Simultaneous mobilization of macro- and trace elements (MTEs) and polycyclic aromatic hydrocarbon (PAH) compounds from soil with a nonionic surfactant and [S,S]-ethylenediaminedisuccinic acid (EDDS) in admixture: PAH compounds.

A laboratory study was conducted to assess the feasibility of a washing process with nonionic surfactant in combination with EDDS for the simultaneous mobilization of MTEs and PAH compounds from a field-contaminated soil. Unit processes consisting of complexometric extraction and surfactant-assisted mobilization were combined with reagent regeneration and detoxification steps to generate innocuous products. Thirty minutes of ultrasonic mixing of the soil with a combination of 20 mL L(-1) surfactant suspension and a sparing quantity (2 mmol) of EDDS mobilized virtually all of the benzo[α] pyrene (B(a)P) and chrysene (Cry) and an appreciable portion of the burdens of Cd, Cr, Mn, Ni, Pb and Zn, lesser amounts of the As and Cu, but only small quantities of Al and Fe. Relative to individual reagents, combinations of surfactant (Brij98), with EDDS increased the recovery of B(a)P but seemingly did not influence Cry extraction efficiencies perceptibly. Nine sequential washes with the same initial dosage of mobilization aids decreased the quantities of both PAHs to levels in the soil that conformed to recommended maxima. What resulted was a soil that had been cleaned and a limited quantity of innocuous wash water.

Simultaneous mobilization of trace elements and polycyclic aromatic hydrocarbon (PAH) compounds from soil with a nonionic surfactant and [S,S]-EDDS in admixture: metals.

This study evaluated the efficacy of soil washing with a nonionic surfactant (Brij98) in combination with a complexing reagent (ethylenediaminedisuccinic acid, [S,S]-EDDS) for the simultaneous mobilization of macro- and trace elements (MTEs) and PAH compounds from a field-contaminated soil. Soil fractionation studies indicated that an appreciable fraction of the Al, Ca, Cu, Fe and Mn was associated with the residual fraction but that much of the other trace elements (As, Cd, Cr, Ni, Pb and Zn) might be susceptible to soil washing. Ultrasonically aided mixing of the field contaminated soil with Brij98 and a sparing quantity (2 mmol) of [S,S]-EDDS, simultaneously mobilized virtually all of the benzo[α]pyrene {B(a)P} and chrysene (CRY) and appreciable quantities of the trace elements (Cd, Cr, Mn, Ni, Pb, Zn) burdens. The recovery of both PAHs and trace elements were increased from the soil organic matter (SOM)-rich soil. This report concerns the fate of MTEs during soil washing. Multiple ultra-sonically aided washes (five or nine) with the same dosage of reagents mobilized virtually all of PAHs and decreased the levels of Cd, Cr, Ni, Pb and Zn to comply with recommended maxima. By contrast, the levels of As and Cu remained excessive after the treatments.

Scaling up a treatment to simultaneously remove persistent organic pollutants and heavy metals from contaminated soils.

Soil washing is a treatment process that can be used to remediate both organic and inorganic pollutants from contaminated soils, sludges, and sediments. A soil washing procedure was evaluated utilizing about 100g samples of soil that had been field-contaminated with arsenic, chromium, copper, pentachlorophenol (PCP), polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs). The highest level of mobilization/detoxification was achieved in three soil washes with a mixture of 0.1M [S,S]-ethyelnediaminedisuccinate ([S,S]-EDDS) and 2% Brij 98 at pH 9 with 20 min of ultrasonication treatment at room temperature. This combination mobilized 70% of arsenic, 75% of chromium, 80% of copper, 90% of PCP, and 79% of PCDDs and PCDFs, so that the decontaminated soil met the maximum acceptable concentrations of the generic C-level criteria regulated by the Ministère du Développement Durable, de l'Environnement et des Parcs for the Province of Québec, Canada. The organic pollutants were back-extracted from the aqueous suspension with hexane. Heavy metals were virtually completely precipitated from the aqueous washing suspension with Mg(0) particles at room temperature. The PCP was detoxified by catalytic hydrodechlorination with a stream of 5% (v/v) H(2)-supercritical CO(2) that transported the organosoluble fraction through a reaction chamber containing 2% Pd/γ-Al(2)O(3). In toto, this soil washing procedure demonstrates that persistent organic pollutants and selected heavy metals can be co-extracted efficiently from a field-contaminated soil with three successive washes with the same soil washing solution containing [S,S]-EDDS and a non-ionic surfactant (Brij 98) in admixture. An industrial-scale ex situ soil washing procedure with a combination of a non-ionic surfactant and a complexing reagent seems to be a plausible remediation technique for this former wooden utility pole storage facility.

