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The enhancement of surface functional groups on biochar is essential to improving its toxic metals adsorption capacity. In this study, we used two solutions: NaOH (aq) and NaOH dissolved in absolute ethanol (C2H5OH) to dope the surface of powdered oiltea camellia shell. Then, the shells were pyrolyzed at 500 °C for 120 min to obtain NaOH-modified biochar (SBC), NaOH–C2H5OH-modified biochar (EBC), and the undoped sample (BC). After modification, the special surface area, O-containing functional groups, especially C=C were improved. The specific surface area of EBC and SBC (91.76 and 56.83 m2g−1, respectively) were superior to that of the BC (36.98 m2g−1). With NaOH–C2H5OH, more C=C groups were introduced via elimination reaction, enhancing its adsorption properties. EBC consistently showed higher adsorption efficiency than BC for Cd(II) and Pb(II). Moreover, the spectroscopic analysis revealed that Cd(II)- π , Pb(II)- π interactions were the predominant mechanisms for the toxic metals’ collection on the EBC, each contributing 75.45% and 58.60%, respectively. Besides, the O-functional groups onto EBC surface bonded easily to Pb(II) than Cd(II) in the mixture solution. Therefore, EBC produced in the NaOH–C2H5OH system, as efficient and cost-effective biochar, is promising for toxic metals adsorption.

Heavy metal passivators could reduce the transfer of heavy metal ions from soil to crops and exhibit great potential in safe cropping in heavy metal contaminated agricultural soils. However, the effects of heavy metal passivators on microbial diversity and microorganisms-based biogeochemical processes in agricultural soil are poorly explored. In this study, the effects of three heavy metal passivators, viz. lime, silicon (Si) fertilizer, and gypsum, on the structure and function of microorganisms in cadmium (Cd) contaminated paddy soils were investigated through activity of soil enzyme, microbial abundance and community structure by an in situ paddy field plot experiment. Our results showed that lime application changed the activity of phosphatase and urease through increasing bio-available phosphorus (AP) content in soil and soil pH, respectively. Lime application increased abundance and richness of the prokaryotic microbes in paddy soil, while gypsum application increased evenness of the eukaryotic microbes. Si fertilizer application resulted in the increase of evenness of both prokaryotic and eukaryotic microbes. The results presented in this study suggest that application of heavy metal passivator lime, Si fertilizer, and gypsum could improve microbial diversity and function in Cd contaminated paddy soil.

Manganese oxides are naturally occurring powerful oxidants and scavenger which can control the mobility and bioavailability of arsenic (As). However, the effect of synthetic nanostructured manganese oxides on the mobilization and transportation of As at actual paddy soils are poorly understood, especially in the low or medium background Mn concentration soil. In the present study, a novel Nano manganese oxide with higher reactivity and surface area has been synthesized. A 90-d soil incubation experiment combined with pot and field rice cultivation trials were designed to evaluate the effectiveness of exogenous α-MnO2 nanorods on the mobilization and transportation of As in soil-rice systems. Our results proved that the addition of α-MnO2 nanorods can effectively control the soil-to-solution partitioning of As under anaerobic conditions. After treatment with different amounts of α-MnO2 nanorods, the content of effective As decreased with the increasing of residual As and insoluble binding As (Ca-As and Fe-As). Besides, the enhanced oxidation of As (III) into As(V) by α-MnO2 nanorods increased the adsorption of As onto indigenous iron(hydr) oxides which greatly reduced the soil porewater As content. Additionally, pot experiment and filed applications are further proved that the influx of As into aerial parts of rice plants (stems, husk and leaves) was strictly prohibited after treatments with different amount of α-MnO2 nanorods; more interestingly, significantly negative correlations have been observed between As and Mn in rice, which indicated that as Mn is increased in soil, As in brown rice decreases. Our results demonstrated that the use of α-MnO2 nanorods in As polluted paddy soil containing low levels of background Mn oxides can be a promising remediation strategy.

