Xiao-quan Shan

Stability of titania nanoparticles in soil suspensions and transport in saturated homogeneous soil columns.

The stability of TiO(2) nanoparticles in soil suspensions and their transport behavior through saturated homogeneous soil columns were studied. The results showed that TiO(2) could remain suspended in soil suspensions even after settling for 10 days. The suspended TiO(2) contents in soil suspensions after 24h were positively correlated with the dissolved organic carbon and clay content of the soils, but were negatively correlated with ionic strength, pH and zeta potential. In soils containing soil particles of relatively large diameters and lower solution ionic strengths, a significant portion of the TiO(2) (18.8-83.0%) readily passed through the soils columns, while TiO(2) was significantly retained by soils with higher clay contents and salinity. TiO(2) aggregate sizes in the column outflow significantly increased after passing through the soil columns. The estimated transport distances of TiO(2) in some soils ranged from 41.3 to 370 cm, indicating potential environmental risk of TiO(2) nanoparticles to deep soil layers.

Kinetics and thermodynamics of sorption of nitroaromatic compounds to as-grown and oxidized multiwalled carbon nanotubes

The sorption kinetics and thermodynamics of 1,3-dinitrobenzene (DNB), m-nitrotoluene (mNT), p-nitrophenol (pNP), and nitrobenzene (NB) on as-grown and nitric acid-oxidized multiwalled carbon nanotubes (MWCNTs) were investigated. The sorption kinetics was well described by a pseudo-second-order rate model, while both Langmuir and Freundlich models described the sorption isotherms well and the sorption thermodynamic parameters of equilibrium constant (K(0)), standard free energy (DeltaG), standard enthalpy (DeltaH), and standard entropy changes (DeltaS) were measured. The values of DeltaH and DeltaG suggested that the sorption of nitroaromatics (NACs) onto MWCNTs was exothermic and spontaneous. The structure, number, and position of nitro groups of NACs were the main factors affecting the sorption rate and capacity. Treatment of the MWCNTs with nitric acid increased both the surface area and the pore volume and introduced oxygen-containing functional groups to the MWCNTs, which depressed the sorption of NACs onto MWCNTs.

Comparison between fractionation and bioavailability of trace elements in rhizosphere and bulk soils.

Rhizosphere is a microbiosphere and has quite different chemical, physical and biological properties from bulk soils. A greenhouse experiment was performed to compare the difference of fractionation and bioavailability of trace elements Cr, Ni, Zn, Cu, Pb and Cd between rhizosphere soil and bulk soil. In the meantime, the influence of air-drying on the fractionation and bioavailability was also investigated by using wet soil sample as a control. Soils in a homemade rhizobox were divided into four zones: rhizosphere, near rhizosphere, near bulk soil and bulk soil zones, which was designated as S1, S2, S3 and S4. Elemental speciations were fractionated to water soluble, exchangeable and carbonate bound (B1), Fe-Mn oxide bound (B2), and organic and sulfide bound (B3) by a sequential extraction procedure. Speciation differences were observed for elements Cr, Ni, Zn, Cu, Pb and Cd between the rhizosphere and bulk soils, and between the air-dried and wet soils as well. The concentrations of all six heavy metals in fraction B1 followed the order of S2 > S3 > S1 > S4 and for B2, the order was S2 > S3 S4 > S1. For B3, the order was S1 > S3 S4 > S2, while for Cd the order was S2 > S3 approximately/= S4 > S1. The air-drying increased elemental concentration in fractions B1 and B2 by 20-50% and decreased in fraction B3 by about 20-100%. Correlation analysis also indicated that the bioavailability correlation coefficient of fraction B1 in rhizosphere wet soil to plants was better than that between either air-dried or nonrhizosphere soils. Therefore, application of rhizosphere wet soils should be recommended in the future study on the speciation analysis of trace elements in soils and bioavailability.

Speciation of rare earth elements in soil and accumulation by wheat with rare earth fertilizer application

