Chiral organochlorine pesticide signatures in global background soils

Chiral pesticides frequently undergo enantioselective degradation in soils. Prior studies to characterize chiral signatures have focused on treated agricultural soils, rather than background (untreated) soils, and tracking signatures in the atmosphere for source apportionment purposes. In this study, we investigated the chiral signatures in 65 background soils collected from different locations across the world. The soils were taken from different ecosystems (e.g., grasslands, forests), and the enantiomeric fractions (EFs) of chiral chlordanes, alpha-hexachlorocyclohexane (alpha-HCH), and o,p'-DDT were determined. Chlordanes in most of the soils showed the usual pattern of enantioselective degradation seen in agricultural soils, depletion of (+)-trans-chlordane (TC) and (-)-cis-chlordane (CC). However, some samples showed opposite enantiomer degradation patterns for TC, CC, and chlordane compound MC5. Correlations were tested between the deviation of EFs from racemic (DEVrac = absolute value of 0.500 - EF), the percent soil organic matter (% SOM), annual mean temperature, and the ratio of TC to the more stable compound trans-nonachlor (TN). Significant positive correlations were found between DEVrac and % SOM for TC and CC (p = 0.0022 and 0.0031), but not for the other OCPs. No significant correlations were found between DEVrac and annual mean temperature for any of the OCPs. DEVrac for TC was negatively correlated with the TC/TN ratio, but the regression was driven by two points with high ratios of TC/CC. Removing these two points resulted in a nonsignificant regression. The range of EFs for TC, CC, and alpha-HCH in soils was greater than in ambient air, providing evidence of in situ degradation after atmospheric deposition in some cases. Variable EFs in soil suggest that caution is needed when considering the enantiomer signatures in air as a marker of volatilization of weathered soil-derived organochlorines.     

Enantioselective degradation of organochlorine pesticides in background soils: variability in field and laboratory studies

Variability in the enantioselective degradation of chiral organochlorine pesticides (alpha-HCH, cis- and trans-chlordane (CC and TC), and o,p'-DDT) in the field and laboratory was investigated. Background soils presumably receive the same EF signature of a compound via atmospheric deposition and then degrade that compound in a way that can vary over small spatial areas. Background soils from woodland and grassland areas were sampled to compare chiral signatures and determine the spatial variability within a few square meters. The enantiomer fractions, EF = areas of the (+)/[(+)+(-)]-enantiomers, showed variability between and within ecosystems. For example, the EF of CC varied between 0.272 -and 0.558 in nine samples taken over a few square meters, and a range of 0.431-0.506 was found within depths of a few centimeters. Woodland and grassland soils were spiked with alpha-HCH, TC, CC, and o,p'-DDT, and one portion was placed in the field to monitor changes in EF under in situ conditions and the other taken to the laboratory. In general, the enantiomer degradation preferences in the laboratory paralleled those in the field, with some differences. Soil organic matter content and pH exerted a minor influence on this variability. The results of this study have implications for the use of chiral compounds to make inferences about air-soil exchange and for the mechanisms of biodegradation/ biotransformation of anthropogenic compounds in soils.     

Spatial and temporal trends of chiral organochlorine signatures in Great Lakes air using passive air samplers

Passive air samples (PAS) were collected and analyzed to assess the spatial and temporal trends of chiral organochlorine signatures in the Laurentian Great Lakes. Samples were collected from 15 sites and analyzed for the concentrations and enantiomer signature of chlordanes and alpha-hexachlorocyclohexane (alpha-HCH). Levels of the chlordanes were typically 4 times higher in urban areas than what were observed at rural and remote locations, exhibiting strong urban-rural gradients. Near racemic residues were seen for the chlordane enantiomers in samples collected from sites located in Toronto and Chicago, which can be attributed to continued emissions of historical use of the technical chlordane mixture, while the chiral signature observed at sites located in rural and remote locations was indicative of an aged source. Knowledge of the spatial and temporal distribution of the enantiomer signatures of chlordane and alpha-HCH in air is useful for distinguishing sources of these compounds to ambient air. Results suggest that potential sources, such as those associated with Toronto and Chicago, have limited influence over the levels at rural and remote sites within the Great Lakes. Sources that are relatively close to sample sites, however, have a strong influence on levels observed at those sites. For instance, results indicate that Lake Superior continues to act as a source of alpha-HCH to sites located on its shores. Generally, it appears that during the warmer months, local enhanced surface-air exchange influences air concentrations and that during the cooler periods of the year, levels in the atmosphere are more strongly influenced by advective transport from source regions.     

