[Evaluation of phosphate-containing amendments on remediation effect and influential factors in a lead/zinc mining tailings contaminated soil using TCLP and forms].

A pot experiment was conducted to evaluate the effects of phosphate-containing (P) amendments on the toxicity and bioavailability of Pb and Zn in a soil contaminated by mining tailings using toxicity characteristic leaching procedure (TCLP) and water soluble, exchangeable leaching procedures in order to find out the appropriate P application rates to reduce the soil TCLP extractable Pb to below the USA EPA's regulatory limit levels. The results showed that TCLP extractable Pb concentrations were significantly decreased by up to 93.3% for MPP treatments and up to 68.5% for SSP treatments after P application. The dose required to reduce leachable Pb below the EPA's regulatory limit level was found to be around the molar ratio of v(P/Pb) = 0.6 for MPP and 1.8 for SSP. It was also found both MPP and SSP could reduce the exchangeable Pb and Zn concentrations that all bio-available Zn forms including water soluble, exchangeable, and TCLP extractable forms in soil were significantly and negatively correlated to soil pH values, indicating that the content of Zn in the soil was mostly controlled by soil pH value even after P application. These results suggest that P as MPP and SSP could successfully decrease the toxicity and bioavailability of Pb and Zn in the contaminated soil.

[Effect of chlorine and phosphorus on water soluble and exchangeable lead in a soil contaminated by lead and zinc mining tailings].

Effect of chlorine on in situ lead immobilization using phosphorus in a soil contaminated by lead and zinc mining tailings was evaluated. The results showed that water soluble and exchangeable Pb were reduced by 92.0%-95.1% in the soil after P application. It was also suggested that application dosage of phosphorus at the P/Pb molar ratio of 0.6, was enough to remediate Pb toxicity in the soil. Compared to without Cl treatment at the level of molar ratio of 0.6 P/Ph, water soluble and exchangeable Pb in the soil treated with Cl was reduced markedly. It was concluded that the effects chlorine addition on in situ lead (Pb) immobilization using phosphate were improved. Visual MINTEQ model was employed to figure out Pb and P species distribution and saturation indices for minerals in the soils treated by P and Cl. The results showed that Pb activity was controlled by lead phosphate in the soil, especially pyromorphite [Pb5(PO4)3Cl], which would be the reason for Pb bioactivity reduction in the soil after application of Cl and P. The effective Pb bioactivity reduction indicated that addition of Cl was necessary to to improve in situ lead immobilization using phosphorous in the lead-contaminated soil.

[Effects of phosphorus application on translocation of lead, zinc and cadmium in the soil-plant system].

A pot experiment was conducted to determine the influence of phosphorus (P) application on the translocation and accumulation of lead (Pb), zinc (Zn), and cadmium (Cd) in a soil solid-liquid-plant system using a plant Swamp Morningglory (Ipomoea aquatica Forak) as an indicator and Visual MINTEQ model. A contaminated soil containing 22,830 mg x kg(-1) Pb, 746 mg x kg(-1) Zn, and 10 mg x kg(-1) Cd was in the root was significantly decreased after P application, while the Zn concentration were increased, but no impact on Cd concentration after P application, compared to the control. Further more, concentrations of Pb, Zn, and Cd in plant tissue were sharply reduced after P application by 53%-92%, 35%-71%, and 59%-86%, respectively; Concentrations decreased exponentially with increasing amount of P; Relationship between Pb and Zn (r = 0.993, p < 0.01), between Pb and Cd (r = 0.986, p < 0.01) suggested that there was a positive relationship between the mechanisms controlling the phytoavailability of Pb, Zn, and Cd. It was suggested that Cd concentrations in the soil solution were reduced generally by P application as a result of the increased soil pH, and Zn concentrations were no change, but Pb concentrations were increased. Species distribution showed that PbHPO4, PbOH+ and PbH2PO4+ were the main complexation species of Pb in the soil equilibrium solution after P application. It was also suggested that Pb accumulation by root were negatively correlated to Pb in soil solution with coefficient of -0.872 (p < 0.05), and that water soluble Zn and Cd concentrations were reduced while the concentrations in root tissues were increased after P addition. These results indicate the difference between Zn, Cd and Pb and suggest that P as KH2PO4 successfully decreased the phytotoxicity of Pb, Zn, and Cd in the contaminated soil.

