Organochlorine Pesticides In Air Research Articles

Cross-regional scale studies of organochlorine pesticides in air in China: Pollution characteristic, seasonal variation, and gas/particle partitioning

Few simultaneous studies of organochlorine pesticides (OCPs) in the atmosphere have been conducted across Southeast and Northeast China, and no data on the gas/particle (G/P) partitioning behaviors of several current-use OCPs are available. In this study, a one-year synchronous monitoring program was conducted for OCPs in Chinese atmosphere spanning 30° latitude and 60 °C temperature. A total of 111 pairs of gas and particle samples were collected from Mohe and Harbin in Northeast China and from Shenzhen in Southeast China. The detection frequency for 66.7 % of the OCPs exceeded 80 %, indicating their prevalence in the atmosphere. The concentrations of individual OCPs spanned six orders of magnitude, indicating different pollution levels. Highest levels of hexachlorobenzene were observed at all sites. Banned OCPs were found predominantly in secondary distribution patterns, whereas current-use OCPs were dominated by primary distribution patterns. In Harbin and Mohe, the concentrations of OCPs were highest in summer, followed by autumn and winter. No obvious seasonal variation was observed in Shenzhen associated with different cultivation types. At all three sites, OCPs were predominantly found in the gas phase, and higher percentages of particle-phase OCPs were observed in Harbin and Mohe than in Shenzhen. In this study, G/P partitioning models were used to study the G/P partitioning mechanism of OCPs. The Li–Ma–Yang model provided the most accurate prediction of the G/P partitioning behavior of OCPs with high molecular weights and low vapor pressures, particularly at low temperatures. However, OCPs with lower molecular weights and higher vapor pressures were predominantly in the equilibrium state, for which the Junge–Pankow model was suitable. This systematic cross-scale study provides new insights into pollution, G/P partitioning, and the environmental behavior of OCPs in the atmosphere.

Variations in the Concentration of Polychlorinated Biphenyls and Organochlorine Pesticides in Air over the Northern Hovsgol Region in 2008–2015

The variations in the concentration of polychlorinated biphenyls (PCBs) and organochlorine pesticides (OCPs) in atmospheric air in the northern Lake Hovsgol region in 2008–2015 is analyzed using passive air sampling data. It was found that the concentrations vary from background values (comparable with those for other high-mountain regions) to the levels typical of large settlements. The quantitative and qualitative variations in the concentration of PCBs and OCPs in air are recorded. The variations characterize the influence of both natural (seasonal variations in temperature and average annual temperature anomalies over the land and sea across the globe and Northern Hemisphere) and anthropogenic factors. There is a trend towards the increase in hexachlorobenzene (HCB) levels and the decrease in hexachlorocyclohexane (HCH) and dichlorodiphenyltrichloroethane (DDT) levels in the atmosphere. No significant variation in the total PCB was found in 2011–2015. The results of the modeling of PCB and OCP fluxes in the air-soil system in the analyzed region demonstrate that deposition prevails over volatilization that corroborates the significance of atmospheric transport for the PCB and OCP inflow to the Lake Hovsgol region.

Use of passive samplers to detect organochlorine pesticides in air and water at wetland mountain region sites (S-SE Brazil).

Low-density polyethylene (LDPE) passive samplers were deployed in upland surface waters and the overlying atmosphere during May and June 2012, to determine the transport and trends of freely dissolved and gaseous organochlorine pesticides (OCPs) along altitudinal gradients in mountain regions in south and southeast Brazil. Gaseous OCP concentrations were dominated by hexachlorobenzene (3.0-29 pg m(-3)) and endosulfans (Ʃ = α-endosulfan + β-endosulfan + endosulfan sulphate, 170-260 pg m(-3)), whereas freely dissolved endosulfans were significantly higher than all other OCPs (p < 0.001). The presence of some target pesticides at the highest elevation sites indicated their efficient high-altitude transport from regional sources. Air-water exchange gradients indicated net deposition of most volatile and recently banned OCPs (e.g., HCB, endosulfan) over Brazilian mountains. Moreover, the exposure of these sites to large-scale continental airflows with varying source contributions may partly explain the atmospheric deposition of selected OCPs over upland freshwaters at tropical and subtropical mountains sites in Brazil. These findings, coupled with LDPE passive air and water sampling measurements, point out the potential inputs from distant sources of semi-volatile chemicals to the two high-altitude sites.

