Fate and Transport of High Explosives in a Sandy Soil: Adsorption and Desorption

Several areas of the Massachusetts Military Reservation (MMR) have soils with significant levels of high explosives (HE) contamination because of a long history of training and range activities (such as open burning, open detonation, disposal, and artillery and mortar firing). Site-specific transport and attenuation mechanisms were assessed in sandy soils for three contaminants of concern: the nitramine hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), and the nitroaromatics 2,4-dinitrotolune (2,4-DNT) and 2,4,6-trinitrotoluene (TNT). For all three contaminants, linear distribution coefficients (K_d) were dependent on the fraction of organic carbon in soil. The nitroaromatics sorbed much more strongly than RDX in both soils. Over 120 hours, the desorption rate of RDX from field contaminated surface soil was much slower than its sorption rate, with the desorption K_d (1.5 L/kg) much higher than K_d for sorption (0.37 L/kg). Desorption of 2,4-DNT was negligible over 120 hours. Thus, applying sorption-derived K_d values for transport modeling may significantly overestimate the flux of explosives from MMR soils. Based on multiple component column transport tests, RDX will be the most mobile of these contaminants in MMR soils. In saturated columns packed with uncontaminated soil, RDX broke through rapidly, whereas the nitroaromatics were significantly attenuated by irreversible sorption or abiotic transformations.     

Metal Transport and Bioavailability in Soil Contaminated with CCA-Treated Wood Leachates

A laboratory study was conducted to investigate metal transport and accumulation within soils contaminated with As, Cr, and Cu from CCA-treated wood leachates. New blocks of CCA-treated wood were leached using synthetic rainwater. Soil columns were constructed and filled with three different soils, including a sandy soil, an organic soil and a clay soil. The leachate was applied intermittently until 80 pore volumes were eluted through each column. Metal concentrations (Cu, Cr, and As) were measured in the leachate before passage through the columns as well as in each elutriate fraction collected. Chemical analysis was complemented with toxicity testing using Ceriodaphnia dubia, Selenastrum capricornutum, and MetPLATE?. Following application of 80 pore volumes of leachate, the columns were dissected and the profile of the metal concentrations within each column was determined. A comparison of the arsenic, chromium and copper leaching patterns found arsenic to be the most mobile, with copper the most retained in the soil columns (As < Cr < Cu). Transport patterns of As differed in the three soil types, with observed mobility highest in the sandy soil and lowest in the clay soil. The three metals accumulated in the top layer of soil. Arsenic posed the greatest risk when soil concentrations were compared to risk-based target levels. Although metals were detected in soil elutriates, no toxicity was detected in any of the soil column elutriates using any of the three toxicity assays.     

Virus movement in soil columns flooded with secondary sewage effluent.

Secondary sewage effluent containing about 3 X 10(4) plaque-forming units of polio virus type 1 (LSc) per ml was passed through columns 250 cm in length packed with calcareous sand from an area in the Salt River bed used for ground-water recharge of secondary sewage effluent. Viruses were not detected in 1-ml samples extracted from the columns below the 160-cm level. However, viruses were detected in 5 of 43 100-ml samples of the column drainage water. Most of the viruses were adsorbed in the top 5 cm of soil. Virus removal was not affected by the infiltration rate, which varied between 15 and 55 cm/day. Flooding a column continuosly for 27 days with the sewage water virus mixture did not saturate the top few centimeters of soil with viruses and did not seem to affect virus movement. Flooding with deionized water caused virus desorption from the soil and increased their movement through the columns. Adding CaCl2 to the deionized water prevented most of the virus desorption. Adding a pulse of deionized water followed by sewage water started a virus front moving through the columns, but the viruses were readsorbed and none was detected in outflow samples. Drying the soil for 1 day between applying the virus and flooding with deionized water greatly reduced desorption, and drying for 5 days prevented desorption. Large reductions (99.99% or more) of virus would be expected after passage of secondary sewage effluent through 250 cm of the calcareous sand similar to that used in our laboratory columns unless heavy rains fell within 1 day after the application of sewage stopped. Such virus movement could be minimized by the proper management of flooding and drying cycles.     

Virus movement in soil columns flooded with secondary sewage effluent.

