[Effect of Combined Application of an Enterobacter and Sulfur Fertilizer on Cadmium and Arsenic Accumulation in Rice].

The aim of this study was to explore the effects of different sulfur fertilizers combined with sulfate-reducing bacteria on the accumulation of cadmium and arsenic in rice and the formation of iron plaque under long-term flooding conditions and to provide a reference for the safe production of rice fields polluted by moderate and mild cadmium and arsenic. We adopted a pot experiment, selecting two sulfur fertilizers, sulfur and calcium sulfate, and Enterobacter M5 with sulfate-reducing ability, and designed six treatments of single application and combined application of different sulfur fertilizers and M5. The results showed that the combined application of calcium sulfate and M5(CM5) had the best effect on reducing available cadmium and arsenic in rice rhizosphere soil. The combined application of sulfur fertilizer or M5 could reduce the content of cadmium and inorganic arsenic in early season rice grains by 8%-51% and 42%-61%, respectively, under flooding conditions. The content of cadmium and inorganic arsenic in late rice grains decreased by 81%-92% and 41%-62%, respectively. The treatment of the combined application of sulfur and M5(SM5) and CM5 had the best effect on reducing cadmium and arsenic content in both early and late season rice grains. SM5 and CM5 could promote the adsorption of cadmium and arsenic by iron plaque, and the extracted cadmium and arsenic content of ACA in both treatments was significantly higher than that of CK. The extracted iron content of ACA in the CM5 treatment was also significantly higher than that of CK, which indicates that the combined application of calcium sulfate and M5 would promote the formation of iron plaque. The results showed that the combined application of sulfur fertilizer and M5 was better than single application in reducing the content of cadmium and arsenic in grains, whereas the combined application of calcium sulfate and M5 was the best and most stable method.

[Spatial Distribution Characteristics and Assessment of Heavy Metal Pollution in Cultivated Soil of Agricultural Small Watershed in Typical Mining Area in South China].

In order to clarify the spatial distribution characteristics and the present situation of heavy metal pollution in cultivated soil of a typical mining basin in southern China, the contents of Cd, As, Mn, Cu, Zn, and Pb in cultivated soil in the selected small watershed were determined, and the spatial distribution characteristics of heavy metals were analyzed using the spatial interpolation method. Further, the ecological risk was evaluated using the geo-accumulation index and potential ecological risk coefficient (PERC). The results showed that the average contents of Pb, Zn, Cu, As, and Cd in the topsoil (0-20 cm) in the small watershed were approximately 11.9, 3.8, 8.2, 4.7, and 14.2 times that of the background value in Hunan soil, respectively. Compared with the soil risk screening value of agricultural land, the over-standard rates of Pb, Zn, Cu, As, and Cd were approximately 24%, 56%, 75%, 44%, and 48%, respectively. Zn and Mn showed medium variation, whereas Pb, As, Cu, and Cd showed strong variation, which indicated that there was an obvious enrichment of heavy metals in the small watershed. The spatial analysis results showed that there was an obvious consistent characteristic of six heavy metals in the topsoil, that is, there was enrichment in the mining activity area and its downstream and the township streets in the west of the small watershed. Additionally, there were high value points of some heavy metals on both sides of the main river, indicating that the main pollution sources in the study area were mining and metallurgy activities and sewage irrigation. The results of the geo-accumulation index and potential ecological risk index showed that there was compound pollution of heavy metals, in which the degree of Cd pollution was the highest, and the soil of both sides of the river could pose the strongest potential ecological risk.

Multiple mechanisms collectively mediate tungsten homeostasis and resistance in Citrobacter sp. Lzp2.

