Release of Chemicals from Contaminated Soils

At sites that contain contaminated soils, there can be questions about the magnitude of risk posed by the chemicals in the soils and about the cleanup levels that should be achieved. Knowledge about the rate of release of chemicals is important to answers to such questions. This article: (1) describes a laboratory protocol to obtain rate of release information for chemicals in soils, and (2) provides estimates of the rate of release of individual polyaromatic hydrocarbon (PAH) compounds from several manufactured gas plant (MGP) site soils. The data were analyzed using an empirical two-site model. Different fractions of PAH were released rapidly from these soils. For one soil, this fraction was less than 20%, for others, the fraction ranged from 36 to 85%. The first-order rate constant (k2) of PAH released during the slow phase of chemical release ranged from 0.0001 to 0.01 per hour.     

Modeling Radiological Risks to Human Health from Contaminated Soils: Comparing MEPAS,MMSOILS, and RESRAD

Computer-based multimedia models are key analytical tools for assessing potential exposure to environmental contaminants as the U.S. Department of Energy remediates its sites at the nuclear weapons complex. This study applies MEPAS, MMSOILS, and RESRAD to actual release site data from the 903 Pad Source Area within Operating Unit 2 at the Rocky Flats Environmental Technology Site using a common set of assumptions. The analysis compares the similarity of multimedia model output in terms of (1) prediction of transport, (2) determination of an individual's lifetime exposure, and (3) estimation of radiological risks to human health from contaminated soils. This case study presents fairly routine exposure pathways and offers a good illustration of the way in which multimedia models can be used to assess potential radiological risk to human health from contaminated soils.     

Removal of Lead from a Calcareous Soil by Chloride Complexation

Remediation of a lead-contaminated calcareous soil using NaCl solutions was examined. The removal of Pb from a coarser fraction of the soil was found to be 83% after three successive extractions at a NaCl concentration of 8?M, whereas an average of 9% of the calcium was removed. Multibatch extractions of Pb from finer soil containing a higher level of Pb were also performed. The removal of Pb from this soil after six successive extractions with 8?M NaCl was found to be 93%. The removal of Pb increased with time in a batch test and approached 80% after 90?h. It was found that the data were adequately described by a first-order rate, and hence it is believed that a single reaction mechanism controlled the release of Pb (i.e., from carbonate bound or exchangeable Pb fractions in the soil). Increasing removal of Pb was found as the volume of water added was increased as the mass of NaCl in solution remained constant. The removal of Pb from the leachate was found to be 90%, 99.7%, and 35% with lime (25.20?g/L), sodium carbonate (4.48?g/L), and calcium carbonate (82.0?g/L) addition, respectively. In the case of sodium carbonate, the removal of Pb was further improved when the pH was adjusted to 8.2. The recycling of free chloride that was generated from leachate resulted in 91% removal of Pb from the soil (particle size < 4.75?mm) after six recycles.     

Lead fractionation and bioaccessibility in contaminated soils with variable chemical properties

Abstract

The hazard imposed by trace elements within soils is dependent on soil properties and the relative distribution of metal species. Hence, a greenhouse column study was conducted to investigate the geochemical speciation and bioaccessibility of lead (Pb) as a function of soil properties. Four different soil types (Immokalee, Belle Glade, Tobosa and Millhopper series) varying in physico-chemical properties were selected and amended with Pb as Pb(NO₃) at 400, 800, and 1,200 mg kg^?1. A sequential extraction was employed to define the reactive metal pool, which was correlated with Pb bio-accessibility as determined by the physiologically based extraction test. Results show that Pb was mainly distributed in soluble+exchangeable phase in Immokallee (82%) and Millhopper (45%) series, and carbonate and Fe+Mn oxide fractions in Belle Glade (14–74%) and Tobosa (31–64%) series at time zero. With soil aging, Pb underwent chemical transformations in the soils and the majority of added Pb was associated with Fe+Mn oxide fraction (64–81%). Also, Pb bioaccessibility varied widely as a function of soil type and soil aging. Gastric phase (IVG-S) extracted 34–81% and 29–75% and the absorbed intestinal phase (IVG-AI) extracted 12–79% and 12–45% of amended Pb in all the soils at time zero and 6 months, respectively. Among soil types, Tobosa and Belle Glade showed reduced bioaccessibility relative to Immokalee and Millhopper. Statistical analysis revealed that the IVG-S Pb decreases as soil organic matter and cation exchange capacity (CEC) increases and total P decreases. While the Mehlich extractable P and Ca+Mg, total Fe+Al and organic matter predicted the Pb in an intestinal system.     

