50 ratio and phospho-compost elaborated from PR (20%), sewage sludge (46%), and wheat residues (34%), while the chemical treatment was obtained by a 30% acidulation of PR by phosphoric acid. Control treatments consisting of zero P application (control), PR alone, and TSP alone were considered to assess the effectiveness of the abovementioned techniques to improve PR agronomic efficiency. A pot experiment was conducted in sandy soil (Jorf Lasfar, central Morocco) for 60 days in a completely randomized design considering eight treatments. All treatments, except the control, were amended with 52 mg kg^?1 of P from different PR-based fertilizers before sowing. At the flowering stage (60-day-old plants), results indicated that all PR treatments significantly improved plant growth, root nodulation, and nutrient uptake compared to the control. The relative agronomic efficiency of pretreated PR was significantly higher with phospho-compost treatment (86%) than the partially acidulated PR (78%) or the PR/TSP blend 50:50 (64%). Likewise, P uptake, P use efficiency, number of root nodules, and N uptake all were improved under PR treatments. Our finding revealed that the biological technique based on phospho-compost yielded better compared to chemical and physical treatments.

     

Effect of metal tolerant plant growth promoting Bradyrhizobium sp. (vigna) on growth, symbiosis, seed yield and metal uptake by greengram plants

The nickel and zinc tolerant plant growth promoting Bradyrhizobium sp. (vigna) RM8 was isolated from nodules of greengram, grown in metal contaminated Indian soils. The plant growth promoting (PGP) potentials of strain RM8 was assessed both in the presence and absence of nickel and zinc under in vitro conditions. Strain RM8 tolerated a high level of nickel (300 microg ml(-1)) and zinc (1400 microg ml(-1)) on yeast extract mannitol agar medium. Bradyrhizobium sp. (vigna) strain RM8 produced 13.3 microg ml(-1) of indole acetic acid in Luria Bertani broth at 100 microg ml(-1) of tryptophan which increased to 13.6 microg ml(-1) at 50 microg Ni ml(-1) and 13.5 microg ml(-1) at 300 microg Zn ml(-1). Strain RM8 was positive for siderophore, HCN and ammonia both in the absence and presence of nickel and zinc. The PGP activity of this strain was further evaluated with increasing concentrations of nickel and zinc using greengram as a test crop. The bioinoculant enhanced the nodule numbers by 82%, leghaemoglobin by 120%, seed yield by 34%, grain protein by 13%, root N by 41% and shoot N by 37% at 290 mg Ni kg(-1) soil. At 4890 mg Zn kg(-1) soil, the bioinoculant increased the nodule numbers by 50%, leghaemoglobin by 100%, seed yield by 36%, grain protein by 13%, root N by 47% and shoot N by 42%. The bioinoculant strain RM8 reduced the uptake of nickel and zinc by plant organs compared to plants grown in the absence of bioinoculant. This study suggested that the bioinoculant due to its intrinsic abilities of growth promotion and attenuation of the toxic effects of nickel and zinc could be exploited for remediation of metal from nickel and zinc contaminated sites.     

Effect of BPA on the germination,root development,seedling growth and leaf differentiation under different light conditions in Arabidopsis thaliana

Bisphenol A (BPA) is a well-known environmental toxic substance, which exerts unfavorable effects through endocrine disruptor (ER)-dependent and ER-independent mechanisms to threaten ecological systems seriously. BPA may also interact with other environmental factors, such as light and heavy metals, to have a synergetic effect in plants. However, there is little data concerning the toxic effect of BPA on the primary producers-plants and its possible interaction with light-dependent response. Here, the effects of BPA on germination, fresh weight, tap root length, and leaf differentiation were studied in Arabidopsis thaliana under different parts of light spectrum (dark, red, yellow, green, blue, and white light). Our results showed that low-dose BPA (1.0, 5.0 μM) caused an increase in the fresh weight, the tap root length and the lateral root formation of A. thaliana seedlings, while high-dose BPA (10.0, 25.0 μM) show an inhibition effect in a dose-dependent manner. Unlike karrikins, the effects of BPA on germination fresh weight and tap roots length under various light conditions are similar, which imply that BPA has no notable role in priming light response in germination and early seedling growth in A. thaliana. Meanwhile, BPA exposure influences the differentiation of A. thaliana leaf blade significantly in a light-dependent manner with little to no effect in dark and clear effect under red illumination.     

Arsenic species and leachability in the fronds of the hyperaccumulator Chinese brake (Pteris vittata L.)