Tungsten (W) is an emerging contaminant, and current knowledge on W resistance profiles of microorganisms remains scarce and fragmentary. This study aimed to explore the physiological responses of bacteria under W stress and to resolve genes and metabolic pathways involved in W resistance using a transcriptome expression profiling assay. The results showed that the bacterium Citrobacter sp. Lzp2, screened from W-contaminated soil, could tolerate hundreds of mM W(VI) with a 50% inhibiting concentration of ∼110 mM. To cope with W stress, Citrobacter sp. Lzp2 secreted large amounts of proteins through the type VI secretory system (T6SS) to chelate W oxoanions via carboxylic groups in extracellular polymeric substances (EPS), and could transport cytosolic W outside via the multidrug efflux pumps (mdtABC and acrD). Intracellular W is probably bound by chaperone proteins and metal-binding pterin (tungstopterin) through the sulfur relay system. We propose that tetrathionate respiration is a new metabolic pathway for cellular W detoxification likely producing thio-tungstate. We conclude that multiple mechanisms collectively mediate W homeostasis and resistance in Citrobacter sp. Lzp2. Our results have important implications not only for understanding the intricate regulatory network of W homeostasis in microbes but also for bio-recovery and bioremediation of W in contaminated environments.

[Inactivation of Cd and As by an Enterobacter Isolated from Cd and As Contaminated Farmland Soil].

A strain of Enterobacter was screened from cadmium and arsenic contaminated farmland soil and its passivation mechanism of cadmium and arsenic were explored through removing performance and characterization experiments. The results showed that the screened strain M5 was identified as Enterobacter sp. with a sulfate-reduction function, and its maximum resistance concentration was approximately 1 mmol·L-1 to cadmium and arsenic. In the simulation system, the maximum removal efficiencies of cadmium and arsenic were 94.13% and 27.26% by strain M5, respectively. The results of SEM-EDS and XRD confirmed that Cd and As were fixed to CdS and As2S3, and XPS results showed that carboxyl groups, hydroxyl groups, and amide groups on the surface of the bacteria were mainly involved in biological adsorption. These results can provide new ideas and a theoretical basis for microbial applications to soil remediations for heavy metal pollution.

Nano-ferrihydrite colloidal particles mediated interfacial interactions of arsenate and cadmium: Implications for their fate under iron-rich geological settings.

Arsenic (As) and cadmium (Cd) often coexist in paddy soils. Nano-ferrihydrite colloidal particles (NFPs) are ubiquitous at redox active interfaces of the paddy system and are well-known to play a critical role in controlling the solubility and bio-availability of As and Cd. However, the mutual interaction between As and Cd on NFPs remains elusive. Herein, batch experiments and in-situ spectroscopic techniques were used to investigate the effects of the interaction pattern (sequential reaction) of Cd(II) and As(V) on their respective adsorption on the surfaces of NFPs. Two scenarios were designed: Cd(II) pre-saturated NFPs and As(V) pre-saturated NFPs. Adsorption of Cd(II) was increased by 1.67, 4.08, and 5.21 times in As(V)-saturated NFPs, but only by 1.05, 1.11, and 1.15 times for As(V) in Cd(II)-saturated NFPs. Further, we determined the pH-dependent mutually beneficial cooperation pathways as mediated by the surface of NFPs. At lower pH (5), As(V) tended to promote Cd(II) adsorption, whereas Cd(II) tended to enhance As(V) adsorption at higher pH (> 5.5). X-ray photoelectron spectroscopy (XPS) indicated that both pre-saturated Cd(II) and As(V) altered the local coordination environment of their counterpart ions. Furthermore, results from in-situ attenuated total reflection-Fourier-transform infrared spectroscopy (ATR-FTIR) and second derivative peak shape fitting revealed two types of ternary surface complexes, namely Cd(II)-bridged and As(V)-bridged complexes, which were responsible for the distinct Cd(II) and As(V) co-adsorption behavior on the surface of NFPs under different conditions. These findings help us understand how co-presence Cd and As behave in an iron-rich geological setting and will aid in the development of related restoration technologies.

The ignored risk: heavy metal pollution of medicine and food homologous substances.

