Concentration, Distribution and Comparison of Total and Bioavailable Metals in Top Soils and Plants Accumulation in Zanjan Zinc Industrial Town-Iran

Migration patterns of heavy metals from solid waste stockpile soils by native plants for ecological restoration in arid and semi-arid regions of Northwest China

Ecological remediation with native plants is the main measure to control the pollution of solid waste in Northwest China. However, the heavy metal transport characteristics of these native plants are still unidentified. This study analyzed the distribution of 16 heavy metals in native plants in the desulfurization gypsum yard (DGY), the gangue yard (GY) and the fly ash yard (FAY). The results showed that the soil contained many heavy metals in high concentrations. For instance, As concentrations were comparable to the global soil background values, whereas Cr and Mn concentrations in the area were 2-3 times greater than the global soil background values. The content of heavy metals in the plant root system increased first, then decreased as the distance from the yard increased. Ni, Pb, and Cd migrated well in Artemisia frigida Willd and Artemisia sieversiana Ehrhart ex Willd, with A. sieversiana showing a particularly strong migration in GY. A. sieversiana, on the other hand, was more successful at migrating Cd at DGY and had a similar capability for Mg migration in all three locations. Festuca rubra L was potentially suitable for planting in GY for Ni removal. In conclusion, the migration patterns of different heavy metals were not alike for plants in the three landfills. The results provided a basis for plant selection for ecological restoration in arid and semi-arid regions.

Effects of plant growth-promoting bacteria on EDTA-assisted phytostabilization of heavy metals in a contaminated calcareous soil

The objective of this research was to determine the combined effects of ethylenediaminetetraacetic acid (EDTA) and plant growth-promoting rhizobacteria (PGPR) on the phytostabilization of Cd, Pb, and Zn by corn and chemical fractionation of these elements in soil. Three heavy metal-resistant bacteria (P18, P15, and P19) were selected. All strains, belonging to the fluorescent pseudomonads, exhibited plant growth-promoting properties, including phosphorus solubilization and production of siderophore, indole acetic acid, and 1-aminocyclopropane-1-carboxylic acid deaminase. Applying EDTA individually or in combination with bacterial strains (P18 and P15) significantly increased shoot biomass. The highest dry shoot biomass was recorded in the combined treatment of EDTA and P15-inoculated pots. Application of EDTA in PGPR-inoculated pots increased concentrations of heavy metals in corn shoots and roots compared to the control. The highest concentration of Zn in corn root and shoot was observed in P15 + EDTA treatment, which were 2.0-fold and 1.3-fold higher than those in the untreated soil. Results of chemical speciation showed that the co-application of EDTA and fluorescent pseudomonads strains increased the bioavailability of Zn, Pb, and Cd by their redistribution from less soluble fractions to water-soluble forms. It was concluded that bacterial inoculation could improve the efficiency of EDTA in phytostabilization of heavy metals from multi-metal contaminated soils.

Plant-microbiome assisted and biochar-amended remediation of heavy metals and polyaromatic compounds ─ a microcosmic study

