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.     

Combined effect of natural organic matter and surfactants on the apparent solubility of polycyclic aromatic hydrocarbons

Both natural organic matter (NOM) and surfactants are known to enhance the apparent aqueous solubility of hydrophobic organic contaminants (HOCs) in aqueous systems. In this study, the combined effect of NOM and surfactants on enhancing the solubility of HOCs was investigated, since both may occur and affect the fate and transport of HOCs in natural aqueous environments. Experimental results indicated that the apparent solubility of naphthalene, phenanthrene, and pyrene in NOM and anionic surfactant solution was lower than their solubility in NOM solution alone. However, the apparent solubility of an HOC in NOM and nonionic surfactant solution is almost the same as the sum of the HOC's solubility in NOM solution plus its solubility in nonionic surfactant solution. The observation that apparent aqueous solubility of HOCs in NOM and anionic surfactant solution is decreased is probably due to the fact that the cations that are released when the anionic surfactant dissociates may form ion pairs with acidic or phenolic groups associated with the NOM. This serves to increase the size of hydration of these groups, thereby decreasing the effective size of the nonpolar moieties associated with the NOM, and thus decreasing hydrophobic partitioning of the HOCs into the NOM. The results presented here will help us to understand the effect of NOM and surfactants on the fate and transport of HOCs in aquatic systems.     

Forest fertilization with wood ash: effect on the distribution and storage of polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs)

Before wood ash can be safely used as a fertilizer in forests, possible negative effects such as input of organic contaminants or remobilization of contaminants already stored in the soil must be investigated. The objective of this study was to examine the effects of wood ash application on concentrations, storage, and distribution of polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs) in a Swiss forest soil. In May 1998, we added 8 Mg wood ash ha(-1) to a forest soil. We determined 20 PAHs and 14 PCBs in the organic layer, in the bulk mineral soil, and in soil material taken from preferential flow paths and from the matrix before and after the wood ash application. In the control plots, the concentrations of PAHs in the organic layer indicated moderate pollution (sum of 20 PAHs: 0.8-1.6 mg kg(-1)), but sum of PCB concentrations was high (21-48 microLg kg(-1)). The wood ash had high concentrations of PAHs (sum of 20 PAHs: 16.8 mg kg(-1)), but low concentrations of PCBs (sum of 14 PCBs: 3.4 microg kg(-1)). The wood ash application increased the PAH concentrations in the organic horizons up to sixfold. In contrast, PCB concentrations did not change in the Oa horizon and decreased up to one third in the Oi and Oe horizons. The decrease was probably caused by the mobilization of stored PCBs because of the high pH of the wood ash. This probably results in a higher mobility of dissolved organic matter, acting as PCB carrier. In the mineral soil, the preferential flow paths of the A horizon contained more PAHs and PCBs (+20 +/- 15% and +43 +/- 60%, respectively) than the matrix. This was particularly true for higher molecular weight compounds (molecular weight > 200 g mol(-1)). Below 50 cm depth, concentrations of PAHs and PCBs were smaller in the preferential flow paths, suggesting that in deeper depths, processes acting as sinks dominated over inputs in the preferential flow paths.     

Removal of uranium(VI) from contaminated sediments by surfactants

Uranium(VI) sorption onto a soil collected at the Melton Branch Watershed (Oak Ridge National Laboratory, TN) is strongly influenced by the pH of the soil solution and, to a lesser extent, by the presence of calcium, suggesting specific chemical interactions between U(VI) and the soil matrix. Batch experiments designed to evaluate factors controlling desorption indicate that two anionic surfactants, AOK and T77, at concentrations ranging from 60 to 200 mM, are most suitable for U(VI) removal from acidic soils such as the Oak Ridge sediment. These surfactants are very efficient solubilizing agents at low uranium concentrations: ca. 100% U(VI) removal for [U(VI)]o,sorbed = 10(-6) mol kg-1. At greater uranium concentrations (e.g., [U(VI)]o,sorbed = ca. 10(-5) mol kg-1), the desorption efficiency of the surfactant solutions increases with an increase in surfactant concentration and reaches a plateau of 75 to 80% of the U(VI) initially sorbed. The most probable mechanisms responsible for U(VI) desorption include cation exchange in the electric double layer surrounding the micelles and, to a lesser extent, dissolution of the soil matrix. Limitations associated with the surfactant treatment include loss of surfactants onto the soil (sorption) and greater affinity between U(VI) and the soil matrix at large soil to liquid ratios. Parallel experiments with H2SO4 and carbonate-bicarbonate (CB) solutions indicate that these more conventional methods suffer from strong matrix dissolution with the acid and reduced desorption efficiency with CB due to the buffering capacity of the acidic soil.     

