Soil-air Partition Coefficients Research Articles

Soil-Air Partition Coefficients of Persistent Organic Pollutants Decline from Climate Warming: a Case Study in Yantai County, Shandong Province, China

Recognizing the kinetics of the soil-air partition coefficients (Ksoil-air) of persistent organic pollutants (POPs) under distinct scenarios of changing climate conditions is crucial for well understanding the response of POPs exchange process across the air-soil interface to climate warming. Taking Yantai County, Shandong Province, China, as a case study, the Ksoil-air values of HCH, DDE, DDD, and DDT in cropland soil under two levels of soil organic matter (SOM) (0.5% and 1.7%) were projected under future climate scenarios by employing representative concentration pathway (RCP) climate scenarios and a multiple linear model of the Ksoil-air of POPs. Compared to baseline conditions, future climate conditions would shift substantially, and daily Ksoil-air values of HCH, DDE, DDD, and DDT under future climate scenarios would decline by approximately 23–91 (× 105), 5,542–21,703 (× 105), 78–309 (× 105), and 18,986–74,133 (× 105), respectively, under future climate scenarios than under baseline conditions when the SOM content was 0.5% or by approximately 9,167–360,45 (× 105), 128,533–508,592 (× 105), 31,513–123,038 (× 105), and 444,513–1738,367 (× 105), respectively, when the SOM level was 1.7%, or by approximately 2–13% under two levels of SOM. Annual Ksoil-air values of HCH, DDE, DDD, and DDT would decline by approximately 3.51–7.54 (× 105), 842.06–1,806.46 (× 105), 11.83–25.66 (× 105), and 2,840.13–6,153.16 (× 105), respectively, when the SOM content was 0.5%, or by approximately 1,397.47–2,997.98 (× 105), 19,739.82–42,347.56 (× 105), 4,713.44–10,211.70 (× 105), and 66,579.06–144,244.10 (× 105), respectively, when the SOM content was 1.7%, or by approximately 8–18% under two levels of SOM. Moreover, Ksoil-air showed daily, monthly, and seasonal temporal changes within whole years and high temporal yearly fluctuation. Daily and annual Ksoil-air values were lower under 0.5% SOM content than under 1.7% SOM content. The results suggested that the adsorbing capacity of soil to POPs would decrease, and many more POPs in the soil would volatilize to the atmosphere from climate warming.

Influence of Adjuvants on Pesticide Soil–Air Partition Coefficients: Laboratory Measurements and Predicted Effects on Volatilization

A solid-phase fugacity meter was used to measure the soil-air partition coefficients of three semivolatile pesticides (chlorpyrifos, pyrimethanil, and trifluralin) in the absence of additional adjuvants (Ksoil-air,AI), as part of commercial formulations (Ksoil-air,formulation), and as formulation mixtures with an additional spray adjuvant added (Ksoil-air,formulation+sprayadjuvant). Chlorpyrifos Ksoil-air,formulation values were also measured over 15-30 °C, allowing for the change in internal energy of the phase transfer reaction (Δsoil-airU) to be calculated and compared to the Δsoil-airU for Ksoil-air,AI from the literature. Measured Ksoil-air values were then used as input parameters in a pesticide volatilization model to understand how their variability affects pesticide volatilization rates under different conditions. Initial experiments conducted at ∼24 °C indicated that all pesticides volatilized more readily in the presence of adjuvants than in their absence and that the additional spray adjuvant had minimal impact. The Δsoil-airU values were 328 and 90 kJ/mol for chlorpyrifos in the absence and presence of formulation adjuvants, respectively, suggesting that adjuvants may weaken or disrupt intermolecular attractions between pesticide molecules and soil. At temperatures below 24.5 °C, modeled chlorpyrifos volatilization rates were higher in the presence of adjuvants than in their absence; however, the opposite occurred at temperatures above 24.5 °C.

The Abandoned E-Waste Recycling Site Continued to Act As a Significant Source of Polychlorinated Biphenyls: An in Situ Assessment Using Fugacity Samplers.

