A study on the effects of lead, cadmium and phosphorus on the lead and cadmium uptake efficacy of Viola baoshanensis inoculated with arbuscular mycorrhizal fungi

The effect of indigenous arbuscular mycorrhizal (AM) fungi on lead (Pb) and cadmium (Cd) uptake by the hyperaccumulator plant Viola baoshanensis was studied in greenhouse pot experiments. Seedlings of V. baoshanensis inoculated without or with indigenous AM fungi were grown in paddy soil with the addition of Pb at 0, 500, 1000 and 1500 mg kg(-1), or of Cd at 0, 50,100, 200 mg kg(-1), or in mine soil with the addition of phosphorus at 0, 50, 250, 500 mg kg(-1). AM colonization increased shoot biomass at low phosphorus levels, and this beneficial effect was diminished or reversed by high phosphorus availability. AM colonization decreased shoot Cd concentrations regardless of the availability of Cd and phosphorus, but the mechanisms involved varied with Cd availability. At low Cd bioavailability, reduced Cd uptake was due to decreased Cd translocation from the roots to the shoots, whereas that was attributed to reduced root uptake at high Cd bioavailability. In contrast, the effect of AM colonization on shoot Pb varied with the availability of phosphorous and Pb. Our results show that the interactions between V. baoshanensis and indigenous AM fungi were modified by the availability of Pb, Cd and phosphorus.     

Heavy metal phytoextraction—natural and EDTA-assisted remediation of contaminated calcareous soils by sorghum and oat

The abilities of sorghum (Sorghum bicolor L.) and oat (Avena sativa L.) to take up heavy metals from soils amended with ethylenediaminetetraacetic acid (EDTA) were assessed under greenhouse conditions. Both plants were grown in two soils contaminated with heavy metals (Gujranwala—silty loam and Pacca—clay loam). The soils were treated with 0, 0.625, 1.25, and 2.5 mM EDTA kg^?1 soil applied at both 45 and 60 days after sowing (DAS); the experiment was terminated at 75 DAS. Addition of EDTA significantly increased concentrations of Cd, Cr, and Pb in roots and shoots, and bio-concentration factors and phytoextraction rates were also increased. Post-harvest soil analysis showed that soluble fractions of metals were also increased significantly. The increase in Cd was ≈ 3-fold and Pb was ≈ 15-fold at the highest addition of EDTA in Gujranwala soil; in the Pacca soil, the increase was less. Similarly, other phytoremediation factors, such as metal translocation, bio-concentration factor, and phytoextraction, efficiency were also maximum when soils were treated with 2.5 mM EDTA kg^?1 soil. The study demonstrated that sorghum was better than oat for phytoremediation.     

Heavy metal risk assessment for potatoes grown in overused phosphate-fertilized soils

The long-term application of phosphate fertilizers on vegetable production fields has raised concerns about the potential health risks of heavy metal contamination of crops grown on contaminated soils in the Hamadan province, western Iran. This study found that long-term fertilizer use led to a growing accumulation of heavy metals in soils. High concentrations of elemental As, Cd, Cr, Cu, Pb, and Zn were found in potatoes sampled from overused phosphate-fertilized soils, which increased the daily intake of metals in food. However, the ingestion of potatoes from soils affected by phosphate fertilizers posed a low health risk when compared with the health risk index of <1 for heavy metals. Nevertheless, heavy metal concentrations should be periodically monitored in vegetables grown in these soils. It would also be beneficial to implement effective remediation technologies to minimize possible impacts on human health.     

Impacts of epigeic, anecic and endogeic earthworms on metal and metalloid mobility and availability

The introduction of earthworms into soils contaminated with metals and metalloids has been suggested to aid restoration practices. Eisenia veneta (epigeic), Lumbricus terrestris (anecic) and Allolobophora chlorotica (endogeic) earthworms were cultivated in columns containing 900 g soil with 1130, 345, 113 and 131 mg kg(-1) of As, Cu, Pb and Zn, respectively, for up to 112 days, in parallel with earthworm-free columns. Leachate was produced by pouring water on the soil surface to saturate the soil and generate downflow. Ryegrass was grown on the top of columns to assess metal uptake into biota. Different ecological groups affected metals in the same way by increasing concentrations and free ion activities in leachate, but anecic L. terrestris had the greatest effect by increasing leachate concentrations of As by 267%, Cu by 393%, Pb by 190%, and Zn by 429% compared to earthworm-free columns. Ryegrass grown in earthworm-bearing soil accumulated more metal and the soil microbial community exhibited greater stress. Results are consistent with earthworm enhanced degradation of organic matter leading to release of organically bound elements. The degradation of organic matter also releases organic acids which decrease the soil pH. The earthworms do not appear to carry out a unique process, but increase the rate of a process that is already occurring. The impact of earthworms on metal mobility and availability should therefore be considered when inoculating earthworms into contaminated soils as new pathways to receptors may be created or the flow of metals and metalloids to receptors may be elevated.     