Multiyear Measurements of Flame Retardants and Organochlorine Pesticides in Air in Canada's Western Sub-Arctic.

Fourteen polybrominated diphenyl ethers (PBDEs), 14 non-BDE flame retardants (FRs), and 25 organochlorine pesticides (OCPs) were analyzed in air samples collected at Little Fox Lake (LFL) in Canada's Yukon Territory from August 2011 to December 2014. LFL is a long-term monitoring station operated under the Northern Contaminants Program (NCP) and one of only a few stations that contribute to the assessment of air pollution levels and pathways to the sub-Arctic region. BDE-47 was the most abundant congener among the 14 PBDEs, followed by BDE-99. Non-BDE FRs pentabromotoluene (PBT) and dechlorane plus (DP) were detected in all the samples. Dechlorane 602, 2,3-dibromopropyl-2,4,6-tribromophenyl ether (DPTE), hexabromobenzene (HBB), and 2-ethylhexyl-2,3,4,5-tetrabromobenzoate (EH-TBB) were also detected in >75% of all samples. PBDEs have shown a decreasing tendency as of 2013, which may reflect the phase-out of penta- and octa-BDE mixtures has led to significant decline in the atmosphere. The highest concentrations of OCPs were observed for hexachlorobenzene (HCB), with a median concentration of 61 pg/m(3), followed by α-hexachlorocyclohexane (α-HCH) and α-endosulfan. Potential source contribution function (PSCF) highlights Northern Canada, Pacific, and East Asia as potential sources in warm seasons; whereas in cold seasons, the chemicals mainly came from the Pacific Rim.

Air-Seawater Exchange of Organochlorine Pesticides along the Sediment Plume of a Large Contaminated River.

Gaseous exchange fluxes of organochlorine pesticides (OCPs) across the air-water interface of the coastal East China Sea were determined in order to assess whether the contaminated plume of the Yangtze River could be an important regional source of OCPs to the atmosphere. Hexachlorocyclohexanes (HCHs), chlordane compounds (CHLs), and dichlorodiphenyltrichloroethanes (DDTs) were the most frequently detected OCPs in air and water. Air-water exchange was mainly characterized by net volatilization for all measured OCPs. The net gaseous exchange flux ranged 10-240 ng/(m2·day) for γ-HCH, 60-370 ng/(m2·day) for trans-CHL, 97-410 ng/(m2·day) for cis-CHL, and ∼0 (e.g., equilibrium) to 490 ng/(m2·day) for p,p'-DDE. We found that the plume of the large contaminated river can serve as a significant regional secondary atmospheric source of legacy contaminants released in the catchment. In particular, the sediment plume represented the relevant source of DDT compounds (especially p,p'-DDE) sustaining net degassing when clean air masses from the open ocean reached the plume area. In contrast, a mass balance showed that, for HCHs, contaminated river discharge (water and sediment) plumes were capable of sustaining volatilization throughout the year. These results demonstrate the inconsistencies in the fate of HCHs and DDTs in this large estuarine system with declining primary sources.

Persistent Organic Pollutants (POPs) in the atmosphere of agricultural and urban areas in the Province of Buenos Aires in Argentina using PUF disk passive air samplers

