Solid- and solution-phase organics dictate copper distribution and speciation in multicomponent systems containing ferrihydrite, organic matter, and montmorillonite

Copper retention by ferrihydrite, leaf compost, and montmorillonite was studied over 8 months in systems that emulate a natural soil where different solid phases compete for Cu through a common solution in a compartmentalized batch reactor. Copper speciation in solution (total dissolved, DPASV-labile, and free) and exchangeable and total Cu in individual solid phases were determined. Organic carbon in solution (DOC) and that retained by the mineral phases were also determined. Cu sorption reached steady-state after 4 months and accounted for 80% of the Cu initially added to the system (0.15 mg L(-1)). The remaining 20% stayed in solution as nonlabile (82.8%), labile (17%), and free (0.2%) Cu species. Copper sorption followed the order organic matter > silicate clays > iron oxides. Within each solid phase, exchangeable Cu was < or = 10% of the total Cu sorbed. DOC reached steady state (22 mg L(-1)) after 4 months and seemed to control Cu solubility and sorption behavior by the formation of soluble Cu-DOC complexes and by sorbing onto the mineral phases. DOC sorption onto ferrihydrite prevented Cu retention by this solid phase. Using a multicomponent system and 8 months equilibrations, we were able to capture some of the more important aspects of the complexity of soil environments bytaking into account diffusion processes and competition among solid- and solution-phase soil constituents in the retention of a metal cation.     

Bioaccessibility of arsenic(V) bound to ferrihydrite using a simulated gastrointestinal system

The risk posed from incidental ingestion to humans of arsenic-contaminated soil may depend on sorption of arsenate (As(V)) to oxide surfaces in soil. Arsenate sorbed to ferrihydrite, a model soil mineral, was used to simulate possible effects on ingestion of soil contaminated with As-(V) sorbed to Fe oxide surfaces. Arsenate sorbed to ferrihydrite was placed in a simulated gastrointestinal tract (in vitro) to ascertain the bioaccessibility of As(V) and changes in As(V) surface speciation caused by the gastrointestinal system. The speciation of As was determined using extended X-ray absorption fine structure (EXAFS) analysis and X-ray absorption near-edge spectroscopy (XANES). The As(V) adsorption maximum was found to be 93 mmol kg(-1). The bioaccessible As(V) ranged from 0 to 5%, and surface speciation was determined to be binuclear bidentate with no changes in speciation observed post in vitro. Arsenate concentration in the intestine was not constant and varied from 0.001 to 0.53 mM for the 177 mmol kg(-1) As(V) treated sample. These results suggest that the bioaccessibility of As(V) is related to the As(V) concentration, the As(V) adsorption maximum, and that multiple measurements of dissolved As(V) in the intestinal phase may be needed to calculate the bioaccessibility of As(V) adsorbed to ferrihydrite.     

Multiscale assessment of methylarsenic reactivity in soil. 1. Sorption and desorption on soils

Methylated forms of arsenic (As), monomethylarsenate (MMA), and dimethylarsenate (DMA) have historically been used as herbicides and pesticides. Because of their large application to agriculture fields and the toxicity of MMA and DMA, the persistency of these compounds in the environment is of great concern. MMA and DMA sorption and desorption were investigated in soils, varying in mineralogical and organic matter (OM) contents. Sorption studies showed that the MMA sorption capacity and rate were greater than DMA sorption. Al/Fe-oxyhydroxides were the main sorbents in the soils, and the sorption capacity was proportional to the Al/Fe concentration in the soils. Extended X-ray absorption fine structure (EXAFS) studies showed that both MMA/DMA-Fe interatomic distances were around 3.3 ?, which were indicative of bidentate binuclear inner-sphere complex formation. Desorption studies showed that not all of the sorbed MMA or DMA was desorbed due to the strong binding between MMA/DMA and Al/Fe-oxyhydroxide surfaces via possible inner-sphere complex formation. The amount of the desorbed MMA and DMA decreased as the sorption residence time increased. For example, 77% of sorbed MMA was desorbed from the Reybold subsoil after 1 day residence time, while 66% of sorbed MMA was desorbed from the soil after six months of residence time. The decreases in desorption were likely due to As speciation changes from MMA/DMA to inorganic arsenate, which was more strongly bound to the surface.     

