Effect of complexation on the accumulation and elimination kinetics of cadmium and ciprofloxacin in the earthworm Eisenia fetida.

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.

Adsorption of 2,4,6-trichlorophenol by multi-walled carbon nanotubes as affected by Cu(II).

Adsorption equilibrium of 2,4,6-trichlorophenol (TCP) on multi-walled carbon nanotubes (MWCNTs) was investigated to explore the possibility of using MWCNTs for concentration, detection and removal of TCP from contaminated water. The adsorption of TCP on MWCNTs at pH 4 was nonlinear, reversible and best fit by a Polanyi-Manes model. Oxidation treatment increased surface area and introduced hydrophilic carboxylic groups to the defect sites of MWCNTs, hence increased the sorption of TCP and Cu(II) individually. Cu(II) suppressed the sorption of TCP on oxidized MWCNTs15A, but had little effect on as-grown MWCNTs15. TCP had no influence on Cu(II) sorption to either. The mechanisms of Cu(II) suppression effect on TCP adsorption are ascribed to the formation of surface complexes of Cu(II), which was verified by X-ray absorption spectroscopy. Cu(II) exerts a cross-linking effect of functional groups on adjacent tubes, creating a more tightly knit bundle and suppressing the condensation of TCP in the pore spaces between the tubes. The large hydration sphere around surface complexes of Cu(II) may also intrude or shield hydrophilic sites, leading to the "crowding out" of TCP around the Cu(II)-complexed sites.

Biomimetic accumulation of PAHs from soils by triolein-embedded cellulose acetate membranes (TECAMs) to estimate their bioavailability.

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 (R2=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.

Effect of microbial activity, soil water content and added copper on the temporal distribution patterns of HCB and DDT among different soil organic matter fractions.

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 311days. 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.

Adsorption of metal ions on lignin.

This study investigated the adsorption of the heavy metal ions Pb(II), Cu(II), Cd(II), Zn(II), and Ni(II) on a lignin isolated from black liquor, a waste product of the paper industry. Lignin has affinity with metal ions in the following order: Pb(II)>Cu(II)>Cd(II)>Zn(II)>Ni(II). The adsorption kinetic data can be described well with a pseudosecond-order model and the equilibrium data can be fitted well to the Langmuir isotherm. Metal ion adsorption was strongly dependent on pH and ionic strength. Surface complexation modelling was performed to elucidate the adsorption mechanism involved. This shows that lignin surfaces contain two main types of acid sites attributed to carboxylic- and phenolic-type surface groups and the phenolic sites have a higher affinity for metal ions than the carboxylic sites.

Adsorption of cadmium onto Al(13)-pillared acid-activated montmorillonite.

The optimal preparation conditions for Al(13)-pillared acid-activated Na(+)-montmorillonite (Al(13)-PAAMt) were (1) an acid-activated Na(+)-montmorillonite (Na(+)-Mt) solution of pH 3.0, (2) a OH(-)/Al(3+) molar ratio of 2.4 and (3) Al(3+)/Na(+)-Mt ratio of 1.0 mmol g(-1). The effects of OH(-)/Al(3+) and Al(3+)/Na(+)-Mt ratios on the adsorption of Cd(2+) onto Al(13)-PAAMt were studied. A comparison of the adsorption of Cd(2+) onto Al(13)-PAAMt, Al(13)-pillared Na(+)-montmorillonite (Al(13)-PMt) and Na(+)-Mt suggested that Al(13)-PAAMt had higher adsorption affinity for Cd(2+) than the other two adsorbents. A pseudo-second-order model described the adsorption kinetics well. Cadmium adsorption followed the Langmuir two-site equation, while desorption was hysteretic.

Effect of lead on the sorption of phenol onto montmorillonites and organo-montmorillonites.

The effect of lead (Pb) on the sorption of phenol onto montmorillonite-based sorbents was studied using a batch equilibration method when phenol and Pb were sorbed simultaneously and either Pb or phenol was previously sorbed. The sorbents were Na(+)-, Ca(2+)-, hexadecyl trimethylammonium (HDTMA)-Na(+)-, and HDTMA-Ca(2+)-montmorillonites. Pb diminished the sorption of phenol largely onto Na(+)- or Ca(2+)-montmorillonites, while phenol had little effect on the sorption of Pb onto all sorbents. Pb had no effect on the sorption of phenol onto HDTMA-Na(+)- or HDTMA-Ca(2+)-montmorillonites either. The sorption capacity of phenol followed the order HDTMA-Na(+)- > HDTMA-Ca(2+)- > Na(+)- > Ca(2+)-montmorillonites. The pseudo-second-order equation described the kinetics of phenol sorption well. Sorption isotherms of phenol followed the Freundlich equation. Phenol sorption on HDTMA-Na(+)- and HDTMA-Ca(2+)-montmorillonites was linear, while that on Na(+)- and Ca(2+)-montmorillonites was nonlinear.