Passive air samplers consisting of polyurethane foam (PUF) disks were deployed in a network of eight sites across agricultural and urban areas in the Province of Buenos Aires in Argentina to assess levels of polychlorinated biphenyls (PCBs) and organochlorine pesticides (OCPs) during two sampling periods in 2006 and 2007. Concentrations (pg m−3) of PCBs in air ranged from BDL to 360, with an average at urban sites of Bahia Blanca (200±130) about one order of magnitude higher than at agricultural sites in the Province of Buenos Aires (20±20). Endosulfan exhibited the highest concentrations of all the chemicals investigated with a maximum of 16 000pg m−3 in the agricultural area. The remaining OCPs had lower levels (pg m−3) in the following ranges: ΣHCH (α−+γ− hexachlorocyclohexane) from 1 to 50, HEPT (heptachlor) and HEPX (heptachlor epoxide) from BDL to 20, chlordanes (Σtrans–chlordane, cis–chlordane and trans–nonachlor) from 1 to 40, dieldrin from BDL to 30, and p,p′–DDE (the only isomer of DDT that was detected) from BDL to 20. Concentrations of OCPs in air were highest at Bahia Blanca city and generally higher during the warmer sampling period. This study is one of the first investigations of the POPs composition in ambient air in the Province Buenos Aires of Argentina. The results support the Global Monitoring Plan of the Stockholm Convention on POPs and specifically, the need for air data to contribute to the regional report of the GRULAC (GRoUp of Latin American and Caribbean countries) region.

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.

Levels and potential sources of atmospheric organochlorine pesticides at Korea background sites

Data are presented for 11 organochlorine pesticides (OCPs) measured by high volume air samplers at three background sites (monthly for one site, seasonally for two sites) in South Korea during June 2008 and December 2009, and levels, seasonal variations and potential sources of high levels of OCPs and impact of long-range transport (LRT) were discussed. Geometric mean (GM) concentrations of OCPs in air samples (pg m−3) were highest for HCB (80, 15.0–256), HCH (71, 10.8–547), a currently used pesticide, DDT (3.50, ND-56.5), and Chlordane (1.15, ND-10.5). Other chemicals regularly detected included, Heptachlor (0.41, ND-2.59), Drins (0.61, ND-4.36) and Mirex (0.04, ND-0.78). Seasonal variation of OCPs was featured by higher concentrations in summer and lower in winter period. This could be associated with their temperature-driven re-volatilization from historical source and recent application of some OCPs (such as dicofol, HCH etc). Ratios of specific OCPs isomers suggest that dominant source of air HCHs in Korea background sites is technical HCH with a little input of lindane in recent time, and dominant source of air DDT is old and used technical DDT with a little bit of dicofol type DDT, and current air chlordane in Korean background sites mainly come from the source of historically used chlordane. The results from this study will provide comparable and scientifically sound data of OCP in background air and will contribute to further long-term POPs monitoring program in East Asia.

Passive air sampling of organochlorine pesticides in a northeastern state of India, Manipur

Abstract Thirty-six polyurethane foam disk passive air samplers (PUF-PAS) were deployed over a year during January to December, 2009 at three locations, i.e., Imphal (urban site), Thoubal (rural site) and Waithou (alpine site) of Manipur, to assess the seasonal local atmospheric emission of selected organochlorine pesticides (OCPs). The average concentration of HCHs monitored at mountain site during hot season (Mar, Apr, and May) and rainy seasons (Jun, Jul, Aug, and Sep) were 403 and 349 pg/m 3, respectively. DDTs had a high concentration with 384 pg/m 3 at rural site and 379 pg/m 3 at urban site during hot seasons. Endosulfans and chlordane were found high in concentration during hot seasons (260 pg/m 3) and low during retreating monsoon seasons (44 pg/m 3) at rural site. Most of the OCPs concentrations were high during cultivation period. The OCP concentrations of rainy season were highly correlated (p < 0.01) with OCPs of hot seasons. Further, positive correlation ( p < 0.05) was also obtained between cold seasons and retreating monsoon. Principal component analysis showed a significant correlation among the four seasons and distribution pattern of OCPs in air. Back trajectory analysis by using HYPSLIT model showed a long range air transport of OCPs to the present study area. Present OCP levels at Manipur is an outcome of both local emission and also movement of air mass by long range atmospheric transport.

