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The effects of humic acid (HA) on copper (Cu(II)) adsorption onto few-layer reduced graphene oxide (FRGO) and few-layer graphene oxide (FGO) were investigated using a batch equilibration method, micro-Fourier transform infrared spectroscopy, and extended X-ray absorption fine structure spectroscopy (EXAFS). The results showed that HA was adsorbed on FRGO through it-it interaction. The adsorbed HA introduced O-containing functional groups and negative charges to FRGO surfaces, increasing Cu(II) adsorption through chemical complexation and electrostatic attraction. In contrast, HA was adsorbed onto FGO mainly through polar interactions, due to its rich O-containing functional groups. The adsorbed HA had little effect on Cu(II) adsorption onto FGO because the shielding effect of HA on Cu(II) adsorption was offset by newly introduced adsorption sites of HA on FGO. EXAFS results suggested that Cu(II) was adsorbed on FRGO and FGO mainly through the coordination with their O-containing functional groups. When HA was added at pH 4.0 and 6.0, more Cu(II) was adsorbed on HA-coated FRGO. At pH 8.0, a portion of Cu(II) in solution precipitated on FRGO surface, while the presence of HA led to the formation of FRGO-HA-Cu ternary surface complexes instead of Cu(II) precipitation. (C) 2014 Elsevier Ltd. All rights reserved.

Perfluorinated compounds (PFCs) are of particular environmental concern. The migration of PFCs from soil to plants is a likely pathway for PFCs to enter the human food chain. This study aimed to investigate the uptake mechanisms of perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA) by maize (Zea mays L. cv. TY2). Hydroponic greenhouse experiments were performed. The kinetics of PFOS and PFOA uptake fitted Mechaelis-Menten equation well, suggesting their carrier-mediated influx processes. Uptake of PFOS was insensitive to metabolic inhibitors (NaN3 and Na3VO4). In contrast, treated with NaN3 and Na3VO4 reduced the uptake of PFOA by 83 and 43 % respectively. PFOS uptake was decreased by 31 % and 25 % when plants were treated with aquaporin inhibitors, AgNO3 and glycerol, respectively, while aquaporin inhibitors had no effect on PFOA uptake. Anion channel blockers, 4, 4′-diisothiocyanostibene-2,2′-disolfonate (DID) and 5-nitro 2-(3-phenylpropylamine) benzoic acid (NPPB) inhibited the uptake of PFOS by 33 % and 30 %, respectively. Anion channel blocker anthracene-9-carboxylic acid (9-AC) decreased the uptake of PFOA by 28 %. No competitive uptake was found between PFOS and PFOA. Uptake of PFOS and PFOA by maize may have different mechanisms.

Multi-walled carbon nanotubes (MWCNTs) are superadsorbents for perfluorooctane sulfonate (PFOS) and heavy metals, which coexist in wastewater. The interaction between PFOS and Cu(II) with regard to their adsorption and desorption on MWCNTs was evaluated in this study. The adsorption of PFOS on MWCNTs enhanced with an increase of Cu(II). Desorption of PFOS showed no hysteresis without Cu(II), while pronounced hysteresis with Cu(II). Increases of the adsorption and the occurrence of desorption hysteresis of PFOS in the presence of Cu(II) may due to the PFOS adsorption via a Cu(II) bridge. The adsorption of Cu(II) increased with an increase of PFOS. The desorption hysteresis factors in the presence of PFOS were lower than those in the absence of PFOS. Increases of the adsorption and decreases of desorption hysteresis factors may be attributed to the Cu(II) adsorption via a PFOS bridge. Results obtained by X-ray absorption spectroscopy verified the formation of inner-sphere complexes between Cu(II) and functional groups of MWCNTs without PFOS, while out-sphere complexes with large amount of PFOS. The effect of Cu(II) and PFOS adsorption on the zeta potential of MWCNTs was also studied. The results showed that the coexistence of Cu(II) and PFOS greatly affects their sorption and desorption behaviors on MWCNTs thereby their fate and transport in wastewater. (C) 2012 Elsevier B.V. All rights reserved.

Effect of norfloxacin (Nor) on the sorption of 1,3-dinitrobenzene (1,3-DNB), and PAHs (naphthalene (NAPH), phenanthrene (PHEN) and pyrene (PYR)) to K(+)-montmorillonite was studied. Nor suppressed 1,3-DNB sorption due to their competition for the same sorption sites. 1,3-DNB was sorbed on K(+)-montmorillonite surface via cation-polar interaction and n-π electron donor-acceptor interaction. Nor also was sorbed on these sites through cation exchange, cation bridging and/or surface complexation. Nor increased three PAHs sorption on montmorillonite and the enhanced magnitude was positively correlated with the π-donor strength of three PAHs. The enhanced sorption of PAHs by Nor was primarily attributed to π-π interaction between π-electron-depleted quinoline ring of Nor and π-electron-rich PAHs. Compared with cation (Nor(+)) and anion (Nor(-)), zwitterion (Nor(±)) of Nor increased PHEN and PYR sorption more pronounced due to additional cation-π interaction between the sorbed Nor(±) and PAHs. (1)H NMR spectrum provided direct evidence for π-π and cation-π complexation between PAHs and Nor(+) in solution by ring-current-induced upfield chemical shifts of amino group and methylene group of Nor(+).

Azolla, which is an aquatic fern, has proved to be effective in the uptake and accumulation of metals from polluted waters. Azolla spp., namely A. microphylla cv. MH3 and A. caroliniana Willd, were chosen as model plants so that Cd(II) could be accumulated from aqueous solution. An increase in uptake time and the concentration of Cd(II) in aqueous solution resulted in more Cd(II) accumulation in both species. Modified Michaelis–Menten equation was employed to describe the concentration-dependent kinetics of Cd(II) uptake through the roots of A. microphylla cv. MH3, and the values of Km and Vmax were found to be 0.23 mg/L and 16.49 μg/(g.f.wt.h), respectively. Cd(II) uptake by A. microphylla cv. MH3 occurs partly through Ca(II) channels and has the potential to be mediated by Zn(II) transporters.