Secondary sewage effluent containing about 3 X 10(4) plaque-forming units of polio virus type 1 (LSc) per ml was passed through columns 250 cm in length packed with calcareous sand from an area in the Salt River bed used for ground-water recharge of secondary sewage effluent. Viruses were not detected in 1-ml samples extracted from the columns below the 160-cm level. However, viruses were detected in 5 of 43 100-ml samples of the column drainage water. Most of the viruses were adsorbed in the top 5 cm of soil. Virus removal was not affected by the infiltration rate, which varied between 15 and 55 cm/day. Flooding a column continuosly for 27 days with the sewage water virus mixture did not saturate the top few centimeters of soil with viruses and did not seem to affect virus movement. Flooding with deionized water caused virus desorption from the soil and increased their movement through the columns. Adding CaCl2 to the deionized water prevented most of the virus desorption. Adding a pulse of deionized water followed by sewage water started a virus front moving through the columns, but the viruses were readsorbed and none was detected in outflow samples. Drying the soil for 1 day between applying the virus and flooding with deionized water greatly reduced desorption, and drying for 5 days prevented desorption. Large reductions (99.99% or more) of virus would be expected after passage of secondary sewage effluent through 250 cm of the calcareous sand similar to that used in our laboratory columns unless heavy rains fell within 1 day after the application of sewage stopped. Such virus movement could be minimized by the proper management of flooding and drying cycles.     

Measurement of the apparent diffusion coefficient of N‐butane in soil

Measurements of in‐soil diffusion coefficients and the application of an appropriate diffusional model can allow for a more accurate prediction of soil gas concentrations and movement to locate subterranean contamination of volatile materials. The present study was undertaken to measure and evaluate the “apparent in‐soil diffusion coefficient”; for n‐butane through soil columns under non‐steady‐state conditions. The term “apparent in‐soil diffusion coefficient”; refers to a numerical coefficient that primarily describes the movement of the material by diffusion but also contains effects due to other mechanisms (e.g., adsorption and solubility).

Six test columns were evaluated at three soil porosity levels ranging from 0.30 to 0.43 and at two column temperature conditions, nominally 18°C and 7°C. Soil columns measured 25.4 cm in diameter by 84 cm in height and contained a moist sand/silt/clay mixture. The numerical range for the apparent in‐soil diffusion coefficients for n‐butane was 0.447 × 10^‐3cm²/s to 0.561 × 10^‐3cm²/s. The lower coefficient values were associated with lower soil porosity levels and cooler column conditions.     

Effect of Irrigation Water Quality on the Leaching and Desorption of Phosphorous from Soil

Knowledge of the rate of decrease of nutrients 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 Ca²⁺ concentration of irrigation water on phosphorus (P) leaching and kinetic release in columns of sandy soil. Phosphorous sorption in the presence of CaCl₂ solutions with Ca²⁺ concentrations of 3, 5, 10, and 15 mM CaCl₂ was determined to understand the transport and leaching of P in the sandy soil. The geochemical Visual MINTEQ was used to calculate saturation indices. A considerable number of leachate samples contained P at concentrations that could cause eutrophication. Total P leached from soil due to application of different CaCl₂ solutions ranged from 1.7 to 1.8 kg ha^?1 after 20 pore volumes had passed through the soil. Comparison of the leaching experiments results with the kinetic desorption data indicated that leaching removed on average 50 times less P than cumulative P desorbed by successive extractions with different CaCl₂ solutions. Leaching in presence of different CaCl₂ solutions was controlled by rate-limited dissolution of calcium hydroxyappatite and ß-tricalcium phosphate.     

Virus movement in soil during saturated and unsaturated flow

Virus movement in soil during saturated and unsaturated flow was compared by adding poliovirus to sewage water and applying the water at different rates to a 250-cm-long soil column equipped with ceramic samplers at different depths. Movement of viruses during unsaturated flow of sewage through soil columns was much less than during saturated flow. Viruses did not move below the 40-cm level when sewage water was applied at less than the maximum infiltration rate; virus penetration in columns flooded with sewage was at least 160 cm. Therefore, virus movement in soils irrigated with sewage should be less than in flooded groundwater recharge basins or in saturated soil columns. Management of land treatment systems to provide unsaturated flow through the soil should minimize the depth of virus penetration. Differences in virus movement during saturated and unsaturated flow must be considered in the development of any model used to simulate virus movement in soils.     