The study has been carried out to develop a plant-microbes assisted remediation technology to accelerate polyaromatic hydrocarbons (PAHs) degradation and heavy metals (HMs) removal in a microcosmic experiment. The quaternary mixture of PAHs (phenanthrene, anthracene, pyrene, and benzo[a] pyrene) and metals (Cr, Ni, and Pb) spiked the soil, constructing a microcosm; the microcosms were bioaugmented with newly developed plant bacterial consortia (Cpm₁ and Cpm₂). The microcosms were amended with biochar (sieved particle size 0.5-2 mm) as redox regulators to reduce oxidative stress of plant-microbe systems. To formulate the two plant-bacterial consortia, plant species were collected and bacteria were isolated from oil spill soil. The bacterial strains used in two formulated consortia includes ─ Cpm₁ (Enterobacter cloacae HS32, Brevibacillus reuszeri HS37, and Stenotrophomonas sp. HS16) and Cpm₂ (Acinetobacter junii HS29, Enterobacter aerogenes HS39 and Enterobacter asburiae HS22). The PAHs degradation and metal removal efficacy of the consortia (Cpm₁ and Cpm₂) were studied after 24 weeks of trial. The physicochemical properties of microcosm's soil (M₂ and M₃) were assessed after experimentation, which resulted in the finding that the soil exhibits dropped in pH from basic to neutral after application of the plant microbe's consortium. The electrical conductivity was lower in M₂ and M₃ soils, with a range between 1.60 and 1.80 mS/cm after the treatment. The Gas Chromatography/Mass Spectrometry (GC/MS) results illustrate how metabolites with the different molecular weight (M.W) were found in M₂ and M₃ soils (184─446), as a result of the plant-microbes mediated rhizodegradation of four spiked PAHs. The metals in microcosm's soil are very low in concentration after 24 weeks of trial when compared to control(M₁). The Cr, Ni and Pb removal percentages were found in 45.79, 42.19 and 44.85 in M₂. However, the removal percentages were found to be 45.41, 41.47 and 44.25 respectively for these same HMs in M₃ soil. Both the consortia that were newly developed showed similar trends of metals removal and PAHs degradation. This study provides a breakthrough in the area of rhizosphere engineering with the goal of maintaining a sustainable application of plant-microbes in ecosystem services.

The influences of selected soil properties on Pb availability and its transfer to wheat (Triticum aestivum L.) in a polluted calcareous soil

Accumulated anthropogenic heavy metals in the surface layer of agricultural soils may be transferred through the food chain via plant uptake processes. The objectives of this study were to assess the spatial distribution of lead (Pb) in the soils and wheat plants and to determine the soil properties which may affect the Pb transferring from soil to wheat plants in Zanjan Zinc Town area, northwestern Iran. A total of 110 topsoil samples (0-20 cm) were systematically collected from an agricultural area near a large metallurgical factory for the analyses of physico-chemical properties and total and bioavailable Pb concentrations. Furthermore, a total of 65 wheat samples collected at the same soil sampling locations were analyzed for Pb concentration in different plant parts. The results showed that elevated Pb concentrations were mostly found in soils located surrounding the industrial source of pollution. The bioavailable Pb concentration in the studied soils was up to 128.4 mg kg(-1), which was relatively high considering the observed soil alkalinity. 24.6% of the wheat grain samples exceeded the FAO/WHO maximum permitted concentration of Pb in wheat grain (0.2 mg kg(-1)). Correlation analyses revealed that soil organic matter, soil pH, and clay content showed insignificant correlation with Pb concentration in the soil and wheat grains, whereas calcium carbonate content showed significantly negative correlations with both total and bioavailable Pb in the soil, and Pb content in wheat grains, demonstrating the strong influences of calcium carbonate on Pb bioavailability in the polluted calcareous soils.

Evaluation of heavy metal and polycyclic aromatic hydrocarbons accumulation in plants from typical industrial sites: potential candidate in phytoremediation for co-contamination

The heavy metal and polycyclic aromatic hydrocarbons (PAHs) contents were evaluated in surface soil and plant samples of 18 wild species collected from 3 typical industrial sites in South Central China. The accumulative characteristics of the plant species for both heavy metal and PAHs were discussed. The simultaneous accumulation of heavy metal and PAHs in plant and soil was observed at all the investigated sites, although disparities in spatial distributions among sites occurred. Both plant and soil samples were characterized by high accumulation for heavy metal at smelting site, moderate enrichment at coke power and coal mining sites, whereas high level of PAHs (16 priority pollutants according to US Environmental Protection Agency) at coke power site, followed sequentially by coal mining and smelting sites. Based on the differences of heavy metal and PAH accumulation behaviors of the studied plant species, heavy metal and PAH accumulation strategies were suggested: Pteris vittata L. and Pteris cretica L. for As and PAHs, Boehmeria nivea (L.) Gaud for Pb, As, and PAHs, and Miscanthus floridulu (Labnll.) Warb for Cu and PAHs. These native plant species could be proposed as promising materials for heavy metal and PAHs combined pollution remediation.