Phytoextraction and uptake patterns of weathered polychlorinated biphenyl-contaminated soils using three perennial weed species

Three promising phytoextracting perennial weed species [ L. (ox-eye daisy), L. (curly dock), and L. (Canada goldenrod)] were planted in monoculture plots at two polychlorinated biphenyl (PCB)-contaminated sites in southern Ontario and followed over 2 yr to investigate the effects of plant age, contaminant characteristics, and species-specific properties on PCB uptake and accumulation patterns in plant tissues. Results from this study indicate that, for each of these weed species, shoot contaminant concentrations and total biomass are dependent on plant age and life cycle (vegetative and reproductive stages), which affects the total amount of PCBs phytoextracted on a per-plant basis. Even at suboptimal planting densities of 3 to 5 plants m, all three weed species extracted a greater quantity of PCBs per unit area (4800-10,000 μg m) than the known PCB-accumulator L. ssp (cv Howden pumpkins) (1500-2100 μg m) at one of the two sites. Calculated PCB extractions based on theoretical optimal planting densities were significantly higher at both sites and illustrate the potential of these weeds for site remediation. This study also demonstrates that plants may accumulate PCBs along the stem length in a similar manner as plants.     

Surfactant-soil interactions during surfactant-amended remediation of contaminated soils by hydrophobic organic compounds: a review

Surfactants are amphiphilic molecules that reduce aqueous surface tension and increase the solubility of hydrophobic organic compounds (HOCs). Surfactant-amended remediation of HOC-contaminated soils and aquifers has received significant attention as an effective treatment strategy - similar in concept to using soaps and detergents as washing agents to remove grease from soiled fabrics. The proposed mechanisms involved in surfactant-amended remediation include: lowering of interfacial tension, surfactant solubilization of HOCs, and the phase transfer of HOC from soil-sorbed to pseudo-aqueous phase. However, as with any proposed chemical countermeasures, there is a concern regarding the fate of the added surfactant. This review summarizes the current state of knowledge regarding nonionic micelle-forming surfactant sorption onto soil, and serves as an introduction to research on that topic. Surfactant sorption onto soil appears to increase with increasing surfactant concentration until the onset of micellization. Sorbed-phase surfactant may account for the majority of added surfactant in surfactant-amended remediation applications, and this may result in increased HOC partitioning onto soil until HOC solubilization by micellar phase surfactant successfully competes with increased HOC sorption on surfactant-modified soil. This review provides discussion of equilibrium partitioning theory to account for the distribution of HOCs between soil, aqueous phase, sorbed surfactant, and micellar surfactant phases, as well as recently developed models for surfactant sorption onto soil. HOC partitioning is characterized by apparent soil-water distribution coefficients in the presence of surfactant.     

Enhanced desorption of herbicides sorbed on soils by addition of Triton X-100

A study of the desorption of atrazine (1-chloro-3-ethylamino-5-isopropylamino-2,4,6-triazine) and linuron [1-methoxy-1-methyl-3-(3,4-dichlorophenyl)urea] adsorbed on soils with different organic matter (OM) and clay contents was conducted in water and in the presence of the non-ionic surfactant Triton X-100 at different concentrations. The aim was to gain insight into soil characteristics in surfactant-enhanced desorption of herbicides from soils. Adsorption and desorption isotherms in water, in all Triton X-100 solutions for atrazine, and in solutions of 0.75 times the critical micelle concentration (cmc) and 1.50cmc for linuron fit the Freundlich equation. All desorption isotherms showed hysteresis. Hysteresis coefficients decreased for linuron and increased or decreased for atrazine in Triton X-100 solutions. These variations were dependent on surfactant concentration and soil OM and clay contents. In the soil-water-surfactant system desorption of linuron from all soils was always greater than in the soil-water system but for atrazine this only occurred at concentrations higher than 50cmc. For the highest Triton X-100 concentration (100cmc), the desorption of the most hydrophobic herbicide (linuron) was increased more than 18-fold with respect to water in soil with an OM content of 10.3% while the atrazine desorption was increased 3-fold. The effect of Triton X-100 on the desorption of both herbicides was very low in soil with a high clay content. The results indicate the potential use of Triton X-100 to facilitate the desorption of these herbicides from soil to the water-surfactant system. They also contribute to better understanding of the interactions of different molecules and surfaces in the complex soil-herbicide-water surfactant system.     