[Evaluation on environmental quality of Pb, Zn and Cu contents in vegetable plantation soils and vegetables in Hangzhou suburb].

Contents of heavy metals (Pb, Zn, Cu) in soils from 4 main vegetable plantations in Hangzhou suburb were investigated to evaluate environmental quality of heavy metals of soils and vegetables. Different evaluation methods and evaluation standards of heavy metals were used for comparison. Kriging method was applied to study the spatial variability of heavy metals in soil-vegetable system. The distribution maps of the spatial variability of heavy metals in soil-vegetable system in Jianggan District were obtained based on GIS method. The results show that the soils were polluted with Pb, Zn, and Cu using natural background values as evaluation standard. While using National Standard as evaluation standard, the soils were not polluted. Contents of heavy metals in Gongshu District were the highest of four investigated districts. The concentration distribution of heavy metals had different spatial variability. The content of Pb in vegetables was higher than those of Zn and Cu and exceeded the national vegetable sanitation standard. The order for their enrichment coefficients was as follows: Zn> Pb> Cu. The accumulation coefficient for green vegetable was higher than that of Chinese cabbage, indicating green vegetable could easily accumulate heavy metals from soils than Chinese cabbage.

Field demonstration of reduction of lead availability in soil and cabbage (Brassica Chinensis L.) contaminated by mining tailings using phosphorus fertilizers.

A field demonstration of reduction of lead availability in a soil and cabbage (Brassica Chinensis L.) contaminated by mining tailings, located in Shaoxing, China was carried out to evaluate the effects of applications of phosphorus fertilizers on Pb fractionation and Pb phyto-availability in the soil. It was found that the addition of all three P fertilizers including single super phosphate (SSP), phosphate rock (PR), and calcium magnesium phosphate (CMP) significantly decreased the percentage of water-soluble and exchangeable (WE) soil Pb and then reduced the uptake of Pb, Cd, and Zn by the cabbage compared to the control (CK). The results showed that the level of 300 g P/m(2) soil was the most cost-effective application rate of P fertilizers for reducing Pb availability at the first stage of remediation, and that at this P level, the effect of WE fraction of Pb in the soil decreased by three phosphorus fertilizers followed the order: CMP (79%)>SSP (41%)>PR (23%); Effectiveness on the reduction of Pb uptake by cabbage was in the order: CMP (53%)>SSP (41%)>PR (30%). Therefore our field trial demonstrated that it was effective and feasible to reduce Pb availability in soil and cabbage contaminated by mining tailings using P fertilizers in China and PR would be a most cost-effective amendment.

[Evaluation on environmental quality of heavy metals in soils and vegetables based on geostatistics and GIS].

Contents of heavy metals (Pb, Zn, Cd, Cu) in soils and vegetables from Dongguan town in Shangyu city, China were studied using geostatistical analysis and GIS technique to evaluate environmental quality. Based on the evaluation criteria, the distribution of the spatial variability of heavy metals in soil-vegetable system was mapped and analyzed. The results showed that the distribution of soil heavy metals in a large number of soil samples in Dongguan town was asymmetric. The contents of Zn and Cu were lower than those of Cd and Pb. The concentrations distribution of Pb, Zn, Cd and Cu in soils and vegetables were different in spatial variability. There was a close relationship between total and available contents of heavy metals in soil. The contents of Pb and Cd in green vegetables were higher than those of Zn and Cu and exceeded the national sanitation standards for vegetables.