The recycling of e-waste has attracted significant attention due to emissions of polychlorinated biphenyls (PCBs) and other contaminants into the environment. We measured PCB concentrations in surface soils, air equilibrated with the soil, and air at 1.5-m height using a fugacity sampler in an abandoned electronic waste (e-waste) recycling site in South China. The total concentrations of PCBs in the soils were 39.8-940 ng/g, whereas the concentrations in air equilibrated with the soil and air at 1.5 m height were 487-8280 pg/m(3) and 287-7380 pg/m(3), respectively. The PCB concentrations displayed seasonal variation; they were higher in winter in the soils and higher in summer in the air, indicating that the emission of PCBs from the soil was enhanced during hot seasons for the relatively high temperature or additional sources, especially for low-chlorinated PCBs. We compared two methods (traditional fugacity model and fugacity sampler) for assessing the soil-air partition coefficients (Ksa) and the fugacity fractions of PCBs. The results suggested that the fugacity sampler provided more instructive and practical estimation on Ksa values and trends in air-soil exchange, especially for low-chlorinated PCBs. The abandoned e-waste burning site still acted as a significant source of PCBs many years after the prohibition on open burning.

Partitioning of Dichloro-diphenyl-trichloroethane and Its Metabolites Between Artificial Solid Media and Air

Soil–air partitioning is an important diffusive process affecting the environmental fate of organic compounds. In this study, the soil–air partition coefficients (KSA) for dichloro-diphenyl-trichloroethane and its metabolites (designated as DDTs, the sum of p, p′- and o, p′-isomers of DDT, DDD, and DDE) over a temperature range from 5 to 50 °C in artificial solid media were determined by a solid–fugacity meter. The results showed that log KSA gradually increased with soil organic carbon content (fOC). A reversed relationship was observed between log KSA values and the environmental temperatures (T). The enthalpy changes (ΔHSA) indicated that o, p′-isomers required more energy to release from artificial solid media to the gas phase. Moreover, with increasing temperature, the slope of the regression line of log KSA vs. log KOA (octanol–air partition coefficient) was approaching to 1. Based on factors influencing soil–air partitioning and the experimental data, a multiple parameter (T, fOC, and KOA) model was used to predict the KSA values for DDTs.

Soil-air partitioning of polychlorinated biphenyls and total dichloro-diphenyl-trichloroethanes

Soil-air partitioning is an important diffusive process that affects the environmental fate of organic compounds and human health. In this review, factors affecting the soil-air partitioning of polychlorinated biphenyls (PCBs) and total dichloro-diphenyl-trichloroethanes (p,p'- and o,p'- isomers of DDT, DDD, and DDE) are discussed. Hydrophobicity is an important factor that influences soil-air partition coefficients (KSA), and its effect can be explained through enthalpy of phase change for soil-air partitioning transfer (ΔHSA). For more hydrophobic compounds, a sharp increase in the KSA of PCBs and organochlorines can be seen in the early aging period. During the aging period, the temperature has a significant effect on the more hydrophobic organic compounds. The content and properties of soil or- ganic matter influence the KSA of the target compounds. Generally, KSA decreases with increasing rela- tive humidity in soils. The linear trend between KSA and temperature (T) changes at 0 °C. Freezing the air or soil in experiments would change the research results. On the basis of factors influencing soil-air partitioning, a multipleparameter (T, organic carbon fraction (fOC), and octanol-air partition coefficient (KOA)) model is put forward to predict the KSA values for PCBs and total DDTs.