Spatial and temporal distribution of polychlorinated biphenyl (PCB) concentrations in soils of an industrialized city in Turkey

Surface soil (0-5 cm) samples from 43 sampling sites covering the entire urban territory of Bursa, an industrialized city in Turkey, were collected in each season and analyzed for 83 polychlorinated biphenyls (PCBs). The mean concentration of total PCBs (Σ83 PCBs) among all sites over the four seasons was 2121.51 pg/g dry weight (dw), with a range of 207.61-5461.95 pg/g dw. Total PCB concentrations in the soil samples collected near an industrial region were the highest in all seasons. In general, PCB patterns were dominated by low-chlorinated homologue groups (≤ 5 Cl groups at a 79% level). The predominant homologue group found in Bursa city soils was the penta-CBs (29.1%) followed by the tetra-CBs (25.5%) and tri-CBs (17.6%). A total of seven dioxin-like PCB congeners (CB-77, 81, 105, 114, 118, 123, and 126) were found in every sampling location and their mean total concentration for all locations and seasons was 259.27 pg/g dw, with a range of 7.02-1581.13 pg/g dw. A significant relationship (r = 0.77, p < 0.01) was found between the concentrations of dioxin-like PCBs and the seasonal average sum of PCB concentrations. A correlation between light congeners (相似文献   

Polycyclic aromatic hydrocarbon removal from soil by surfactant solubilization and Phanerochaete chrysosporium oxidation

Surfactant soil washing can remove polycyclic aromatic hydrocarbons (PAHs) from contaminated soil, and the white rot fungus, Phanerochaete chrysosporium Burdsall in Burdsall & Eslyn, can oxidize PAHs. The objective of this study was to develop a novel bioremediation technology using a combination of abiological surfactant soil washing followed by PAH biological oxidation in soil washwater using P. chrysosporium in a rotating biological contactor (RBC) reactor. Soil used for experimentation was an 11-month aged contaminated soil spiked with a total of nine PAHs: acenaphthene, fluorene, phenanthrene, fluoranthene, pyrene, chrysene, benzo(a)pyrene, dibenz(a-h)anthracene, and benzo(ghi)perylene. After 11 months of aging, recovery percentages of high molecular weight PAHs [i.e., from chrysene to benzo(ghi)perylene] were greater than 86%, while those of low molecular weight PAHs (i.e., from acenaphthene to pyrene) were less than 19%. Total removal efficiency for any of the nine PAHs was greater than 90% using a combination of surfactant soil washing and P. chrysosporium oxidation of soil washwater in the RBC reactor when used in batch operation, and greater than 76% when used in continuous operation. The treatment of PAH-contaminated soil using a combination of surfactant soil washing and subsequent PAH removal from the resultant washwater in an RBC reactor, in the presence of immobilized P. chrysosporium, permits (i) a rapid abiological cleanup of soil for compliance with relevant soil quality standards and (ii) PAH biological removal in soil washwater for compliance with aqueous discharge standards.     

Influence of quaternary ammonium on sorption of selected metal cations onto clinoptilolite zeolite

Clay minerals and zeolites have large cation exchange capacities, which enable them to be modified by cationic surfactant to enhance their sorption of organic and anionic contaminants. In this study, the influence of quaternary ammonium surfactants on sorption of five metal cations (Cs+, Sr+, La3+, Pb2+, and Zn2+) onto a clinoptilolite zeolite was investigated. Generally, the metal cation sorption capacity and affinity for the zeolite decreased, indicating that presorbed cationic surfactants blocked sorption sites for metal cations, as the surfactant loading on the zeolite increased. Cesium and Pb2+ sorption was affected to a small extent, indicating that selective sorption for Cs+ and specific sorption for Pb2+ play an important role in addition to cation exchange. Sorption of cationic surfactants on zeolite preloaded with different metal cations showed a strong correlation with the chain length of the surfactant tail group, while the roles of the charges and types of the metal cations were minimal. As the chain length increases, the critical micelle concentration decreases and the surfactant molecules become more hydrophobic, resulting in progressive bilayer coverage. Desorption of presorbed metal cations by cationic surfactants was strongly affected by the surfactant chain length and metal type. More metal cations, particularly Sr2+ and Zn2+, desorbed with an increase in surfactant chain length. The results, in combination with those from organic and oxyanion sorption on surfactant-modified zeolite, may be used for future surfactant modification to target sorption and desorption of a specific type of contaminant or a mixture of different types of contaminants.     