Arsenic speciation and phytoavailability in contaminated soils using a sequential extraction procedure and XANES spectroscopy

In this study, a sequential extraction procedure (SEP) and X-ray absorption near edge structure (XANES) spectroscopy were used to determine the solid-phase speciation and phytoavailability of arsenic (As) of historically contaminated soils from As containing pesticides and herbicides and soils spiked with As in the laboratory. Brassica juncea was grown in the contaminated soils to measure plant available As in a glasshouse experiment. Arsenic associated with amorphous Fe oxides was found to be the dominant phase using both SEP and XANES spectroscopy. Arsenic predominantly existed in arsenate (As(V)) form in the soils; in a few samples As was also present in arsenite (As(III)) form or in scorodite mineral. Arsenic concentration in shoots showed significant (p < 0.001-0.05) correlations with the exchangeable As (r = 0.85), and amorphous Fe oxides associated As evaluated by the SEP (r = 0.67), and As associated with amorphous Fe oxides as determined by XANES spectroscopy (r = 0.51). The results show that As in both fractions was readily available for plant uptake and may pose a potential risk to the environment. The combination of SEP and XANES spectroscopy allowed us the quantitative speciation of As in the contaminated soils and the identification of valence and mineral forms of As. Such detailed knowledge on As speciation and availability is vital for management and rehabilitation of As-contaminated soils.     

Thermally induced changes in metal solubility of contaminated soils is linked to mineral recrystallization and organic matter transformations

Soils are biogeochemical systems under continual modification by biological and chemical processes. Trace element solid-solution partitioning is thus influenced by long-term changes to these solid phases. We study Pb, Cd, Zn, and Cu solution speciation and solid-phase dynamics in two soils of volcanic origin (Te Akatea and Egmont, high in noncrystalline aluminosilicates), an oxisol from Brazil (Oxisol, high in oxides of Al and Fe), and several sludge-treated soils (labeled NYS soils, high in organic materials). Total soluble (by ICP) and labile (by ASV) concentrations of Pb, Cd, Zn, and Cu were determined after incubation of the soils for about 1.5 yr at room (23 degrees C) and elevated (70 degrees C) temperatures. Changes occurring to the solid phases were monitored by FTIR and extraction with oxalate and pyrophosphate. It is shown that induced hydrolysis or decomposition of organic materials in soils results in increases in both labile and total soluble concentrations of Pb, Cd, Cu, and Zn in solution. Labile and total soluble concentrations of Cu and Zn increase concomitantly with dissolved organic carbon (DOC); the nonlabile soluble fraction also increases with increasing DOC. Similarly, the concentration of Cd and Pb in solution increases with increasing DOC; however, most soluble Cd and Pb is asv-labile. Only in the Egmont soil (mineralogy dominated by proto-imogolite allophane) was reduced Pb solubility observed after prolonged equilibration and heating. Lead solubility increased after partial crystallization of amorphous minerals in the Te Akatea and the Oxisol. Thus, for most of the metal-soil systems studied, prolonged thermal treatment at 70 degrees C increased total soluble and asv-labile metals, suggesting that aging effects on metals in contaminated soils could release metals to labile forms in some cases.     

Linking solid phase speciation of Pb sequestered to birnessite to oral Pb bioaccessibility: implications for soil remediation

Lead (Pb) sorption onto oxide surfaces in soils may strongly influence the risk posed from incidental ingestion of lead-contaminated soils. In this study, Pb was sorbed to a model soil mineral, birnessite, and was placed in a simulated gastrointestinal tract (in vitro) to simulate the possible effects of ingestion of a soil contaminated with Pb. The changes in Pb speciation were determined using extended X-ray absorption fine structure and X-ray absorption near edge spectroscopy. Birnessite has a very high affinity for Pb with a sorption maximum of 0.59 mol Pb kg(-1) (approximately 12% Pb sorbed by mass) in which there was no detectable bioaccessible Pb (< 0.002%). Surface speciation of the birnessite Pb was determined to be a triple corner sharing complex in the birnessite interlayer. Lead sorbed to Mn oxide in contaminated media will have a very low (approximately equal to 0) Pb bioaccessibility and present little risk associated with incidental ingestion of soil. These results suggest that birnessite, and other Mn oxides would be powerful remediation tools for Pb-contaminated media because of their high affinity for Pb.     