Assessment of Bioavailability of Soil-Sorbed Atrazine

Bioavailability of pesticides sorbed to soils is an important determinant of their environmental fate and impact. Mineralization of sorbed atrazine was studied in soil and clay slurries, and a desorption-biodegradation-mineralization (DBM) model was developed to quantitatively evaluate the bioavailability of sorbed atrazine. Three atrazine-degrading bacteria that utilized atrazine as a sole N source (Pseudomonas sp. strain ADP, Agrobacterium radiobacter strain J14a, and Ralstonia sp. strain M91-3) were used in the bioavailability assays. Assays involved establishing sorption equilibrium in sterile soil slurries, inoculating the system with organisms, and measuring the CO₂ production over time. Sorption and desorption isotherm analyses were performed to evaluate distribution coefficients and desorption parameters, which consisted of three desorption site fractions and desorption rate coefficients. Atrazine sorption isotherms were linear for mineral and organic soils but displayed some nonlinearity for K-saturated montmorillonite. The desorption profiles were well described by the three-site desorption model. In many instances, the mineralization of atrazine was accurately predicted by the DBM model, which accounts for the extents and rates of sorption/desorption processes and assumes biodegradation of liquid-phase, but not sorbed, atrazine. However, for the Houghton muck soil, which manifested the highest sorbed atrazine concentrations, enhanced mineralization rates, i.e., greater than those expected on the basis of aqueous-phase atrazine concentration, were observed. Even the assumption of instantaneous desorption could not account for the elevated rates. A plausible explanation for enhanced bioavailability is that bacteria access the localized regions where atrazine is sorbed and that the concentrations found support higher mineralization rates than predicted on the basis of aqueous-phase concentrations. Characteristics of high sorbed-phase concentration, chemotaxis, and attachment of cells to soil particles seem to contribute to the bioavailability of soil-sorbed atrazine.     

Virus movement in soil during saturated and unsaturated flow.

Virus movement in soil during saturated and unsaturated flow was compared by adding poliovirus to sewage water and applying the water at different rates to a 250-cm-long soil column equipped with ceramic samplers at different depths. Movement of viruses during unsaturated flow of sewage through soil columns was much less than during saturated flow. Viruses did not move below the 40-cm level when sewage water was applied at less than the maximum infiltration rate; virus penetration in columns flooded with sewage was at least 160 cm. Therefore, virus movement in soils irrigated with sewage should be less than in flooded groundwater recharge basins or in saturated soil columns. Management of land treatment systems to provide unsaturated flow through the soil should minimize the depth of virus penetration. Differences in virus movement during saturated and unsaturated flow must be considered in the development of any model used to simulate virus movement in soils.     

Prediction of leachate concentrations in petroleum‐contaminated soils

The efficacy of cleanup methods in reducing gasoline contamination at spill sites is typically determined by measuring benzene, toluene, xylene (BTX), and total petroleum hydrocarbon (TPH) concentrations in soil samples. Although these values may provide a direct measurement of soil contamination, they may not be indicative of what is transferred to percolating water. This study addresses this issue by measuring TPH, toluene, m‐ and p‐xylene, and naphthalene levels in gasoline‐contaminated soil columns before and after forced‐air venting and relating these values to the aqueous‐phase concentrations measured when water is percolated through the same columns.

Sandy soils with and without organic matter were packed into glass columns. The soils were brought to residual water and residual gasoline saturations by applying a vacuum to a ceramic pressure plate at the column bottom. Venting was performed by passing clean, moist air through the columns. The columns were subsequently leached under unsaturated conditions.

Soil samples were taken from the bottom of the columns upon completion of the venting or leaching phases of the experiments. Toluene, m‐ and p‐xylene, naphthalene, and TPH values were measured in soil samples extracted with either freon or methanol. Aqueous phase concentrations of these compounds were predicted using measured soil concentrations and either Raoult's law or organic matter‐water and fuel‐water partitioning theory (Boyd and Sun, 1990). The predicted results were compared with measured leachate concentrations from the same columns.

Mole fractions estimated from soil concentrations and TPH values used in Raoult's law gave good predictions of aqueous phase concentrations for compounds that had a high mole fraction in the residual nonaqueous phase liquid (NAPL). For compounds at low concentrations in the residual NAPL, an approach using a distribution coefficient that accounted for both the organic matter and residual NAPL in the soil provided better estimates than those based on Raoult's law.     

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.     