Influence of various organic molecules on the reduction of hexavalent chromium mediated by zero-valent iron.

Hexavalent chromium is a priority pollutant in many countries. Reduction of Cr(VI) to Cr(III) is desirable as the latter specie is an essential nutrient for maintaining normal physiological function and also has a low mobility and bioavailability. A variety of naturally-occurring organic molecules (containing alpha-hydroxyl carbonyl, alpha-hydroxyl carboxylate, alpha-carbonyl carboxylate, phenolate, carboxylates and/or thiol groups, siderophore, ascorbic acid); chelating agents (ethylenediaminetetraacetic acid derivates, acetyacetone) and others were examined their reducing activity towards a surfactant preparation (Tween 20) containing Cr(VI) and Fe(0) under a variety of reaction conditions. An appreciable enhancement (up to 50-fold) of the pseudo-first-order rate constant was achieved at acidic and circum neutral pH values for those compounds capable of reducing Cr(VI) (alpha-hydroxyl carboxylate, ascorbic acid, cysteine). Comparable enhancements were obtained for certain chelating agents (ethylenediaminetetraacetic acid derivates and siderophores) which is attributed to the formation of complexes with reaction products, such as Cr(III) and Fe(III), which impede the precipitation of Cr(III) and Fe(III) hydroxides and Cr(x)Fe(1-)(x)(OH)(3) and thus reduce passivation of the Fe(0) surface. The results suggest that these molecules might be used in effective remediation mediated by Fe(0) of Cr(VI)-contaminated soils or groundwater in a wide range of pH, thus increasing reaction rates and long-term performance of permeable reductive barriers.

Reduction of hexavalent chromium mediated by micron- and nano-scale zero-valent metallic particles.

A variety of zero-valent metals (Al(0), Cu(0), Fe(0), Mg(0), Ni(0), Si(0) and Zn(0)), and Cu(0) and Fe(0) nano-sized particles were evaluated for reactivity towards the reduction of Cr(VI) in a surfactant preparation (Tween 20) under a selection of reaction conditions. At circum neutral pHs, a rapid inactivation of the surface was observed for almost all of the tested metals and complete reduction of Cr(VI) was achieved at acidic pH only by using Cu(0), Fe(0), Mg(0) or Zn(0). A considerable increase in reactivity (up to 100-fold) was observed for reductive remediation with nano-sized particles. The use of a solid support as a dispersant and stabilizer circumvented the tendency of freshly prepared nano-particles to either react with surrounding media or agglomerate, resulting in the formation of much larger flocs and appreciable loss in reactivity. The formation of clusters by polymeric structures provided an extra protection of the nano-particle surface with a striking improvement in their reactivity mainly at more alkaline conditions. Therefore the incorporation of an innocuous stabilizer can substantially enhance the stability of nano-particles for environmental transformations.

Reduction of hexavalent chromium mediated by micro- and nano-sized mixed metallic particles.

A variety of micron-scale mixed metallic particles (Pd/Fe, Ag/Fe, Cu/Fe, Zn/Fe, Co/Fe, Mg/Fe, Ni/Fe, Al/Fe, Si/Fe, Pd/Cu and Pd/Zn; and Pd/Cu/Fe, Pd/Zn/Fe and Zn/Cu/Fe) and selected nano-sized bimetallic analogs (Pd/Fe, Cu/Fe and Pd/Cu) were evaluated for reducting activity with Cr(VI) in a surfactant preparation (Tween 20) under a variety of reaction conditions. Relative to the reactivity of the zero-valent iron, the tested bimetallic mixtures (Pd/Fe>Pd/Zn>Ag/Fe>Ni/Fe>Zn/Fe>Pd/Cu>Cu/Fe) appreciably increased the pseudo-first-order rate constant. The Zn/Cu/Fe represented a cost-effective preparation providing comparable or improved kinetic parameters relative to the more expensive palladized bimetallic mixtures. The Pd/Fe, Cu/Fe and Pd/Cu nano-sized particles proved to be more reactive (up to 100-fold) for the reductive remediation of Cr(VI). The results were comparable when working with nano-sized Cu and Fe particles, suggesting that the cementation of a noble metal serves not only as a reaction catalyst but also provides protection to the metallic surface, impeding its rapid inactivation.