Bio-accumulation and distribution of heavy metals in black mustard (Brassica nigra Koch)

There has been carried out a comparative research, which to allow us to determine the quantities and the depots of accumulation of Pb, Cu, Zn and Cd in the vegetative and reproductive organs of Brassica nigra, as well as to identify the possibilities of growing on soils, contaminated by heavy metals and its use for the purposes of the phytoremeditation. Experiments have been implemented in field and in controlled conditions. B. nigra is tolerant towards the heavy metals and could be successfully grown in regions of low and moderate level of contamination with heavy metals, without lowering of the quantity and quality of the manufactured production. The depots for accumulation, in case it is being grown on contaminated soils without Cu follows the order: roots > fruit's shells > stems > seeds. In the case of its growing on non-contaminated soils the order roots > fruit's shells > seeds > stems preserves for the Pb, while the order for the Cu, Zn, and Cd is: fruit's shells > seeds > stems > roots. A relation is determined between the quantity of the total and the mobile forms of metals on one hand, and their total quantity in the plants in the field, as well as, in the pot experiments, on the other. A drastic exclusion is made by the Pb in the pot experiments, as its basic part is blocked in compounds that are hardly soluble. Its absorption by the plants is almost entirely blocked, which is almost a degree lower than that obtained in the field experiments and is commensurable with the results obtained in non-contaminated soils. Clarification of the reasons causing this effect requires additional examinations and above all, fractionation of the soil and determination of the forms and depots of localization of Pb compounds.     

Environmental variation between habitats and uptake of heavy metals by Urtica dioica

The observation from previous surveys, that Urtica dioica plants that had grown in metal contaminated soil in the floodplains of the former Rhine estuary in different habitats, but at comparable total soil metal concentrations, showed significant differences in tissue metal concentrations, led to the hypothesis that variation in other environmental characteristics than soil composition and chemical speciation of metals between habitats is also important in determining uptake and translocation of metals in plants. A field survey indicated that differences in root Cd, Cu and Zn concentrations might partly be explained by variation in speciation of metals in different habitats. However, shoot concentrations showed a different pattern that did not relate to variation in soil metal concentrations. In a habitat experiment Urtica dioica plants were grown in artificially contaminated soil in pots that were placed in the four habitats (grassland, pure reed, mixed reed, osier bed) that were also included in the field survey. After seven weeks the plants showed significant differences in Cu and Zn concentrations in roots and aboveground plant parts and in distribution of the metals in the plants between habitats. It was concluded that variation between habitats in environmental characteristics other than soil composition can explain as much variation in plants as can variation in soil metal concentrations and/or speciation. The implications for assessment of soil metal contamination and uptake by plants are discussed.     

Effect of long-term application of treated sewage water on heavy metal accumulation in vegetables grown in Northern India

Use of industrial and wastewater for irrigation is on the rise in India and other developing countries because of scarcity of good-quality irrigation water. Wastewaters contain plant nutrients that favour crop growth but leave a burden of heavy metals which can enter the food chain and is a cause of great concern. The present study was undertaken on the long-term impact of irrigation with treated sewage water for growing vegetables and the potential health risk associated with consumption of such vegetable. Treated sewage water (TSW), groundwater (GW), soil and plant samples were collected from peri urban vegetable growing areas of Northern India (Varanasi) and analysed to assess the long-term effect of irrigation with TSW on Cd, Cr, Ni and Pb build-up in soils and its subsequent transfer into commonly grown vegetable crops. Results indicate that TSW was richer in essential plant nutrients but contained Cd, Cr and Ni in amounts well above the permissible limits for its use as irrigation water. Long-term application of TSW resulted in significant build-up of total and DTPA extractable Cd, Cr, Ni and Pb over GW irrigated sites. TSW also resulted in slight lowering in pH, increase in organic carbon (1.6 g kg^− 1) and cation exchange capacity (5.2 cmol kg^− 1). The tissue metal concentration and relative efficiency of transfer of heavy metals from soil to plant (transfer factor) for various groups of vegetables were worked out. Radish, turnip and spinach were grouped as hyper accumulator of heavy metals whereas brinjal and cauliflower accumulated less heavy metals. Health risk assessment by consumption of vegetables grown with TSW indicated that all the vegetables were safe for human consumption. However, significant accumulation of these heavy metals in soil and plant needs to be monitored.     