Persistent organic pollutants in soil near the Changwengluozha glacier of the Central Tibetan Plateau, China: Their sorption to clays and implication

Twenty-seven soil samples were collected at ca. 5000m from the Changwengluozha glacier. In addition to soil components, the concentration of 23 organochlorine pesticides (OCPs) and 16 polycyclic aromatic hydrocarbons (PAHs) were analyzed. Clay minerals were found to play a key role in the accumulation of OCPs/PAHs in soil. The sorption ratio of chemical to clay was ordered in the OCPs and PAHs to the vapor pressure in a negatively correlated fashion. Because of the negative relationship between vapor pressure and the soil–air partition coefficients (KSA), it was understood that the higher sorption ratio responded to a higher KSA, which indicated the fate of the contaminants in soil. The soil near the Changwengluozha glacier functioned as a “sink” for OCPs in the decreasing order of 2,4′-DDT, 4,4′-DDD, HCB, δ-HCH, and α-HCH and for PAHs in an decreasing order of Pyr, Flu, Fl, Ace, and Acy.

Soil-Air exchange controls on background atmospheric concentrations of organochlorine pesticides

Abstract. Soils are the major terrestrial reservoir of persistent organic pollutants, and thus net volatilization from soil, when it happens, may exert a control on the atmospheric occurrence and variability of organic pollutants. Here, we report and discuss the concentrations of legacy organochlorine pesticides (OCPs) such as hexachlorobenzene (HCB), hexaclorocyclohexanes (HCH) and dichlorodiphenyltrichloroethane (DDT) in the atmosphere and in soils, their measured fugacities in soil, the soil-air partition coefficients (KSA) and soil-air fugacity ratios (fs/fa) in rural background areas of N-NE Spain and N-NW England. Four sampling campaigns were carried out in Spain and UK to assess seasonal variability and differences between sampling sites. KSA values were significantly dependent on soil temperature and soil organic matter quantity, and to a minor extent on organic matter type. HCH isomers and DDT metabolites in soil are close to equilibrium with the overlying atmosphere at rural background areas of Spain with a tendency to volatilize and deposit during warm and cold periods, respectively. The mixture of HCH and DDT found in the atmosphere is clearly strongly influenced by the mixture of HCH and DDT which escapes from soil, with significant correlations between them (r2 ranging between 0.63–0.76 and p-level<0.001 for the Ebro sampling sites), thus suggesting a close coupling of air and soil concentrations, demonstrating that net volatilization from soil control the atmospheric levels of OCPs in the Northern Spain background atmosphere. Conversely, soils at rural UK sites were usually a sink for atmospheric DDT and HCH, but not for HCB. The negative statistically significant relationship found between log KSA and the log (fs/fa) ratio, suggests that high latitude regions, due to the high soil organic matter content and lower temperatures, will act as larger traps and accumulate more atmospheric OCPs. Thus, the extent to which soils are secondary sources to the atmosphere is currently dependent on the reservoir potential of soils for OCPs and shows a marked seasonality in their strength.

Factors Influencing the Soil–Air Partitioning and the Strength of Soils as a Secondary Source of Polychlorinated Biphenyls to the Atmosphere

Soils are a major reservoir of persistent organic pollutants, and soil-air partitioning and exchange are key processes controlling the atmospheric concentrations and regional fate of pollutants. Here, we report and discuss the concentrations of polychlorinated biphenyls (PCBs) in soils, their measured fugacities in soil, the soil-air partition coefficients (K(SA)) and soil-air fugacity gradients in rural background areas of N-NE Spain and N-NW England. Four sampling campaigns were carried out to assess seasonal and daily variability and differences between sampling sites. K(SA) values were significantly dependent on soil temperature and soil organic matter quantity, and to a minor extent organic matter type. All the PCB congeners in the soil are close to equilibrium with the atmosphere at rural Ebro sites, but soil fugacities tend to be higher than ambient air fugacities in early and late summer, consistent with the influence of temperature on soil-air partitioning. Therefore, during warm periods, soils increment their strength as secondary sources to the atmosphere. The mixture of PCBs found in the atmosphere is clearly strongly influenced by the mixture of PCBs which escape from soil, with significant correlations between them (R(2) ranging between 0.35 and 0.74 and p-level <0.001 for the Ebro sampling sites). Conversely, the close-to-equilibrium to net sink status of rural UK sites, suggest a close coupling of air and soil concentrations, but it is not possible to elucidate the importance of these soils as secondary sources yet, and presumably there are still significant primary sources to the regional/global environment.