Effect of electrokinetics on the bioaccessibility of polycyclic aromatic hydrocarbons in polluted soils

Bioaccessibility is one of the most relevant aspects to be considered in the restoration of soils using biological technologies. Polycyclic aromatic hydrocarbons (PAH) usually have residual fractions that are resistant to biodegradation at the end of the biological treatment. In some situations, these residual concentrations could still be above legal standards. Here, we propose that the available knowledge about electroremediation technologies could be applied to enhance bioremediation of soils polluted with PAH. The main objective of this study was to show that a previous electrokinetic treatment could reduce the PAH residual fractions when the soil is subsequently treated by means of a bioremediation process. The approach involved the electrokinetic treatment of PAH-polluted soils at a potential drop of 0.9 to 1.1 V/cm and the subsequent estimations of bioaccessibility of residual PAHs after slurry-phase biodegradation. Bioaccessibility of PAH in two creosote-polluted soils (clay and loamy sand, total PAH content averaging 300 mg/kg) previously treated with an electric field in the presence of nonionic surfactant Brij 35 was often higher than in untreated controls. For example, total PAH content remaining in clay soil after bioremediation was only 62.65 +/- 4.26 mg/kg, whereas a 7-d electrokinetic pretreatment had, under the same conditions, a residual concentration of 29.24 +/- 1.88 mg/kg after bioremediation. Control treatments without surfactant indicated that the electrokinetic treatment increased bioaccessibility of PAHs. A different manner of electric field implementation (continuous current vs. current reversals) did not induce changes in PAH bioaccessibility. We suggest that this hybrid technology may be useful in certain bioremediation scenarios, such as soils rich in clay and black carbon, which show limited success due to bioavailability restrictions, as well as in highly heterogeneous soils.     

Adsorption of eosin dye on activated carbon and its surfactant based desorption

The performance of activated carbon has been investigated for the adsorption of eosin dye dissolved in water. Eosin is anionic in nature and highly toxic. The effects of initial dye concentration, contact time, pH and temperature on adsorption of eosin by a fixed amount of activated carbon (1.0 g/L) have been studied in batch and column mode. The equilibrium data are successfully fitted to the Freundlich adsorption isotherm. The adsorption rate data are successfully explained by a pseudo second-order kinetic model. Breakthrough curves for column adsorption have also been studied. The regeneration of spent carbon by desorbing the dye has been experimentally investigated applying a surfactant enhanced carbon regeneration (SECR) technique using both cationic and anionic surfactants. An empirical kinetic model for dye desorption from the commercial activated carbon (CAC) using different surfactant and desorption techniques, viz. change in pH, has been proposed. The comparison between the model and the experimental results is found to be satisfactory.     

洗涤法处理含油土壤的研究

研究了用洗涤法处理含油土壤，考察了洗涤剂种类与浓度、洗涤温度、液固比、洗涤时间、表面活性剂、洗涤液直接循环使用次数对洗涤效果的影响，结果表明：当混合减浓度为10000mg／L、洗涤温度为70℃、液固比2：1、洗涤时间20min时，可将含油量为30％的土壤洗至残油率仅为0．3％左右。OP、EL型表面活性剂的加入对洗涤效果没有改善，特别有意义的是洗涤液能够直接循环使用而对洗涤效果基本无影响，这不仅能够减少用水量，还可以大大减少废水的排放量，降低操作费用及废水处理费用。该洗涤法不涉及物质的相变过程，混合碱由廉价的无机碱和无机盐组成，故能量消耗低，处理费用也低，且洗脱下来的原油可回收。     