Lead Distribution in Plant Residues Amended Calcareous Soils as a Function of Incubation Time

We investigated the effect on lead (Pb) fractionation of the addition of plant residues and incubation time in three metal-amended calcareous soils of Iran. Four amended treatments with plant residues (helianthus, potato, rape, and wheat) were established at the rate of 2% and incubated for four weeks at 25°C and constant moisture. Lead was added to amended-soils at the rate of 200 mg kg^?1 as chloride. A control without amendments but with Pb (control) was also set up. The samples were incubated for 3, 72, 168, 336, 672, 1008, and 1344 h at 25°C and constant moisture. After incubation, the soils were sequentially fractionated into water-soluble plus exchangeable (EXCH), organically bound (OM), inorganically bound (CARB), and residual (RES) forms. There were changes in the proportional distribution of Pb in all three studied soils during 1344 h of incubation with spiked Pb. In general, the proportions of Pb associated with the most weakly bound fraction (EXCH) tended to decrease, with corresponding increases in the other three more strongly binding fractions during the incubation. Application of plant residues increased Pb significantly in EXCH fractions in studied soils. Among the plant residues, application of potato residue gave the highest increase in EXCH fractions in two soils, which may be related to its lower C/N ratio. The higher proportions of EXCH fraction of spiked and amended soils in these calcareous soils indicate the higher potential of downward leaching and runoff transport, especially at the early stage of pollution.     

The Effect of Electrolyte Type and Concentration on the Release of Cd,Cu, Ni,and Zn in Some Contaminated Calcareous Soils

This paper reports the results of desorption experiments of cadmium (Cd), copper (Cu), nickel (Ni), and zinc (Zn) from some contaminated calcareous soils under four electrolyte types (CaCl₂, MgCl₂, NaCl and Na₂SO₄) with different electrolyte concentrations (0.5, 4 and 10 mM). Among electrolytes, CaCl₂ significantly released more metals from soils. There was a negative relationship between total Cu and Zn content and percentage of Cu and Zn released (average of electrolyte concentrations) using CaCl₂ solution, indicating a higher Cu and Zn released when their total content was low. Generally, Cd, Cu, and Zn speciation was affected by both type of electrolytes and their concentrations, whereas Ni speciation stayed mostly stable and was almost unaffected by applied solutions. It can be suggested that beside competition with cations, chloro-complexation is important parameter in Cd release, while CuOH⁺, and to some extent ZnOH⁺ are important species affecting release of Cu and Zn. The distribution coefficient (K_d) values for each metals greatly varied with the types of electrolytes and electrolyte concentration. On the basis of average percentage of metal released under different electrolytes and concentrations the following sequences was found: Cd > Cu > Ni > Zn. The results are important in understanding the mobility of metals under different solutions and indicating that, Cd and Zn soils may pose a higher and lower mobility and ecological risk in contaminated calcareous soils, respectively.     

Reducing Copper Availability in Contaminated Soils Using Drinking Water Treatment Residuals

Copper mobility and availability in soil environments is largely controlled by Cu sorption reactions as well as its chemical forms. In this study, equilibrium, kinetic batch experiments, and a chemical fractionation scheme were carried out to evaluate effects of drinking water treatment residual (DWTR) application on sorption and bioavailability of Cu in three arid zone soils having different properties. Distinct differences in the amounts of Cu sorbed among the different soils were observed where highest sorption was associated with clay, OM, and CEC contents. The quantity of Cu sorbed on the three studied soils drastically increased as a result of increasing rates of DWTR application from 2% to 12% (w/w). Freundlich distribution coefficient (K_f) values indicate that Cu sorption affinities for the studied soils followed the trend Typic torrifluvent (TF) > Typic calciorthids (CO) > Typic torripsamment (TP) soils. The sorption of Cu was initially fast with 95, 92, and 73% of Cu sorbed on TF and CO and TP unamended soils, respectively, in the first 60 min. Following the initial fast reaction, the sorption reaction continued for 63 h, after which only a small amount of additional sorption occurred (2–6%). The parabolic diffusion law and the power function models described Cu sorption kinetics in all the sorbents studied equally well as the R² values were quite high and SE values were low. Addition of DWTR drastically reduced non-residual (NORS) Cu and simultaneously increased residual (RS) Cu fractions. At 12% application rate, DWTR decreased NORS-Cu in nonamended soils from 10.9 to 4.2, from 50.2 to 21.5, and from 78.6 to 33.3% in TF, CO, and TP soils, respectively. Our results suggest that as the application rate of DWTR to Cu-contaminated soils increased, more Cu was associated with the residual fractions, which decreased potential Cu mobility and bioavailability in these soils.     