Catalytic hydrogenation of polyaromatic hydrocarbon (PAH) compounds in supercritical carbon dioxide over supported palladium.

A series of supported palladium catalysts were evaluated for their ability to mediate the complete hydrogenation of polycyclic aromatic hydrocarbon (PAH) compounds. Benzo[a]pyrene (B[a]P) or phenanthrene (Phe) in hexane was merged with a hydrogen-carbon dioxide [5% (w/w) H(2)/CO(2)] stream and transferred to a flow through mini-reactor (capacity ca. 1 g) that was maintained at 90 degrees C under a back-pressure of 20.68 MPa. Effluent from the reactor trapped in hexane was monitored/quantified by gas chromatography-mass spectrometry. Catalyst formulations supported on iron powder, high density polyethylene (HDPE) or gamma-alumina were prepared and compared in terms of hydrogenation activity as measured by the quantity of substrate per unit time that could be perhydrogenated to toxicologically innocuous products. Both of the Pd preparations supported on gamma-alumina were more efficient than a commercial Pd(0) (5% w/w) on gamma-Al(2)O(3) formulation or preparations supported on HDPE or the iron powder. Bimetallic mixtures with Pd increased the hydrogenation activity when co-deposited with Cu or Ni but not with Ag or Co. However, increases in hydrogenation activity by increasing the loading of Pd (or bimetallic mixture) on this surface were limited. Despite using supercritical carbon dioxide (scCO(2)) to swell the surfaces of the polymer, the deposition of nanoparticles within the polyethylene formulation was appreciably less active than either the oxidic or the Fe(0) formulations.

Continuous catalytic hydrogenation of polyaromatic hydrocarbon compounds in hydrogen-supercritical carbon dioxide.

A continuous hydrogenation device was evaluated for the detoxification of selected tri-, tetra-, or pentacyclic polyaromatic hydrocarbon (PAH) compounds {anthracene, phenanthrene, chrysene, and benzo[a]pyrene (B[a]P)} by hydrogenation. A substrate stream in hexane, 0.05-1.0% (w/v), was mixed with hydrogen-carbon dioxide (H2-CO2, 5-30% v/v) and delivered to a heated reactor column (25 cm x 1 cm) containing palladium supported on gamma alumina (Pd0/gamma-Al2O3) that was terminated with a capillary restrictor. The flow rate from the reactor, approximately 800 mL min(-1) decompressed gas, corresponded to 4 mL min(-1) fluid under the operating conditions of the trials. Reaction products were recovered by passing the reactor effluent through hexane. At 90 degrees C, the anthracene or phenanthrene substrate was hydrogenated only partially to octahydro and dodecahydro species and contained only a minor quantity of totally hydrogenated products. For substrates with increasing numbers of fused aromatic rings, the hydrogenation efficiency was decreased further. However, at an increasing temperature (90-150 degrees C) and increasing mobile phase flow rate (20.68 MPa corresponding to 2100 mL min(-1) decompressed gas), B[a]P and chrysene were hydrogenated, virtuallytotally, to their corresponding perhydro analogues (eicosahydrobenzo[a]pyrenes and octadecahydrochrysenes), respectively. That this approach might be useful for decontaminating soil extracts was supported by companion in vitro trials in which the substrate and products were assayed for mutagenic activity with five bacterial strains that are auxotrophic for histidine (Salmonella typhimurium TA98, TA100, TA1535, and TA1537) or tryptophan (Escherichia coliWP2 uvrA), using the bacterial reverse mutation assay (modified Ames test). Generally, substantial increases in revertant colony counts were not observed with any of the strains following exposure to the hydrogenation products in the absence or presence of the 10 or 30% S9 mix, which is consistent with the loss of mutagenic activity from these hydrogenation products.

Simultaneous mobilization of heavy metals and polychlorinated biphenyl (PCB) compounds from soil with cyclodextrin and EDTA in admixture.