Land application of solid wastes leads to the accumulation of both metals and antimicrobials in soils. To understand the effects of metal and antibiotic interaction on their accumulation by the earthworm Eisenia fetida, uptake and elimination kinetics and subcellular distribution of cadmium (Cd) and ciprofloxacin (CIP) were determined. The kinetics was accurately described by a one-compartment first-order kinetic model. Bioaccumulation kinetics and subcellular distribution of CIP were not affected by Cd addition. However, Cd exhibited different metabolic and subcellular distribution patterns. With CIP, Cd uptake flux and elimination rate constants were about 2.2 and 9.8 times, respectively, those without CIP. In the presence of CIP, Cd redistributed from fractions D (associated with granules) and E (associated with tissue fragments and cell membranes) to fraction C (associated with cytosol). Without CIP, Cd in fraction C could not be excreted, whereas with CIP, Cd in fraction C was significantly excreted, and the excretion rate constant was consistent with that of CIP. A good relationship was found between CIP and Cd in earthworms during uptake and elimination periods (p < 0.01). Our results indicated that the Cd CIP complex may be taken up, stored, and eliminated by earthworms.

The effect of lead on the adsorption of diuron and dichlobenil on multiwalled carbon nanotubes (MWCNTs) was investigated to explore the possible application of MWCNTs for removal of both herbicides from contaminated water. The adsorption of diuron and dichlobenil on MWCNTs at pH 6 was nonlinear and fit the Polanyi-Manes model well. The adsorption of diuron and dichlobenil was closely correlated with specific surface areas and micropore volumes of MWCNTs. An increase in oxygen content of MWCNTs with same diameters and similar surface areas decreased the adsorption of diuron and dichlobenil, while increased the adsorption of lead. Micro-Fourier transform infrared spectroscopic study indicated that hydrogen bonding is a main mechanism responsible for the adsorption of diuron or dichlobenil onto MWCNTs-O. Oxygen containing groups, mainly carboxylic groups, significantly increased the adsorption of lead through the formations of outer-sphere and inner-sphere complexes, which are verified by X-ray absorption spectroscopic measurements. Oxygen containing groups and the presence of lead diminished the adsorption of diuron and dichlobenil. The suppression mechanisms of lead were ascribed to hydration and complexation of lead with carboxylic groups, which may occupy part of surface of MWCNTs-O. The large hydration shell of lead cations may intrude or shield hydrophobic and hydrophilic sites, resulting in a decreased adsorption of diuron and dichlobenil at the lead-complexed moieties. (C) 2011 Elsevier B.V. All rights reserved.

The mutual effects of metal cations (Cu(2+), Pb(2+), Zn(2+), and Cd(2+)) and p-nitrophenol (NP) on their adsorption desorption behavior onto wheat ash were studied. Results suggested that Cu(2+), Pb(2+), and Zn(2+) diminished the adsorption and increased the desorption of NP remarkably, while Cd(2+) had no such effect. In contrast, NP diminished the adsorption of Cu(2+), Pb(2+), and Zn(2+) onto ash, however, this suppression effect depended on the initial concentrations of metal cations. NP had no effect on Cd2+ adsorption on ash. Fourier transform infrared (FT-IR) and X-ray absorption spectroscopic (XAS) studies suggested the following mechanisms responsible for the metal suppression effect on NP adsorption: (1) large hydrated Cu(2+), Pb(2+), and Zn(2+) shells occupied the surface of ash and prevent nonspecific adsorption of NP onto ash surface; (2) Cu(2+), Pb(2+), and Zn(2+) may block the micropores of ash, resulting in decreased adsorption of NP; (3) complexation of Cu(2+), Pb(2+), and Zn(2+) was likely via carboxyl, hydroxylic and phenolic groups of wheat ash and these same groups may also react with NP during adsorption. As a "soft acid", Cd(2+) is less efficient in the complexation of oxygen-containing acid groups than Cu(2+), Pb(2+), and Zn(2+). Thus, Cd(2+) had no effect on the adsorption of NP on wheat ash.

Decabromodiphenyl ether (BDE209) is poorly absorbed by mammals, and little information is available on the toxicokinetics of BDE209 and its metabolites in fish. In the present study, rainbow trout (Oncorhynchus mykiss) were administered to 100 ng/g and 500 ng/g body wet weight of BDE209 via a single intraperitoneal injection and parent BDE209 and its metabolites were sequentially monitored for 28 days. The results showed that toxicokinetic profiles of BDE209 could be described by the one-compartment model. In the higher dose group (500 ng/g wet weight), the calculated half-life (t 1/2) and elimination rate (k e) were 17.7 d and 0.039/d in the liver, and 100.3 d and 0.007/d in the muscle, respectively. Three major methoxylated brominated diphenyl ethers (MeO-BDEs) were detected with 2,2′,4,4′-tetrabromo-5-methoxydiphenyl ether (5-MeO-BDE47) being detected in all tissue samples. There was no significant temporal change of 5-MeO-BDE47 concentration in the muscle, whereas an exponential increase was observed in the liver. Therefore, the metabolism rate of BDE209 depended on the administered dose. BDE209 was hardly accumulated in the muscle of rainbow trout, while the liver was a primary metabolic organ. MeO-BDEs were formed via metabolism of BDE209, which probably played a significant role in fish toxicology as a potential indicator.

The impact of two types of natural organic matters (NOM), humic acid (HA) and lipid, on char properties and sorption affinities for phenanthrene was studied. Char was coated with HA and lipid at a concentration of 0.060, 0.250 and 0.500 g/g char. HA, lipid, char and coated char were characterized and their sorption behaviors for phenanthrene were compared. Coating with NOM increased the polarity and aliphaticity, and reduced the specific surface area (SSA) of char, depending on the coated amount and the type of NOM. At the lower HA and lipid loading there was a strong attenuation of N(2)-assessible SSA. The SSA attenuation was less pronounced at larger HA and lipid loadings, which was most likely due to the preferential sorption at reactive sites and formation of clusters. The sorption isotherms of phenanthrene on char and coated char fitted Freundlich equation well, suggesting that all sorption isotherms were nonlinear, with N values in the range of 0.495-0.873. Coated char with HA and lipid decreased the organic carbon-normalized sorption coefficients K(Foc) and increased the N values. Lipid was more effective than HA in decreasing SSA. phenanthrene sorption capacity and sorption isotherm nonlinearity. The N values were correlated positively with the aliphaticity and negatively with pore volume of sorbents. The results of this investigation demonstrated that different NOM plays a different role in attenuating the SSA and sorption affinity of char for phenanthrene. (C) 2009 Elsevier B.V. All rights reserved.

