[Influence of sulfur on the speciation transformation and phyto-availability of heavy metals in soil: a review].

The biogeochemical cycle of sulfur can directly affect the speciation transformation of heavy metals in soils and their accumulation in plants. The toxicity of heavy metals in plants can be alleviated by their complexation with sulfur compounds like phytochelatins or metallothiones, consisting of the major mechanisms of phytodetoxification. Sulfur deficiency is becoming one of the limiting factors that influence Chinese agricultural production. Although the applications of sulfur fertilizer in soil have received much attention in recent years, the interaction mechanism of heavy metal with sulfur metabolism has not been studied extensively. In this paper, we reviewed current research advance on the impact of sulfur on the speciation transformation of soil heavy metals and their accumulation in plants, discussed the effect of sulfur on the detoxification mechanism of heavy metal in plants and provided further research prospective in this field.

[Application prospect about bioremediation of polychlorinated biphenyls-contaminated soil with immobilized microorganism technique: a review].

As one type of the persistent organic pollutants, polychlorinated biphenyls (PCBs) are tremendously harmful to organisms. These compounds are easily absorbed onto soil particles and able to accumulate in soil after they are released into the environment. Bioremediation technology of PCBs-contaminated soils has become a research hotspot in recent years, and immobilized microorganism technique has high developing and applying value because of its unique advantages in environmental remediation. This paper reviewed the chief remediation technology of PCBs-contaminated soils and then analyzed the characteristics of immobilized microorganism technique and its research progress in remediation of organic polluted soil. Finally, the feasibility and problems of this technique in remediation of PCBs-contaminated soil were also discussed.

[Research advances in uptake, translocation, accumulation and detoxification of Pb in plants].

Contamination of soils by lead (Pb) is of widespread occurrence because of the industrialization, urbanization, mining, and many other anthropogenic activities. It is urgent and necessary for scientists to uncover the mechanisms of uptake, translocation, accumulation and detoxification of Pb in plants for the following two reasons. First, it helps target and regulate the key process of Pb uptake by crops and vegetables and minimize the threat of Pb introduction to the food chain. Second, it helps cultivate Pb hyperaccumulating plants that can absorb and sequester excessive amounts from contaminated soils in their biomass without incurring damage to basic metabolic functions. The purpose of this review was to summarize the research advances in uptake, translocation and accumulation of Pb in plants and address the mechanisms by which plants or plant systems detoxify Pb. The further researches on the foliar uptake, the interactions between soil components and plant cell wall, as well as the integrated technologies for phytoremediation of Pb-contaminated soils were prospected.

[Eco-toxicological effect of metal-based nanoparticles on plants: Research progress].

The rapid development of nanotechnology and the potential environmental risk of wide application of artificial nanoparticles (NPs) have raised considerable concerns. Metal-based nanoparticles (MB NPs) have dual-toxicity of metal and NPs, and thus, their bio-toxicity and ecological risk are the hotspots in the studies of nanotoxicology. Plant, as a main component of ecosystem, is a potential pathway for NPs bioaccumulation and entering into food chain. This paper discussed the MB NPs absorption, translocation, and accumulation by plants, and summarized the eco-toxicological effect of MB NPs on plants and related mechanisms. The factors affecting the phytotoxicity of MB NPs were approached, and the research progress on the eco-toxicological effect of MB NPs on plants, especially on food crops, was reviewed. Also, the existing problems in present MB NPs phytotoxicity studies were analyzed, and the future research directions were proposed.

[Preliminary analysis of manganese uptake mechanism in the hyperaccumulator Phytolacca americana L].

Phytolacca americana L. (P. americana) is a manganese (Mn) hyperaccumulator plant discovered in southern China, and knowledge of Mn uptake characteristics and mechanisms on this plant may provide essential and critical information for phytoremediation. Synchrotron radiation X-ray fluorescence spectroscopy (SRXRF) microprobe was empolyed in this study to explore the Mn distribution in the root cross-section of P. americana, and effects of metabolic inhibitors (DNP and Na3VO4) and Ca-channel inhibitor (LaCl3) on Mn uptake of P. americana was also investigated under laboratory conditions. Results showed that P. americana has strong abilities for absorpting and accumulating Mn, and the Mn concentration in root, stem, and leaf of P. americana may reach up to 402, 208, and 601 mg x kg(-1) DW, respectively, even only treated with 5 micromol x L(-1) Mn. The highest Mn content can be found in the vascular bundle of root, and then the epidermis, while the lowest Mn content can be observed in the cortex. The Mn content increased when shifted from cortex to vascular bundle, indicating that there was an active transportation in Mn absorption of P. americana root, and the inhibitory effect of DNP and Na3VO4 on Mn uptake further verified the possibilities of active absorption. The Mn uptake was inhibited by 30% with LaCl3, suggesting that Mn uptake in P. americana also closely related to the Ca-channel.