Phosphorus Movement and Retention by Two Calcareous Soils

To predict P sorption and leaching behavior in calcareous soils, we examined the adsorption and movement of applied P in columns of two calcareous soils. Phosphorus and various other ions were monitored in the leachate of the soil column by passing a 100 mg P l^?1 solution through the soil column. Concentrations of P, K⁺, Ca²⁺, Mg²⁺, Na⁺, HCO^? ₃, Cl^?, EC and pH were determined in the leachates. Movement of K⁺ and P ions was retarded due to K⁺ ion-exchange and P adsorption and precipitation, respectively. Phosphorus leaching was affected by supersaturation with respect to P-Ca minerals, but undersaturated with respect to Mg-P minerals. Phosphorus retention based on batch and miscible displacement experiments revealed profound discrepancies that can be attributed to the short residence time of P in the miscible displacement. Breakthrough curves of P and K⁺ were analyzed by a CXTFIT program. The equilibrium model provides good results to the transport process of P and K⁺. Results indicated that the mobility of P in these calcareous soils reflects that a high downward movement of water-soluble P in soils may occur and much attention should be paid to leaching of P and potential contamination of P to surface and ground waters.     

The Effect of Traffic Density on Lead Contents in Roadside Soils: An Analysis of Published Data

Data from eight published studies were combined to show that the influence of traffic density on Pb contents in roadside soils increases with proximity to the road.     

石油污染土壤生物降解生态条件研究

生物治理是石油污染土壤主要的有效的治理方法。微生物、污染物及环境等方面的因素都影响着生物降解效率。通过最佳生物降解条件的研究,提出了提高生物降解效率的措施。     

Comparison of Extractants for Removing Heavy Metals from Contaminated Clayey Soils

This article describes the removal of heavy metals from contaminated clayey soils by soil washing using various extractants. Two clayey soils, kaolin, a low buffering soil with pH of 5, and glacial till, a high buffering soil with pH of 8, were used to represent various soil conditions. These soils were spiked with chromium (Cr), nickel (Ni), and cadmium (Cd) to simulate improper disposal of typical electroplating waste constituents. The following extracting solutions were investigated for the removal of heavy metals from the soils: deionized water, distilled water, and tap water; acetic acid and phosphoric acid; chelating agents ethylenediaminetetraacetic acid (EDTA) and citric acid; and the oxidizing agents potassium permanganate and hydrogen peroxide. The effect of extractant concentration on removal of heavy metals was also investigated. Complete removal of Cr was achieved using 0.1?M potassium permanganate for kaolin, while a maximum of 54% was removed from glacial till. A maximum Ni removal of 80% was achieved using tapwater for kaolin, while a maximum removal of 48 to 52% was achieved using either 1?M acetic acid or 0.1?M citric acid for glacial till. A maximum Cd removal of 50% was achieved using any of the extractants for kaolin, while a maximum removal of 45 to 48% was obtained using either acids or chelating agents for glacial till. Overall, this study showed that complete removal of Cr, Ni, and Cd from clayey soils is difficult to achieve using the soil-washing process, and also the use of one extractant may not be effective in removing all metals. A sequential extraction using different extractants may be needed for the removal of multiple metal contaminants from clayey soils.     

Effect of Sodium and Magnesium on Kinetics of Phosphorus Release in Some Calcareous Soils of Western Iran

Knowledge of the rate of release of phosphorus (P) from soils resulting from poor water quality application is essential for long-term planning of crop production while minimizing the impact on groundwater quality. In this study, we examined the effect of sodium adsorption ratio (SAR) and Ca:Mg ratio of water on P release of some calcareous soils from western Iran. Nine different solutions at a total electrolyte concentration of 100 mmol_c l^?1 and three levels of SAR (5, 15, 45) each with Ca:Mg ratios of 1:3, 1:1, or 3:1, prepared using solutions of NaCl, CaCl₂, and MgCl₂, were used to extract P from the soils. The geochemical Visual MINTEQ was used to calculate saturation indices and P species at the initial and end of P release. Significantly different quantities of P were extracted by the solutions. The maximum (average of five soils) (233.6 mg kg^?1) and the minimum (162.9 mg kg^?1) P were extracted by an SAR 45 solution with a Ca:Mg ratio of 1:3 and SAR 15 solution with Ca:Mg ratio of 3:1, respectively. Elovich model adequately described P release. The release rate for SAR 15 with Ca:Mg of 3:1 and SAR 45 with Ca:Mg 1:3 ranges from 16.3 to 31.3 mg kg^?1 h^?1 and from 20.0 to 32.8 mg kg^?1 h^?1, respectively. In the initial stage of P release the solution samples in most soils were saturated with respect to hydroxyapatite, octacalcium phosphate, ß-tricalcium phosphate, and undersaturated with respect to dicalcium phosphate dihydrate, dicalcium phosphate, and mangnesium phosphates. At the end of P release, all solutions were saturated with respect to hydroxyapatite and under saturated with respect to other phosphate minerals. The results imply that P release from soils could be increased during use of saline and sodic irrigation water containing high Mg concentration and that P fertilization management may need modification.     