Hydrophobicity of soil colloids and heavy metal mobilization: effects of drying

Drying of soil may increase the hydrophobicity of soil and affect the mobilization of colloids after re-wetting. Results of previous research suggest that colloid hydrophobicity is an important parameter in controlling the retention of colloids and colloid-associated substances in soils. We tested the hypothesis that air-drying of soil samples increases the hydrophobicity of water-dispersible colloids and whether air-drying affects the mobilization of colloid-associated heavy metals. We performed batch experiments with field-moist and air-dried (25 degrees C) soils from a former sewage farm (sandy loam), a municipal park (loamy sand), and a shooting range site (loamy sand with 25% C(org)). The filtered suspensions (<1.2 microm) were analyzed for concentrations of dissolved and colloidal organic C and heavy metals (Cu, Cd, Pb, Zn), average colloid size, zeta potential, and turbidity. The hydrophobicity of colloids was determined by their partitioning between a hydrophobic solid and a hydrophilic aqueous phase. Drying increased hydrophobicity of the solid phase but did not affect the hydrophobicity of the dispersed colloids. Drying decreased the amount of mobilized mineral and (organo-)mineral colloids in the sewage farm soils but increased the mobilization of organic colloids in the C-rich shooting range soil. Dried samples released less colloid-bound Cd and Zn than field-moist samples. Drying-induced mobilization of dissolved organic C caused a redistribution of Cu from the colloidal to the dissolved phase. We conclude that drying-induced colloid mobilization is not caused by a change in the physicochemical properties of the colloids. Therefore, it is likely that the mobilization of colloids in the field is caused by increasing shear forces or the disintegration of aggregates.     

Effect of surfactants on solubilization and degradation of phenanthrene under thermophilic conditions

The bioavailability and biodegradation of polycyclic aromatic hydrocarbons (PAHs) can be increased through the addition of surfactants. Previous studies of this nature have been conducted under mesophilic conditions. Hence, the aim of the present study was to investigate the effects of synthetic surfactants and biosurfactants on solubilization and degradation of phenanthrene (PHE) in a series of batch solution experiments under thermophilic conditions. Tween 80, Triton X-100, and biosurfactants produced from Pseudomonas aeruginosa strain P-CG3 (P-CG3) and Pseudomonas aeruginosa ATCC 9027 (P. 9027) were used in this study. Surfactants effectively enhanced the solubility of PHE at 50 degrees C and the biosurfactant from P-CG3 was most effective with a 28-fold increase in apparent solubility of PHE at a concentration of 10 x critical micelle concentration (CMC) compared with the controls. However, addition of synthetic surfactants or biosurfactants inhibited the biodegradation of PHE in mineral salts medium by an isolate Bacillus sp. B-UM. Degradation of PHE diminished with increasing surfactant concentrations, and PHE degradation was completely inhibited for all the surfactants tested when the concentrations were greater than their respective CMC. The growth test suggested that Tween 80 and biosurfactants were degradable, but preferential utilization of these surfactants as substrates was not the mechanism for explaining the inhibition of PHE biodegradation. Because of the hydrophobic property of B-UM, degradation inhibition of PHE by surfactants was probably due to the reduction of direct contact between bacterial cells and PHE.     

Transport of cadmium and assessment of phytotoxicity after electrokinetic remediation

The use of ethylene diamine tetraacetic acid (EDTA) on the electrokinetic removal of cadmium-contaminated soil was evaluated. A total of four different tests were conducted using EDTA as a washing solution as well as a purging solution at the electrode compartments. The efficiency of electrokinetic extraction was significantly influenced by the pH of the soil medium. The results show that EDTA was effective in desorbing cadmium at a high pH, with Cd-EDTA(-) anion complexes migrating toward the anode. At low pH values near the anode area, cadmium existed as Cd(2+), migrating toward the cathode. Such contradicting directions of cadmium have resulted in its detrimental removal from the soil cell. However, accumulation of cadmium near the cathode was observed at the end of the tests due to the dominating low pH in the soil cell. The phytotoxicity after the electrokinetic process was investigated using Sorghum saccharatum, Lepidium sativum and Sinapis alba plants. The germination index was a major endpoint estimated by measuring seed germination and shoot elongation. The results obtained show that the phytotoxicity was increased after electrokinetic extraction. Despite, the extensive cadmium removal from two-thirds of the cell, the low pH of the soil was the principal parameter exhibiting the phytotoxicity.     