A survey was conducted to investigate the effects of cadmium (Cd), arsenic (As), chromium (Cr), lead (Pb), and copper (Cu) in medicine and food homologous substances (MFHs) on human health. Nine common and typical MFHs (Dendrobium, Bulbus lilii, Poria, Semen nelumbinis, Radix puerariae, Gardenia jasminoides, Hordeum vulgare L, Semen coicis, and Ganoderma Karst) in the form of medicinal slices ready for decoction were purchased from pharmacies. Five among the MFHs (Dendrobium, Bulbus lilii, Poria, Semen nelumbinis, and Radix puerariae) were further obtained from a local field as raw materials for comparison. The results showed that raw materials of MFHs collected from the field had higher contents of heavy metal and greater health risks than medicinal slices purchased from pharmacy. Generally, the heavy metal residues in MFHs of different medicinal parts were different, and MFHs from roots or stems had significantly higher contents of heavy metals than those from fruits or seeds. Most importantly, the contents of Cd in Bulbus lilii and As in wild Poria from field were higher than the contents described in the Pharmacopoeia of the People's Republic of China (ChP). Non-carcinogenic and carcinogenic risk assessments revealed that Poria from field had larger non-carcinogenic and carcinogenic risks to human health; Bulbus lilii showed no non-carcinogenic risk but exhibited carcinogenic risks, whereas Cr showed carcinogenic risks in all samples. Given that MFHs are incorporated in regular foods, care should be taken to minimize health hazards caused by heavy metals to human. This study creates awareness on the safety issues associated with MFHs, and provides basic information for establishing the maximum allowable contents of medicinal and food substances in normal diets.

Natural dissolved organic matter (DOM) affects W(VI) adsorption onto Al (hydr)oxide: Mechanisms and influencing factors.

Tungsten (W) is a contaminant with health implications whose environmental behaviors are not understood well. Sorption to mineral surfaces is one of the primary processes controlling the mobility and fate of W in soils, sediments, and aquifers. However, few papers published hitherto have not yet figured out the influences of dissolved organic matter (DOM) on this process. Here, we examine W(VI) adsorption behaviors onto Al (hydr)oxide (AAH) in the presence or absence of DOM derived from plant rhizosphere, using batch experiments coupled with X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR). The morphology and functional group analyses results show that DOM can facilitate the aggregation of AAH and block surface Al-OH groups. Coexisting DOM inhibits W(VI) adsorption onto AAH at acidic to neutral pH (4-7), and the presence of either Na + or PO43- can exert a completely different impact on W(VI) adsorption. XPS and FTIR characterizations further demonstrate surface W complexes with the Al-OH groups of AAH and carboxyl groups of DOM. There is no reduction of W(VI) during the adsorption processes, and poly-tungstate species are formed on the surface of both AAH and AAH-DOM coprecipitates. This study provides the first evidence of the roles of natural DOM on W sequestration at the mineral-water surface, which has an important implication for the prediction of the migration and bioavailability of W in natural environments.

Ferrihydrite-organo composites are a suitable analog for predicting Cd(II)-As(V) coexistence behaviors at the soil solid-liquid interfaces.

Organomineral assemblages are building units of soil micro-aggregates and exert their essential roles in immobilizing toxic elements. Currently, our knowledge of the adsorption and partitioning behaviors of coexisting Cd-As onto organomineral composites is limited. Herein, we carefully studied Cd-As cosorption onto ferrihydrite organomineral composites made with either living or non-living organics, i.e., bacteria (Delftia sp.) or humic acid (HA), using batch adsorption and various spectroscopies. Batch results show that As(V) only enhances Cd(II) sorption on pure Fh at pH < 6 but cannot promote Cd(II) sorption to Fh-organo composites. However, Cd(II) noticeably promotes As(V) sorption at pH>~5-6. Synchrotron micro X-ray fluorescence indicates that Cd(II) adsorbs predominately to the bacterial fraction (Cd versus P, r = 0.924), whereas As(V) binds mainly to the Fh fraction (As versus Fe, r = 0.844) of the Fh-bacteria composite. On Fh-HA composite, however, Cd(II) and As(V) are both primarily sorbed by the Fh fraction (Cd/As versus P, r > 0.8), based on the scanning transmission electron microscopy-energy disperse spectroscopy analyses. Elemental distribution characterization also manifests the co-localization of Cd(II) and As(V) within the organomineral composite, particular in Fh-HA composite (Cd versus As, r = 0.8), which is further identified as the Fh-As-Cd ternary complex based on the observations (higher frequencies at ~753-761 cm-1) of attenuated total reflection Fourier-transform infrared spectroscopy. Moreover, this ternary interaction is more pronounced in Fh-HA than in Fh-bacteria. In summary, our results suggest that Cd-As coadsorption behaviors on Fh-organo composites are different from those on pure minerals, and the presence of bacteria/HA can significantly affect metal (loid)s speciation, distribution, and ternary interaction. Therefore organomineral composites are a more suitable analog than pure mineral phases to predict the mobility and fate of Cd-As in natural environments.