Nematode-Capturing Hyphomycetes from Soils over Xerophytic Calcareous Rock in Upper Bavaria*

Nematode-capturing hyphomycetes were isolated from soil and plant debris on the south slope of a hill in the Jurassic of Upper Bavaria. The following species were found: Arthrobotrys arthrobotryoides, A. dactyloides, A. oligospora, A. superba, Dactylella astenopaga, Monacrosporium cionopagum, M. psychrophilum. Endozoic fungal parasites of nematodes were not isolated. With one fungal propagule of nematode-destroying fungi in 1.7 g soil, the density is only slightly lower than values given for agricultural soils.     

Lead and Cadmium Contamination in Roadside Soils in Irbid City,Jordan: A Case Study

This study evaluates the amount and distribution of Pb and Cd in roadside soils adjacent to two main roads in Irbid, Jordan, from October 2001 to July 2002. A total of 260 samples were collected from Irbid-Howara Street and Yarmouk University Street. Lead and Cd content were measured using Graphite Furnace Atomic Absorption Spectrometry. The environmental significance of this study is discussed in terms of the influence of traffic density on Pb and Cd concentrations in roadside soils, and enrichment factors were calculated to evaluate the degree of pollution. The accuracy of the results obtained has been examined and two standard reference materials, CRM 142 R (soil) and SRM 2709 (soil), were analyzed to confirm the accuracy of the results. The precision of the measurements was assessed in terms of relative standard deviation (RSD) using five replicate analyses of samples collected from the roadside sites. RSD values for Pb and Cd were found to be less than 6%. The overall Pb concentration in roadside soil samples was 325 and 431 μg g^?1 for Pb and 1.142 and 1.135 μg g^?1 for Cd in Yarmouk University Street and Irbid-Houwa Street, respectively. Results indicated that levels of Pb and Cd were decreasing as the distance from the road increases. Enrichment factor results were 655 and 826 for Pb, and 252 and 237 for Cd in Yarmouk University Street and Irbid-Houwa Street, respectively.     

Amendment Optimization to Enhance Lead Extractability from Contaminated Soils for Phytoremediation

Eight lead-contaminated soils and one background soil artificially contaminated with several lead compounds were examined to determine the factors that limit lead extractability and thus plant availability during phytoremediation, as lead must be in soluble form for plant uptake to occur. The effect of the chemical form of the lead as well as the association of the lead among the different soil chemical fractions on lead extractability was specifically addressed. Results indicate that all the added lead forms tested except PbCrO₄ were readily extracted and believed to be available for plant uptake, operationally defined as EDTA-extractable lead, as EDTA is the primary soil amendment for phytoremediation of lead-contaminated soils. Sequential extraction of the eight lead-contaminated soils that previously had been extracted with EDTA shows that the EDTA-extractable or plant available lead corresponds to mainly the exchangeable and carbonate fractions of each soil. Lead associated with oxide, organic, and residual fractions were less effectively targeted and solubilized by EDTA and therefore are not as readily available for plant uptake. Attempts to increase the available pool of soluble lead included the combination of EDTA with organic acids, reducing agents, and surfactants. Results from these studies indicate that high concentrations or extremely low pH conditions are required to enhance the plant available pool of lead by the organic acids and reducing agents. Surfactants, particularly caprylic acid in combination with 0.25 mM EDTA, were shown to be as effective as 0.50 mM EDTA alone. An amendment formulation combining less EDTA with surfactants is attractive for phytoremediation because of the biodegradability and cost concerns commonly associated with using larger amounts of EDTA.     

Statistical Analysis of Chemical Release Rates from Soils

Two statistical methods for determining the precision of best-fit model parameters generated from chemical rate of release data are discussed. One method uses the likelihood theory to estimate marginal confidence intervals and joint confidence regions of the release model parameters. The other method uses Monte Carlo simulation to estimate statistical inferences for the release model parameters. Both methods were applied to a set of rate of release data that was generated using a field soil. The results of this evaluation indicate that the precision of F (the fraction of a chemical in a soil that is released quickly) is greater than the precision of k₁ (the rate constant describing fast release), which is greater than the precision of k₂ (the rate constant describing slow release). This occurs because more data are taken during the time period described by F and k₁ than during the time period described by F and k₂. In general, estimates of F will be relatively precise when the ratio of k₁ to k₂ is large, estimates of k₁ for soil/chemical matrices with a high F will be relatively precise, and estimates of k₂ for soil/chemical matrices with a low F will be relatively precise, provided that sufficient time is allowed for full release.     