This study evaluated the efficacy of a washing process with cyclodextrin in combination with ethylenediaminetetraacetate (EDTA) for the simultaneous mobilization of heavy metals and PCBs from a field contaminated soil. Ultrasonically aided mixing of the field contaminated soil with a combination of cyclodextrin solution (10%, w/v) and a sparing quantity (2 mmol) of EDTA, simultaneously mobilized appreciable quantities of PCBs and much of the analyte metal (Cd, Cr, Cu, Mn, Ni, Pb, Zn) burdens. Relative to the action of individual reagents, a combination of randomly methylated (RAMEB) or hydroxypropyl beta-cyclodextrin (HPCD) with EDTA did not alter the PCB extraction efficiency nor did the presence of cyclodextrin change the efficiency of mobilization of most heavy metals (Al, Cd, Cr, Fe, Mn, Ni, and Zn) but did increase the recovery of Cu and Pb modestly. Three sonication-washes with the same charge of reagents mobilized appreciable quantities of PCBs (40-76%) and quantitatively extracted the labile fraction of Cd, Cu, Mn, and Pb. RAMEB proved to be more efficient than HPCD for PCB extractions. Three successive extractions with a single charge of cyclodextrin mobilized almost as much PCB (RAMEB, 76%; HPCD, 40%) as did the companion extractions that used fresh reagents each time (RAMEB, 78%; HPCD, 42%). Collectively, these studies demonstrated that PCB compounds and selected heavy metals can be co-extracted efficiently from soil with three successive washes with the same washing suspension containing EDTA and cyclodextrin.

A washing procedure to mobilize mixed contaminants from soil: II. Heavy metals.

We conducted a laboratory study to assess the efficiency of nonionic and anionic surfactants in combination with a sparing quantity of ethylenediaminetetraacetate (EDTA) to simultaneously extract heavy metals (HMs) and polychlorinated biphenyl (PCB) compounds from a field-contaminated soil. A soil wash that mobilized both HMs and PCBs was combined with back-extraction with hexane to remove PCBs from the aqueous wash. The aqueous washing suspension was then regenerated by precipitation of the HMs induced by corrosion and hydrolysis of zero-valent Mg to provide a cleaned soil and innocuous extract. Finally, the washing suspension was recycled twice to mobilize more contaminants from the soil particulate fraction. After ultrasonic equilibration, EDTA in admixture with a nonionic surfactant did not appreciably change the efficiency of mobilization of most heavy metals (Al, Cd, Cr, Fe Mn, Ni, and Zn), but did increase the recovery of Cu and Pb. The release of EDTA from HM complexes was efficient for most metals (99%) but was influenced by the chemical characteristics of the surfactant. The EDTA recovery (62-65%) after three cycles of soil washing, hexane back-extraction, and Mg(0) treatment was similar for all reagent combinations. In toto, these studies demonstrate that after treatment with ultrasound, selected heavy metals can be coextracted efficiently from soil with a single washing suspension containing EDTA and a nonionic surfactant.

A washing procedure to mobilize mixed contaminants from soil: I. Polychlorinated biphenyl compounds.

We conducted a laboratory study to assess the feasibility of a washing process with nonionic and anionic surfactants in combination with ethylenediaminetetraacetate (EDTA) for the simultaneous mobilization of heavy metals and polychlorinated biphenyls (PCBs) from a field-contaminated soil. Unit processes consisting of complexometric extraction and surfactant-assisted mobilization were combined with reagent regeneration and detoxification steps to generate innocuous products. Ten minutes of ultrasonic mixing of the soil with a combination of 30 mL L(-1) surfactant suspension and a sparing quantity (2 mmol) of EDTA mobilized appreciable quantities of PCBs, virtually all of the available Cd, Cu, Mn, and Pb, and lesser amounts of the Zn, Ni, and Cr but only small quantities of Al and Fe. Relative to individual reagents, combinations of surfactant (Brij 98, Triton X-301, or Triton XQS-20) with EDTA did not influence PCB extraction efficiencies perceptibly. Of the three surfactants, the Brij 98 proved to be the most efficient for three successive extractions with a single charge, mobilizing 83% of the PCBs, whereas companion extractions that used fresh reagent each time mobilized 87% of the soil PCB content. The decreased PCB mobilization with the same quantity of anionic surfactant (71 or 68%) resulted from losses during the EDTA regeneration process with zero-valent Mg. In toto, these studies demonstrate that PCB compounds and selected heavy metals can be coextracted efficiently from soil with three successive washes with the same washing suspension containing EDTA and a nonionic surfactant.

Catalytic hydrogenation of polycyclic aromatic hydrocarbons over palladium/gamma-Al2O3 under mild conditions.