Predicting bioavailability of metals from sludge-amended soils

We attempted to develop a protocol for fixing the maximum permissible limit of sludge in agricultural lands based on transfer of metals from sludge-amended soils to human food chain. For this purpose, spinach was grown as a test crop on acid and alkaline soils with graded doses of sludge (0, 1.12, 2.24, 4.48, 8.96, 17.9, 35.8, 71.6, 142 and 285 g kg^?1 of soil) in a pot experiment. Biomass yield of spinach was increased due to sludge application in both acid and alkaline soils. Among the chemical extractants, EDTA extracted the highest amount of metals from sludge-amended soil followed by diethylenetriaminepentaacetic acid (DTPA) and CaCl₂. Elevated levels of Zn, Cu, Fe, Mn, Ni, Cd and Pb in spinach were observed due to sludge application over control. Application of sludge was more effective in increasing metal content in spinach grown on acid soil than alkaline soil. Solubility-free ion activity model as a function of pH, organic carbon and extractable metal was far more effective in predicting metal uptake by spinach grown on sludge-amended soils as compared to that of chemical extractants. Risk in terms of hazard quotient (HQ) for intake of metals through consumption of spinach by humans grown on sludge-treated soils was computed for different metals separately. In a 90-day pot experiment, safe rates of sludge application were worked out as 4.48 and 71.6 g kg^?1 for acid and alkaline soils, respectively.     

Lead contamination of an agricultural soil in the vicinity of a shooting range

In this study, coupled Pb concentration/Pb isotope data were used to evaluate the effect of a shooting range (operational for over 30 years) on Pb contamination of adjacent agricultural soils and the associated environmental risks. Lead was mainly concentrated in the arable layer of the contaminated agricultural soils at total concentrations ranging from 573 to 694 mg kg^???1. Isotopic analyses (²⁰⁶Pb/²⁰⁷Pb) proved that Pb originated predominantly from the currently used pellets. Chemical fractionation analyses showed that Pb was mainly associated with the reducible fraction of the contaminated soil, which is in accordance with its predominant soil phases (PbO, PbCO₃). The 0.05 M EDTA extraction showed that up to 62% of total Pb from the contaminated site is potentially mobilizable. Furthermore, Pb concentrations obtained from the synthetic precipitation leaching procedure extraction exceeded the regulatory limit set by the United States Environmental Protection Agency for drinking water. Ion exchange resin bags showed to be inefficient for determining the vertical distribution of free Pb^2?+? throughout the soil profile. Increased Pb concentrations were found in the biomass of spring barley (Hordeum vulgare L.) sampled at the studied site and two possible pathways of Pb uptake have been identified: (1) through passive diffusion-driven uptake by roots and (2) especially through atmospheric deposition, which was also proved by analyses of a bioindicator species (bryophyte Hypnum cupressiforme Hedw.). This study showed that shooting ranges can present an important source of Pb contamination of agricultural soils located in their close vicinity.     

Health risk assessment of heavy metals for edible parts of vegetables grown in sewage-irrigated soils in suburbs of Baoding City,China

With the long-term application of wastewater to vegetable production fields, there is concern about potential health risks of heavy metals contaminating the edible parts of vegetables grown in contaminated soils in the suburban areas of Baoding City, China. The average concentration of elemental Zn in sewage-irrigated soil was the highest (153.77 mg kg⁻¹), followed by Pb (38.35 mg kg⁻¹), Cu (35.06 mg kg⁻¹), Ni (29.81 mg kg⁻¹), and Cd (0.22 mg kg⁻¹) which were significantly higher (P < 0.05) than those in the reference soil. The results showed that long-term sewage irrigation had led to a growing accumulation of heavy metals in the soils, especially for Cd, Zn, and Pb. Furthermore, the concentrations of elemental Cd, Zn, and Ni in vegetables (e.g., Beassica pekinensis L., Allium fistulosum L., Spinacia oleracea L.) collected from the wastewater-irrigated soils exceeded the maximum permissible limits, and this also increased the daily intake of metals by food. However, compared with the health risk index of <1 for heavy metals, the ingestion of vegetables from the soils irrigated with sewage effluent posed a low health risk. Nevertheless, heavy metal concentrations should be periodically monitored in vegetables grown in these soils together with the implementation effective remediation technologies to minimize possible impacts on human health.