Temporal changes in the distribution of exogenous HCB and DDT among different soil organic matter fractions were studied under sterile and non-sterile conditions, different soil water contents, and different concentrations of added Cu(2+). The residence time was 311 days. Soil organic matter was fractionated into fulvic acid (FA), humic acid (HA), bound-humic acid (BHA), lipid, and insoluble residue (IR) fractions by a methyl isobutyl ketone (MIBK) method. Results revealed that there is a mass transfer tendency of DDT and HCB from FA, HA and BHA to IR and lipid fractions with increasing residence time. Microbial activity accelerated the mass transfer, while the addition Of Cu(2+) slowed it down. The HCB and DDT transfer rate decreased as the soil moisture increased from 1.9% to 60%, but increased when soil moisture increased further to 90%. A two-compartment first order kinetic model was used to describe the mass transfer from FA, HA and BHA. (C) 2007 Elsevier Ltd. All rights reserved.

A new passive sampling device (PSD), a triolein-embedded cellulose acetate membrane (TECAM), was used to biomimetically accumulate naphthalene, phenanthrene, pyrene and benzo[a]pyrene from ten spiked soils and a soil spiked with different concentrations of these polycyclic aromatic hydrocarbons (PAHs). TECAM exposure conditions were optimized. The quantities of PAHs accumulated by TECAMs were positively and linearly related to their concentrations in the soil. PAHs accumulated by TECAMs were negatively related to soil organic matter (SOM) and positively related to the dissolved organic carbon (DOC) according to the results obtained from ten spiked soils. Aging time (1-150 days) had a significant effect on accumulation of PAHs by TECAMs. A good linear relationship (R-2 = 0.970-0.993) was observed between TECAM-accumulated PAHs and PAHs accumulated by earthworms (Eisenia andrei). The data indicate that TECAM represents a useful surrogate to estimate the bioavailability of PAHs and perhaps other hydrophobic organic contaminants (HOCs) in soils. (c) 2007 Elsevier Ltd. All rights reserved.

The effect of indole-3-acetic acid (IAA) on lead (Pb) accumulation in maize (Zea mays L. cv. TY2) seedlings, and the responses of maize to Pb, IAA or Pb + IAA stress were investigated under hydroponic conditions. Exogenous IAA significantly increased Pb accumulation in roots, but significantly decreased Pb accumulation in shoots over the culture period of 5 days. Increased Pb uptake in maize roots partly took place through calcium and potassium channels, and also depended upon membrane potential. Lipid peroxidation in terms of malondialdehyde (MDA) content was enhanced, indicating that Pb and/or IAA caused oxidative stress in maize seedlings. Under stress conditions the antioxidant defense mechanism was activated. Some antioxidant enzymes such as superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) were up-regulated compared to the control. Pb, IAA or Pb + IAA treatments resulted in a general reduction of macro- and micronutrient contents, especially of K, Ca and Mn. Compared to a single Pb or IAA treatment, treatment with a combination of Pb + IAA induced more severe oxidative stress on maize roots and shoots as inferred from the higher observed MDA and lower nutrient contents. A Fourier transform infrared (FTIR) spectroscopic study indicated that Pb reacted with the carboxylic acid group of the IAA pyrrole cycle.

Residence time-dependent distribution patterns of hexachlorobenzene (HCB) and dichlorodiphenyltrichloroethane (DDT) among different soil organic matter fractions of three Chinese soils were investigated. Soil organic matter (SOM) was fractionated into fulvic acid (FA), humic acid (HA), bound-humic acid (BHA), lipid, and insoluble residue (IR) fractions using methyl isobutyl ketone (MIBK) method. Results revealed that as the residence time prolonged, the amounts of HCB and DDT in the FA, HA and BHA fractions decreased, while those in the lipid and IR fractions increased. One- and two-compartment first order, and one- and two-parameter pore-diffusion kinetic models were used to describe the mobility of HCB and DDT from the FA, HA and BHA fractions. The results suggest that excellent agreements were achieved between the experimental data and fits to the two-compartment first order kinetic model (R-2 > 0.97). The transfer rates of HCB and DDT followed the order FA > HA > BHA. (C) 2007 Elsevier Ltd. All rights reserved.

An indirect CE method was developed for the study of low-molecular weight organic acids (LMWOAs) in maize under the stress of cadmium. The influences of indirect reagents (phthalate, salicylic acid, and benzoic acid), coion concentration, and pH were studied. A buffer composed of 15 mmol/L benzoate and 0.2 mmol/L CTAB (pH 5.7) was used in the organic acid determination. The detection limit ranged between 0.5 and 6 micromol/L. The RSD (n = 14) of the method was found to be in the range of 0.11-0.49% for migration time and 1.25-4.72% for peak area. In the maize roots, obvious increases of LMWOAs were observed when the plants were under the stress of cadmium and/or organic acids. The recovery of standard organic acids added in real samples ranged from 85 to 116%.

Current bioavailability assessments of light rare earth elements (LREEs) are often carried out under greenhouse conditions. This work was to identify which soil properties are mostly related to LREE bioavailability and what extraction method is the most promising approach for assessing bioavailability of LREEs to wheat under field conditions. A comparison was made between four commonly used extractants (DTPA, EDTA, CaCl2 and CH3COOH), and the results suggested that the LREE concentrations in wheat roots significantly Correlated with soil pH and amorphous Fe oxide contents in soils, but were independent of soil organic matter (SOM), crystalline Fe and Mn oxide contents, and cation exchange capacity (CEC). The contents of LREEs in shoots were independent of any soil properties. Both DTPA- and EDTA-extractable LREEs were significantly correlated to LREE concentrations in wheat roots and shoots. DTPA extractable LREEs were comparable to LREEs in wheat roots, however, the EDTA exetractable LREEs overestimated the LREE accumulation in wheat roots. Neither root nor shoot LREEs showed significant correlation with CH3COOH extractable LREEs, suggesting that the CH3COOH extraction method was not suitable for predicting LREE bioavailability. CaCl2 method was unable to estimate the LREE bioavailability due to poor data distribution in correlation analysis. Overall, DTPA extraction method was preferred to other extraction methods for estimating bioavailability of LREEs to wheat. (C) 2007 Elsevier B.V. All rights reserved.

