Mechanism of lead immobilization by oxalic acid-activated phosphate rocks

Lead （Pb） chemical fixation is an important environmental aspect for human health. Phosphate rocks （PRs） were utilized as an adsorbent to remove Pb from aqueous solution. Raw PRs and oxalic acid-activated PRs （APRs） were used to investigate the effect of chemical modification on the Pb-binding capacity in the pH range 2.0-5.0. The Pb adsorption rate of all treatments above pH 3.0 reached 90%. The Pb binding on PRs and APRs was pH-independent, except at pH 2.0 in activated treatments. The X-ray diffraction analysis confirmed that the raw PRs formed cerussite after reacting with the Pb solution, whereas the APRs formed pyromorphite. The Fourier Transform Infrared spectroscopy analysis indicated that carbonate （CO32-） in raw PRs and phosphate （PO43-） groups in APRs played an important role in the Pb-binding process. After adsorption, anomalous block-shaped particles were observed by scanning electron microscopy with energy dispersive spectroscopy. The X-ray photoelectron spectroscopy data further indicated that both chemical and physical reactions occurred during the adsorption process according to the binding energy. Because of lower solubility of pyromorphite compared to cerussite, the APRs are more effective in immobilizing Pb than that of PRs.

Phosphate Solubilizing Ability and Phylogenetic Diversity of Bacteria from P-Rich Soils Around Dianchi Lake Drainage Area of China

The phylogenetic diversity of phosphate solubilizing bacteria （PSB） distributed in P-rich soils in the Dianchi Lake drainage area of China was characterized, and the tricalcium phosphate （TCP） solubilizing activities of isolated PSB were determined. Among 1 328 bacteria isolated from 100 P-rich soil samples, 377 isolates （28.39% of the total） that exhibited TCP solubilization activity were taken as PSB. These PSB showed different abilities to solubilize TCP, with the concentrations of solubilized P in bacterial cultures varying from 33.48 to 69.63 mg L^（-1）. A total of 123 PSB isolates, with relatively high TCP solubilization activity （〉 54.00 mg L^（-1））, were submitted for restriction fragment length polymorphism （RFLP） analysis, which revealed 32 unique RFLP patterns. Based on these patterns, 62 representative isolates, one to three from each RFLP pattern, were selected for 16S rRNA sequencing. Phylogenetic analysis placed the 123 PSB into three bacterial phyla, namely Proteobacteria, Aetinobacteria and Firmicutes. Members of Proteobacteria were the dominant PSB, where 107 isolates represented by 26 RFLP patterns were associated with the genera of Burkholderia, Pseudomonas, Acinetobacter, Enterobacter, Pantoea, Serratia, Klebsiella, Leclercia, Raoultella and Cedeeea. Firmicutes were the subdominant group, in which 13 isolates were affiliated with the genera of Bacillus and Brevibacterium. The remaining 3 isolates were identified as three species of the genus Arthrobacter. This research extends the knowledge on PSB in P-rich soils and broadens the spectrum of PSB for the development of environmentally friendly biophosphate fertilizers.

Facile synthesis of Ag/La2O2CO3 hierarchical micro/nanostructures for antibacterial activity and phosphate removal

In this study,hierarchical Ag/La2 O2 CO3 micro/nanostructures(MNSs)were synthesized by in situ loading Ag nanoparticles(NPs)on the surface of the La2 O2 CO3 MNSs.The prepared La2 O2 CO3 MNSs present flower-like shape and can be tuned by the molar ratio of La(NO3)3 and CO(NH2)2.In the molar ratio of 1:2 to 1:55,the La2 O2 CO3 MNSs mainly consist of polyhedral rods,irregular rods and irregular spindles and their size is about 10,8 and 7μm,respectively.After loading Ag NPs,the spindle-like Ag/La2 O2 CO3 MNSs were used for phosphate removal and antibacterial activity.At the initial phosphate concentration of20 mg/L,the removal rate is 59.6%.The Ag/La2 O2 CO3 MNSs have significant antibacterial activity and their MIC values for S.aureus and E.coli are 31.3 and 15.6μg/mL,respectively.The results indicate that Ag/La2 O2 CO3 MNSs may have good application prospects in open water to inhibit bacterial growth.

Integration of Chemical Methods and Biomarkers for Assessment of Chlorimuron-Ethyl Bioavailability in Soil

Bioavailability is a critical factor for assessing the environmental risk of organic pollutants in soil. In this study, extractions with 3 different solvents, including 2 aqueous solutions, calcium chloride(CaCl_2) and a phosphate buffer solution(PBS), and a mixture of aqueous solution and organic solvent, a PBS-methanol(8:2,volume/volume) mixture(PBS-M), were performed to assess the bioavailability of chlorimuron-ethyl in soil in comparison to a battery of toxicity tests in wheat seedlings. The results indicated that the peroxidase(POD) activity in wheat leaves after 7 d of exposure was one of the sensitive biomarkers of chlorimuron-ethyl in soil.The extractability of chlorimuron-ethyl by all the 3 solvents decreased with exposure time, and the rate of decrease of the PBS-M extraction between 1 and 7 d of exposure was substantially higher than those of the aqueous solution extractions. Chlorimuron-ethyl gradually changed from a water-soluble form into a soil organic matter(SOM)-bound form in the soil. The PBS extraction correlated best with the POD activity in the leaves after 7 d of exposure.