Soil Fugacity Research Articles

Revolatilisation of soil-accumulated pollutants triggered by the summer monsoon in India

Abstract. Persistent organic pollutants that have accumulated in soils can be remobilised by volatilisation in response to chemical equilibrium with the atmosphere. Clean air masses from the Indian Ocean, advected with the onset of the summer monsoon, are found to reduce concentrations of hexachlorocyclohexane (HCH), dichlorodiphenyltrichloroethane (DDT) and its derivatives, endosulfan and polychlorinated biphenyls (PCBs) in air at a mountain site (all in the range 5–20 pg m−3) by 77 %, 70 %, 82 % and 45 %, respectively. The analysis of fugacities in soil and air suggest that the arrival of summer monsoon triggers net volatilisation or enhances ongoing revolatilisation of the now-banned chemicals HCH and PCBs from background soils in southern India. The response of the air–soil exchange was modelled using a regional air pollution model, WRF-Chem PAH/POP. The results suggest that the air is increasingly polluted during transport by the south-westerly monsoon winds across the subcontinent. Using a multidecadal multimedia mass balance model, it is found that air–surface exchange of HCH and DDT have declined since the ban of these substances from agriculture, but remobilisation of higher chlorinated PCBs may have reached a historical high, 40 years after peak emission.

Environmental behaviour of polychlorinated biphenyls in a paddy field: Impact factors and canopy effects

Paddy fields play an important role in the transport of persistent organic pollutants (POPs) due to the filter effects of canopy and their wide distribution. Thus, most studies have been focusing on the filter effects of canopy for POPs. However, shielding effects of canopy might also influence transport and portion of POPs between top and bottom. To investigate these two important processes, our study involved 30 polychlorinated biphenyls (PCBs) in a paddy field. Samples of bulk depositions, surface water, and air were taken to investigate the occurrence and the behaviour of PCBs. We found that rice canopy has potentially crucial effects on the transport of PCBs. The results showed slightly higher abundances for most of high‑chlorine PCBs (81.0%) at the top of the canopy, indicating that the high‑chlorine PCBs were intercepted by the rice leaves. Moreover, our study showed that the PCBs in surface water and soil tended to escape into air according to air, water, and soil fugacity. And we found higher atmospheric PCB levels (103 pg m−3) at the bottom of the canopy than top (88.9 pg m−3), indicating canopy shielding effects on escaped PCBs. In addition, the study showed that the PCBs intercepted by the rice canopy may occur in surface water and soil due to air movement and precipitation. These results suggest that paddy fields can enrich POPs, and effects of the environmental factors on POPs transport need to be investigated further.

Seasonal soil/snow-air exchange of semivolatile organic pollutants at a coastal arctic site (Tromsø, 69°N)

Soils are a major reservoir of semivolatile organic pollutants such as polychlorinated biphenyls (PCBs) and polycyclic aromatic hydrocarbons (PAHs), and exert a control on their atmospheric occurrence. We present here an assessment of the atmospheric occurrence and seasonality of soil/snow-air partitioning and exchange of PCBs, PAHs, hexachlorobenzene (HCB), and hexachlorocyclohexanes (HCHs) in the arctic city Tromsø, northern Norway. The fugacities of the organic pollutants in soils and snow were determined using a soil fugacity sampler by equilibrating the air concentrations with those in the surface soil/snow. The concentrations in soils did not show a significant seasonality. Conversely, the ambient air concentrations and the soil (or snow) fugacity showed a clear seasonality for PCBs, HCH, HCB and some PAHs, related to temperature. Fugacities in soil/snow were correlated with those in the ambient gas phase, suggesting a close seasonal air-soil/snow coupling. Generally, there was a net deposition or close to equilibrium conditions during the winter, which contrasts with the net volatilization observed during the warmer periods. The chemicals with lower octanol-air partition coefficients showed a larger tendency for being volatilized and thus remobilized from this coastal arctic environment. Conversely, the more hydrophobic compounds were close to air-soil/snow equilibrium or showed a net deposition.

Predicting Polycyclic Aromatic Hydrocarbon Bioavailability to Mammals from Incidentally Ingested Soils Using Partitioning and Fugacity.