[Adsorption Properties of Oiltea Camellia Shell-Modified Biochar and Effects of Coupled Waterlogging on Soil Cd Morphology].

Using oiltea camellia shells, a typical agricultural waste, in Hunan as feedstock, Na2SiO3 solution was used to impregnate oiltea camellia shells and modified biochar was prepared under oxygen-limited conditions. We have studied the adsorption efficiencies of Cd in solution by different biochars and the resistance efficiencies of Cd activity in soil by biochars coupled with flooding. Scanning electron microscopy, Brunauer-Emmett-Teller analysis, and Fourier transform infrared spectroscopy were used to reveal the physicochemical properties of the biochars. The results showed that compared with the camellia oil shell biochar, the modified camellia oil shell biochar (MBC) obtained more special surface areas and functional groups, which showed stronger adsorptive capacities for Cd. A waterlogging soil incubation experiment showed that flooding could simultaneously increase the soil pH values and decrease the acid-soluble Cd component. More available Cd was transformed into the residual state as the flooding time increased, and biochar addition coupled with flooding could lead to further improvement of acid-soluble Cd transformation to the residual state and reduce the acid-soluble Cd content. The concentration of acid-soluble Cd was significantly negatively correlated with the increase in biochar dosage. At 60 d of flooding, the acid-soluble Cd content was 0.33 mg·kg-1 (a decreased amplitude of approximately 45.0%) in 5.0% additional of MBC disposal. Thus, sodium silicate-modified biochar is a novel and effective material for the remediation of Cd-contaminated water and soil, and the research results provide a reference for the resource recovery of Camellia oleracea organic waste.

Inoculation of Cd-contaminated paddy soil with biochar-supported microbial cell composite: A novel approach to reducing cadmium accumulation in rice grains.

Bioremediation of heavy metal-contaminated soil using metal-resistant microbes is a promising remediation technology. However, as exogenous bacteria sometimes struggle to survive and grow when introduced to new soils, it is important to develop appropriate carriers for microbial populations. In this study, we report a novel approach to remediating Cd-contaminated rice paddy soil using biochar-supported microbial cell composites (BMCs) produced from agricultural waste (cornstalks). Pot experiments showed that amendment with BMC was more efficient at reducing root and grain Cd content than pure bacteria, while improving soil Cd fractionation toward more stabilized and less labile forms. Bacteria in the BMC medium grew more readily with more abundant metabolites than those raised in free cells, probably because biochar provides shelter via porous structures (as confirmed by scanning electron microscopy) as well as additional nutrients. Overall, the improved long-term production of microbial biomass caused by BMC inoculation results in a higher remediation efficiency. Our results demonstrate the feasibility of using biochar as an appropriate carrier for metal-tolerant bacteria to remediate Cd-contaminated paddy fields.

Competitive binding of Cd, Ni and Cu on goethite organo-mineral composites made with soil bacteria.