Ubiquitous Net Volatilization of Polycyclic Aromatic Hydrocarbons from Soils and Parameters Influencing Their Soil−Air Partitioning

Soils are a major reservoir of organic pollutants, and soil-air partitioning and exchange are key processes controlling the regional fate of pollutants. Here, we report and discuss the soil concentrations of polycyclic aromatic hydrocarbons (PAHs), their soil fugacities, the soil-air partition coefficients (K(SA)) and soil-air gradients for rural and semirural soils, in background areas of N-NE Spain and N-NW England. Different sampling campaigns were carried out to assess seasonal variability and differences between sampling sites. K(SA) values were dependent on soil temperature and soil organic quantity and type. Soil fugacities of phenanthrene and its alkyl homologues were 1-2 orders of magnitude higher than their ambient air fugacities for all sampling sites and periods. The soil to air fugacity ratio was correlated with soil temperature and soil redox potential. Similar trends for other PAHs were found but with lower fugacity ratios. The ubiquitous source of PAHs from background soils to the atmosphere found in all temperate regions in different seasons provides an indirect evidence of potential in situ generation of two to four ring PAHs and their alkyl homologues in the surface soil. We discuss this hypothetical biogenic source and other potential processes that could drive the high soil to air fugacity ratios of some PAHs.

Retention of Nonionic Organic Compounds on Thermally Treated Soils

To achieve a higher efficiency of thermal remediation of soil contaminated with organic compounds, the retention mechanisms of organic compounds on thermally treated soil need to be understood adequately. In this study, a soil-column gas chromatography approach was developed to determine the soil-air partition coefficients (K(SA)) at 300 degrees C for a diverse set of nonionic organic compounds bearing many different functional groups; and the retention mechanisms of these organic compounds on two typical soils, isohumisols and ferralisols, were characterized using a polyparameter linear free energy relationship (pp-LFER). The K(SA) values (mL g(-1)) of typical volatile organic compounds (VOCs) with lower boiling points were <1.5 and in some cases even below 1.0, suggesting the rapid removal of VOCs from soils at 300 degrees C. Moreover, the K(SA) values were found to be a strong function of the soil-column temperature T (K), and be almost independent of the carrier-gas flow rate. Significant differences in molecular interactions were noted among various soil-solute pairs. The relative contributions of nonspecific van der Waals forces to the retention of test polar solutes were higher on isohumisols than on ferralisols. In contrast to the reported pp-LFER models for natural soils and soil components at normal environmental temperatures, our results suggest that elevated temperature remarkably reduces H-bond interactions between polar organic compounds and the soil matrix, thus allowing accelerated desorption of polar organic compounds from soils during thermal treatment.

Development of a Soil Fugacity Sampler for Determination of Air−Soil Partitioning of Persistent Organic Pollutants under Field Controlled Conditions

Soils are the main reservoir of persistent organic pollutants (POPs) and thus air-soil exchange and partitioning are key processes controlling the fate and transport of POPs at regional and global scales. To date, soil fugacity has been estimated from models of the soil-air partition coefficients, with the associated unavoidable uncertainties; or by experimental procedures in the laboratory with uncertain application in field conditions. The development of an operational soil fugacity sampler is presented here; one which ensures optimal field data of the POP fugacity in soil and environmentally relevant surface (soil+grass, etc.) and therefore ensuring accurate soil-air partition coefficients and surface-air fugacity gradients. The sampler flow rate is optimized, sampler reproducibility is assessed, and equilibrium between the gas and soil concentrations of polychlorinated biphenyls and polycyclic aromatic hydrocarbons is demonstrated. The development and comprehensive validation of a soil fugacity sampler opens the door for the first time to field studies that accurately determine the variables driving the soil-air partitioning and fluxes of POPs.