As a prelude to the optimization of a continuous decontamination system, catalytic hydrogenations of selected tri-, tetra- and penta-cyclic aromatic hydrocarbon compounds over commercial alumina supported palladium were investigated under mild conditions ( approximately 90 degrees C/0.42 MPa H2) and interpreted in the light of reports from the literature. Acenaphthylene, acenaphthene, anthracene, phenanthrene, chrysene and benzo[alpha]pyrene were hydrogenated, virtually completely, to saturated polycyclic hydrocarbon compounds with no appreciable evidence of carbon-carbon bond rearrangement during equilibration. With comparable operating conditions, triphenylene was only partially hydrogenated; the central ring remained unsaturated. The effects of reaction temperature, time of equilibration and supporting gases on hydrogenation were evaluated. Whereas near-critical CO2 had no perceptible influence on rate/course of the reaction, nitrogen decreased the reaction rate somewhat.

Effect of surfactant alkyl chain length on soil cadmium desorption using surfactant/ligand systems.

The effect of surfactant alkyl chain length on soil Cd desorption was studied using nonionic surfactants of polyethylene oxide (PEO) of PEO chain lengths of 7.5 (Triton X-114), 9.5 (Triton X-100), 30 (Triton X-305), or 40 units (Triton X-405) in combination with the I- ligand. Triplicate 1 g soil samples were equilibrated with 15 ml of surfactant-ligand mixture, at concentrations of 0.025, 0.50 or 0.10, and 0.0, 0.168 or 0.336 mol/l, respectively. After shaking the samples for 24 h, the supernatant fraction was analyzed for Cd content to determine the percent of Cd desorbed from the soil. After five successive washings, 53%, 40% and 25% of Cd had been desorbed by 0.025, 0.050 or 0.10 mol/l of Triton X-114, respectively, in the presence of 0.336 mol/l of I-, whereas with the same conditions, Triton X-100 desorbed 61%, 57% and 56% Cd and either Triton X-305 or Triton X-405 desorbed 51, 40 and 14 to 16% Cd. The most efficient Cd desorption was obtained using 0.025 mol/l Triton X-100 in admixture with 0.336 mol/l I-. Increased surfactant concentration was detrimental to Cd desorption consistent with a process that blocked ligand access to the soil particle surface. After 5 washings,the cumulative cadmium desorption decreased with increasing surfactant alkyl chain length, indicating that the metal-ligand complexes are preferably stabilized by the micelles' hydrophobic octyl phenyl (OP) group rather than by the hydrophilic PEO group. In the absence of ligand, the surfactants alone desorbed less than 1% Cd from the contaminated soil, suggesting that the ligand, rather than the surfactant, extracts the metal, to be subsequently stabilized within the surfactant micelles.

Simultaneous soil Cd and PCB decontamination using a surfactant/ligand solution.

The simultaneous desorption of Cd and PCBs, from a contaminated soil, was investigated using a surfactant/ligand solution. The test surfactants were combinations of a nonionic surfactant [polyethylene oxide (PEO) of chain length 7.5 (Triton X-114), 9.5 (Triton X-100), 30 (Triton X-305), or 40 units (Triton X-405)], with iodide (I-). Triplicate 1 g soil samples were equilibrated, during 24h, with 15 mL of surfactant/ligand solution, at 0.025 or 0.50 and 0.0, 0.168, or 0.336 mol L(-1), respectively. The supernatant fraction was then separated from the particulates by centrifugation and analyzed for Cd to determine Cd desorption efficiency. After five consecutive washings, the treated soil samples were analyzed for PCB content to determine the desorption efficiency of this class of toxicant. Desorption of Cd increased with both increasing ligand concentration and decreasing surfactant chain length and concentration. The maximum Cd desorption efficiency (61%), was obtained with Triton X-100 at 0.025 mol L(-1), in the presence of I at 0.336 mol L(-1). After 5 successive washings, virtually quantitative PCB desorption (below limits of detection for tetra-, penta-, and hexachloro biphenyl compounds) had been achieved with most of surfactant/ligand combinations. Maximum desorption efficiency was achieved using either shorter chain length surfactant (n = 7.5 or 9.5) in combination with a higher ligand concentration, or using longer chain length surfactants (n = 30 and 40) with a lower ligand concentration. Thus, heavy metals and PCBs can be desorbed simultaneously from a contaminated soil with the same washing reagents, namely a surfactant-ligand combination. The optimum surfactant-ligand combination for the simultaneous desorption of both heavy metals and PCBs was a short chain length (n = 7.5 or 9.5) surfactant at low concentration admixed with 0.336 mol L(-1) I-.