A greenhouse study was conducted to investigate the accumulation of rare earth elements (REEs), La, Ce, Pr and Nd, in winter wheat (Triticum aestivum L.), and the speciation of these elements in soil following the application of REE-based fertilizers. Improved crop yield was confirmed by the experiment. The accumulation behavior of La, Ce, Pr and Nd in wheat varied depending on the concentration of REE fertilizer application, i.e. increased with increasing REE concentration at low fertilization application, constant over the medium REE range, and decreased with increasing REE concentration at high fertilizer application. Significant negative correlation was obtained between REE contents in roots and soil pH (r = -0.5787 to -0.8442 for La). REEs in both the fertilized and unfertilized soils were fractionated by a three-stage sequential extraction procedure into three chemically distinct fractions: water soluble, exchangeable and carbonate bound (B1), Fe-Mn oxide bound (B2), and organic and sulfide bound (B3). REEs in fertilized soils were found mainly in the B2 and B3 fractions, with only a small amount in the B1 fraction. REEs in B1 and B2 fractions were negatively correlated with soil pH (r = -0.6892 to -0.8927 and -0.7462 to -0.9482). Significant correlation was obtained between REEs in B1 fraction and REE contents in root. The correlation coefficients ranged from 0.6159 to 0.7410 when fertilizer application was lower than 20.0 mg/kg soil. No acceptable relationship was observed between REE contents in shoot and any of the extractable fractions in soils.

Physiological effects of magnetite (Fe3O4) nanoparticles on perennial ryegrass (Lolium perenne L.) and pumpkin (Cucurbita mixta) plants.

Abstract To date, knowledge gaps and associated uncertainties remain unaddressed on the effects of nanoparticles (NPs) on plants. This study was focused on revealing some of the physiological effects of magnetite (Fe3O4) NPs on perennial ryegrass (Lolium perenne L.) and pumpkin (Cucurbita mixta cv. white cushaw) plants under hydroponic conditions. This study for the first time reports that Fe3O4 NPs often induced more oxidative stress than Fe3O4 bulk particles in the ryegrass and pumpkin roots and shoots as indicated by significantly increased: (i) superoxide dismutase and catalase enzyme activities, and (ii) lipid peroxidation. However, tested Fe3O4 NPs appear unable to be translocated in the ryegrass and pumpkin plants. This was supported by the following data: (i) No magnetization was detected in the shoots of either plant treated with 30, 100 and 500 mg l−1 Fe3O4 NPs; (ii) Fe K-edge X-ray absorption spectroscopic study confirmed that the coordination environment of Fe in these plant shoots was similar to that of Fe-citrate complexes, but not to that of Fe3O4 NPs; and (iii) total Fe content in the ryegrass and pumpkin shoots treated with Fe3O4 NPs was not significantly increased compared to that in the control shoots.

The role of earthworms (Eisenia fetida) in influencing bioavailability of heavy metals in soils

The effects of earthworm (Eisenia fetida) activity on soil pH, dissolved organic carbon (DOC), microbial populations, fraction distribution and bioavailability of heavy metals (Zn, Cu, Cr, Cd, Co, Ni, and Pb) in five Chinese soils were investigated using pot experiments. A three-step extraction procedure recommended by the European Community Bureau of Reference (BCR; now Standards, Measurements and Testing Programme of the European Community) was used to fractionate the metals in soils into water soluble, exchangeable and carbonate bound (B1), Fe-oxides and Mn-oxides bound (B2) and organic matter and sulfide bound (B3). After the soils were treated with earthworms, the soil pH, water-soluble metal fraction and DOC increased. A significant correlation was obtained between the increased DOC and the increased metals in the water-soluble fraction. The heavy metals in fraction B1 increased after earthworm treatments, while those in fraction B3 decreased. No significant differences were observed for heavy metals in fraction B2. The microbial populations in soil were enumerated with the dilution plate method using several media in the presence of earthworms. The microbial populations increased due to earthworm activity. The biomass of wheat shoots and roots, and the heavy metal concentrations in wheat roots and shoots, were also increased due to the earthworm activity. The present results demonstrated that earthworm activity increases the mobility and bioavailability of heavy metals in soils.

Effect of organic acids on adsorption and desorption of rare earth elements

Effect of citric, malic, tartaric and acetic acids on adsorption of La, Ce, Pr and Nd by and desorption from four typical Chinese soils was studied. Generally, adsorption capacities of rare earth elements (REEs) were significantly correlated with the cation exchange capacity (CEC) of soils. In the presence of acetic acids adsorption of REEs was similar to that in the presence of Ca(NO3)2. However, in the presence of citric, malic and tartaric acids adsorption of REEs by Heilongjiang, Zhejiang and Guangdong soils decreased to varying extents if compared with that in the presence of nitrate and acetic acid. The significance of suppression followed the order of citric acid > malic acid > tartaric acid > acetic acid, which was consistent with the order of stability of complexes of REEs with these organic acids. However, the adsorption increased with increasing equilibrium solution pH. For Jiangxi soil with low soil pH, CEC and organic matter these organic acids exerted an even more serious suppression effect on the adsorption of REEs. Another feature of the relationship between the adsorption of REEs and equilibrium solution pH was that the adsorption of REEs decreased with increase of pH from 2 to 4.5 and then slightly increased with further increase of pH. Desorption of REEs varied with soils and with organic acids as well. REEs were released easily from Heilongjiang, Zhejiang and Guangdong soils in the presence of organic acid. Generally, desorption of REEs decreased with increasing equilibrium solution pH. Effect of organic acids on desorption of REEs from Jiangxi soil was more complicated. In the presence of citric and malic acids no decrement and/or slight increase in desorption of REEs were observed over the equilibrium solution pH from 3 to 6.5. The reasons for this were ascribed to the strong complexing capacity of citric and malic acids and low soil pH, CEC and organic matter of Jiangxi soil.