Soil is a heterogeneous porous media that is comprised of a variety of organo-mineral aggregates. Sorption of heavy metals onto these composite solids is a key process that controls heavy metal mobility and fate in the natural environment. Pollution from a combination of heavy metals is common in soil, therefore, understanding the competitive binding behavior of metal ions to organo-mineral composites is important in order to predict metal mobility and fate. In this study, batch experiments were paired with spectroscopic studies to probe the sorption characteristics of ternary CdNiCu sorbates to a binary organo-goethite composite made with Bacillus cereus cells. Scanning electron microscopy shows that goethite nano-sized crystals are closely associated with the bacterial surfaces. Sorption experiments show a larger adsorptivity and affinity for Cu than Cd/Ni on goethite and B. cereus, and the goethite-B. cereus composite. X-ray photoelectron spectroscopy reveals that carboxylate and phosphate functional moieties present on the bacterial cell walls are primarily responsible for metal sorption to the goethite-B. cereus composite. Synchrotron-based X-ray fluorescence shows that Cu and Ni are predominately associated with the bacterial fraction of the goethite-B. cereus composite, whereas Cd is mainly associated with the goethite fraction. The findings of this research have important implications for predicting the mobility and fate of heavy metals in soil multi-component systems.

[Bioavailability of Silicon Fertilizer Coupled Water Management on Soil Bioavailability and Cumulative Control of Rice in Compound Contaminated Paddy Soils].

The effect of wet irrigation (CK), agronomic measure flooding (WF), instantaneous silicon fertilizer combined with flooding measures (FYsi), mineral silicon fertilizer combined with flooding measures (FKsi), and a mix of two kinds of silicon fertilizer combined with flooding measures (FYK) on the bio-availability of As and Cd in soil and the accumulation of As and Cd in rice were investigated by pot experiments. The results showed that the pH of the soils combined with flooding measures was increased by 0.12-0.72 units with similar trends of an increase and then a decrease before finally become neutral. The Eh of the soil combined with flooding was significantly decreased, but the Eh of soil after flooding treated by FYsi, FKsi, and FYK combined with the flooding was significantly higher than that treated by WF, and the content of Cd in brown rice was reduced by 38.83%-65.05% compared with that treated by CK. The WF and FYK treatments can significantly reduce the accumulation of Cd in brown rice, resulting in the lowest Cd contents in brown rice of 0.98 and 0.72 mg·kg-1, respectively. The contents of As in brown rice treated by FYsi, FKsi, and FYK were decreased by 23.80%, 38.10%, and 47.62%, respectively, compared with that with the CK treatment, except that the content of As in brown rice treated by WF increased by 36.64%. FYsi and FYK treatments had the best inhibitory effect on the accumulation of As in brown rice, with the lowest As contents of 0.13 mg·kg-1 and 0.11 mg·kg-1 in brown rice (P <0.01), respectively. There was an extremely significant correlation between the contents of extractable Cd and the total content of Cd in the brown rice (P <0.05), and there was no significant difference between the contents of extractable As and the total content of As in the brown rice. Therefore, FYsi, FKsi, and FYK can effectively inhibit the accumulation of Cd and As in rice grown in Cd-As compound polluted soil, and FYK showed the best performance.

Inoculation of soil with cadmium-resistant bacterium Delftia sp. B9 reduces cadmium accumulation in rice (Oryza sativa L.) grains.

Bioremediation of heavy metal polluted soil using metal-resistant bacteria has received increasing attentions. In the present study, we isolated a heavy metal-resistant bacterial strain from a Cd-contaminated soil, and conducted pot experiments to evaluate the effect of bacterial inoculation in soil on soil Cd speciation, rice grain biomass and Cd accumulation. We find that the isolated bacterial strain is a Gram-negative bacterium, and named as Delftia sp. B9 based on the 16S rDNA gene sequence analysis. TEM-EDS manifests that Cd can be bioaccumulated inside cell, resulting in intracellular dissolution. The Cd contents of rice grain in the two rice cultivars (early and late rice) are all below the standard limit for Food Safety of People's Republic of China (0.2 mg/kg) after the treatment of both living and non-living cells. Non-living cells are more applicable than the use of living cells for the short time bioremediation. The average content of soil exchangeable fraction of Cd decreases whereas the residual fraction increases with bacterial inoculation. All our results suggest Delftia sp. B9 is able to the stabilization of Cd in soil and reduce Cd accumulation in rice grain, therefore, this strain is potentially suitable for the bioremediation of Cd-contaminated paddy soils.