Differences in soil properties and bacterial communities between the rhizosphere and bulk soil and among different production areas of the medicinal plant Fritillaria thunbergii.

To explore rhizosphere effects, geographical differences and their effects on the bacterial community associated with the geoherb Fritillaria thunbergii, some physicochemical properties of soil samples (3 sampling sites × 2 habitats (rhizosphere and bulk soil)) were measured and the soil bacterial community detected by PCR-denaturing gradient gel electrophoresis (DGGE). Among the three regions, soil pH varied between 4.48 and 7.73 indicating that F. thunbergii could grow both in acid and slightly alkaline soil. As the authentic Dao-di producing area, Ningbo showed the highest soil quality with the highest content of organic matter (OM) (2.46%), phosphatase (268 mg kg(-1) 24 h(-1)) and urease activity (1481 mg kg(-1) 24 h(-1)). In comparison with the bulk soil, pH, organic carbon content, and phosphatase and urease activities were all lower in the rhizosphere, suggesting that the roots may secrete some unique metabolites in root exudates. Statistical analyses showed that soil properties of Ningbo and Panan in Zhejiang province were more similar to each other than those in Nantong in Jiangsu province. In addition, PCR-DGGE analysis showed that main bacterial population identified in F. thunbergii was proteobacteria (18 bands, 55%), acidobacteria (4, 12%), actinobacteria (4, 12%) and bacterioidetes (6, 18%). Overall, soil properties and microbial communities varied not only between the rhizosphere and bulk soil but also among the three regions. We suggest that the plant, together with the soil properties, cooperatively shape the structure of the rhizosphere bacteria, and that the soil properties have a close relationship with the geoherbalism of F. thunbergii.

Enhancement of copper availability and microbial community changes in rice rhizospheres affected by sulfur.

The role of sulfur on the availability of Cu and the bacterial community in rice rhizospheres was investigated by pot experiments. With sulfur addition, pH in rhizosphere soil decreased and Mg(NO3)2 extractable Cu increased significantly. The bacterial community composition also changed with sulfur addition. Some specific clones having high similarity to Thiobacillus, which indicated that sulfur oxidation in the rice rhizosphere could increase the availability of Cu. These results suggested that sulfur source which could provide substrate to sulfur oxidizing bacteria and enhance the availability of Cu was not a suitable sulfur fertilizer for Cu polluted soil.

[Applications of synchrotron-based X-ray absorption near-edge structure spectroscopy in identifying solid state phosphorus speciation: a review].

Solid state phosphorous is an important phosphorus speciation controlling the phosphorous bioavailability and mobility in the environment. Synchrotron-based X-ray absorption near-edge structure (XANES) spectroscopy, with its unique advantage of being a non-destructive method in identifying the local chemical information of target element at molecular level in situ, has become one of the frontier technologies for characterizing the speciation of chemical substances and clarifying the microscopic mechanisms of chemical reactions, attracting extensive attention in the field of environmental chemistry. This paper briefly introduced the basic theory of phosphorus XANES spectroscopy, summarized the applications of XANES spectroscopy in the researches of solid state phosphorus speciation in minerals, soils, and organic fertilizers, and analyzed the challenges and prospects of the applications of XANES spectroscopy in identifying the solid state phosphorus speciation in the environmental samples. It was pointed out that XANES spectroscopy should combine with other microscopic spectroscopic techniques and macroscopic analytical methods, complementing each other, to provide a comprehensive and effective technical support for the research of the speciation characterization and transformation mechanisms of phosphorus in the environment.

[Effects of sulfur on microbial activity and community structure in a lead-polluted paddy soil].

A pot experiment was conducted to study the microbial activity and community structure in a lead-polluted paddy soil under effects of amendment with different concentration sodium thiosulfate. The amendment of the sulfur-containing substrate increased the soil oxidation-reduction potential and respiration rate, promoted the growth of soil sulfur-oxidizing bacteria, and induced some changes in soil microbial community structure. The clone sequencing indicated that the specific bands of soil microbes in sodium thiosulfate treatments had very high similarity to Bateroidetes, Thiobacillus, beta-proteobacteria, and Acidobacteria. Significant changes were observed in the contents of soil carbonate- and Fe/Mn oxide- bound Pb after the amendment of sodium thiosulfate.

Heavy metal availability and impact on activity of soil microorganisms along a Cu/Zn contamination gradient.