This paper reports the adsorption of benzoic acid from water on cetyl trimethylammonium exchanged montmorillonite (CTAB-montmorillonite). Important factors are the adsorbent concentration, ionic strength, equilibrium time and pH. The largest adsorption is at pH 9. The adsorption kinetics data fitted the pseudo-second-order equation. The adsorption isotherms at different pH were linear indicating a partition mechanism. Up to about 61% of the dissolved benzoic acid was adsorbed by CTAB-montmorillonite. These results indicate that CTAB-montmorillonite is a potential adsorbent for benzoic acid.

Effects of an arbuscular mycorrhizal (AM) fungus (Glomus caledonium) on accumulation and metabolism of atrazine in maize grown in soil contaminated with different concentrations of atrazine were investigated in a series of pot experiments. Roots of mycorrhizal plants accumulated more atrazine than non-mycorrhizal roots. In contrast, atrazine accumulation in shoot decreased in mycorrhizal compared with non-mycorrhizal plants. No atrazine derivatives were detected in the soil, either with or without mycorrhizal colonization. However, atrazine metabolites, deethylatrazine (DEA) and deisopropylatrazine (DIA), were detected in plant roots and the AM colonization enhanced the metabolism. After plant harvest atrazine concentrations decreased markedly in the soils compared to the initial concentrations. The decreases were the most in rhizosphere soil and then near-rhizosphere soil and the least in bulk soil. Mycorrhizal treatment enhanced atrazine dissipation in the near-rhizosphere and bulk soils irrespective of atrazine application rates.

In order to understand the role of phosphate in the reactions of heavy metals on mineral surfaces, phosphate was used to modify goethite and then adsorption of copper and cadmium on the pristine and phosphate-modified goethite was investigated. Compared with the pristine goethite, the phosphate-modified goethite had a higher adsorption capacity and a faster adsorption rate. Surface characteristics, such as specific surface area, pore size distribution, zeta potential and surface charges, were then systematically investigated in order to examine the relevant mechanism for the enhancement of copper and cadmium adsorption onto the phosphate-modified goethite. It was found that the decreased surface charge contributed most to the higher adsorption capacity and the enlarged average pore size was mainly responsible for the fast adsorption kinetics, while there was no direct link between specific surface area and the adsorption capacity.

Low molecular weight organic acids are important components of root exudates and therefore, knowledge regarding the mechanisms of cadmium (Cd) uptake and distribution within plants under the influence of organic acids, is necessary for a better understanding of Cd behavior in the plant–soil system. In this study, acetic and malic acids increased the uptake of Cd by maize (Zea mays L. cv. TY2) roots and enhanced Cd accumulation in shoots under hydroponic conditions. Concentration-dependent net Cd influx in the presence and absence of organic acids could be resolved into linear and saturable components. The saturable component followed Michaelis–Menten kinetics, which indicated that Cd uptake across the plasma membrane was transporter-mediated. While the Km values were similar, the Vmax values in the presence of acetic and malic acids were respectively 6.0 and 3.0 times that of the control. Zinc transporters were the most probable pathways for Cd accumulation. It was hypothesized that Cd(II)–organic acid complexes associated with the root zone, could decompose and liberate Cd2+ for subsequent absorption by maize roots; and that in the layer of the roots or within the root free space, depletion of Cd2+ was buffered by the presence of Cd(II)–organic acid complexes. Plant response to elevated Cd levels involved overproduction of organic acids in maize roots as a resistance mechanism to alleviate Cd toxicity.

Oxalate is exuded by plants in the rhizosphere and plays an important role in the soil/root interactions. Phosphate fertilizer is widely used all over the world and may influence the behavior of arsenic (As) in soils. In this study oxalate and phosphate were used as extractants to investigate their effects on the release of As from three As-contaminated soils and the chemical speciation of As. Concentrations of arsenite (As(III)) and arsenate (As(V)) released progressively increased by increasing the concentrations of oxalate or phosphate. The released As(V) content was higher than that of As(III) and the differences between As(V) and As(III) released by oxalate was more obvious than by phosphate. Greenhouse experiment was conducted to evaluate the effects of oxalate and phosphate on As uptake by wheat (Triticum vulgare L.). Addition of oxalate or phosphate resulted in the increase of As accumulation in both wheat root and shoot and the effect of phosphate was more obvious than that of oxalate.

Combined use of batch equilibration adsorption and X-ray absorption spectroscopy (XAS) was employed to study the mechanisms of competitive adsorption of Ph, Cu, and Cd on Danish and Heilongjiang peat in single- and multi-solute systems. The adsorption capacity and initial adsorption rate on the same peat in single-solute systems followed the order Ph > Cu > Cd. Both the adsorbed amount of each metal (q '(m)) and its initial adsorption rate were decreased in multi-solute systems. It was observed that the adsorbed amounts of metals at low-energy adsorption sites (q(m,l)) decreased pronouncedly compared to those at high-energy adsorption sites (q(m,2)), indicating that the competitive adsorption of Ph, Cu and Cd occurred mainly at the low-energy adsorption sites. XAS study revealed that both Ph and Cu were coordinated in peat predominantly to carboxylic moieties without excluding the hydroxyl groups, thereby providing an insight into the mechanism of competitive adsorption of Ph and Cu on peat. (c) 2006 Elsevier Ltd. All rights reserved.

Studies on arsenate (As(V)) sorption and desorption have been mainly limited to soil minerals and sorption and desorption reactions in whole soils are poorly understood. In this study the sorption of As(V) by and phosphate-induced desorption from a Chinese red soil were studied in the presence of oxalate and humic acid (HA). Arsenate was strongly sorbed mainly through ligand exchange reactions on the soil. Arsenate sorption decreased in the presence of oxalate or HA. Oxalate and HA influenced As(V) sorption mainly by competing for sorption sites and reducing sorption sites, and oxalate could also decrease sorption through dissolving clay minerals. Oxalate and HA could also facilitate As(V) desorption from the soil. Both sorption and desorption kinetics were two stage processes. Sorption kinetics conducted from 0.2–840 h showed that As(V) sorption increased with increasing residence time. Sorption equilibrium was retarded and the maximum sorption decreased in the presence of oxalate or HA. Phosphate-induced desorption kinetics conducted on the soil with 24 h and 840 h of sorption equilibrium time showed a significant effect of equilibrium time on As(V) desorption. The presence of oxalate or HA during the sorption process resulted in more As(V) desorption. Due to the degradation of oxalate, soil treated with oxalate and with a sorption equilibrium time of 840 h showed no significant difference in desorption kinetics from untreated soil.