Implications of mercury speciation in thiosulfate treated plants

Mercury uptake was induced in two cultivars of Brassica juncea under field conditions using thiosulfate. Analysis was conducted to better understand the mechanism of uptake, speciation of mercury in plants, and redistribution of mercury in the soil. Plant mercury and sulfur concentrations were increased after thiosulfate treatment, and a linear correlation between mercury and sulfur was observed. Mercury may be absorbed and transported in plants as the Hg-thiosulfate complex. The majority of mercury in treated plant tissues (two cultivars) was bound to sulfur in a form similar to β-HgS (66-94%). Remaining mercury was present in forms similar to Hg-cysteine (1-10%) and Hg-dicysteine (8-28%). The formation of β-HgS may relate to the transport and assimilation of sulfate in plant tissues. Mercury-thiosulfate complex could decompose to mercuric and sulfate ions in the presence of free protons inside the plasma membrane, while sulfide ions would be produced by the assimilation of sulfate. The concomitant presence of mercuric ions and S(2-) would precipitate β-HgS. The mercury concentration in the rhizosphere decreased in the treated relative to the nontreated soil. The iron/manganese oxide and organic-bound fractions of soil mercury were transformed to more bioavailable forms (soluble and exchangeable and specifically sorbed) and taken up by plants.     

2,4-D sorption in iron oxide-rich soils: role of soil phosphate and exchangeable Al

This study examined herbicide retention in iron oxide-rich variable charge soils (Ultisols) under no cultivation (forest), agriculture (farm), and turf maintenance (golf course) to explore the following hypothesis: inorganic phosphate accumulation from soil fertilization and liming to decrease exchangeable aluminum (Al) content will influence carboxylic acid herbicide sorption onto soils and leaching into groundwater. A suite of soil properties, including mineralogy (particularly soil iron and aluminum oxide content), exchangeable Al content, and soil phosphate content, influenced sorption of the anionic, 2,4-D. In general, 2,4-D sorption was lower in the presence of phosphate, possibly due to competition between phosphate and 2,4-D for surface sites or increase in surface negative charge resulting from phosphate sorption. Additionally, 2,4-D sorption was greater in the presence of exchangeable Al. It appears that 2,4-D may form surface complexes with or be electrostatically attracted to exchangeable aluminum in the soil. Our results suggest that carboxylic acid herbicides may be more easily leached in intensively managed Ultisols subject to continued phosphate fertilization and liming.     

Multiscale assessment of methylarsenic reactivity in soil. 2. Distribution and speciation in soil

Methylated forms of arsenic (As), monomethylarsenate (MMA) and dimethylarsenate (DMA), have historically been used as herbicides and pesticides. Because of their large application to agriculture fields and the toxicity of MMA and DMA, the distribution, speciation, and sorption of methylated As to soils requires investigation. Monomethylarsenate and DMA were reacted with a soil up to one year under aerobic and anaerobic conditions. Microsynchrotron based X-ray fluorescence (μ-SXRF) mapping studies showed that MMA and DMA were heterogeneously distributed in the soil and were mainly associated with iron oxyhydroxides, e.g., goethite, in the soil. Micro-X-ray absorption near edge structure (XANES) spectra collected from As hotspots showed MMA and DMA were demethylated to arsenate over one year incubation under aerobic conditions. Monomethylarsenate was methylated to DMA, and DMA was maintained as DMA over a 3 month incubation under anaerobic conditions. Arsenic-iron precipitation, such as the formation of scorodite (FeAsO(4)·2H(2)O), was not observed, indicating that MMA and DMA were mainly associated with Fe-oxyhydroxides as sorption complexes.     

Effect of soil fulvic acid on nickel(II) sorption and bonding at the aqueous-boehmite (gamma-AIOOH) interface

The influence of soil-derived fulvic acid (SFA) on Ni(II) sorption and speciation in aqueous boehmite (gamma-AIOOH) suspensions was evaluated using a combination of sorption experiments and Ni K-edge extended X-ray absorption fine structure (EXAFS) spectroscopy measurements. Co-sorption of SFA at the aqueous-boehmite interface modifies both the extent of Ni(II) sorption as well as the local structure of the sorbing Ni(II) ions. In SFA-free suspensions, Ni(II) sorbs by forming inner-sphere bidentate mononuclear complexes with surface aluminol groups. Addition of SFA increases Ni(II) sorption at pH conditions below the sorption edge observed in SFA-free suspensions and diminishes Ni(II) sorption at pH above the SFA-free sorption edge. When SFA is co-sorbed to boehmite, Ni(II) sorbs by forming both ligand-bridging ternary surface complexes (Ni(II)-SFA-boehmite) as well as surface complexes in which Ni(II) remains directly bonded to aluminol groups, that is, binary Ni(II)-boehmite or metal-bridging ternary surface complexes (SFA-Ni(II)-boehmite). The relative contribution of the individual sorption complexes depends heavily on geochemical conditions; the concentration of ligand-bridging complexes increases with increasing SFA sorption and decreasing pH. The local structure of sorbed Ni(II) does not change with increasing reaction time even though the extent of sorption continues to increase. This supports a slow uptake mechanism where surface or intraparticle diffusion processes are rate-limiting. This work demonstrates that the association of humic constituents with soil minerals can significantly modify the mechanisms controlling trace metal sorption and transport in heterogeneous aquatic environments.     