Cd sequestration by bacteria-aluminum hydroxide composites.

Microbe-associated aluminum (Al) hydroxides occur naturally in aquatic and geologic environments and they might play a crucial role in the sequestration of trace metals because these composite solids comprise both reactive mineral and organic surface, but how they do it still remains unknown. Here we replicate Al hydroxide organo-mineral composite formation in soil and sediments by synthesising composites using Pseudomonas putida cells, during coprecipitation with Al hydroxide. Morphological and ATR-FTIR analysis show closely attached nano-sized Al hydroxides on the bacterial surface. For composites dominated by either bacteria or Al hydroxide, an enhanced metal adsorption is observed on the composites than on pure Al hydroxide at pH < 6. Cd uptake by the mainly Al mineral composite is approximately additive, i.e., the sum of the end-member metal adsorptivities, whereas that on the mainly bacteria composite is non-additive. This non-additive sorption is not only due to the blockage of surface reactive sorption sites, but more importantly the changes of surface charge when bacteria and Al mineral are interacted. EXAFS results show that Cd is predominately sorbed as a bidentate corner-sharing complex on the amorphous Al hydroxide surface and a carboxyl-binding on the bacterial surface. This study has important implications for understanding both Al and trace metal cycling in microbe-rich geologic environments.

Comparison of three types of oil crop rotation systems for effective use and remediation of heavy metal contaminated agricultural soil.

Selecting suitable plants tolerant to heavy metals and producing products of economic value may be a key factor in promoting the practical application of phytoremediation polluted soils. The aim of this study is to further understand the utilization and remediation of seriously contaminated agricultural soil. In a one-year field experiment, we grew oilseed rape over the winter and then subsequently sunflowers, peanuts and sesame after the first harvest. This three rotation system produced high yields of dry biomass; the oilseed rape-sunflower, oilseed rape-peanut and oilseed rape-sesame rotation allowed us to extract 458.6, 285.7, and 134.5 g ha-1 of cadmium, and 1264.7, 1006.1, and 831.1 g ha-1 of lead from soil, respectively. The oilseed rape-sunflower rotation showed the highest phytoextraction efficiency (1.98%) for cadmium. Lead and cadmium in oils are consistent with standards after extraction with n-hexane. Following successive extractions with potassium tartrate, concentrations of lead and cadmium in oilseed rape and peanut seed meals were lower than levels currently permissible for feeds. Thus, this rotation system could be useful for local farmers as it would enable the generation of income during otherwise sparse phytoremediation periods.

Manganese Dioxide nanosheet suspension: A novel absorbent for Cadmium(II) contamination in waterbody.

A MnO2 nanosheet (MnO2-NS) suspension was prepared from tetramethylammonium hydroxide (TMA⋅OH), H2O2, and MnCl2⋅4H2O, and its efficiency for Cd(II) removal from aqueous solutions was investigated. The maximum adsorption capacity of the MnO2-NS for Cd(II) was evaluated to be about 348 mg/g, which is thus far the highest value reported for MnO2 at pH 6.0. This high adsorption capacity is attributed to efficient ion exchange. X-ray photoelectron spectroscopy (XPS) revealed that Cd(II) was adsorbed on MnO2 as CdO and Cd(OH)2. After Cd(II) adsorption, the suspended MnO2-NS aggregated and precipitated within 5.0 min from solution. Therefore, dispersive MnO2-NS can be used to remove Cd(II) from wastewater rapidly and with high efficiency.

[Phytoexclusion potential studies of Si fertilization modes on rice cadmium].