Anionic polyacrylamide effects on soil sorption and desorption of metolachlor,atrazine, 2,4-D,and picloram

Polyacrylamide (PAM) treatment of irrigation water is a growing conservation technology in irrigated agriculture in recent years. There is a concern regarding the environmental impact of PAM after its application. The effects of anionic PAM on the sorption characteristics of four widely used herbicides (metolachlor, atrazine, 2,4-D, and picloram) on two natural soils were assessed in batch equilibrium experiments. Results showed that PAM treatment kinetically reduced the sorption rate of all herbicides, possibly due to the slower diffusion of herbicide molecules into interior sorption sites of soil particles that were covered and/or cemented together by PAM. The equilibrium sorption and desorption amounts of nonionic herbicides (metolachlor and atrazine) were essentially unaffected by anionic PAM, even under a high PAM application rate, while the sorption amounts of anionic herbicides (2,4-D and picloram) were slightly decreased and their desorption amounts increased little. The impact mechanisms of PAM were related to the molecular characteristics of PAM and herbicides. The negative effects of PAM on the sorption of anionic herbicides are possibly caused by the enhancement of electrostatic repulsion by presorbed anionic PAM and competition for sorption sites. However, steric hindrance of the large PAM molecule weakens its influence on herbicide sorption on interior sorption sites of soil particles, which probably leads to the small interference on herbicide sorption, even under high application rates.     

Organic ligand effects on enzymatic dephosphorylation of myo-inositol hexakis dihydrogenphosphate in dairy wastewater

Animal manure contains partially digested feed fiber and grains where phosphorus (P) is bound in organic compounds that include myo-inositol 1,2,3,5/4,6-hexakis dihydrogenphosphate or phytic acid (IP6). Information is needed on the effects of other (non-IP6) organic ligands (LIGND) on the enzymatic dephosphorylation of IP6, which is a potential source of dissolved orthophosphate P (PO4-P) in the soil-manure-water system. The effects of 1,2-cyclohexane diamino-tetraacetate (CDTA), diethylenetriamine-N,N,N',N',N'-pentaacetate (DTPA), ethylenediamine-N,N,N',N'-tetraacetate (EDTA), oxalate (OXA), and phthalate (PHTH) and LIGND to IP6 molar ratio and charge concentration ratio on IP6 dephosphorylation were studied to determine controlling mechanisms of IP6 persistence in manure. Solution PO4-P concentrations were analyzed by ion chromatography as the phosphomolybdate-ascorbic acid method partly includes IP6-P. Uncomplexed IP6 dephosphorylation by Aspergillus ficuum (Reichardt) Henn. phytase EC 3.1.3.8 at pH 4.5 and 6 is unaffected by the presence of LIGNDs. As the concentrations of Ca2+, Al3+, or Fe3+ increase, dephosphorylation is reduced. Their inhibitory effect lessens in the presence of LIGNDs, in the following order: CDTA = EDTA > DTPA > OXA > or = PHTH. Whether CDTA or EDTA is the most effective LIGND depends upon the acidity of the suspension and LIGND charge concentration, reducing the inhibitory effect of polyvalent counterions to the point of promoting the hydrolysis of a manure phytase-hydrolyzable phosphorus (PHP) fraction that is otherwise unavailable. Therefore, ligand-induced changes increase the mobilization and dephosphorylation of complexed organic P, above and beyond the simple dissolution of inorganic phosphates. An analytical method for potentially bioavailable PHP in animal manure should include a LIGND as extracting reagent. Also, potential LIGNDs in an organic carbon-rich dairy wastewater may increase the release of PHP and environmental dispersion of PO4-P.     

Activated carbon immobilizes residual polychlorinated biphenyls in weathered contaminated soil

Activated carbon (AC) has recently been shown to be effective in sequestering persistent organic pollutants (POPs) from aquatic sediments. Most studies have demonstrated significant reductions of POP concentrations in water and in aquatic organisms; however, limited data exist on the possibility of using AC to immobilize remaining POPs at terrestrial contaminated sites. Under greenhouse conditions, pumpkin ssp cv. Howden) were grown, and red wiggler worms () were exposed to an industrial contaminated soil containing a mixture of polychlorinated biphenyls (PCBs), i.e., Aroclors 1254 and 1260) treated with one of four concentrations of AC (0.2, 0.8, 3.1, and 12.5%) for 2 mo. The addition of AC to contaminated soils virtually eliminated the bioavailability of PCBs to the plant and invertebrate species. There were reductions in PCB concentrations of more than 67% in ssp and 95% in . These data suggest that AC could be included as part of comprehensive site closure strategy at PCB-contaminated sites.