Adsorption kinetics, isotherms and thermodynamics of atrazine on surface oxidized multiwalled carbon nanotubes

The adsorption kinetics, isotherms and thermodynamic of atrazine on multiwalled carbon nanotubes (MWCNTs) containing 0.85%, 2.16%, and 7.07% oxygen was studied. Kinetic analyses were performed using pseudo-first-order, pseudo-second-order and intraparticle diffusion models. The regression results showed that the pseudo-second-order law fit the adsorption kinetics. The calculated thermodynamic parameters indicated that adsorption of atrazine on MWCNTs was spontaneous and exothermic. Standard free energy (DeltaG(0)) became less negative when the oxygen content of MWCNTs increased from 0.85% to 7.07% which is consistent with the low adsorption affinity of MWCNTs for atrazine.

Coadsorption of ciprofloxacin and Cu(II) on montmorillonite and kaolinite as affected by solution pH.

The coadsorption of ciprofloxacin (Cip) and Cu(II) on montmorillonite and kaolinite was studied between pH 4.0 and 9.5. At pH < 5.0, Cu(2+), Cip(+) and [Cu(II)(Cip(+/-))](2+) were the main species in solution. Between pH 5.0-7.0 [Cu(II)(Cip(+/-))](2+) was the dominant complex species. Above pH 8.0 [Cu(II)(Cip(-))(2)](0) precipitated. The presence of Cu(II) exerted no effect on the Cip sorption onto montmorillonite at low pH, whereas it increased Cip sorption on montmorillonite at pH > 6.0 due to the stronger affinity of Cip-Cu(II) complexes compared to sole Cip(-) or Cip(+/-), or Cip sorption via a Cu(II) bridge increased. In contrast, Cip increased Cu(II) adsorption on montmorillonite at pH < 7.0, whereas it decreased the adsorption of Cu(II) on kaolinite at pH 6.0-8.0. Cip was sorbed onto the kaolinite surface via interaction of carboxyl groups over the entire pH range. At pH 4.0-4.7, Cip(+) sorption onto kaolinites positively charged surface was more favorable than sorption of Cip-Cu(II) complexes. Batch experiments and FTIR analyses indicated that the coordination between Cip(+/-), Cip(-) and Cu(II) were most likely present on kaolinite surface at pH 7.0. At pH > 8.0, Cu(OH)(2) (s) and [Cu(II)(Cip(-))(2)](0) precipitated out of solution or on the montmorillonite or kaolinite surface, which was not considered evidence for either the sorption of Cip or the adsorption of Cu(II).

Survey of phthalate pollution in arable soils in China

The problem of pollution by phthalates is of global concern due to their widespread occurrence, toxicity and endocrine disruption properties. The contamination by phthalates such as dimethyl phthalate (DMP), diethyl phthalate (DEP), di-n-butyl phthalate (DBP) and di(2-ethylhexyl) phthalate (DEHP) in 23 arable soils throughout China was investigated to evaluate the present pollution situation. The survey results demonstrated that phthalates were ubiquitous pollutants in soils in China. The total concentrations of phthalates differed from one location to another, and ranged from 0.89 to 10.03 mg kg(-1) with a median concentration of 3.43 mg kg(-1). Among the phthalates, DEHP was dominant and detected in all 23 soils. DEP and DBP were also in abundance, and DMP was rarely detected. Similar contamination patterns were observed in all 23 soils. A distinct feature of phthalate pollution in China was that the average concentration in northern China was higher than that in southern China. In addition, a close relationship was observed between the concentration of phthalates in soils and the consumption of agricultural film. The correlation showed that the application of agriculture film might be a significant pollution source of phthalates in arable soils of China. The potential risk of phthalates in soils was assessed on the basis of current guide values and limits.