The effect of earthworm (Eisenia fetida) activity on soil pH, dissolved organic carbon (DOC), fraction distribution pattern and bioavailability of rare earth elements (REEs) Y, La, Ce, Pr and Nd in nine Chinese soils were investigated using pot experiments. A three-step extraction procedure recommended by the European Community (Standards, Measurements and Testing Programme) was used to fractionate REEs in soils into water soluble, exchangeable and carbonate bound (B1), Fe- and Mn-oxides bound (B2) and organic matter and sulfide bound (B3). Inoculated with earthworms, the soil pH, DOC and water-soluble rare earth elements fraction increased. A significant correlation was obtained between the increased DOC and the increased water-soluble REEs. REEs in fraction B1 increased after earthworm inoculation, while those in fraction B3 decreased. No significant differences were observed for REEs in fraction B2. The biomass and the concentrations of REEs in wheat shoots and roots increased after the treatment with earthworms. The results demonstrated that earthworm activity increased the mobility and bioavailability of REEs in soils.

Interactions between anions and cations are important to understand the chemical processes of pollutants in environment. In this study, batch experiments were carried out to investigate the simultaneous adsorption of Cu and Cd on hematite as affected by phosphate. Phosphate pretreatment suppressed the maximum adsorption of Cu and Cd on hematite and moved the adsorption pH edges to a higher pH range. Phosphate application time had a marked impact on Cu and Cd adsorption and longer contact time resulted in more reduction of Cu and Cd adsorption. Results of back-titration, Fourier transform infrared (FTIR) spectroscopy study and ionic strength effect on the adsorption revealed that Cu and Cd were adsorbed on hematite mainly through the inner-sphere complex formation mechanism and phosphate treatment reduced the inner-sphere adsorption sites, thus decreasing Cu and Cd adsorption on hematite.

An attempt has been made to elucidate the effects of soil properties on arsenate adsorption by modeling the relationships between adsorption capacity and the properties of 16 Chinese soils. The model produced was validated against three Australian and three American soils. The results showed that nearly 93.8% of the variability in arsenate adsorption on the low-energy surface could be described by citrate-dithionite extractable Fe (Fe(CD)), clay content, organic matter content (OM) and dissolved organic carbon (DOC); nearly 87.6% of the variability in arsenate adsorption on the high-energy surface could be described by Fe(CD), DOC and total arsenic in soils. Fe(CD) exhibited the most important positive influence on arsenate adsorption. Oxalate extractable Al (Al(OX)), citrate-dithionite extractable Al (Al(CD)), extractable P and soil pH appeared relatively unimportant for adsorption of arsenate by soils.

Laboratory batch experiments were carried out to study the adsorption of arsenate on 16 Chinese soils with different physicochemical properties. Wide differences in arsenate adsorption were observed, and the Jiangxi and Hubei soils were more effective sorbents for arsenate than other soils. The Langmuir one-surface and two-surface equations were used to model the arsenate adsorption data. Except for the Jiangxi and Hubei soils, the Langmuir one-surface equation gave reasonably good fits to the arsenate adsorption data. However, the Langmuir two-surface equation generally provided a better fit than the Langmuir one-surface equation. For soils with relative high organic matter (OM), dissolved organic carbon (DOC) or extractable phosphate, the Langmuir one-surface and two-surface equations described the adsorption isotherms similarly. In contrast, for soils with relatively low contents of OM, DOC or extractable phosphate, the Langmuir two-surface equation gave the better fit to the arsenate adsorption data.

Low-molecular-weight-organic-anions (LMWOAs) are important exudates of plants and may influence the mobility and bioavailability of metals or metalloids. In the present study the effects of selected LMWOAs, citrate, malate and oxalate, on the release of arsenite (As(III)) and arsenate (As(V)) in a contaminated soil were investigated. The organic anions have significant influence upon the release of arsenic from the soil, and a linear relationship exits between the released arsenic and the concentration of LMWOAs in the extractants. pH effects on the arsenite and arsenate adsorption were not significant over the range from 3 to 7. The amounts of arsenite and arsenate released were significantly correlated with the release of Fe, Mn and Al, suggesting that arsenic was mainly released from Fe-, Mn- and Al-oxides or hydroxides in soil. The ratio of released arsenite to arsenate was not influenced by LMWOAs.

Bioavailability of phthalate congeners, dimethyl phthalate, diethyl phthalate, di-n-butyl phthalate (DBP), di-(2-ethylhexyl) phthalate (DEHP), and dioctyl phthalate, to earthworms (Eisenia fetida) were studied when earthworms were exposed to two artificially contaminated agricultural and forest soils. Only DBP and DEHP were detected in earthworms. The uptake kinetics of DBP and DEHP in earthworms was fast within the initial 10 days followed by a nearly steady state for the subsequent 20 days. An equilibrium partitioning model could be used to describe the uptake kinetics of DBP and DEHP by earthworm in two types of soils (r = 0.709-0.864). The average biota-to-soil accumulation factors (BSAFs) of DBP and DEHP at 5 mg kg(-1) in soil were 0.27 +/- 0.07 and 0.17 +/- 0.03, respectively, in agricultural soil, while the BSAFs were 0.21 +/- 0.06 and 0.07 +/- 0.02, respectively, in forest soil. The concentrations of phthalates in earthworms increased with increasing concentrations of phthalates in soil. There was a significant correlation between logC(soil) and logC(worm), with r = 0.999-0.993, demonstrating a single linear partitioning of phthalates between soil and earthworms. The bioavailability of DBP and DEHP was assessed by Soxhlet, methanol, and methanol-water (1:1) extraction methods. Our results indicated that the extractable amounts of freshly added DBP and DEHP in soils by these extraction methods were significantly correlated with those in earthworms. It was observed that the extractable DBP and DEHP by the methanol and methanol-water (1:1) extraction methods decreased with their increasing residence time in soil. In contrast, the amount extracted by the Soxhlet extraction method did not show a similar decline. Therefore, Soxhlet extraction was a poor indicator of the bioavailability of DBP and DEHP to earthworms in soil, which could lead to overestimation of the risk of soil-associated DBP and DEHP. The extractable DBP and DEHP by methanol and methanol-water (1:1) significantly decreased over 440 days. Compared with the methanol-water (1:1) extraction method, the methanol extraction method was preferred for its ability to predict the bioavailability of DBP and DEHP in aged soils.