Cadmium reactivity in metal-contaminated soils using a coupled stable isotope dilution-sequential extraction procedure

To better understand the intrinsic reactivity of Cd, four soils having diverse sources of Cd contamination (total Cd: 22-34 mg kg(-1)) were investigated using a stable isotope dilution-sequential extraction procedure (SID-SEP) during a 59-week incubation. Samples were spiked with carrier-free 111Cd and periodically extracted into five operationally defined fractions; the 111Cd:10Cd ratios were measured by inductively coupled plasma-mass spectrometry. The total labile pool of Cd (E value) was calculated as well as the labile Cd within each extracted fraction. Results for three of the soils (Cd sources: natural, sewage sludge, smelter emissions) were quite similar. The overall %E after 2-week equilibration was 35-49% of total soil Cd. Within fraction 2 (sorbed/carbonate), 70-75% of the Cd was isotopically labile, while within fraction 3 (oxidizable) only 35-41% of the Cd was labile within 2 weeks. The fourth (reducible) and fifth (residual) fractions were dominated by nonlabile Cd. Although all E values increased somewhat from 2 to 59 weeks, none of the extracted fractions reached isotopic equilibrium with the soluble/exchangeable Cd extracted during step 1. Because fractions 2 and 3 dominated the native Cd in all three soils, the total labile pool was contributed primarily (85-98%) by these two fractions. A fourth soil (mine spoil-contaminated) was demonstrably different: after 2 weeks, the overall %E was just 13 and, although 82% of the total Cd was present in the oxidizable fraction, just 2% of that was isotopically labile. The nonlability of Cd in this soil could be ascribed to the predominance of inorganic forms, most likely occluded Cd in sphalerite. No single Cd fraction from the SEP nor any combination of fractions showed a good correspondence with the size of the isotopically labile pool. Our results suggest that conventional SEPs may be of limited utility for predicting bioavailability, for example, during ecological risk assessment.     

Enhanced sorption of trichloroethene by smectite clay exchanged with Cs+

Trichloroethene (TCE) is one of the most common pollutants in groundwater, and Cs+ can be a cocontaminant at nuclear facilities. Smectite clays have large surface areas, are common in soils, have high affinities for some organic contaminants, and hence can potentially influence the transport of organic pollutants entering soils and sediments. The exchangeable cations present near smectite clay surfaces can radically influence the sorption of organic pollutants by soil clays. This research was undertaken to determine the effect of Cs+, and other common interlayer cations, such as K+ and Ca2+, on the sorption of TCE by a reference smectite clay saponite. Cs-saturated clay sorbed the most TCE, up to 3500 mg/kg, while Ca-saturated smectite sorbed the least. We hypothesize that the stronger sorption of TCE by the Cs-smectite can be attributed to the lower hydration energy and hence smaller hydrated radius of Cs+, which expands the lateral clay surface domains available for sorption. Also, Cs-smectite interlayers are only one or two water layers thick, which may drive capillary condensation of TCE. Our results implicate enhanced retention of TCE in aquifer materials containing smectites accompanied by Cs+ cocontamination.     

四种食用菌中重金属和砷的总量测定及形态分析

以黑木耳、香菇、金针菇和灰树花四种食用菌作为研究对象,采用电感耦合等离子体发射光谱（ICP-OES）测定As、Pb、Cd、Cr、Cu五种元素的总量;采用Tessier连续浸提法制备样品,对以上五种元素进行形态分析。结果表明:四种食用菌中重金属和砷总量符合大部分相关国家限量标准。重金属和砷的形态分析表明,四种食用菌中As均以离子交换态为主;Pb在四种食用菌中存在形态差异很大;除金针菇外其他三种食用菌中Cd均以水溶态和离子交换态为主;Cr在各食用菌中存在形态差异很大;除黑木耳外其他三种食用菌中Cu均以水溶态为主。本文表明连续浸提法可用于食用菌重金属和砷的形态分析,反映食用菌中重金属及砷的形态分布信息。      