Is an adjusted rhizosphere-based method valid for field assessment of metal phytoavailability? Application to non-contaminated soils.

Previously recommended rhizosphere-based method (RHIZO) applied to moist rhizosphere soils was integrated with moist bulk soils, and termed adjusted-RHIZO method (A-RHIZO). The A-RHIZO and RHIZO methods were systematically compared with EDTA, DTPA, CaCl2 and the first step of the Community Bureau of Reference (BCR1) methods for assessing metal phytoavailability under field conditions. Results suggested that moist bulk soils are equally suited or even better than rhizosphere soils to estimate metal phytoavailability. The A-RHIZO method was preferred to other methods for predicting the phytoavailability of Ni, Cu, Zn, Cd, Pb and Mn to wheat roots with correlation coefficients of 0.730 (P<0.001), 0.854 (P<0.001), 0.887 (P<0.001), 0.739 (P<0.001), 0.725 (P<0.001) and 0.469 (P<0.05), respectively. When including soil properties, other extraction methods were also able to predict phytoavailability reasonably well for some metals. Soil pH, organic matter and Fe-Mn oxide contents, and cation-exchange capacity mostly influenced the extraction and phytoavailability of metals.

Effect of arbuscular mycorrhizal fungus (Glomus caledonium) on the accumulation and metabolism of atrazine in maize (Zea mays L.) and atrazine dissipation in soil.

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.

Effect of lead on the sorption of 2,4,6-trichlorophenol on soil and peat.

The effect of lead on the sorption of 2,4,6-trichlorophenol (2,4,6-TCP) on soil and peat was investigated using a batch equilibration method. Lead markedly diminished the sorption of 2,4,6-TCP, and 2,4,6-TCP had little effect on lead sorption. Peat was a more effective adsorbent for 2,4,6-TCP than soil. The desorption hysteresis of 2,4,6-TCP verified the presence of high-energy sorption sites. Mechanisms of lead suppression effect on the 2,4,6-TCP sorption included the following: Firstly, lead accelerated the aggregation of colloids, the aggregates covered the surface in part and shrunk the pore sizes of the adsorbents, hence decreased the sorption of 2,4,6-TCP. Secondly, X-ray absorption and Fourier transform infrared spectroscopy study suggested that lead competed with 2,4,6-TCP for carboxylic, phenolic and Si-OH groups of organic matter and clay minerals. Such competition was partly responsible for the overall suppression effect of lead on the sorption of 2,4,6-TCP.

Temporal change in the distribution patterns of hexachlorobenzene and dichlorodiphenyltrichloroethane among various soil organic matter fractions.

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 (R2>0.97). The transfer rates of HCB and DDT followed the order FA>HA>BHA.

The ageing effect on the bioaccessibility and fractionation of arsenic in soils from China.

Ingestion of contaminated soil has been recognized as an important exposure pathway of arsenic for humans, especially for children through outdoor hand-to-mouth activities. An improved sequential extraction procedure was employed in an attempt to reveal the relationship between bioaccessibility and fractionation of As in five soils from China. Arsenic bioaccessibility in acidic ( approximately pH 4.5) soils reached approximately stable levels after a sharp decline within one week of ageing. In contrast, As bioaccessibility in higher pH (>6.0) soils was found to be significantly higher and took two weeks of ageing to reach stable levels. The artificially added As was more labile than indigenous As. The main proportions of added As were found in the specifically sorbed and amorphous and poorly-crystalline hydrous Fe/Al oxide-bound fractions. Correlation analysis shows that the non-specifically and specifically sorbed As are likely to constitute the main proportion of bioaccessible soil As. The soil content of amorphous and crystalline Fe/Al oxides and soil pH appear to be the key factors controlling, not only the time needed to reach a steady state, but also the magnitude of the bioaccessibility of As added to the soils.

Uptake of atrazine and cadmium from soil by maize (Zea mays L.) in association with the arbuscular mycorrhizal fungus Glomus etunicatum.

A greenhouse pot experiment was carried out to investigate the effect of the arbuscular mycorrhizal fungus Glomus etunicatum on the uptake of atrazine (ATR) and cadmium (Cd) from soil by maize (Zea mays L.). Mycorrhizal colonization led to an increase in the accumulation of Cd and ATR in maize roots but a decrease in the shoots. Atrazine alleviated the adverse effects of Cd on maize growth, and this was more pronounced in the inoculated plants. An increase in Cd accumulation by maize roots was observed when ATR was also present. After harvest, the residual ATR concentration in the soil decreased markedly. With mycorrhizal inoculation the amount of residual ATR decreased more in the bulk soil but less in the rhizosphere soil compared to the noninoculated controls. Cadmium application significantly decreased the ATR residual concentrations in both the rhizosphere and bulk soils irrespective of inoculation treatment.