A rapid separation and preconcentration method was developed for the determination of trace metals Cu, Zn, Cd, and Pb in seawater using a minicolumn packed with thiol cotton fiber (TCF) coupled with inductively coupled plasma mass spectrometry (ICP-MS). Preconcentration parameters, such as seawater sample volume and flow rate and eluent hydrochloric acid concentration, volume and flow rate, were optimized. Under the optimized conditions, trace metals Cu, Zn, Cd, and Pb in seawater can be determined with no interference from saline matrices. When a sample volume of 1500 ml and a sample flow rate of 15 ml min(-1) were used, the preconcentration factor of 1500 and RSD value of

There is no method recognized as a universal approach for evaluation of bioavailability of heavy metals in soil. Based on the simulation of the rhizosphere soil conditions and integration of the combined effects of root-soil interactions as a whole, a rhizosphere-based method has been proposed. Wet fresh rhizosphere soil was extracted by low-molecular-weight organic acids (LMWOAs) to fractionate metal fractions of soil pools, which were then correlated with the metal contents of wheat roots and shoots. The rhizosphere-based method was compared with other one-step extraction methods using DTPA, EDTA, CaCl2, and NaNO3 as extractants and the first step of the Community Bureau of Reference (BCR) method. Simple correlation and stepwise multiple regression analysis were used for the comparison. Simple correlation indicated that the extractable Cu, Zn, Cr, and Cd of soils by the rhizosphere-based method were significantly correlated with the metal contents of wheat roots. For DTPA, BCR1 and EDTA methods there was a relatively poor correlation between the extractable Cu, Zn and Cd of soil and metal contents of wheat roots. Stepwise multiple regression analysis revealed that the equation of the rhizosphere-based method was the simplest one, and no soil properties variables needed to be added. In contrast, the equations of other one-step extraction methods were more complicated, and soil properties variables needed to be entered. The most distinct feature of the rhizosphere-based method was that the recommended method was suitable for acidic, neutral and near alkaline soils. However, the DTPA and EDTA extraction methods were suitable for calcareous soils only-or-only for acidic soils. The CaCl2, and NaNO3 extraction methods were only Suitable for exchangeable metals. In short, the rhizosphere-based method was the most robust approach for evaluation of bioavailability of heavy metals in soils to wheat. (c) 2004 Elsevier Ltd. All rights reserved.

Humic acids and clays are important soil components that influence the sorption and desorption of organic contaminants; however, it is unclear how humic acids influence the sorption of organic contaminants onto clays and their subsequent desorption. Sorption and desorption of 2,4,6-trichlorophenol (2,4,6-TCP) by and from humic acid-modified K(+)- and Ca(2+)-montmorillonite and -illite were compared with unmodified clays using batch equilibration methods. Commercial humic acid and the humic acid extracted from forest soil were employed in this experiment. The adsorbed amount of 2,4,6-TCP by commercial humic acid was almost twice as large as that adsorbed by the extracted soil humic acid. More 2,4,6-TCP was sorbed onto K(+)- and Ca(2+)-illite than onto K(+)- and Ca(2+)-montmorillonite. K(+) clays were more effective in adsorbing 2,4,6-TCP than Ca(2+) clays. Sorption of 2,4,6-TCP on humic acid-modified Ca(2+)- and K(+)-montmorillonite and -illite increased as compared with unmodified clays. The sorption nonlinearity of 2,4,6-TCP on humic acid-modified Ca(2+)- and K(+)-illite increased remarkably as compared with the unmodified clays. The sorption nonlinearity of 2,4,6-TCP on humic acid-modified Ca(2+)- and K(+)-montmorillonite increased slightly in contrast to unmodified montmorillonites. By comparing sorption and desorption results, we observed hysteresis for all sorbents including humic acids, clays, and humic acid-modified clays. Sorption nonlinearity and hysteresis were dependent on the structure of humic acids. Higher aromaticity of humic acids resulted in greater sorption nonlinearity and desorption hysteresis. In addition, sorption capacity (K(f)') was positively correlated with the humic acid content of the sorbents. These results show that modification of humic acids on clays can not only increase the adsorption ability of clays but also affect the sorption nonlinearity of 2,4,6-TCP, and the desorption hysteresis was probably due to the structural characteristics of humic acids.

Time effect on the fractionation of Cu, Zn, Pb, and Cd in three typical Chinese soils was investigated. A total of 500 mg kg−1 of Cu, Zn, Pb and 2.5 mg kg−1 of Cd were added to soils as nitrates. Metals in the incubated soils were fractionated termly from 3 h to 8 weeks by the sequential extraction procedure, in which the metal fractions were experimentally defined as exchangeable, carbonate-, Fe–Mn oxide-, organic matter-bound and residual fractions. Results showed that the changes of Cu, Pb and Zn in fraction distribution were biphasic by an initial rapid step followed by a slow one. Metals in exchangeable fraction were increased in the first 3 h, and then decreased, such decreases could be simulated by a diffusion equation and the decrease rate followed the order Pb>Cu>Zn≫Cd. Metals bound to Fe–Mn oxides and organic matter increased consistently in the 8-week incubation. There were almost no changes for the metals in the residual fraction. After 3-h incubation most of Cd added to soils presented in the exchangeable fraction. The content of Cd in each fraction changed slightly in the 8-week incubation. Soil pH played an important role in metal fraction distribution patterns. Jiangxi soil, with low soil pH, tended to keep more metals added in exchangeable fraction and the changes of metals in each fraction were not as remarkable as in other two soils. High organic matter content resulted in the increased organic matter-bound fraction.

Summary • Organic acids play an important role in metal uptake by, and accumulation in, plants. However, the relevant mechanisms remain obscure. • Acetic, malic and citric acids increased the uptake of lanthanum (La) by barley (Hordeum vulgare) roots and enhanced La content in shoots under hydroponic conditions. • Concentration-dependent net La influx in the absence and presence of organic acids yielded nonsaturating kinetic curves that could be resolved into linear and saturable components. The saturable component followed Michaelis–Menten kinetics. The Km values were similar; however, the Vmax values in the presence of acetic, malic and citric acids were 4.3, 2.8, 1.5-times that of the control, respectively. • Enhanced uptake of La by organic acids was mediated mainly, but not solely, by Ca2+ channels. X-ray absorption spectroscopic techniques provided evidence of La–oxygen environment and established that La(III) was coordinated to 11 oxygen atoms that are likely to be involved in the binding of La(III) to barley roots via carboxylate groups and hydration of La(III).