Soil and dust ingestion is one of the major human exposure pathways to contaminated soil; however, pollutant transfer from ingested substances to humans cannot currently be confidently predicted. Soil polycyclic aromatic hydrocarbon (PAH) bioavailability is likely dependent upon properties linked to chemical potential and partitioning such as fugacity, fugacity capacity, soil organic carbon, and partitioning to simulated intestinal fluids. We estimated the oral PAH bioavailability of 19 historically contaminated soils fed to juvenile swine. Between soils, PAH blood content, with the exception of benzo(a)pyrene, was not linked to fugacity. In contrast, between individual PAHs, using partitioning explained PAH blood content (area under the curve = 0.47 log fugacity + 0.34, r(2) = 0.68, p < 0.005, n = 14). Soil fugacity capacity predicts PAH soil concentration with an average slope of 0.30 (μg PAH g(-1) soil) Pa(-1) and r(2)'s of 0.61-0.73. Because PAH blood content was independent of soil concentration, soil fugacity correlated to PAH bioavailability via soil fugacity's link to soil concentration. In conclusion, we can use fugacity to explain PAH uptake from a soil into blood. However, something other than partitioning is critical to explain the differences in PAH uptake into blood between soils.

Emerging Flame Retardants, PBDEs, and HBCDDs in Indoor and Outdoor Media in Stockholm, Sweden

Dust, indoor air, outgoing air from ventilation systems, outdoor air, and soil were sampled in and around Stockholm, Sweden during the winter and spring 2012. The concentrations of several emerging flame retardants (EFRs), polybrominated diphenyl ethers (PBDEs), and isomers of hexabromocyclododecane (HBCDD) were measured. The most commonly found EFR was 1,2-dibromo-4-(1,2 dibromoethyl)cyclohexane (TBECH or DBE-DBCH), which was found in nearly all indoor, ventilation, and outdoor air samples, most dust samples, but not in soil samples. Other frequently detected EFRs included pentabromotoluene (PBT), hexabromobenzene (HBB), 2,3,4,5-tetrabromo-ethylhexylbenzoate (EHTBB), 2,3,4,5-tetrabromo-bis(2-ethylhexyl) phthalate (BEH-TEBP), and decabromodiphenyl ethane (DBDPE). PBDE concentrations were significantly lower in air and dust samples compared to a previous study in Stockholm. In outdoor air, DBE-DBCH, PBT, EHTBB, DBDPE, and PBDEs showed an "urban pulse" with concentrations increasing as samples were taken in more urban areas compared to rural areas. These EFRs show similar environmental behavior as PBDEs. Higher brominated BDEs showed this same urban pulse in soil but lower brominated BDEs did not. Air-soil fugacity fractions were calculated, and these indicated that most compounds are undergoing net deposition from atmosphere to soil, with the higher brominated PBDEs furthest from equilibrium.

Organochlorine pesticides in surface soils from obsolete pesticide dumping ground in Hyderabad City, Pakistan: Contamination levels and their potential for air–soil exchange

This study was conducted to examine organochlorine pesticides (OCPs) contamination levels in the surface soil and air samples together with air–soil exchange fluxes at an obsolete pesticide dumping ground and the associated areas from Hyderabad City, Pakistan. Among all the sampling sites, concentrations of OCPs in the soil and air samples were found highest in obsolete pesticide dumping ground, whereas dominant contaminants were dichlorodiphenyltrichloroethane (DDTs) (soil: 77–212,200ngg−1; air: 90,700pgm−3) and hexachlorocyclohexane (HCHs) (soil: 43–4090ngg−1; air: 97,400pgm−3) followed by chlordane, heptachlor and hexachlorobenzene (HCB). OCPs diagnostic indicative ratios reflect historical use as well as fresh input in the study area. Moreover, the air and soil fugacity ratios (0.9–1.0) at the dumping ground reflecting a tendency towards net volatilization of OCPs, while at the other sampling sites, the fugacity ratios indicate in some cases deposition and in other cases volatilization. Elevated concentrations of DDTs and HCHs at pesticide dumping ground and its surroundings pose potential exposure risk to biological organisms, to the safety of agricultural products and to the human health. Our study thus emphasizes the need of spatio-temporal monitoring of OCPs at local and regional scale to assess and remediate the future adverse implications.

Levels, distribution and air–soil exchange fluxes of polychlorinated biphenyls (PCBs) in the environment of Punjab Province, Pakistan

An initial survey of the concentrations of polychlorinated biphenyl (PCB) compounds in air and soils across industrial and agricultural areas of Punjab Province, Pakistan, was conducted from January to March 2011. The total concentration of all PCBs (<Sigma>31 PCBs) ranged from 34 to 389pgm−3 in air and from 7 to 45ngg−1 dry weight in soils, where both ranges were similar to the average ranges in other areas of the world. PCBs were elevated across industrial regions near urban and industrial sources. Consistently low air concentrations of PCBs at the agricultural sites suggest that they are less widespread or uniformly distributed in the Pakistani atmosphere. The calculated air and soil fugacity fraction values indicated that soils are a potential secondary source of PCBs in agricultural areas, whereas they are in equilibrium or atmospheric deposition in industrial and urban areas. TEQ concentrations of dioxin-like PCBs for soil samples met the Canadian standard. However, local authorities should address the human health threats from urban and industrial soils in Punjab Province, Pakistan.