Arsenic speciation is important not only for understanding the mechanisms of arsenic accumulation and detoxification by hyperaccumulators, but also for designing disposal options of arsenic-rich biomass. The primary objective of this research was to understand the speciation and leachability of arsenic in the fronds of Chinese brake (Pteris vittata L.), an arsenic hyperaccumulator, with an emphasis on the implications for arsenic-rich biomass disposal. Chinese brake was grown for 18 weeks in a soil spiked with 50 mg As kg(-1) as arsenate (AsO4(3-)), arsenite (AsO3(3-)), dimethylarsinic acid (DMA), or methylarsonic acid (MMA). Plant samples were extracted with methanol/water (1:1) and arsenic speciation was performed using high performance liquid chromatography coupled with atomic fluorescence spectrometry. The impacts of air-drying on arsenic species and leachability in the fronds were examined in the laboratory. After 18 weeks, water-soluble arsenic in soil was mainly present as arsenate with little detectable organic species or arsenite regardless of arsenic species added to the soil. However, arsenic in the fronds was primarily present as inorganic arsenite with an average of 94%. Arsenite re-oxidation occurred in the old fronds and the excised dried tissues. Arsenic species in the fronds were slightly influenced by arsenic forms added to the soil. Air-drying of the fronds resulted in leaching of substantial amounts of arsenic. These findings can be of significance when looking at disposal options of arsenic-rich biomass from the point of view of secondary contamination.     

Hexavalent chromium reduction and plant growth promotion by Staphylococcusarlettae strain Cr11

Cr(VI), a mutagenic and carcinogenic pollutant in industrial effluents, was effectively reduced by an indigenous tannery effluent isolate Staphylococcus arlettae strain Cr11 under aerobic conditions. The isolate could tolerate Cr(VI) up to 2000 and 5000 mg L⁻¹ in liquid and solid media respectively. S. arlettae Cr11 effectively reduced 98% of 100 mg L⁻¹ Cr(VI) in 24 h. Reduction for initial Cr(VI) concentrations of 500 and 1000 mg L⁻¹ was 98% and 75%, respectively in 120 h. The isolate was also positive for siderophore, indole acetic acid, ammonia and catalase production, phosphate solubilization and biofilm formation in the presence and absence of Cr(VI). The isolate showed halotolerance (10% NaCl) and cross tolerance to other toxic heavy metals such as Hg²⁺, Ni²⁺, Cd²⁺ and Pb²⁺. Bacterial inoculation of Triticum aestivum in controlled petri dish and soil environment showed significant increase in percent germination, root and shoot length as well as dry and wet weight in Cr(VI) treated and untreated samples. This is the first report of simultaneous Cr(VI) reduction and plant growth promotion for a S. arlettae strain.     

Arsenic in the food chains of a revegetated metalliferous mine tailings pond.

The environmental distribution, transfer and ecotoxicological risk associated with arsenic in a grassland ecosystem established on metalliferous mine tailings has been determined. High levels of arsenic in the mine tailings (630 +/- 34 mg kg-1) were not reflected in live vegetation due to the physico-chemical nature of the tailings which mitigate against plant uptake. However, elevated levels of arsenic were associated with plant litter. Low concentrations of arsenic in herbivorous invertebrates mirrored those found in their food, although there was evidence of minor detrivoral food chain transfer. Dietary exposure of small mammals to arsenic was well below that demonstrated to induce a toxicological response, and tissue concentrations were consistently below analytical detection limits. There appears to be little ecotoxicological risk associated with arsenic residues at the mine site investigated.     

Microcystin-LR-induced phytotoxicity in rice crown root is associated with the cross-talk between auxin and nitric oxide

Irrigation with cyanobacterial-blooming water containing microcystin-LR (MC-LR) poses threat to the growth of agricultural plants. Large amounts of rice (Oryza sativa) field in the middle part of China has been irrigating with cyanobacterial-blooming water. Nevertheless, the mechanism of MC-LR-induced phytotoxicity in the root of monocot rice remains unclear. In the present study, we demonstrate that MC-LR stress significantly inhibits the growth of rice root by impacting the morphogenesis rice crown root. MC-LR treatment results in the decrease in IAA (indole-3-acetic acid) concentration as well as the expression of CRL1 and WOX11 in rice roots. The application of NAA (1-naphthylacetic acid), an IAA homologue, is able to attenuate the inhibitory effect of MC-LR on rice root development. MC-LR treatment significantly inhibits OsNia1-dependent NO generation in rice roots. The application of NO donor SNP (sodium nitroprusside) is able to partially reverse the inhibitory effects of MC-LR on the growth of rice root and the expression of CRL1 and WOX11 by enhancing endogenous NO level in rice roots. The application of NO scavenger cPTIO [2-(4-carboxy-2-phenyl)-4,4,5,5-tetramethylinidazoline-1-oxyl-3-oxide] eliminates the effects of SNP. Treatment with NAA stimulates the generation of endogenous NO in MC-LR-treated rice roots. Treatment with NO scavenger cPTIO abolishes the ameliorated effect of NAA on MC-LR-induced growth inhibition of rice root. Treatment with SNP enhanced IAA concentration in MC-LR-treated rice roots. Altogether, our data suggest that NO acts both downstream and upstream of auxin in regulating rice root morphogenesis under MC-LR stress.     