Controlled environment soil‐core microcosm unit for investigating fate,migration, and transformation of chemicals in soils

The controlled environment soil‐core microcosm unit (CESMU) methods embody a collection of techniques that began with soil sampling in the field and continued throughout the laboratory investigation of chemical fate, migration, and transformation in site‐specific soils; it was a cost‐effective investigative methodology that could be used to screen chemical materials before initiating high‐cost environmental field studies. Intact soil cores were collected in the field using a hydraulically controlled probe, delivering intact soil‐cores with minimal disturbance directly into high‐density polyethylene pipe (10.3‐cm ID). The inert polyethylene pipe was an effective hydrophobic barrier that remained an integral part of the soil‐core column, obviating subsequent transfers of soil. In the laboratory, each soil column was fitted with a porous ceramic plate and a polyethylene endcap containing fittings for teflon tubing, so that a tension could be applied at the bottom of each soil column (30–35 kPa) to mimic field conditions, thus preventing the undue buildup of water within columns that otherwise would change the chemical, physical, and biological properties of the soil. The intact soil‐cores were housed in the CESMU chamber, a controlled temperature unit with sufficient capacity for maintaining constant temperature within entire soil‐cores. Synthetic rain was added twice a week by peristaltic pump at rates simulating rainfall. Leachates were collected under tension via teflon tubing into flasks in darkness and kept at soil column temperature inside CESMU until harvested for analyses. Soil columns were harvested at intervals for sectioning by depth, extraction, and soil analyses. CESMU methods are applicable to investigations of water movement, soil chemistry, solute transport/transformation, and effects on plants.     

Assessment of bioavailability of soil-sorbed atrazine

Bioavailability of pesticides sorbed to soils is an important determinant of their environmental fate and impact. Mineralization of sorbed atrazine was studied in soil and clay slurries, and a desorption-biodegradation-mineralization (DBM) model was developed to quantitatively evaluate the bioavailability of sorbed atrazine. Three atrazine-degrading bacteria that utilized atrazine as a sole N source (Pseudomonas sp. strain ADP, Agrobacterium radiobacter strain J14a, and Ralstonia sp. strain M91-3) were used in the bioavailability assays. Assays involved establishing sorption equilibrium in sterile soil slurries, inoculating the system with organisms, and measuring the CO(2) production over time. Sorption and desorption isotherm analyses were performed to evaluate distribution coefficients and desorption parameters, which consisted of three desorption site fractions and desorption rate coefficients. Atrazine sorption isotherms were linear for mineral and organic soils but displayed some nonlinearity for K-saturated montmorillonite. The desorption profiles were well described by the three-site desorption model. In many instances, the mineralization of atrazine was accurately predicted by the DBM model, which accounts for the extents and rates of sorption/desorption processes and assumes biodegradation of liquid-phase, but not sorbed, atrazine. However, for the Houghton muck soil, which manifested the highest sorbed atrazine concentrations, enhanced mineralization rates, i.e., greater than those expected on the basis of aqueous-phase atrazine concentration, were observed. Even the assumption of instantaneous desorption could not account for the elevated rates. A plausible explanation for enhanced bioavailability is that bacteria access the localized regions where atrazine is sorbed and that the concentrations found support higher mineralization rates than predicted on the basis of aqueous-phase concentrations. Characteristics of high sorbed-phase concentration, chemotaxis, and attachment of cells to soil particles seem to contribute to the bioavailability of soil-sorbed atrazine.     

不同污染负荷土壤中镉和铅的吸附－解吸行为

采用一次平衡法,对3种不同污染负荷土壤Cd2 和Pb2 的吸附-解吸行为进行了比较.结果表明,低污染负荷土壤对Cd2 和Pb2 的吸附能力高于高污染负荷土壤.3种土壤对Cd2 的吸附等温线与Freundlich方程有较好的拟合性,Pb2 的等温吸附过程可用Langmuir方程与Freundlich方程来描述.双常数方程是描述这3种不同污染负荷土壤中Cd2 和Pb2 吸附动力学行为的最优模型,其次为Elovich方程,最差模型是一级动力学方程.Pb2 的解吸滞后现象较Cd2 明显.高污染负荷土壤的吸附态Cd2 、Pb2 解吸率高于低污染负荷土壤,Cd2 、Pb2 解吸量与其初始吸附量之间的关系符合二次幂方程.3种土壤Cd2 、Pb2 的解吸速率随重金属初始浓度的增加而增加,随解吸时间的延长而降低.     