Climatic and Biogeochemical Controls on the Remobilization and Reservoirs of Persistent Organic Pollutants in Antarctica

After decades of primary emissions, reservoirs of persistent organic pollutants (POPs) have accumulated in soils and snow/ice in polar regions. These reservoirs can be remobilized due to decreasing primary emissions or due to climate change-driven warmer conditions. Results from a sampling campaign carried out at Livingston Island (Antarctica) focusing on field measurements of air-soil exchange of POPs show that there is a close coupling of the polychlorinated biphenyls (PCBs) in the atmosphere and snow/ice and soils with a status close to air-surface equilibrium to a net volatilization from Antarctic reservoirs. This remobilization of PCBs is driven by changes in temperature and soil organic matter (SOM) content, and it provides strong evidence that the current and future remobilization and sinks of POPs are a strong function of the close coupling of climate change and carbon cycling in the Antarctic region and this is not only due to warming. Whereas an increase of 1 °C in ambient temperature due to climate change would increase current Antarctic atmospheric inventories of PCBs by 21-45%, a concurrent increase of 0.5% SOM would counteract the influence of warming by reducing the POP fugacity in soil. A 1 °C increase in Antarctic temperatures will induce an increase of the soil-vegetation organic carbon and associated POPs pools by 25%, becoming a net sink of POPs, and trapping up to 70 times more POPs than the amount remobilized to the atmosphere. Therefore, changes in soil biogeochemistry driven by perturbations of climate may increase to a larger degree the soil fugacity capacity than the decrease in air and soil fugacity capacity due to higher temperatures. Future research should focus on quantifying these remobilization fluxes and sinks for the Antarctic region.

Polycyclic aromatic hydrocarbons (PAHs) in particle-size fractions of urban topsoils

Polycyclic aromatic hydrocarbons’ (PAHs) concentrations in bulk samples are commonly used to assess contamination but PAHs are unevenly distributed among particle-size fractions. Seventeen urban surface soil samples from the city of Xuzhou, China, were collected and then fractionated into five size fractions (2,000–300, 300–150, 150–75, 75–28, and <28 μm). The concentrations of 12 US EPA PAHs were measured using gas chromatograph/mass spectrometry in various fractions, and the bulk soil samples and distribution patterns of PAHs in different particle-size fractions were investigated. The mean concentration of total PAHs in bulk soil samples was 1,879 ng/g. The median concentrations for all individual PAH were higher for the 75–2,000 μm fraction than for the <75 μm fraction. The distribution factors for various PAHs in <28 μm soil fraction were closely correlated (r = −0.661, p < 0.019) to bulk soil fugacity capacity. The values of PAH isomer indicated that traffic emissions might be the major origin of PAHs in Xuzhou surface soils. Spearman correlation analysis was performed and the result suggested that soil organic carbon might be a factor controlling the concentrations of PAHs in soils.

Organochlorine pesticides in air and soil and estimated air–soil exchange in Punjab, Pakistan

This study provides the first systematic data on the distribution of organochlorine pesticides (OCPs) in the soils and atmosphere of the Punjab province, Pakistan. Atmospheric concentrations of OCPs were estimated by using the polyurethane foam passive air sampling (PUF-PAS) technique. DDTs (dichlorodiphenyltrichloroethane), HCHs (hexachlorocyclohexane) and chlordane were the dominant OCPs found in both soil and air samples. The average concentrations of DDTs, HCHs and chlordane were 350, 55 and 99pgm−3 in air and 40, 7.8 and 3.8ngg−1 in soils, respectively. Air–soil exchange of OCPs was estimated by calculating the fugacities in soil and air. Fugacity fraction (ff) values indicate that soils are acting as a secondary source to contaminate the atmosphere at certain sampling stations.

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&lt;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.

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.

Organochlorine Pesticides Contaminated Surface Soil As Reemission Source in the Haihe Plain, China

