[Effects of Different Control Measures on Cadmium and Lead Accumulation and Quality in Lettuce].

To explore the safe utilization technology of farmland polluted by the heavy metals cadmium (Cd) and lead (Pb) and to realize the safe production of agricultural products, a pot experiment was conducted to investigate the effects of two soil passivators and five foliar inhibitors on Cd and Cd-accumulation and quality of lettuce with low Pb and Cd accumulation (KCW). The results showed that different control measures had different effects on the soil pH value of lettuce, and the application of 45 g·m-2biochar-based passivator had the most significant difference in improving the soil pH value, which was increased by 0.8 units compared with that in CK. By using 72 g·m-2 of humic acid passivator yielded notable difference in reducing the soil pH value of lettuce. A reduction of 0.25 units was achieved compared with that in CK. Among all the control measures, the application of 45 g·m-2 biocharcoal-based passivation agent had the best effect on reducing soil available Cd content, which was significantly reduced by 53% compared with that in CK, and the application of 135 g·m-2biocharcoal-based passivation agent had the best effect on reducing soil available Pb content, which was significantly reduced by 64% compared with that in CK. Spraying 0.8% FAK-Zn foliar inhibitor not only had the best control effect on reducing Cd and Pb contents in the edible parts of lettuce, which were significantly reduced by 77% and 60%, respectively, compared with that in CK, but it also significantly reduced Cd and Pb enrichment coefficients and transport coefficients from the root to the edible parts of the lettuce. Different control measures had different effects on the nutritional quality of lettuce, and 0.4% FAK-Zn foliar inhibitor had the best effect on soluble protein. The 0.6% FAK-Zn had the best effect on soluble sugar, and the 0.4% FAK-Zn inhibitor had the best effect on vitamin C content. The application of biocarbon-based passivator could effectively repair lettuce soil polluted by Cd and Pb, whereas the application of FAK-Zn leaf surface inhibitor could effectively inhibit the accumulation, absorption, and transfer of Cd and Pb in lettuce; improve the nutritional quality of lettuce; provide a theoretical basis for safe production of vegetables polluted by heavy metals; and promote the recycling of resources and environment.

Synergistic Reduction of Arsenic Uptake and Alleviation of Leaf Arsenic Toxicity in Maize (Zea mays L.) by Arbuscular Mycorrhizal Fungi (AMF) and Exogenous Iron through Antioxidant Activity.

Arbuscular mycorrhizal fungi (AMF) play key roles in enhancing plant tolerance to heavy metals, and iron (Fe) compounds can reduce the bioavailability of arsenic (As) in soil, thereby alleviating As toxicity. However, there have been limited studies of the synergistic antioxidant mechanisms of AMF (Funneliformis mosseae) and Fe compounds in the alleviation of As toxicity on leaves of maize (Zea mays L.) with low and moderate As contamination. In this study, a pot experiment was conducted with different concentrations of As (0, 25, 50 mgꞏkg-1) and Fe (0, 50 mgꞏkg-1) and AMF treatments. Results showed that under low and moderate As concentrations (As25 and As50), the co-inoculation of AMF and Fe compound significantly increased the biomass of maize stems and roots, phosphorus (P) concentration, and P-to-As uptake ratio. Moreover, the co-inoculation of AMF and Fe compound addition significantly reduced the As concentration in stem and root, malondialdehyde (MDA) content in leaf, and soluble protein and non-protein thiol (NPT) contents in leaf of maize under As25 and As50 treatments. In addition, co-inoculation with AMF and Fe compound addition significantly increased the activities of catalase (CAT), peroxidase (POD), and superoxide dismutase (SOD) in the leaves of maize under As25 treatment. Correlation analysis showed that stem biomass and leaf MDA content were very significantly negatively correlated with stem As content, respectively. In conclusion, the results indicated that the co-inoculation of AMF and Fe compound addition can inhibit As uptake and promote P uptake by maize under low and moderate As contamination, thereby mitigating the lipid peroxidation on maize leaves and reducing As toxicity by enhancing the activities of antioxidant enzymes under low As contamination. These findings provide a theoretical basis for the application of AMF and Fe compounds in the restoration of cropland soil contaminated with low and moderate As.

[Investigation of Dominant Plants and Analysis of Ecological Restoration Potential in Lailishan Tin Tailings].

