Immobilization Mechanism of Nano-Hydroxyapatite on Lead in the Ryegrass Rhizosphere Soil Under Root Confinement.

The immobilization effect and mechanism of nano-hydroxyapatite(NHAP) on Pb in the ryegrass rhizosphere soil were studied by root-bag experiment. The speciation analysis results revealed that the residual Pb concentrations in the rhizosphere soil significantly increased after NHAP application. The acid-soluble and reducible Pb concentrations significantly decreased, indicating that NHAP had obviously immobilized Pb. Meanwhile, NHAP significantly promoted the secretion of tartaric acid from ryegrass roots, resulting the rhizosphere soil pH had been below that of the control group. This helped to relieve the stress of Pb on ryegrass, also promoted the dissolution of NHAP, resulting the formation of stable precipitation with more Pb ions. NHAP increased the rhizosphere soil pH by 0.03 to 0.17, which promoted the conversion of Pb to non-utilizable bioavailability. The total Pb mass balance indicated only a very small proportion Pb transferred to the shoots through ryegrass roots. The formation of pyromorphite by Pband NHAP in soil was accordingly to interpret the dominant mechanism for Pb immobilization.

Toxic effects of antimony on the seed germination and seedlings accumulation in Raphanus sativus L. radish and Brassica napus L.

The germination and growth of seedlings are not only essential stages in plant growth but also indicator of environmental stress. Evaluation of seed germination and early seedling in order to improve the understanding of influential processes of exogenic substances. This study aimed to reveal the possible toxicity of antimony (Sb) using Raphanus sativus L. Radish (radish) and Brassica napus L. (rape) seeds as the experimental materials. With Sb concentrations ranging from 2 to 100 mg/L, the seed germination and seedlings growth were investigated by calculating the germination rate, germinative energy, germination index, vitality index and root elongation. The results indicated that Sb exhibited different levels of toxicity to different plants. The low concentration of Sb increased the germination rate and germination index of rape seeds, whereas high concentrations of Sb sharply decreased the germination rate and germination index when the Sb was greater than 10 mg/L. The radish seeds remained almost constant. The germinative energy of both seeds exhibited the same change. In addition, the root elongation was more sensitive to the antimony pollution than the germination rate was. The vitality index decayed exponentially as the Sb concentration increased for both species of seed. These results have significant ecological meaning in assessing the toxicity of Sb.

Assessment of the Remediation Effect of Nano-hydroxyapatite in Exogenous Pb-contaminated Soil Using Toxicity Characteristic Leaching Procedure and Soil Enzyme Activities.

Lead (Pb) is one of the most abundant metal soil pollutants. In this research, effects of nano-hydroxyapatite (NHAP) on remediation of Pb-contaminated soil were evaluated by the measure of extractable Pb using toxicity characteristic leaching procedure (TCLP) and soil enzyme activities. Results suggested NHAP significantly decreased the concentrations of extractable Pb, achieving the maximum decrement rate of 75.71%. Activity of urease decreased with increasing Pb concentrations. Moreover, activities of alkaline phosphatase, dehydrogenase, and catalase increased at the lower Pb levels and decreased at the higher Pb levels. NHAP had a positive effect on regulating soil enzymes. Thus, soil enzyme activities, especially dehydrogenase, could be used as biological indicators of Pb pollution and NHAP remediation. Moreover, NHAP could reduce the mobility and bioavailability of Pb, while increasing enzyme activities, thereby lowering the leaching risk and biotoxicity of Pb.