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A method based on ion chromatography (IC) and inductively coupled plasma MS (ICP‐MS) was developed for the speciation of arsenic in water and soil extracts. An anion‐exchange column (G3154A/101) was used to separate As(III), As(V), dimethylarsinic acid (DMA), and monomethylarsonic acid (MMA) with excellent resolution. Various ammonium salts, including NH4H2PO4, (NH4)2HPO4, (NH4)2CO3, and NH4HCO3, were examined as eluents to reduce matrix interference from chloride and to solve clogging problems. The best arsenic speciation was obtained within 9 min with excellent resolution and without interference from high chloride concentrations using an eluent containing 7.5 mM (NH4)2HPO4at pH 7.9. The detection limits for the target arsenic species ranged from 0.1 to 0.4 μg/L with direct injection of sample without matrix elimination. The proposed method was effectively demonstrated by determining arsenic species in contaminated waters and soils of Bangladesh.

Abstract. An on-column complexation method has been developed for the simultaneous determination of V(IV) and V(V). Vanadium species were chelated with aminopolycarboxylic acids to form anionic complexes which were separated by capillary zone electrophoresis (CZE) with direct UV detection. Ethylenediaminetetraacetic acid (EDTA), diethylenetriaminepentacetric acid (DTPA), nitrilotriacetic acid (NTA), and N-2-hydroxyethylethlendiaminetriacetric acid (HEDTA) were investigated as both ligand and running electrolyte. Of the ligands studied the complexes of EDTA with V(IV) and V(V) resulted in the highest selectivity and UV response. The conditions used for on-column complexation and separation, including pH, and electrolyte ligand concentration, were examined to achieve reasonable separation selectivity and detection sensitivity. The optimum separation of the anionic forms of V(IV) and V(V) was obtained by use of CZE with UV detection at 185 nm and an electrolyte containing 5 mmol L^-1 EDTA at pH 4.0. Linear calibration plots were obtained in the concentration range10-300 µmol L^-1; detection limits were 3 µmol L^-1 for V(IV) and 1 µmol L^-1 for V(V). The proposed method was demonstrated for the determination of vanadium in groundwater spiked with V(IV) and V(V).

When studying metal sorption by soils, the potential influence of environmental and solution parameters on the experimental systems cannot be ignored. Characteristics of the soil mineral surfaces are the final determinative factors in whether a metal ion will be sorbed, but soil‐solution composition affects both mineral surface properties and whether the metal ions will be in forms that can react with the surfaces. Examples of factors affecting sorption of metals by soil surfaces include ionic strength, cations, anions, and/or organic ligands present in solution, solution pH, and solution metal concentration. In addition, sorption will be affected by external factors such as pressure, temperature, soil/solution ratio, and the manner in which soils to be studied are sampled and stored before investigation. To date, there has been little attempt to standardize experimental protocol, so results obtained using varied systems in different laboratories cannot be readily compared. An initial suggestion that all sorption studies include at least one treatment meeting minimal standards of ionic strength (0.01), background electrolyte (NaNO3), pH (between 5.5 and 6.0), and temperature (25 ± 3°C) is presented as a first step toward enabling improved ability to make interlaboratory comparisons.

Organophosphorus, pyrethroid and chloronicotinyl insecticides have been used to control termites in building structures in recent years. We investigated the degradation behaviour of three insecticides (bifenthrin, chlorpyrifos and imidacloprid) at termiticidal application rates under standard laboratory conditions (25 °C, 60% field moisture capacity and darkness) for 24 months. The study was carried out on one soil and two bedding materials (sand-dolomite and quarry sand), which are commonly used under housing in Australia. Experiments were also conducted to examine the effect of soil moisture on the degradation of these insecticides. Insecticide residues in the samples collected at different days after application were measured by high performance liquid chromatography (HPLC). The rate of degradation of bifenthrin and imidacloprid insecticides was adequately described by a first-order kinetic model (r² = 0.93–0.97). However, chlorpyrifos degradation was biphasic, showing an initial faster degradation followed by a slower rate. Therefore, the degradation data during the slower phase only (after a two-month period) followed the first-order law (r² = 0.95). Soil moisture had little effect on degradation of imidacloprid and bifenthrin. Among the three insecticides, bifenthrin and imidacloprid were most stable and chlorpyrifos the least. Chlorpyrifos showed a major loss (75–90%) of residue during the 24 months incubation period. In the bedding materials, simultaneous accumulation of the primary metabolite of chlorpyrifos, TCP (3,5,6-trichloro-2-pyridinol) was observed. Hydrolysis appeared to have caused the observed rapid loss of chlorpyrifos, especially in the highly alkaline bedding materials (sand-dolomite and quarry sand). © 1999 Society of Chemical Industry