Assessing the labile arsenic pool in contaminated paddy soils by isotopic dilution techniques and simple extractions

Arsenic (As) contamination of paddy soils threatens rice cultivation and the health of populations relying on rice as a staple crop. In the present study, isotopic dilution techniques were used to determine the chemically labile (E value) and phytoavailable (L value) pools of As in a range of paddy soils from Bangladesh, India, and China and two arable soils from the UK varying in the degree and sources of As contamination. The E value accounted for 6.2-21.4% of the total As, suggesting that a large proportion of soil As is chemically nonlabile. L values measured with rice grown under anaerobic conditions were generally larger than those under aerobic conditions, indicating increased potentially phytoavailable pool of As in flooded soils. In an incubation study, As was mobilized into soil pore water mainly as arsenite under flooded conditions, with Bangladeshi soils contaminated by irrigation of groundwater showing a greater potential of As mobilization than other soils. Arsenic mobilization was best predicted by phosphate-extractable As in the soils.     

Time-dependent sorption-desorption behavior of 2,4-dichlorophenol and its polymerization products in surface soils

Contact time-dependent sorption-desorption of 2,4-dichlorophenol (DCP) and DCP polymerization products (DPP) was investigated in the context of agricultural and woodland soils. DPP was generated in soil slurry reactors by the addition of H2O2 to solutions containing horseradish peroxidase (HRP) and DCP. Size-exclusion chromatography confirmed the formation of oligomeric products including dimers, trimers, and tetramers. DCP removal from HRP-amended, soil-free solutions occurred as a result of DPP formation and sorption of DCP to the oligomeric precipitate. In reactors containing soil particles, additional removal occurred due to sorption of residual DCP and DPP to the soil. Sorption of DCP and DPP to the surface soils was rapid and appeared to be complete within 1 day. DPP sorbed to a greater extent than DCP, especially at higher solute concentrations. Water-extraction data indicated that while sorbed DCP was readily released into solution, sorbed DPP was more resistant to desorption. Both DCP and DPP were more readily extracted from the woodland soil than the agricultural soil. Solute extractability decreased with contact time, indicating that sorbent-solute interactions proceeded long after apparent sorption equilibrium at the particle or aggregate scale. Results from this study show that "slow" sorption processes occurring at the molecular scale continue long after apparent sorption equilibrium at the particle scale. This "aging effect" was operational over longer periods for DPP than the parent DCP, thereby ensuring long-term reductions in contaminant mobility in soils treated with peroxidase enzyme.     

Iron(III) modification of Bacillus subtilis membranes provides record sorption capacity for arsenic and endows unusual selectivity for As(V)

Bacillus subtilis is a spore forming bacterium that takes up both inorganic As(III) and As(V). Incubating the bacteria with Fe(III) causes iron uptake (up to ～0.5% w/w), and some of the iron attaches to the cell membrane as hydrous ferric oxide (HFO) with additional HFO as a separate phase. Remarkably, 30% of the Bacillus subtilis cells remain viable after treatment by 8 mM Fe(III). At pH 3, upon metalation, As(III) binding capacity becomes ～0, while that for As(V) increases more than three times, offering an unusual high selectivity for As(V) against As(III). At pH 10 both arsenic forms are sorbed, the As(V) sorption capacity of the ferrated Bacillus subtilis is at least of 11 times higher than that of the native bacteria. At pH 8 (close to pH of most natural water), the arsenic binding capacity per mole iron for the ferrated bacteria is greater than those reported for any iron containing sorbent. A sensitive arsenic speciation approach is thus developed based on the binding of inorganic arsenic species by the ferrated bacteria and its unusual high selectivity toward As(V) at low pH.     

Antimony (Sb) and arsenic (As) in Sb mining impacted paddy soil from Xikuangshan, China: differences in mechanisms controlling soil sequestration and uptake in rice

Foods produced on soils impacted by antimony (Sb) mining activities are a potential health risk due to plant uptake of the contaminant metalloids (Sb) and arsenic (As). Here we report for the first time the chemical speciation of Sb in soil and porewater of flooded paddy soil, impacted by active Sb mining, and its effect on uptake and speciation in rice plants (Oryza sativa L. cv Jiahua). Results are compared with behavior and uptake of As. Pot experiments were conducted under controlled conditions in a climate chamber over a period of 50 days. In pots without rice plants, flooding increased both the concentration of dissolved Sb (up to ca. 2000 μg L(-1)) and As (up to ca. 1500 μg L(-1)). When rice was present, Fe plaque developing on rice roots acted as a scavenger for both As and Sb, whereby the concentration of As, but not Sb, in porewater decreased substantially. Dissolved Sb in porewater, which occurred mainly as Sb(V), correlated with Ca, indicating a solubility governed by Ca antimonate. No significant differences in bioaccumulation factor and translocation factor between Sb and As were observed. Greater relative concentration of Sb(V) was found in rice shoots compared to rice root and porewater, indicating either a preferred uptake of Sb(V) or possibly an oxidation of Sb(III) to Sb(V) in shoots. Adding soil amendments (olivine, hematite) to the paddy soil had no effect on Sb and As concentrations in porewater.     