Remediation of Clay Soils Contaminated with Potentially Toxic Elements: The Santo Amaro Lead Smelter,Brazil, Case

The remediation of clayey soil contaminated by potentially toxic elements is a challenging task, especially because of the low permeability and strong affinity of such toxic elements, which prevent the effective use of low-cost in situ remediation methods. The clay soil from the region of the former Santo Amaro primary lead smelter has high concentrations of potentially toxic elements, especially Pb, Cd, Sb, and Zn. This study presents a preliminary evaluation of remediation by soil washing and thermal stabilization, which can support clean-up initiatives for this site. The treatment results indicate that soil washing using EDTA can be an effective method to clean up the soil; however, the solid-liquid separation step by filtration is slow. Soil thermal treatment at temperatures higher than 800°C in an oxidant atmosphere results in the formation of ceramic structure because of the high smectite content, which stabilizes the potentially toxic elements. The estimated cost for remediation by soil excavation, replacement, and stabilization, of the critically contaminated site at the Santo Amaro region is estimated at about 20 to 30 million US$.     

污染土壤中多环芳烃的共代谢降解过程

1　前　言多环芳烃是一类普遍存在于环境中的重要有机污染物 ,因其致癌性、致畸性、致突变性而被认为是危险物质。由于其水溶性低 ,辛醇 水分配系数高 ,因此 ,该类化合物易于从水中分配到生物体内、沉积层中。土壤成为多环芳烃的重要载体 ,多环芳烃污染土壤的生物修复也因此倍受关注。多环芳烃在土壤中有较高的稳定性 ,其苯环数与其生物可降解性明显呈负相关关系。很少有能直接降解高环数多环芳烃的微生物。研究表明 ,高分子量的多环芳烃的生物降解一般均以共代谢方式开始[1 3] 。共代谢作用可以提高微生物降解多环芳烃的效率 ,改变微生物碳…     

Leaching of BTEX from Aged Crude Oil Contaminated Model Soils: Experimental and Modeling Results

It is generally assumed that soil properties such as organic matter content, porosity, and mineral surface area have a significant effect on the bioavailability and leachability of aged petroleum hydrocarbons. In order to test this hypothesis, nine model soils or sorbents (i.e., fine and coarse quartz sand, montmorillonite and kaolinite clay, peat, 60Å and 150Å silica gel, a loam soil, and non-porous glass beads) were spiked with a crude oil, aged for 27 months in the laboratory, and transferred to glass columns for the performance of continuous flow leaching experiments. The column effluents were periodically sampled for 43 days and analyzed for BTEX. A one-dimensional flow model for predicting the dissolution and dispersion of individual hydrocarbons from a multi-component NAPL such as crude oil was used to fit the leaching data (i.e., the BTEX concentration versus time curves) by adjusting the equilibrium oil-leachate partitioning coefficient (K ^ol ) for each respective hydrocarbon. The Peclet number, which is a measure of dispersion and a required modeling parameter, was measured in separate chloride tracer experiments for each soil column.

Results demonstrate that soil properties did not significantly affect the leaching kinetics of BTEX from the columns. Instead, BTEX leaching curves could be successfully fitted with the one-dimensional NAPL dissolution flow model for all sorbents with the exception of montmorillonite clay. The fitting parameter K ^ol for each hydrocarbon was found to be similar to the K ^ol values that were independently measured for the same crude oil by Rixey et al. (Journal of Hazardous Materials B, 65: 137–156, 1999 Rixey, W. G., Garg, S. and Nie, Y. 1999. Comparison of the fixed-bed and batch leaching characteristics of aromatic compounds in residually trapped crude oils and oily wastes. J. Hazard. Mat. B, 64: 137–156. [CSA][CROSSREF] [Google Scholar]). In addition, the fitted K ^ol values were very similar for BTEX leaching from aged compared to freshly spiked loam soil. These findings indicate that leaching of BTEX in the aged soils that are contaminated with crude oil at the high concentrations commonly found in the environment (i.e., > 20,000 mg/kg) was not affected by soil properties or aging but rather was governed by the equilibrium dissolution of these hydrocarbons from the crude oil NAPL that is coating the soil particles.