Impacts of Soil Organic Matter and Temperature on Sorption of Acetazolamide on Four Soils

Batch sorptions of acetazolamide (AZ) were conducted using four soils from China. Sorption of AZ was found to be impacted by OC, clay content, and soil pH, with higher k_d values for soils with higher clay content. The k_d values of SOM-removed soils are much lower than those of bulk soils. Sorption data were well fitted with a Freundlich model (r² > 0.99). Chelating with the metal ions on the surfaces of soil particles was probably involved. With pH increase, the electrostatic attraction between anionic AZ and positively charged soil surface may increase. The sorption capacity decreased when the temperature increased from 20 to 40°C, and the calculated thermodynamics parameters of ΔG₀, ΔH₀, and ΔS₀ indicated that the sorption was a non-spontaneous, physisorption, and exothermic process. Sorption coefficients (k_d) for the compound in soil were low (ranging from 0.42 to 1.19 L·kg^?1) and indicated that low level sorption of AZ with appreciable risk of ground water contamination.     

Mobilization Assessment and Possibility of Increased Availability of PAHs in Contaminated Soil Using Column Tests

Surfactants are well known to increase solubility/mobility of hydrocarbons and can be used to remediate contaminated water and soil. We wanted to explore if Ivey sol® 106 used at less than the critical micelle concentration (CMC) could effectively mobilize PAH (polycyclic aromatic hydrocarbons) from contaminated soil. The first step was to establish a measurement technique. Hence, a column leaching method was undertaken to investigate mobility of PAH-contaminated soil from a former gaswork facility. The methodology was based on a recycled flow of aqueous solution containing CaCl₂ 0.01M through two different soil columns. In the first column test, the free desorption of hydrocarbons was studied by recycling the solution through the soil column with a peristaltic pump and with a liquid/solid ratio of 2, based on ISO/DIS 18772. The solution was replaced with new solution every three days to aid desorption.

In the second column test, the set-up was similar with the exception of the aforementioned recycling solution. In this case, a second column was filled with a resin, Amberlite XAD-2, which captures PAHs entering the solution through the soil column, cleaning it of hydrocarbons (induced desorption). The results obtained for induced desorption and free desorption with reposition showed that liberation of PAHs in the presence of resins was higher (7%) as opposed to free desorption (below 0.3%). These two experiments demonstrated low mobilization of PAHs.

A third column test was performed using a non ionic surfactant, Ivey-sol® 106, 100 μg g^?1 of soil below the CMC in the recycling solution. The introduction of Ivey-sol® 106 at 0.005%w/v increased desorption of PAHs to 32%, thus demonstrating the potential for increased bioavailability of the PAHs for bioremediation of the soil.     

Effect of soil permeability on virus removal through soil columns

Laboratory experiments were performed on four different soils, using 100 cm long columns, to determine the extent of virus movement when wastewater percolated through the soils at various hydraulic flow rates. Unchlorinated secondary sewage effluent seeded with either poliovirus type 1 (strain LSc) or echovirus type 1 (isolate V239) was continuously applied to soil columns for 3 to 4 days at constant flow rates. Water samples were extracted daily from ceramic samplers at various depths of the column for the virus assay. The effectiveness of virus removal from wastewater varied greatly among the different soil types but appeared to be largely related to hydraulic flow rates. At a flow rate of 33 cm/day, Anthony sandy loam removed 99% of seeded poliovirus within the first 7 cm of the column. At flow rates of 300 cm/day and above, Rubicon sand gave the poorest removal of viruses; less than 90% of the seeded viruses were removed by passage of effluent through the entire length of the soil column. By linear regression analyses, the rate of virus removal in soil columns was found to be negatively correlated with the flow of the percolating sewage effluent. There was no significant difference in rate of removal between poliovirus and echovirus in soil columns 87 cm long. The rate of virus removal in the upper 17 cm of the soil column was found to be significantly greater than in the lower depths of the soil column. This study suggests that the flow rate of water through the soil may be the most important factor in predicting the potential of virus movement into the groundwater. Furthermore, the length of the soil column is critical in obtaining useful data to predict virus movement into groundwater.     

Effect of soil permeability on virus removal through soil columns.