The research used serious situ multi-metal contaminated soils to explore Cd repair potential in rice by adding different kinds of fertilizers, based on the outdoor pot experiment. The experiment was consisted of four treatments including non-used fertilizers (CK), the silicon fertilizer applicated into soil (Tsi), the silicon fertilizer applicated as foliar spray (Ysi) and the silicon fertilizer applicated into soil combined with the foliar spray silicon fertilizer application( Tsi + Ysi). The research examined Cd concentrations in tissues of five key growth periods to reveal cadmium (Cd) migration rules, translocation coefficients, rice biomass and yields. The results showed that, compared to CK, different fertilization methods of Si had significant impacts on decreasing Cd in brown rice and polished rice, but not in rice yields; In addition, Tsi + Ysi had the best effects to decrease Cd in edible grains, which resulted in Cd concentrations of husk, brown rice and polished rice reduced by 62.59%, 58.33% and 65.83%, respectively, and the effects of applying Tsi and Ysi were the second. Therefore, Tsi, Ysi and Tsi + Ysi were confirmed to be potential Cd pollution control technologies to rice.

La-EDTA coated Fe3O4 nanomaterial: preparation and application in removal of phosphate from water.

La-EDTA-Fe3O4 was prepared by a chemical co-precipitation method. The magnetic composite was characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR). Furthermore, the adsorption properties of La-EDTA-Fe3O4 toward phosphate in water were investigated. The uptake rate of phosphate in water by La-EDTA-Fe3O4 was 3-1000 times than that of EDTA-Fe3O4, and reached 97.8% at 7 hr. The adsorption process agreed well with the Freundlich model and kinetics studies showed that the adsorption of phosphate proceeds according to pseudo second-order adsorption kinetics. The maximum removal rate was achieved at pH 6.0-7.0. The La-EDTA-Fe3O4 had good adsorption properties and could be separated well from aqueous solution by a permanent magnet. Therefore, this nanomaterial has potential application for the removal of phosphate from large water bodies.

Ammonia volatilization and availability of Cu, Zn induced by applications of urea with and without coating in soils.

Ammonia volatilization and the distribution of Cu and Zn were investigated in two types of soil treated with coated and uncoated urea. The rate of ammonia volatilization in two weeks after fertilizing with coated urea was 8% in soil 1 (soil derived from river alluvial deposits in Dongting Lake Plain) and 5.15% in soil 2 (red soil derived from quaternary red clay), about half the rates observed when fertilizing with common urea, implying that the hydrolysis speed of the coated urea was lower than for common urea, and that the coated urea can increase nitrogen use efficacy. As for the availability of Cu and Zn, their concentrations decreased in the first week after fertilization, and then increased, which was contrary to the effect of treatment on soil pH. For example, when the pH was 7.99, there was 0.79 mg/kg exchangeable Cu and 0.85 mg/kg exchangeable Zn in the soil derived from river alluvial deposits in Dongting Lake Plain. However, the concentrations of exchangeable Cu and Zn were generally lower for the common urea treatments than those with the coated urea because the peak pH for the common urea treatment was greater. The concentrations of these elements correlated well with pH in the range 4-8 in second order polynomial fits.

[Soil contamination and assessment of heavy metals of Xiangjiang River Basin].

The contents of heavy metals (As, Cd, Cu, Zn, Ni and Pb) in soils from Xiangjiang River Basin, Hunan Province, China, were analyzed by toxicity characteristic leaching procedure (TCLP) and Nemrow method. Results showed that the total contents of As, Cd, Cu, Zn, Ni and Pb were 4.25-549.67, 0.13-76.84, 11.49-281.69, 7.75-7234.81, 5.50-56.65 and 8.60-2084.81 mg x kg(-1), respectively, and the available contents of As, Cd, Cu, Zn, Ni and Pb extracted by TCLP were 0.02-10.97, 0.06-28.41, 0.04-72.29, 0.59-1 152.32, 0.07-10. 65 and 0.17-1 165.58 mg x kg(-1). The contents of available heavy metals extracted by TCLP correlated with total contents of heavy metals. Moreover, the pollution index Nemrow method showed that 72 samples at safety level, alert level, light pollution level, medium pollution level and heavy pollution level ratios were 60.52%, 11.33%, 5.65%, 4.22% and 18.38% separately, illustrating that pollution of heavy metals in soil samples of Xiangjiang River Basin is serious.