All the regulations that define a maximum concentration of metals in the receiving soil are based on total soil metal concentration. However, the potential toxicity of a heavy metal in the soil depends on its speciation and availability. We studied the effects of heavy metal speciation and availability on soil microorganism activities along a Cu/Zn contamination gradient. Microbial biomass and enzyme activity of soil contaminated with both Cu and Zn were investigated. The results showed that microbial biomass was negatively affected by the elevated metal levels. The microbial biomass-C (C(mic))/organic C (C(org)) ratio was closely correlated to heavy metal stress. There were negative correlations between soil microbial biomass, phosphatase activity and NH4NO3 extractable heavy metals. The soil microorganism activity could be predicted using empirical models with the availability of Cu and Zn. We observed that 72% of the variation in phosphatase activity could be explained by the NH4NO3-extractable and total heavy metal concentration. By considering different monitoring approaches and different viewpoints, this set of methods applied in this study seemed sensitive to site differences and contributed to a better understanding of the effects of heavy metals on the size and activity of microorganisms in soils. The data presented demonstrate the relationship between heavy metals availability and heavy metal toxicity to soil microorganism along a contamination gradient.

Trimethylamine (TMA) biofiltration and transformation in biofilters.

Bioremoval of trimethylamine (TMA) in two three-stage biofilters packed with compost (A) and sludge (B), respectively, was investigated. Both biofilters were operated with an influent TMA concentration of 19.2-57.2mgm(-3) for 67 days. Results showed that all of the inlet TMA could be removed by both biofilters. However, removal efficiency and transformation of TMA in each section of both biofilters was different. In the Introduction section, TMA removal efficiency and maximum elimination capacity of the compost medium were greater than those of sludge medium under higher inlet TMA concentration. In comparison with biofilter A, considerably higher NH(3) concentrations in effluent of all three sections in biofilter B were observed after day 19. Although, NO(2)(-)-N concentration in each section of biofilter A was relatively lower, NO(3)(-)-N content in each section of biofilter A increased after day 26, especially in the Materials and method section which increased remarkably due to a lesser amount of TMA and higher ammonia oxidation and nitrification in compost medium. In contrast, neither NO(2)(-)-N nor NO(3)(-)-N were detected in either section of biofilter B at any time throughout the course of the experiment. The cumulative results indicated that compost is more favorable for the growth of TMA-degrading and nitrifying bacteria as compared to the sludge and could be a highly suitable packing material for biodegradation and transformation of TMA.

An investigation of cellular distribution of manganese in hyperaccumlator plant Phytolacca acinosa Roxb. using SRXRF analysis.

Phytolacca acinosa Roxb. (P. acinosa) is a recently discovered manganese hyperaccumulator plant from southern China. It is a good candidate for phytoremediation of manganese(Mn) polluted soil for its high biomass and fast growth. Knowledge of the tissue localization and identification of heavy metals can provide essential information on metal toxicity and bioaccumulation mechanisms. Synchrotron radiation X-ray fluorescence spectroscopy (SRXRF) microprobe was used in this study to investigate the cellular distributions of Mn and other elements in root, stem, leaf, petiole and midrib of P. acinosa. The highest Mn content was found in the vascular tissues of root, stem, petiole and midrib. Cortex in root played a key role in Mn absorption and Mn was limited in the vascular bundle during the process of transportation in stem. Moreover, Mn content in leaf epidermis was higher than that in mesophyll, which suggested that the sequestration of Mn in leaf epidermis might be one of the detoxification mechanisms of P. acinosa. The significance of other elemental (such as P, S, K, Ca, Fe, Zn and Cu) distribution patterns and the correlation with Mn were also discussed.

Biosorption of copper(II) and zinc(II) from aqueous solution by Pseudomonas putida CZ1.

To study Pseudomonas putida CZ1, having high tolerance to copper and zinc on the removal of toxic metals from aqueous solutions, the biosorption of Cu(II) and Zn(II) by living and nonliving P. putida CZ1 were studied as functions of reaction time, initial pH of the solution and metal concentration. It was found that the optimum pH for Zn(II) removal by living and nonliving cells was 5.0, while it was 5.0 and 4.5, respectively, for Cu(II) removal. At the optimal conditions, metal ion biosorption was increased as the initial metal concentration increased. The adsorption data with respect to both metals provide an excellent fit to the Langmuir isotherm. The binding capacity of living cells is significantly higher than that of nonliving cells at tested conditions. It demonstrated that about 40-50% of the metals were actively taken up by P. putida CZ1, with the remainder being passively bound to the bacterium. Moreover, desorption efficiency of Cu(II) and Zn(II) by living cells was 72.5 and 45.6% under 0.1M HCl and it was 95.3 and 83.8% by nonliving cells, respectively. It may be due to Cu(II) and Zn(II) uptake by the living cells enhanced by intracellular accumulation.