Cladosporium sp. strain AJR318,501 was isolated from DDT-contaminated soil by its ability to decolourise the polymeric dye, Poly R-478. When inoculated into potato/dextrose broth containing 100 mg of DDT l−1, a 21% decrease in DDT concentration was observed 12 days after its addition, however, no transformation products were detected by gas chromatography. TLC of culture medium and mycelia extracts revealed 1,1-dichloro-2,2-bis(p-chlorophenyl)ethane and five unknown transformation products associated with the mycelia.

The effect of dilution on the composition of soil solutions of 8 contrasting soils ranging in pH from 5·3 to 8·8 with reference to zinc (Zn) and copper (Cu) was studied. Soil samples were equilibrated with water in various water:soil ratios for 24 h. Equilibrium solutions were extracted and analysed for dissolved organic carbon (DOC), and major and minor elements. The separation of the soil solution at field capacity (FC) was carried out by a drainage method. Although the concentration of ions decreased upon dilution, the total quantity of sodium (Na), potassium (K), Zn, Cu, and DOC extracted per unit of soil weight increased. In contrast, the total quantity of Ca and Mg decreased in most soils. The ratio of Zn and Cu to Ca correlated to dilution level, whereas the ratio of Zn to monovalent cations decreased in low pH soils. The relationship between the quantity of Zn and Cu at different levels of the water : soil ratio in the soils studied showed that the concentration of these trace metals at FC soil moisture can be estimated from the soil extract. Increases in soil moisture content led to a marked change in the ion-pair, free hydrated metal concentrations, and complexation. Log Zn2+ was linearly related to solution pH. Zinc solubility was not consistent with published solubilities of any common minerals. Also, Zn solubility in alkaline soils tended to be higher than reported values in the literature, indicating that soluble metal–organic ligand complexation was underestimated in these soils. The relationship between pH and log Zn2+ was affected by dilution in several ways. soil solution, soil extract, dissolved organic carbon, speciation, dilution, solubility diagram.

The bioavailability of trace metals, their accumulation by organisms, and their toxicity to terrestrial and aquatic organisms can be understood better in terms of trace metal species. Although there are numerous chemical techniques used for the determination of ionic species, most are tedious, time-consuming, and not practical for routine analyses. Alternatives to these chemical techniques are computer speciation models that often have an incomplete database on metal–organic chemistry, yet scientists continue to use these techniques for estimation of trace metal activities. In this study we compare the cation exchange resin (Amberlite) and the MINTEQA2 geochemical model for the speciation of zinc (Zn2+) and copper (Cu2+) in the aqueous phase of 11 soils varying widely in chemical composition. The pHw(1:5) of these soils ranged from 5·3 to 9·1, while the total soil aqueous phase concentrations of Zn and Cu were in the ranges 1–71 and 5–74 µg/L, respectively. Preliminary equilibration studies revealed that 24-h contact between resin and sample solution was sucient to exchange all free ions onto the resin bead. By using this equilibration time, the effects of temperature, solution composition, and pH on the resin distribution coeficients (Kd) for Zn and Cu were investigated. These studies revealed that temperature did not significantly influence the Zn and Cu resin distribution coecient. Solution composition such as the presence of Ca, Mg, and Al, however, had a marked effect on the Kd value. Although the Kd value was not sensitive to changes in solution pH (4·5–7·1), it increased at pH >7·1. These results suggest that soil solution composition must be considered during metal ion speciation using the resin beads. Changes in Zn and Cu concentrations, however, did not influence the Kd values of these metals. The cation exchange resin method was modified for speciation of solutions containing very low concentration (<50 µg/L) of Zn. Comparison of the 2 speciation techniques demonstrated excellent agreement for free hydrated Zn2+ and Cu2+ in the soils studied. zinc, copper, Amberlite.