Enhanced solubilization of arsenic and 2,3,4,6 tetrachlorophenol from soils by a cyclodextrin derivative

The application of extracting aqueous solutions with cyclodextrins in several soil remediation technologies has been increasingly studied but little is known about their removal capacities toward the inorganic species. Herein, the effectiveness of cyclodextrins (CDs) in extracting arsenic, copper, and iron from a mining soil is presented. In a preliminary test of four types of CD aqueous solutions, only the addition of carboxylmethyl-beta-cyclodextrin CMCD (a cyclodextrin derivative) led to a significant enhancement in arsenic removal. An increase in the concentration of copper and iron in the leachates was also observed with CMCD. Kinetic study of arsenic release was carried out at two temperatures (20 and 35 degrees C). The arsenic concentration in the leachates increases with increasing cyclodextrin concentration. At an 80 mM CMCD concentration, arsenic, copper, and iron released in filtrates were about 20-, 1,000-, and 4,000-fold greater, respectively, than that obtained using deionized water. In the soil system, the CMCD capacity removal was found to be higher for cations than for arsenic. Because the tetrachlorophenol can co-occur with arsenic and copper in several contaminated sites, its solubilization by CMCD was also investigated. Extraction experiments were performed to extract 2,3,4,6 tetrachlorophenol (TeCP) in spiked soil with CMCD. The results of batch experiments have shown that CMCD could significantly increase the TeCP extraction from soil. CD sorption on soils as quantified by a fluorescence technique was low, indicating no significant loss of CD during the leaching experiments. The use of CMCD as a flushing agent to enhance the removal of both inorganic and organic pollutants from mixed-contaminated soils appears as a promising remediation method.     

煤基腐殖酸对外源砷胁迫下玉米生长及生理性状的影响简

为了筛选用于砷污染土壤治理的煤基腐殖酸,采用盆栽实验研究了施用不同种类和浓度的煤基腐殖酸及EDTA对外源砷胁迫下玉米株高、株鲜重、株干重、根干重、砷积累量、叶片抗氧化酶（POD,SOD和CAT）活性和脯氨酸含量的影响。结果表明,11种供试煤基腐殖酸均促进了玉米生长,提高了叶片POD、SOD和CAT活性。其中6和10号腐殖酸可降低土壤砷活性和显著抑制玉米吸收和积累砷,而8和9号腐殖酸增加了土壤活性砷和显著促进了玉米对砷的吸收和累积,且不同程度地强于EDTA。除8和9号外,其余腐殖酸均可明显降低玉米叶片脯氨酸的含量。EDTA可显著促进玉米吸收和积累砷,且加剧了砷对玉米的危害。因此,8和9号供试煤基腐殖酸可以替代EDTA活化土壤砷,与植物配合以提高砷污染土壤的植物修复速度和效果,而6和10号供试煤基腐殖酸则可用于土壤砷钝化剂,以保证作物产品的安全。     

煤基腐殖酸对外源砷胁迫下玉米生长及生理性状的影响

为了筛选用于砷污染土壤治理的煤基腐殖酸,采用盆栽实验研究了施用不同种类和浓度的煤基腐殖酸及EDTA对外源砷胁迫下玉米株高、株鲜重、株干重、根干重、砷积累量、叶片抗氧化酶（POD,SOD和CAT）活性和脯氨酸含量的影响。结果表明,11种供试煤基腐殖酸均促进了玉米生长,提高了叶片POD、SOD和CAT活性。其中6和10号腐殖酸可降低土壤砷活性和显著抑制玉米吸收和积累砷,而8和9号腐殖酸增加了土壤活性砷和显著促进了玉米对砷的吸收和累积,且不同程度地强于EDTA。除8和9号外,其余腐殖酸均可明显降低玉米叶片脯氨酸的含量。EDTA可显著促进玉米吸收和积累砷,且加剧了砷对玉米的危害。因此,8和9号供试煤基腐殖酸可以替代EDTA活化土壤砷,与植物配合以提高砷污染土壤的植物修复速度和效果,而6和10号供试煤基腐殖酸则可用于土壤砷钝化剂,以保证作物产品的安全。     

Uptake and biotransformation of arsenate in the lichen Hypogymnia physodes (L.) Nyl

The uptake and metabolism of arsenate, As(V), as a function of time and concentration were examined in the lichen Hypogymnia physodes (L.) Nyl. Lichen thalli were exposed to As(V) in the form of a solution. Exponential uptake of As(V) from 4 microg mL(-1) As(V) solution was accompanied by constant arsenite, As(III), excretion back into the solution. Arsenate taken up into the lichens from 0, 0.1, 1, 10 microg mL(-1) As(V) solutions was partially transformed into As(III), dimethylarsinic acid (DMA) and (mono)methylarsonic acid (MA). 48 h after exposure, the main arsenic compound in the lichens was DMA in 0.1, As(III) in 1 and As(V) in 10 microg mL(-1) treatment. The proportion of methylated arsenic compounds decreased with increasing arsenate concentration in the exposure solution. These results suggest that at least two types of As(V) detoxification exist in lichens; arsenite excretion and methylation.