Characterization of DNA adducts from lung tissue of asphalt fume-exposed mice by nanoflow liquid chromatography quadrupole time-of-flight mass spectrometry.

A bioanalytical method based on nanoflow liquid chromatography coupled to a hybrid quadrupole orthogonal acceleration time-of-flight mass spectrometry was developed to characterize selected polyaromatic hydrocarbon (PAH)-DNA adducts. The collision-induced dissociation of analytes results in characteristic fragmentation patterns that can be utilized to identify the DNA adducts. In the experiment, 32 B6C3F1 mice were exposed daily (4h/day) to asphalt fume in a whole-body inhalation chamber for 10 days; 16 nonexposed mice served as controls. The asphalt fume was generated at 180 degrees C and the concentrations of PAHs in the animal exposure chamber ranged from 152 to 198 mg/m3. The DNA adducts N2-deoxyguanosine-benzo(a)pyrene-7,8-dihydrodiol-9,10-epoxide (N2-dG-BPDE); N6-deoxyadenosine-benzo(a)pyrene-7,8-dihydrodiol-9,10-epoxide (N6-dA-BPDE), and N4-deoxycytidine-benzo(a)pyrene-7,8-dihydrodiol-9,10-epoxide (N4-dC-BPDE) were identified. The concentrations of N2-dG-BPDE, N6-dA-BPDE, and N4-dC-BPDE adducts were determined to be 1.17, 0.97, and 0.68 pmol/mg DNA, respectively, in the lung tissue of exposed mice using the nanoflow technique. The total DNA adducts in exposed lung tissue was determined to be 8.35 pmol/mg DNA by 32P-postlabeling assay. In total, the results indicated that PAH DNA adducts were significantly elevated (p < 0.001) in the lung tissue of asphalt-fume-exposed mice relative to tissue from control animals.

Dechlorination of pentachlorophenol in supercritical carbon dioxide with zero-valent palladium-magnesium bimetallic mixture.

A stream of substrate pentachlorophenol [PCP, 5 mg min(-1) in water-methanol (1 + 4, v/v)] was merged with 1.5 ml min(-1) of supercritical carbon dioxide (scCO2) and delivered to a reactor column (25 cm x 1 cm) of zero-valent palladium-magnesium mixture. The resulting dechlorinations, although very efficient, were not quantitative. For continuous operation at 400 degrees C for 6 h, phenol was the principal product, with lesser quantities of methylated products and only traces of chlorinated products (principally monochlorinated species). PCP deoxygenation was not observed and ring methylation was decreased relative to analogous reactions in hydroxylic organic solvent. With time, the reactor column slowly lost dechlorination activity. Reducing the loading of Pd0 on Mg0 from 2% to 1% (w/w) apparently did not change the course of the reaction; however, the dechlorination capacity was decreased correspondingly. None the less, over 6 h or 5 h of continued operation, the dechlorination efficiency was 0.995 for the 2% (w/w) loading of Pd0 on Mg0 and 0.984 for the 1% (w/w) loading.

Recycling of complexometric extractants to remediate a soil contaminated with heavy metals.

Equilibrations were performed with complexing reagent(s) to mobilise Cd, Cu, Mn, Ni, Pb and Zn from a contaminated urban soil. The metal-laden aqueous extract was treated with zero-valent magnesium (Mg0) or bimetallic mixture (Pd0/Mg0 or Ag0/Mg0) to precipitate the heavy metals from solution while liberating the chelating reagent(s). Post precipitation, the pH of aqueous supernatant fraction was readjusted to approximately 5 and the solution was re-combined with the soil particulates to extract more heavy metal pollutants. A sparing quantity of EDTA (10 mmoles) mobilised 32-54% of the 5 mmoles of heavy-metals from the soil with three cycles but only 0.1% of the iron was removed. Three successive extractions with a mixture of complexing reagents (3 mmoles), 1:1 EDTA plus HEDC [bis-(2-hydroxyethyl)-dithiocarbamate], mobilised approximately 49% of the Pb, approximately 18% of the Zn and approximately 19% of the Mn burden but only 7% of the Cu, and 1% of the Fe from this soil. An appreciable fraction of the mobilised Pb and Cu and a portion of the Zn was cemented to the surfaces of the excess magnesium whereas virtually all of the Fe and Mn was removed from solution as insoluble hydroxides.