Few studies have been carried out so far for measuring concentrations of NH 3 , NO 2 and O 3 in plastic greenhouses. In this study, NH 3 , NO 2 and O 3 concentrations were measured with passive sampler technology in a plastic greenhouse located in the Changsha suburb in southern China over a one and a half month period (November 30, 2008 to January 11, 2009). Soil in the greenhouse was subjected to four treatment (T) types (no N fertilizer T1, common urea T2, coated urea T3 and common urea with nitrification inhibitor dicyandiamide (DCD) T4. The average concentrations (μg/m 3 ) of NH 3 , NO 2 and O 3 in descending order was: T4 (31.66) > T2 (25.93) > T3 (23.52) > T1 (7.96), T2 (10.99) > T3 (8.16) > T4 (7.48) > T1 (5.20), T2 (75.05) > T3 (64.20) > T4 (63.85) > T1 (49.02), respectively. This implied that photochemical reactions took place and that harmful gases accumulated after application of N fertilizer in the plastic greenhouse. DCD inhibited the conversion of ammonium to nitrate, increased NH 3 volatilization and decreased NO 2 level. The coated urea decreased the emissions of NH 3 and increased nitrogen use efficiency. We found significant positive correlations ( p 3 and NO 2 levels. Correlations between soil pH and both NH 3 and NO 2 concentrations were also significant ( p 3 average concentration from March 31, 2009 to April 10, 2009 in the higher latitude of the Yinchuan suburb in northern China was two times greater than that in the Changsha suburb in southern China. The O 3 daily concentrations in the Yinchuan suburb exceeded 160 μg/m 3 (i.e., China's Grade I standard), and the maximal value 214.83 μg/m 3 exceeded 200 μg/m 3 (i.e., China's Grade III standard).

Oiltea camellia shells are a substantial agricultural waste in southern China, but their resource utilization has not been given due attention. In this study, we prepared oiltea camellia shell biochar by pyrolysis (500 °C) in the presence of sodium silicate, and investigated its adsorption capacity for Cd removal. The SEM characterization shows that silicon (Si) is loaded on biochar surfaces as fine particles, and are identified as quartz (SiO2), silicate and C–Si mixture according to X-ray diffraction. Silicate-modification significantly increases (∼45–112%) specific surface area (SSA) and slightly increases (∼5–12%) porosity of biochar. Batch results reveal that Si-modification significantly enhances Cd adsorption, and this increment is more pronounced at pH > 5. Furthermore, silicate-modification promotes the internal diffusion of Cd on biochar. FTIR and XPS analyses suggest that ion exchange with Na+, surface precipitation (CdCO3, CdSiO3 or Cd2SiO4), coordination with π electrons (C C) and complexation with carboxyl and C–Si–O groups are the predominant sorption mechanisms. This study puts a new perspective on the waste utilization of oiltea camellia shells for heavy metal removal from wastewaters or stabilization in contaminated soils.

In order to study the role of mulberry (Moms alba L) as an economic crop for remediation of cadmium (Cd) contaminated soil, the transport of Cd from mulberry to silkworm were investigated. Three varieties of mulberry (Yuesang-11, Nongsang-14, and Qiangsang-1) with three planting densities were cultivated in two heavy metal-contaminated fields named Dongkou in Shaoyang city and Linxiang in Yueyang city in Hunan province respectively. The both field soils were contaminated by heavy metals, especially by Cd. The potential risks of heavy metals in Linxiang's soil were higher than those in Dongkou's because of higher concentrations of Cd. Since the promotion of Cd concentrations in aerial parts (stem, branch and leaf) resulted from the increase of planting density, the method of high planting density is beneficial to improve the efficiency of the remediation of Cd contaminated soil. The percentages of average Cd contents of mulberry in Dongkou accounted for 44%, 20%, 18% and 16% in roots, stems, branches and leaves respectively, while the Cd contents were 38%, 27%, 19% and 16% distributed in roots, stems, branches and leaves respectively. Mulberry leaves from contaminated soils was applied in food source of silkworms in this study. Although there is Cd uptake occurred in silkworm growth and its products (cocoons and chrysalis), Cd contents in cocoons are lower than the national standard (100 μg*kg-1) for textile industry of China. Therefore, mulberry can be regarded as an economical crop to control soil contamination with Cd.

A field experiment was conducted to investigate the effect of bean stalk (BBC) and rice straw (RBC) biochars on the bioavailability of metal(loid)s in soil and their accumulation into rice plants. Phytoavailability of Cd was most dramatically influenced by biochars addition. Both biochars significantly decreased Cd concentrations in iron plaque (35-81 %), roots (30-75 %), shoots (43-79 %) and rice grain (26-71 %). Following biochars addition, Zinc concentrations in roots and shoots decreased by 25.0-44.1 and 19.9-44.2 %, respectively, although no significant decreases were observed in iron plaque and rice grain. Only RBC significantly reduced Pb concentrations in iron plaque (65.0 %) and roots (40.7 %). However, neither biochar significantly changed Pb concentrations in rice shoots and grain. Arsenic phytoavailability was not significantly altered by biochars addition. Calculation of hazard quotients (HQ) associated with rice consumption revealed RBC to represent a promising candidate to mitigate hazards associated with metal(loid) bioaccumulation. RBC reduced Cd HQ from a 5.5 to 1.6. A dynamic factor's way was also used to evaluate the changes in metal(loid) plant uptake process after the soil amendment with two types of biochar. In conclusion, these results highlight the potential for biochar to mitigate the phytoaccumulation of metal(loid)s and to thereby reduce metal(loid) exposure associated with rice consumption.