To investigate the dominant plants in ecological restoration of tin mining areas, field investigations were conducted in a tin tailings area in Lailishan, Yunnan Provence, and 15 dominant plants and corresponding rhizosphere soils were collected. The plant root mycorrhizal infection rate; the copper (Cu), cadmium (Cd), arsenic (As), nickel (Ni), lead (Pb), and tin (Sn) contents; and the chemical properties of the rhizosphere tailings were determined. The transfer and enrichment coefficients of six heavy metals were calculated for each of the 15 plants to comprehensively evaluate the application potential of native plants. The rhizophere tailings had an average pH value of 3.13, which was acidic. The organic matter, total nitrogen, total phosphorus, total potassium, alkaline hydrolyzed nitrogen, and available phosphorus content of the soils was 6.07 g ·kg-1, 5.74 g ·kg-1, 0.62 g ·kg-1, 8.66 g ·kg-1, 30.84 mg ·kg-1, and 2.08 mg ·kg-1 respectively, indicating relatively nutrient-poor soil. The average Cu, Cd, Ni, Pb, As, and Sn contents of the soils were 347.40, 1.02, 1.34, 168.47, 25.81, and 2299.02 mg ·kg-1, respectively. Among the heavy metals, the Cd content reached a third-level pollution warning value. The soil also contained a large amount of Cu and Pb which exhibited a different spatial distribution. This area appears to have a high risk of Cu, Pb, and Cd pollution. In addition, the roots of Olea europaea L. and Eurya japonica Thunb. had a high rate of mycorrhizal infection. Alnus cremastogyne Burk., Bambusa multiplex (Lour.) Raeusch. ex Schult. 'Alphonse-Kar' R. A. Young, Juncus effusus L., and Cyperus rotundus L. var. had a strong ability to absorb and transport heavy metals. The other plants were also adapted to the growth environment of the tin tailings, with the potential to restore the mining area.

Arenimonas taoyuanensis sp. nov., a novel bacterium isolated from rice-field soil in China.

A Gram-stain negative, aerobic, rod-shaped bacterial strain, YN2-31A(T), was isolated from rice-field soil, Taoyuan Village, Yunnan province of China. The bacterium was observed to grow at 20-45 °C (optimum 28 °C), at pH 5.0-10.0 (optimum 7.0), and in the presence of 0-2% (w/v) NaCl (optimum 0-1%). Phylogenetic analysis based on 16S rRNA gene sequences revealed that strain YN2-31A(T) is most closely related to Arenimonas daejeonensis DSM 18060(T) (96.1%), Arenimonas malthae DSM 21305(T) (95.9%), Arenimonas donghaensis DSM 18148(T) (95.1%), Arenimonas composti DSM 18010(T) (94.8%) and Arenimonas maotaiensis JCM 19710(T) (94.8%). The major cellular fatty acids (>10%) were found to be iso-C(18:1) ω9c, iso-C(15:0), Sum In Feature 3 (C(16:1) ω7c/C(16:1) ω6c), and C(16:0). The major ubiquinone was identified as Q-8 and the major cellular polar lipids were identified as diphosphatidylglycerol, phosphatidylglycerol, phosphatidylethanolamine and unidentified phospholipids. The genomic DNA G+C content was determined to be 72.3 mol%. The results of the phylogenetic, genetic, phenotypic and chemotaxonomic analyses suggest that strain YN2-31A(T) represents a novel species of the genus Arenimonas, for which the name Arenimonas taoyuanensis sp. nov. is proposed. The type strain is YN2-31A(T) (=DSM 26777(T) = CCTCC AB2012964(T)).

Use of surface-modified CdTe quantum dots as fluorescent probes in sensing mercury (II).

Thioglycolic acid (TGA)-capped CdTe quantum dots (QDs) were synthesized in aqueous medium, and their interaction with metal cations was studied with UV-vis absorption, steady-state and time-resolved fluorescence spectra. The results demonstrated that Hg(II), Cu(II) and Ag(I) could effectively quench the QD emission based on different action mechanisms: Cu(II) and Ag(I) quenched CdTe QDs because they bound onto particle surface and facilitated non-radiative electron/hole recombination annihilation of QDs; electron transfer process between the capping ligands and Hg(II) was mainly responsible for the remarkable quenching effect of Hg(II). To prevent the approach of metal cations to QD core, the original TGA-capped CdTe QDs were further coated by denatured bovine serum albumin (dBSA). It was found that the dBSA-coated CdTe QDs could be quenched effectively by Hg(II), but Cu(II) and Ag(I) could hardly quench the QDs even at fairly higher concentration levels because the dBSA shell layer effectively prevented the binding of metal cations onto the QD core. On the basis of this fact, a simple, rapid and specific method for Hg(II) determination was proposed. Under optimal conditions, the quenched fluorescence intensity increased linearly with the concentration of Hg(II) ranging from 0.012 x 10(-6) to 1.5 x 10(-6) mol L(-1). The limit of detection for Hg(II) was 4.0 x 10(-9) mol L(-1). The developed method was successfully applied to the detection of trace Hg(II) in real samples.