Mercury contamination of ocean ecosystems is one of many problems in the global environment. In this paper, mercury speciation for surface seawaters sampled from nine coastal sites of China was performed. Speciation analysis of total particulate mercury (HgT)P, total dissolved mercury (HgT)D, monomethylmercury (MMHg)D, dimethylmercury (DMHg)D, mercuric ion (Hg2+)D and mercuric chlorocomplexes ( )D was carried out by cold vapor atomic fluorescence spectrometry (CVAFS) after separation and preconcentration with thiol cotton fiber (TCF) and anion-exchange resin columns. The concentration of (HgT)D ranged from 25.3 to 41.1 ng/L. The concentration of dissolved inorganic mercury was in the range of 12.8–24.7 ng/L, which averaged 55.9% of the total dissolved mercury. Dissolved mercuric chlorocomplexes ( )D appeared to be the principal speciation, averaging 45.7% of total dissolved mercury. The concentration of (MMHg)D was higher in coastal seawaters collected in Beidaihe (2.55 ng/L) and Huludao (2.36 ng/L). In o...

Currently, several single extraction methods are used for the evaluation of the phytoavailability of metals using pot experiments. A systematic comparison, however, is lacking. It is especially true for the field studies. This study was to investigate the phytoavailability of trace elements to vegetables grown on metal-contaminated soils under the field conditions. All soils collected were typical calcareous soils in northern China. Four frequently used methods using CaCl2, diethylenetriaminepentaacetic acid (DTPA), CH3COOH, and water as extractants were compared for phyto-availability. The concentrations of metals extracted by these four extraction methods ranged from 3.42 to 815, 1.51- 6965, 0.732-24473, 0.688-7863, 0.246-685, 1.99-5337 0.203-4649 ng/g for Cr, Ni, Zn, Cu, Cd, Pb and REEs, respectively. Simple correlation analysis indicated that a significant correlation (Cr: r = 0.5411**; Zn: r = 0.6352**; Cd: r = 0.6979**; Pb: r = 0.5537** and REEs: r = 0.5185** -0.6684**) was observed between the CaCl2-extractable metals in soil solution and that in Chinese cabbage. In addition, soil pH, organic matter (OM), and cation exchange capacity (CEC) also affect the phytoavailability. An empirical model was developed to express the combined effect of soil properties on the phytoavailability. The stepwise multiple regression analysis demonstrated that the phytoavailability of trace elements strongly correlated with the extractable fraction by CaCl2, total metal concentration in soils, and soil pH, OM, CEC. This model can describe approximately 75-95% of the variability of metal uptake and the r2 values ranged from 0.741** to 0.954**, which were much better than the single correlation analysis. For celery and cole, a strong correlation was obtained for Cr, Ni, Zn, Cu, Cd, La, Ce, Pr and Nd. For spinach and Chinese cabbage, however, a positive correlation was only observed for 1 and 3 metals, respectively. Generally, the developed empirical model can integrate the combined effects of soil properties, extractable metal fractions in soil solutions and plant species on the phytoavailability of metals to vegetables in the field conditions.

Two extraction procedures, i.e. a single extraction procedure using low-molecular-weight-organic-acids (LMWOAs) as extractant and a sequential extraction procedure recommended by the European Community Bureau of Reference (BCR), were performed to extract metal fractions from wet rhizosphere soil. And the extracted soil solutions were further fractionated as colloidal and truly dissolved fractions. Heavy metals in maize roots were experimentally defined as metals adsorbed on cell wall and metals taken up by cross-membrane by washing with CaCl2. The correlation coefficients between extractable metals from soil and taken up by maize roots and shoots were compared between two extraction methods, and a good correlation was obtained if LMWOAs were used. In contrast, the correlation coefficients were poor when the BCR method was used. (C) 2003 Elsevier Ltd. All rights reserved.

The distribution of heavy metals Cr, Ni, Zn, Cu, Cd, and Pb among the truly dissolved (molecular weight cutoff 0.45 µm) fractions was investigated in the soil solution and surface water. In 15 soil solutions heavy metals were mainly present in the truly dissolved fraction (

Effects of exogenous rare earth elements (REEs) in fertilizer on fraction of heavy metals chromium (Cr), nickel (Ni), zinc (Zn), copper (Cu), lead (Pb), and cadmium (Cd) in 15 Chinese soils and their bioaccumulation by wheat root and shoot were investigated in a greenhouse experiment. Using a three-stage fraction analysis method suggested by the Standard and Testing Program of the European Community (STM), metal fractions were defined as fraction B1 (water soluble, exchangeable, carbonate bound form), B2 (Fe–Mn oxide bound form) and B3 (organic and sulfide bound form). The results revealed that concentrations of elements Cu, Zn, and Pb in fraction B1 increased for all 15 soils in the presence of REEs fertilizer, Cr increased in B1 for 11 soils. Chromium, Cu, Ni, and Zn also universally increased in fraction B3, but no significant changes were found in fraction B2. One-way ANOVA analysis also suggested that the response of heavy metal fractions to REEs fertilizer was significant (P≤0.05) in the order of B3...

Capillary zone electrophoresis was developed to analyze low-molecular-mass organic acids including oxalic, tartaric, formic, malic, citric, succinic, glutaric, acetic and lactic acid. The influences of some crucial parameters such as buffer concentration, pH value, surfactant concentration and separation temperature, on electrophoretic separation were investigated. Under the conditions of 15 mM phthalate containing 0.6 mM tetradecyltrimethylammonium bromide as the run buffer (pH 5.6); separation voltage -15 W (-263.2 V/cm) and temperature 25 degreesC, a satisfactory separation of nine organic acids was accomplished within 7 min. The detection limits (S/N=3) ranged from 0.008 to 0.08 mug/ml and the quantification limits ranged from 0.01 to 0.1 mug/ml for electrokinetic injection. The method was successfully applied to analyze organic acids in different parts of Var splendens (an edible vegetable in China). The recoveries of organic acids in real samples ranged from 88 to 121%. (C) 2003 Elsevier Science B.V. All rights reserved.