Nonsingular adsorption/desorption of chlorpyrifos in soils and sediments: experimental results and modeling

At environmentally relevant concentrations in soils and sediments, chlorpyrifos, a hydrophobic organic insecticide, showed strong adsorption that correlated significantly with organic matter content. Chlorpyrifos desorption followed a nonsingular falling desorption isotherm that was estimated using a memory-dependent mathematical model. Desorption of chlorpyrifos was biphasic in nature, with a labile and nonlabile component. The labile component comprised 18-28% of the original solid-phase concentration, and the residue was predicted to slowly partition to the aqueous phase, implying long-term desorption from contaminated soils or sediments. The newly proposed mechanism to explain sorption/desorption hysteresis and biphasic desorption is the unfavorable thermodynamic energy landscape arising from limitation of diffusivity of water molecules through the strongly hydrophobic domain of soils and sediments. Modeling results suggest that contaminated soils and sediments could be secondary long-term sources of pollution. Long-term desorption may explain the detection of chlorpyrifos and other hydrophobic organic compounds in aquatic systems far from application sites, an observation that contradicts conventional transport predictions.     

Kinetics of Ni sorption in soils: roles of soil organic matter and Ni precipitation

The kinetics of Ni sorption to two Delaware agricultural soils were studied to quantitatively assess the relative importance of Ni adsorption on soil organic matter (SOM) and the formation of Ni layered double hydroxide (Ni-LDH) precipitates using both experimental studies and kinetic modeling. Batch sorption kinetic experiments were conducted with both soils at pH 6.0, 7.0, and 7.5 from 24 h up to 1 month. Time-resolved Ni speciation in soils was determined by X-ray absorption spectroscopy (XAS) during the kinetic experiments. A kinetics model was developed to describe Ni kinetic reactions under various reaction conditions and time scales, which integrated Ni adsorption on SOM with Ni-LDH precipitation in soils. The soil Ni speciation (adsorbed phases and Ni-LDH) calculated using the kinetics model was consistent with that obtained through XAS analysis during the sorption processes. Under our experimental conditions, both modeling and XAS results demonstrated that Ni adsorption on SOM was dominant in the short term and the formation of Ni-LDH precipitates accounted for the long-term Ni sequestration in soils, and, more interestingly, that the adsorbed Ni may slowly transfer to Ni-LDH phases with longer reaction times.     

Solid-solution speciation and phytoavailability of copper and zinc in soils

The soil solution speciation and solid-phase fractionation of copper (Cu) and zinc (Zn) in 11 typical uncontaminated soils of South Australia were assessed in relation to heavy metal phytoavailability. The soils were analyzed for pH (4.9-8.4), soil organic matter content (3.5 to 23.8 g of C kg(-1)), total soil solution metal concentrations, Cu8 (49-358 microg kg(-1)) and Zn8 (121-582 microg kg(-1)), and dissolved organic matter (DOM) (69-827 mg of C L(-1)). The solid-liquid partition coefficient (Kd) ranged from between 13.9 and 152.4 L kg(-1) for Cu and 22.6 to 266.3 L kg(-1) for Zn. The phytoavailability of Cu and Zn could be predicted significantly using an empirical model with the solid-phase fractions of Cu and Zn, as obtained from selective sequential extraction scheme, as components. Phytoavailable Cu and Zn were found to significantly correlate with fulvic complex Cu (r= 0.944, P < 0.0001) and exchangeable Zn (r = 0.832, P = 0.002), respectively. The fulvic complex Cu was found to explain 89.2% of the variation in phytoavailable Cu, where as, the exchangeable Zn together with fulvic complex Zn could explain 78.9% of the variation in phytoavailable Zn. The data presented demonstrate the role of solid-phase metal fractions in understanding the heavy metal phytoavailability. The assessment of the role of solid-phase fractions in heavy metal phytoavailability is a neglected area of study and deserves close attention.