Sources of organochlorine pesticides in air in an urban Mediterranean environment: volatilisation from soil

Organochlorine pesticide (OCP) cycling was studied in the area of Banja Luka, Bosnia and Herzegovina, over 3 days in summer with high temporal (4 h-means) and spatial (3 sites distanced 3-6 km) resolutions. Elevated levels of DDX compounds (i.e. o,p'- and p,p'-isomers of DDT, DDE and DDD, 44-74 pg m(-3) at the urban sites and 27 pg m(-3) as a background level), HCH (α-, β- and γ-isomers, 52-70 vs. 147 pg m(-3)), HCB (34-48 vs. <0.1 pg m(-3)) and pentachlorobenzene (6.8-9.9 vs. 6.0 pg m(-3)) were found. The variation of OCP levels at the two urban sites was not in phase, except for most DDX compounds. This was related to background levels, which for HCH were higher than in the urban area. Vertical profiles between samples collected from 1.1 and 2.3 m (part of the time 0.6 and 2.3 m) above a soil, which was only moderately contaminated by OCPs (0.12 ng g(-1) HCH, 0.11 ng g(-1) DDX, 0.44 ng g(-1) HCB) were analysed. Volatilisation from the ground caused negative vertical concentration gradients of HCH isomers (day and night), but not for HCB (except for 1 day-time sample) and DDX compounds (except p,p'-DDD, day-time, sporadically). The concentration in air and the vertical concentration gradient of the HCH isomers varied with air temperature (day-time maxima), while the variation of the HCB concentration was inversely related to air temperature and was determined by mixing (night-time maxima). α- and β-HCH were volatilised from soil throughout the three days, even during periods of cooling. Fugacity calculations, based on the absorption in soil organic matter as the process determining retention in soil, underestimated the volatilisation of β-HCH and p,p'-DDD. It is concluded that the representativeness of point measurements of OCPs in urban areas is limited by the spatial variability of soil contamination.

Organochlorine Pesticides in Ambient Air in Selected Urban and Rural Residential Areas in the Philippines Derived from Passive Samplers with Polyurethane Disks

The passive sampler with PUF disk was applied to investigate the types and concentrations of organochlorine pesticides (OCPs) in ambient air in three urban and rural residential areas simultaneously at different weather conditions in the Philippines. The concentrations of OCPs derived from the passive samplers indicated clear distinctions in the predominance of certain types and amounts of OCPs in air at different sampling sites and periods of sampling. Chlordanes were detected in concentrations ranging from 218 to 2,324 pg/m³ in the urban residential sites in all the sampling periods, indicating the possible use of these pesticides as termiticides in houses. Endosulfans were detected in two rural sites at 491 pg/m³ and 904 pg/m³ during one sampling period; indicating the possible use of the pesticide in the farm areas at that period.

Feasibility of poplar foliages as bio-monitors for organochlorine pesticides in air

The feasibility of poplar (P. tomentosa) foliages as passive biomonitors for organochlorine pesticides in air was explored. The accumulation patterns of poplar foliages for HCHs, DDTs and HCB were similar, the amount of HCHs, DDTs and HCB increased with foliage growth in spring, and decreased thereafter. There was no obvious distinction in the accumulation styles between the adult leaf and the leaf-litter. This accumulation pattern is likely related to the growing process of the poplar foliage, and was observed for the first time in our work, giving an evidence for the “bud burst effect” in plants. The technical HCH and DDT were used largely in history and not used in recent years, but there was a little usage of lindane and new input of o,p’-DDT in recent years, and dicofol usage may be the main source of o,p’-DDT. Concentrations of HCHs, DDTs and HCB in poplar foliages were similar to those in pine needles at the corresponding period, and there is a positive strong correlation between OCP concentration data of two kinds of trees. It presents no difference in the accumulation style between two kinds of trees. The level of OCPs in the poplar foliage reflected the pollution status of OCPs in air. The result of this work showed that the poplar foliage can be used as the bio-monitor of OCPs in air.

Altitudinal and Chiral Signature of Persistent Organochlorine Pesticides in Air, Soil, and Spruce Needles (Picea abies) of the Alps

The present study investigated the distribution, transportation, and biodegradation of the selected chiral persistent organochlorine pesticides (OCP) in the Alps. In the complex environment, we found the movement and fate of OCP could be defined by many factors. Taking HCE as an example, below the timberline its accumulation from air into SPMD increased with altitude and seasonally changed, but the trends reversed above the timberline. In soil, the tendency of HCE concentrations vs organic materials followed a sigmoid curve, and HCE concentration-altitude correlations are positive in central Alps but negative in southern Alps. The HCE enantiomeric ratios (ERs) in soil correlated to HCE isomers concentrations, the humus pH values, and the sampling site altitudes. HCE shift from humus to mineral soil can also be traced by ERs. The altitudinal and longitudinal trends in needles suggested that alpha-HCH has a more complex movementthan HCE in Alps. In conclusion, altitude conducted condensation, plant canopies, organic material in soil, and geographic specific precipitations may affect OCP distributions and transportation, whereas altitude conducted temperature and soil pH could dictate their fate in the environment.