Study on desorption kinetics of Y, La, and Ce from soils is of importance because it relates to the bioavailability, and potential toxicity of rare-earth elements. In the present study, a column-flow method and three models (first-order, two site first-order, and log-normal distribution first-order kinetics models) were used to describe the desorption kinetics of Y, La, and Ce from four Chinese soils with different physicochemical properties. A high desorption percentage of Y (87.1-96.6%), La (89.9-98.5%), and Ce (57.6-96.4%) from Yingtan soil was attributed to the low soil pH 5.43 and low organic matter of 1.53%. In contrast, a low percentage of Y (27.5-45.7%), La (27.6-53.6%), and Cc (1.09-50.8%) sorbed by Beijing, Tongjiang, and Haerbin soils desorbed probably because of the higher soil pH values of 8.24, 7.16, 7.23, and increased organic matter (36.4%) in Haerbin soil. The results also suggest that the first-order kinetics model did not offer an acceptable description of the data (R-2 0.99). The parameters derived from the kinetic equations indicated that increasing the initial sorption period from 1 to 20 wk could lead to a strong binding of rare-earth elements, resulting in slower desorption.

Surface sediments in Guanting reservoir of Beijing were studied to evaluate the heavy metal pollution. The concentrations of heavy metals lie in the sequence: Zn>Pb>Cr>Cu>Ni>Co>Mo>Cd. Significant relationship (p

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.

A rapid and simple method has been developed for the separation of chromium (III) and Cr(VI) species in river and reservoir water. Chromium (III) can be chelated with 8-hydroxyquinoline immobilized polyacrylonitrile (PAN) fiber, whereas Cr(VI) cannot. Chelated Cr(III) can be eluted with 2 mol l(-1) HCl-0.1 mol l(-1) HNO(3). Cr(VI) in the filtrate and Cr(III) in the eluant were determined by inductively coupled plasma mass spectrometry. The effect of pH, sample flow rate, eluant type and its volume on the concentration effectiveness of Cr(III) was investigated. The recommended method has been applied for the separation and determination of Cr(III) and Cr(VI) in river and reservoir water. The results indicated that the recovery of each individual Cr species ranged from 96 to 107% and the R.S.D. were found to be10% at the level of ng ml(-1). The effect of HNO(3) added in the sampling procedure was also evaluated.

The bioavailability of perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA) in seven biosolids-amended soils without any additionally spiking to earthworms (Eisenia fetida) was studied. The uptake and elimination kinetics of PFOS and PFOA fit a one-compartment first-order kinetic model. PFOS displayed higher uptake and lower elimination rate coefficients, and longer time to reach steady-state (t(ss)) than those of PFOA. The bioaccumulation factors (BAFs) of PFOS and PFOA ranged 1.54–4.12 and 0.52–1.34 g(soil) g(worm)(−1), respectively. The BAFs and tss decreased with increasing concentrations of PFOS and PFOA in soils. Stepwise multiple regression analysis was used to elucidate the bioavailability of PFOS and PFOA. The results showed that the total concentrations of PFOS and PFOA, and organic matter (OM) contents in soils explained 87.2% and 91.3% of the variation in bioavailable PFOS and PFOA, respectively. PFOS and PFOA concentrations exhibited positive influence and OM contents showed the negative influence on the accumulation of PFOS and PFOA in earthworms. Soil pH and clay contents played relatively unimportant role in PFOS and PFOA bioavailability.

The suitability of different extractants for estimating the plant availability of rare earth elements (REEs) in soils was assessed in a greenhouse study. 0.43 M CH3COOH, 0.01 M CaCl2, 0.1 M HCl, and DTPA were used as extractants and winter wheat (Triticum aestivum L.) as a test crop. Soil samples with diverse chemical and physical properties were collected from 9 different rural regions of China. REEs extracted by different extractants from soils were compared with REEs contents in winter wheat grown on the soils with a statistical analysis. The result of correlation analysis showed that 0.1 M HCl gave the best estimate of plant available REEs in soils, which suggested that 0.1 M HCl could provide valuable information on plant uptake of REEs in soils studied.

A comparison was made between the speciation and bioavailability of rare earth elements in rhizosphere and nonrhizosphere soils and between wet and air-dried soils under greenhouse conditions by using a homemade rhizobox. The speciation of rare earth elements in soils is experimentally defined as water soluble, exchangeable and carbonate bound (B1), Fe–Mn oxide bound (B2) and organic matter and sulfide bound (B3). The air-drying process of the wet soils resulted in an increase in rare earth elements in fractions B1 and B2, and a decrease in B3. Generally, a better correlation was obtained between the speciation and bioavailability by using wet soils than that by using air-dried soils, and as the conditions in the former are close to the realistic conditions of plant growth in the environment better plant availability is also achieved between the speciation of rare earth elements in the rhizosphere soils than that in the nonrhizosphere soils. Application of the rhizosphere wet soils is be strongly recommended in the future study on the speciation analysis and bioavailability of trace elements in soils.

This field study describes the distribution and bioaccumulation of rare earth elements (REEs) in wheat, rice and vegetables grown in Jiangxi, Anhui, Beijing and Heilongjiang provinces, located in southern and northern China after application of REE fertilizer at different levels. The results indicate that accumulation of REEs in different parts of plants follows the order: root>leaf>stem>grain. The concentrations of REEs in root, leaf and stem increase remarkably when the REE fertilizers were applied. However, no significant accumulation was observed in cereal grains except for those grown at the Jiangxi site. A significant accumulation of REEs in the edible parts of vegetables was observed, therefore, fertilizers containing REEs are not recommended. The exogenous REEs in the fertilized soil were extracted by a three-stage sequential extraction procedure into three fractions: (1) water soluble, exchangeable and carbonate bound (B1), (2) Fe-Mn oxide bound (B2) and (3) organic matter and sulfide bound (B3). The results demonstrated that all of the exogenous REEs were present in the fractions B1, B2 and B3 with ranges of 1.49-13.91%, 35,23-70.34% and 19.14-60.78% of total, respectively. No exogenous REEs entered the residual form within the field study period. However, the chemical forms of exogenous REEs in the fertilized soil and their bioavailability are dependent on the physicochemical properties of soil and plant species. It seems that REEs present in fraction B1 are more easily available to plants.