Laboratory experiments were performed on four different soils, using 100 cm long columns, to determine the extent of virus movement when wastewater percolated through the soils at various hydraulic flow rates. Unchlorinated secondary sewage effluent seeded with either poliovirus type 1 (strain LSc) or echovirus type 1 (isolate V239) was continuously applied to soil columns for 3 to 4 days at constant flow rates. Water samples were extracted daily from ceramic samplers at various depths of the column for the virus assay. The effectiveness of virus removal from wastewater varied greatly among the different soil types but appeared to be largely related to hydraulic flow rates. At a flow rate of 33 cm/day, Anthony sandy loam removed 99% of seeded poliovirus within the first 7 cm of the column. At flow rates of 300 cm/day and above, Rubicon sand gave the poorest removal of viruses; less than 90% of the seeded viruses were removed by passage of effluent through the entire length of the soil column. By linear regression analyses, the rate of virus removal in soil columns was found to be negatively correlated with the flow of the percolating sewage effluent. There was no significant difference in rate of removal between poliovirus and echovirus in soil columns 87 cm long. The rate of virus removal in the upper 17 cm of the soil column was found to be significantly greater than in the lower depths of the soil column. This study suggests that the flow rate of water through the soil may be the most important factor in predicting the potential of virus movement into the groundwater. Furthermore, the length of the soil column is critical in obtaining useful data to predict virus movement into groundwater.     

Pesticide desorption from soils facilitated by dissolved organic matter coming from composts: experimental data and modelling approach

Dissolved organic matter (DOM) interaction with pesticides was examined studying the ability of DOM to desorb 8 pesticides previously sorbed to soil. DOM was originating from municipal waste composts at two maturity degrees, recovered at 20°C and by hot-pressurised subcritical water. Pesticide desorption depended on their previous sorption on soil. When sorption was low (K_OC ≤ 50, sulcotrione, metalaxyl), water was more efficient than DOM for desorption. On the contrary, when sorption was high (K_OC ≥ 2000, trifluraline), little effect of DOM was observed. For the moderately sorbed pesticides, DOM favoured pesticide desorption compared to water. For the lowest sorbed pesticides (K_OC ≤ 100), hysteresis was increased with larger proportions of DOM extracted with subcritical-water. Dissolved organic matter extracted from fresh-immature compost had larger capacity to mobilize the sorbed pesticides than the DOM from the mature compost. The pesticide desorption resulted from the positive and competitive interactions between pesticide, DOM and soil surfaces. These interactions were modelled considering separate partitioning coefficients. A general equation allowed the deduction of specific coefficients describing interactions in solution between pesticides and the non-sorbed fraction of DOM remaining in solution. This fraction was supposed to contain the most hydrophilic fraction of DOM and was able to interact with the most polar pesticide (amitrol). When pesticide hydrophobicity increased, the partitioning between pesticide and DOM decreased. Modelling the three-phase system (liquid, DOM and solid phases) pointed out that the solid phase played the most important role on pesticide behaviour through the sorption process of DOM and pesticides.     

Effect of Soil Chemical and Physical Properties on Sorption and Desorption Behavior of Lead in Different Soils of India

Lead (Pb) is a non-biodegradable contaminant, present in the environment, especially near lead-based industrial sites, agricultural lands, and roadside soils. Bioavailability of Pb in the soil is controlled by the sorption and desorption behavior of Pb, which are further controlled by the soil chemical and physical properties. In this study, sorption and desorption amounts of Pb in soil were compared with soil physical (sand, silt, clay content) and chemical (pH; electrical conductivity, EC; percent organic carbon, (%OC); cation exchange capacity, CEC) properties. Twenty-six surface soils (0–5cm), expected to vary in physical and chemical properties, were collected from different parts of India and were treated with known concentration of Pb solution (40 μg/L). The amount of Pb sorbed and desorbed were measured and correlated with soil properties using simple linear regressions. Sorption was significantly (p ≤ 0.05) and positively correlated with pH, and %OC; desorption was significantly (p ≤ 0.05) negatively correlated with the same two factors. Stepwise multiple regressions were performed for better correlations. Predicted sorption and desorption amounts, based on multiple regression equations, showed reasonably good fit (R² = 0.79 and 0.83, respectively) with observed values. This regression model can be used for estimation of sorption and desorption amounts at contaminated sites.