Arsenic uptake by arbuscular mycorrhizal maize (Zea mays L.) grown in an arsenic-contaminated soil with added phosphorus.

The effects of arbuscular mycorrhizal (AM) fungus (Glomus mosseae) and phosphorus (P) addition (100 mg/kg soil) on arsenic (As) uptake by maize plants (Zea mays L.) from an As-contaminated soil were examined in a glasshouse experiment. Non-mycorrhizal and zero-P addition controls were included. Plant biomass and concentrations and uptake of As, P, and other nutrients, AM colonization, root lengths, and hyphal length densities were determined. The results indicated that addition of P significantly inhibited root colonization and development of extraradical mycelium. Root length and dry weight both increased markedly with mycorrhizal colonization under the zero-P treatments, but shoot and root biomass of AM plants was depressed by P application. AM fungal inoculation decreased shoot As concentrations when no P was added, and shoot and root As concentrations of AM plants increased 2.6 and 1.4 times with P addition, respectively. Shoot and root uptake of P, Mn, Cu, and Zn increased, but shoot Fe uptake decreased by 44.6%, with inoculation, when P was added. P addition reduced shoot P, Fe, Mn, Cu, and Zn uptake of AM plants, but increased root Fe and Mn uptake of the nonmycorrhizal ones. AM colonization therefore appeared to enhance plant tolerance to As in low P soil, and have some potential for the phytostabilization of As-contaminated soil, however, P application may introduce additional environmental risk by increasing soil As mobility.

Fluorescence-detecting cationic surfactants using luminescent CdTe quantum dots as probes.

A novel fluorescence quenching method for the determination of cationic surfactants (CS), specifically cetyltrimethylammonium bromide (CTAB), dodecyltrimethylammonium bromide (DTAB), and cetylpyridinium chloride (CPC), has been developed using water-soluble luminescent CdTe quantum dots (QDs) modified with thioglycolic acid (TGA). The possible interference from heavy and transition metals (HTM) has been efficiently eliminated through simple sample treatment with mercapto cotton made in-house. Under optimum conditions, the extent of fluorescence quenching of CdTe QDs is linearly proportional to the concentration of CS from 2.0 x 10(-7) to 7.0 x 10(-6) mol L(-1) with a detection limit of 5.0 x 10(-8) mol L(-1). The relative standard deviation for 1.0 x 10(-6) mol L(-1) CTAB is 2.5% (n = 6). The proposed method exhibits high sensitivity and selectivity and furthermore avoided the use of toxic organic solvents and tedious solvent extraction procedures. It has been applied to the determination of trace CS in natural river water and commodity samples with satisfactory results. Potential interference from heavy and transition metals is eliminated during photoluminescence detection of CS through simple sample pre-treatment with mercapto cotton.

Spatial distribution of heavy metals of agricultural soils in Dongguan, China.

Distribution and speciation of heavy metals of agricultural soils(85 surface soil samples and 4 soil profiles) in Dongguan were investigated, while total Cr, Cu, Ni, Pb, Zn(abbreviated as Cr, Cu, Ni, Pb, Zn) and available Cu, Zn(Av-Cu, Av-Zn) were analyzed by a flame absorption spectrophotometer(AAS), and total Cd(Cd) was analyzed using graphite furnace AAS. The content of Cd, Cu and Ni was partially much more than the second grade of GB15618-1995 even though the mean contents of all heavy metal were less than the threshold value of the second grade and only the mean content of Pb was more than the value of national background. Results of descriptive statistic showed that the mean content of heavy metals should depend on land utilization and spatial location at some extent. The heavy metal contents were higher in the Southwest and Northwest than in the Central. In addition, the mean contents of Zn and Pb in Dongguan paddy soils were significantly higher than those of Pearl River Delta(PRD) and Taihu Lake region(TLR). Correlation analyses indicated that there existed significant correlation between Cr and Ni in orchard soils, and among Zn, Cd and Cu, between Av-Cu and Cu, between Av-Zn and Cr, Ni, pH value in vegetable soils, and a weak relationship between Cd, Cu and Pb, between Av-Zn and Zn. Principal component analyses(PCA) showed that the order of importance should be Zn > Pb > Cr > Ni > Cu.