Could gingko foliage serve as a bio-monitor for organochlorine pesticides in air?

The feasibility of gingko (Gingo Biloba) foliage as a passive bio-monitor for organochlorine pesticides in air was explored. The accumulation patterns of hexachlorocyclohexanes (HCHs), dichlorodiphenyltrichloroethanes (DDTs) and hexachlorobenzene (HCB) in gingko foliage were similar; the amounts of HCHs, DDTs and HCB increased with foliage growth in spring and decreased thereafter. This accumulation pattern is likely related to the growing process of the gingko foliage, which was observed for the first time in our work, giving a piece of evidence for the “bud burst effect” in plants. Compared with those in pine needles in 1980’s, the residual levels of HCHs and DDTs have declined obviously in Beijing, indicating that the ban on the production and use of organochlorine pesticides (OCPs) in our country is effective; however, the amount of HCB has increased, indicating great progress of chemical industry in Beijing. The analysis for the source of OCPs in the gingko foliage showed that the technical HCHs and DDTs were used largely in history, but were not used in recent years. A little lidane has been used and there was a new input of o,p′-DDT in recent years; dicofol usage may be the main source of o,p′-DDT. Concentrations of HCHs, DDTs and HCB in gingko foliages were similar to those in pine needles in the corresponding period and there is a strong positive correlation between the OCPs concentration data obtained from these two kinds of trees. It presents no difference in the accumulation style between these two kinds of trees. The level of OCPs in the gingko foliage reflects the pollution status of OCP in air. The result of this work shows that the gingko foliage can be used as a bio-monitor of OCPs in air.

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.

Atmospheric Concentrations and Air−Water Flux of Organochlorine Pesticides along the Western Antarctic Peninsula

Air, seawater, sea ice, and snow were collected during the austral winter (September-October 2001) and summer (January-February 2002) along the Western Antarctic Peninsula. Hexachlorobenzene (HCB) > heptachlor > alpha- and gamma-hexachlorocyclohexane (HCH) and heptachlor epoxide, were the most frequently detected organochlorine pesticides in air. HCB and HCH levels declined over the past 20 years, with a half-life of 3 years for sigmaHCH in Antarctic air. However, heptachlor epoxide levels have not declined in Antarctic air over the past decade, possibly due to continued use of heptachlor in the southern hemisphere. Peak heptachlor concentrations in air were measured coincident with air masses moving into the region from lower latitudes. Levels of lindane were 1.2-200 times higher in annual sea ice and snow compared to alpha-HCH, likely due to greater atmospheric input of gamma-HCH. The ratio of alpha/gamma-HCH in Antarctic air, sea ice and snow was <1, illustrative of a predominance of influx of lindane versus technical HCH to the regional environment. However, alpha/gamma-HCH in seawater was >1, likely due to more rapid microbial degradation of gamma- versus alpha-HCH. Water/air fugacity ratios for HCHs demonstrate continued atmospheric influx of HCHs to coastal Antarctic seas, particularly during late summer.

Organochlorine pesticides in the air around the Taihu Lake, China.