A large amount of organochlorine pesticides (OCPs) including hexachlorocyclohexane isomers (alpha-HCH, beta-HCH, gamma-HCH, and 6-HCH,sigmaHCH asthe total) and dichlorodiphenyltrichloroethane and metabolites (p,p'-DDT, p,p'-DDE, and p,p'-DDD, sigmaDDT as the total) have been applied over the Haihe Plain (an area of 300 000 km2) in Northern China. Even though the agricultural application of these OCPs was terminated more than a decade ago, their residues remain in the environment and continue to represent significant public health concern. In this study, more than 300 surface soil samples were collected from the Haihe Plain for measurement of these OCPs. The measured sigmaHCH and sigmaDDT residues were 3.9 +/- 26 and 64 +/- 260 ng/g as arithmetic means and standard deviations with median values of 0.38 and 6.5 ng/g, respectively. Although the levels were approximately 1 order of magnitude lower than those recorded in 1980s, it was estimated that there were 430 +/- 110 tons of sigmaHCH and 6100 +/- 760 tons of sigmaDDT in the surface soil of the area, respectively. The soils with high levels of OCP residuals were mostly distributed on the fringes of major cities, due to intensive farming and discharge from pesticide producers in the cities. The residuals of sigmaHCHs and sigmaDDTs were significantly correlated to soil organic matter content. Both alpha-HCH/beta-HCH and p,p'-DDT/p,p'-DDE ratios were log-normally distributed and negatively correlated to log(sigmaHCH) and log(sigmaDDT), respectively. Thus these ratios and correlations preclude certainty in distinguishing fresh application from historical usage. According to the total residuals and the distributions of alpha-HCH/beta-HCH and p,p'-DDT/p,p'-DDE ratios, it appears that significant recent input of either the OCPs is very unlikely. The calculated fugacities in soil and air provided quantitative evidence indicating a net and seasonally varied transport of sigmaHCH (0.31 ton/year) and sigmaDDT (1.9 ton/year) from soil to atmosphere in the study area. Such a surface-to-air transport suggested that after the ban, the surface soil had gradually converted from a major sink to an important emission source of OCPs and the reemission will continue for many years to come.

Organochlorine Pesticides in the Soils and Atmosphere of Costa Rica

A survey of the contamination of the physical environment of Costa Rica with banned organochlorine pesticides (OCPs) relied on sampling air and soil at 23 stations acrossthe country in 2004. Average annual air concentrations, determined with XAD-based passive samplers, and surface soil concentrations were generally low when compared to values reported for North and Central America, which is consistent with relatively low historical domestic use and little atmospheric inflow from neighboring countries. Statistical analysis and concentration maps reveal three types of spatial distribution: alpha-hexachlorocyclohexane and p,p'-DDD had a relatively uniform distribution across the country; other DDT-related species were greatly elevated over the national average at Manuel Antonio, a National Park on the Pacific coast; and dieldrin, lindane, and chlordane-related species had higher concentrations in Costa Rica's populated Central Valley. An altitudinal transect of stations in the Central Valley shows declining air-soil concentration ratios with elevation for lindane, likely driven by atmospheric inversions and soil organic carbon content. Enantiomeric composition of chiral OCPs in air and soil was close to racemic, with slight depletion of (-)-alpha-HCH, (-)-cis-chlordane, and (+)-trans-chlordane. Estimated air-soil fugacity fractions are highly uncertain but indicate equilibrium conditions for most OCPs, net volatilization of lindane at some sites, and net deposition for p,p'-DDE. The study demonstrates an approach for quickly evaluating the spatial distribution of OCPs in an understudied area, identifying regionally important contaminants and areas of elevated concentrations.

Model of the Long-Term Exchange of PCBs between Soil and the Atmosphere in the Southern U.K.

Measurements of concentrations of four PCB congeners (PCB-28, -52, -138, and -153) in air, herbage, and soil of the southern U.K. over the period 1942-1992 are compiled to demonstrate that emissions of PCB to the atmosphere increased from low levels in 1940 to a peak in the late 1960s and then fell to low current levels. This emission pulse resulted in a corresponding peak in air concentrations. Soil concentrations have responded to this pulse but with some delay, reaching a maximum in the early 1970s. At that time PCB fugacities in soil apparently exceeded atmospheric fugacities by about a factor of 10 because of nondiffusive deposition processes. Since then, fugacities in air and soil have fallen with a half-life of 10-20 yr probably as a result of volatilization or «degassing» of PCB, although it is possible (but not proved) that the degradation processes are also occurring with a half-life of approximately 15 yr. A simple two-compartment (air-soil) mass balance model is developed and applied to these data which gives a reasonable simulation of the long-term trends in concentration. It is concluded that there is a need to develop and improve models of this type to explain and predict the extent to which soils and vegetation act as a buffer of atmospheric concentrations of persistent chemicals

Screening of risk management options for abandoned wood-preserving plant sites in Alberta, Canada

Several abandoned wood-preserving sites have been identified in Alberta, Canada, which pose a potential threat to human health and the environment. The physiochemical, environmental, and toxicological properties of wood preservatives are discussed together with the predominant human exposure pathways for these chemicals in the environment. A Level II soil fugacity model is used to illustrate the comparative environmental fate of individual organic wood treatment chemicals following release to the soil environment. An evaluation of risk management options at five priority sites is used to illustrate problems associated with the treatment and disposal of mixed organic and inorganic contaminated soils, soil property limitations, and the predominance of organic contaminants within the residual oil phase. The latter reality dominates options for exposure reduction and risk management. Key words: contaminated soils, wood-preserving sites, remediation options, screening, fugacity model.