Effect of copper on the adsorption of p-nitrophenol onto soils.

The effect of copper on adsorption of p-nitrophenol on two typical Chinese soils was investigated using a batch-equilibration method. Adsorption experiments were carried out when both copper and p-nitrophenol were adsorbed simultaneously, and when copper was previously adsorbed on soils. It was observed that adsorption of p-nitrophenol decreased with increasing copper concentrations thereby indicating a competition between copper and p-nitrophenol for occupying the adsorption sites on soils. Moisture increased the hydrated sphere and the acidity of water surrounding the cation, which further reduced the adsorption of p-nitrophenol. Fourier transform infrared spectroscopy study provided the direct evidence for the coordination of p-nitrophenol sorbed by soils with metal cation in n-hexane system. It was observed that the perturbations included a red shift of the nu(asym) (NO) band, a concomitant blue-shift of the nu(sym) (NO) band and a blue-shift of C-N band when compared with the infrared spectra obtained from water solution.

Mechanisms of competitive adsorption of Pb, Cu, and Cd on peat.

Combined use of batch equilibration adsorption and X-ray absorption spectroscopy (XAS) was employed to study the mechanisms of competitive adsorption of Pb, 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 Pb>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 (qm,1) decreased pronouncedly compared to those at high-energy adsorption sites (qm,2), indicating that the competitive adsorption of Pb, Cu and Cd occurred mainly at the low-energy adsorption sites. XAS study revealed that both Pb 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 Pb and Cu on peat.

Effect of phosphate on the adsorption of Cu and Cd on natural hematite.

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.

Oxalate and root exudates enhance the desorption of p,p'-DDT from soils.

The abiotic desorption of p,p'-DDT from seven Chinese soils spiked with p,p'-DDT and the effects of oxalate at 0.001-0.1M and the root exudates of maize, wheat, and ryegrass were evaluated using batch experiments. Soil organic carbon played a predominant role in the retention of DDT. Oxalate significantly increased the desorption of p,p'-DDT, with the largest increments ranging from 11% to 54% for different soils. Oxalate addition also resulted in the increased release of dissolved organic carbon and inorganic ions from soils. Root exudates had similar effects to those of oxalate. Root exudates significantly increased DDT desorption from the soils, and the general trend was similar among the plant species studied for all the soils (p > 0.05). Low molecular weight dissolved organic carbon amendments caused partial dissolution of the soil structure, such as the organo-mineral linkages, resulting in the release of organic carbon and metal ions and thus the subsequent enhanced desorption of DDT from the soils. The enhancing effects of oxalate and root exudates on DDT desorption were influenced by the contents of soil organic carbon and dissolved organic carbon in soils.

Effect of earthworms (Eisenia fetida) on the fractionation and bioavailability of rare earth elements in nine Chinese soils.

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.

Effects of oxalate and phosphate on the release of arsenic from contaminated soils and arsenic accumulation in wheat.

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.

Arsenate sorption on two Chinese red soils evaluated with macroscopic measurements and extended X-ray absorption fine-structure spectroscopy.

Arsenic sorption is the primary factor that affects the bioavailability and mobility of arsenic in soils. To elucidate the characteristics and mechanisms of arsenate, As(V), sorption on soils, a combination of sorption isotherms, zeta potential measurements, and extended X-ray absorption fine-structure (EXAFS) spectroscopy was used to investigate As(V) sorption on two Chinese red soils. Arsenate sorption increased with increasing As(V) concentration and was insensitive to ionic strength changes at pH 6.0. Arsenate, mainly as H2AsO4- in soil solution at pH 6.0, was strongly sorbed mainly through ligand exchange by the two soils. The sorption capacity was affected by the iron and aluminum mineral contents in the soils. The zeta potential measurements showed that As(V) sorption lowered the zeta potential and the points of zero charge of the soils. The EXAFS data indicate that adsorbed As(V) forms inner-sphere complexes with bidentate-binuclear configurations, as evidenced by an As-Fe bond distance of 3.28 +/- 0.04 A and an As-Al bond distance of 3.17 +/- 0.03 A. The two As(V) complexes were stable at different As(V) loadings, whereas the proportions were related to the aluminum and iron mineral contents in the soils. This study illuminated the importance of inclusion of microscopic and macroscopic experiments to elucidate sorption behavior and mechanisms.