Organochlorine (OC) pesticides have been used broadly in China's past, yet very little is known about their atmospheric concentrations and transport. In this work, air samples were collected in the Taihu Lake Region, China, from July 23 to August 11, 2002, to measure concentrations of OC pesticides in air. The average concentrations of alpha and gamma- hexachlorocyclohexane (HCH), hexachlorobenzene (HCB), heptachlor (HEPT), alpha-endosulfan, p,p'-DDT, p,p'-DDE, p,p'-DDD, and o,p'-DDT in the air were 74 and 46, 47, 53, 307, 124, 212, 36, and 767 pg m(-3), respectively. It was interesting to note that the concentrations of p,p'-DDT, p,p'-DDE, and o,p'-DDT were all very high, even though the use of technical DDT has been banned in China since 1983. Moreover, the average concentration ratios of o,p'-DDT/p,p'-DDT and p,p'-DDE/p,p'-DDT were as high as 6.3 and 1.8. This suggested that there could be an unknown source of DDT-related compounds (DDTs), especially o,p'-DDT and p,p'-DDE. It is very likely that this unknown source was the application of dicofol, an acaricide manufactured from technical DDT and used mainly on cotton fields to treat mites in China. Backward trajectory analysis also provided consistent evidence that the high air concentrations of DDTs were related to trajectories from the area north of the Yangtze River, where cotton fields account for a significant fraction of land use.

Soil–air exchange of organochlorine pesticides in the Southern United States

Soil samples were collected from 30 farms in Alabama, Louisiana and Texas during 1999–2000 to determine residues of organochlorine pesticides (OCPs). One or more of the DDT compounds (p,p′-DDT, o,p′-DDT, p,p′-DDD, p,p′-DDE, o,p′-DDE) was above the quantitation limit (0.1 ng g −1 dry weight) in every soil, and toxaphene was above the quantitation limit (3 ng g −1) in 26 soils. Chlordanes, dieldrin and hexachlorocyclohexane (HCH) isomers occurred less frequently (quantitation limits 0.1 ng g −1 for dieldrin and 0.05 ng g −1 for chlordanes and HCHs). OCPs were measured in air at 40 cm above the soil at selected farms to investigate soil-air partitioning. Concentrations of OCPs in air were positively and significantly ( P<0.001–0.004) correlated to soil concentrations for toxaphene, p,p′-DDT, o,p′-DDT, p,p′-DDE, dieldrin, and trans-nonachlor. The regression was weaker ( P=0.022) for cis-chlordane and not significant for trans-chlordane ( P=0.43) nor γ-HCH ( P=0.80). Approach to soil-air equilibrium was assessed by calculating fugacities in the soil and air ( f s and f a) for samples with quantifiable residues in both compartments. The fugacity fraction f s f s +f a =0.5 at equilibrium and is <0.5 or >0.5 for net deposition and net volatilisation, respectively. Fugacity fractions varied greatly for different soil-air pairs, reflecting generally disequilibrium conditions. Mean fugacity fractions indicated near-equilibrium for some OCPs (p,p′-DDE, chlordanes, trans-nonachlor and dieldrin) and net volatilisation for others (p,p′-DDT, o,p′-DDT, toxaphene, γ-HCH). Chiral analysis showed that enantioselective degradation of (+) or (−) o,p′-DDT in soil was accompanied by enrichment or depletion of the corresponding enantiomers in the overlying air, although there appeared to be some dilution by racemic o,p′-DDT from regional air transport.

Emission of chiral pesticides from an agricultural soil in the fraser Valley, british columbia

Several organochlorine pesticides (OCs) are chiral compounds, manufactured as racemic mixtures of enantiomers. Selective degradation in soil and water leads to enantiomeric ratios of parent compounds and metabolites which differ from the 1:1 ratio of the applied pesticide. Volatilization of chiral OCs from soil was investigated at a farm in the Fraser Valley known to contain non-racemic pesticide residues. Air samples were collected from 5–140 cm above the soil on four days in September, 1995 to determine the vertical gradients and enantiomeric composition of the OCs. Concentrations of OCs in air were highest near the soil surface and declined with height. A model of Jury et al. (1984) was modified to examine the relationship between the relative concentrations of OCs in air (normalized to heptachlor epoxide) to those in soil. Results support using the octanol-air partition coefficient (K oa) as a descriptor of soil-air exchange. In the soil, α-hexachlorocyclohexane was depleted by 38% in the (-) enantiomer and the metabolite heptachlor epoxide was enriched by 39% in the (+) enantiomer. Non-racemic OCs were also found in the overlying air, indicating that enantiomeric signatures of chiral pesticides are promising tracers of emissions from soils to the atmosphere.