Concentrations and chiral signatures of polychlorinated biphenyls in outdoor and indoor air and soil in a major U.K. conurbation

Concentrations and chiral signatures of polychlorinated biphenyls (PCBs) were measured in outdoor air (using polyurethane foam (PUF)--disk passive samplers) and surface soil samples taken at approximately monthly intervals over 1 year at 10 locations on a rural-urban transect across the West Midlands of the U.K. In both air and soil, concentrations clearly decrease with increasing distance from the city center, supporting the existence of an urban "pulse", that indicate the West Midlands conurbation to be a source of PCBs to the wider environment. Concentrations of PCBs in outdoor air samples in this study are well below those reported previously for indoor air in the West Midlands. This, combined with comparison of chiral signatures in outdoor air and soil with those in samples of indoor air taken in the West Midlands, suggest strongly that the principal contemporary source of PCBs in this conurbation is ventilation of indoor air and not volatilization from soil. Future reductions in PCB concentrations in outdoor air and ultimately human exposure appear best achieved by action to remove remaining sources of PCBs from existing structures.     

The freshwater invertebrate Mysis relicta can eliminate chiral organochlorine compounds enantioselectively

Accumulation and elimination of chiral polychlorinated biphenyls (PCBs) and organochlorine (OC) pesticides by the opossum shrimp, Mysis relicta, was investigated to determine if zooplankton can stereoselectively process chiral OC contaminants. Concentrations and enantiomer fractions were measured within mysids over a 10-day exposure followed by a 45-day depuration period. Rapid accumulation occurred within mysids exposed to sediment contaminated with racemic chiral OC compounds at microg/g levels. Enantiomer enrichment was observed within mysids for the second-eluting enantiomer and the (-)-enantiomer of PCB 95 and trans-chlordane, respectively, after 7 days of exposure to spiked sediment, and for the second-eluting enantiomers of PCBs 91 and 183 and (-)-PCB 149 over longer time periods. Enantiomer fractions decreased with time during the depuration phase of the experiment for these compounds, showing that their elimination from mysids was stereoselective. Oxychlordane was detected in nonracemic proportions after exposure, indicating that mysids can metabolize trans-chlordane enantioselectively. Minimum elimination rates calculated were higher than biotransformation rates calculated for fish in previous studies, which have been shown to metabolize OC contaminants. This study is the first to show stereoselective processing of chiral OC contaminants by aquatic invertebrates.     

Fate of pesticides in the arid subtropics, Botswana, Southern Africa

Despite a history of pesticide usage, few data exist on their concentrations in air and soil of Southern Africa. To add to the understanding of the processes controlling the fate of organic contaminants in arid regions, the levels, spatial trends, and seasonal variability of pesticides were studied in air and soil from Botswana. XAD resin-based passive air samplers (PAS) were deployed at 15 sites across the country from May 2006 to May 2007. Soil samples were collected from the vicinity of nine of the PAS sampling sites. In addition, 27 24-h high-volume air samples were collected in Maun, at the southeastern edge of the Okavango Delta, every two weeks for one year. Levels of pesticides in PAS were low, with α-endosulfan and lindane being most abundant. Concentrations in soils were extremely low and only soils with high organic carbon contained notable amounts of dieldrin and traces of other pesticides. In particular, air and soil from the Okavango Delta had very low levels even though the area had repeatedly been sprayed with DDT and endosulfan in the past. Air samples from Eastern Botswana, where the majority of the population lives, contained higher levels. Higher air concentrations of α-endosulfan occurred during summer and higher HCB levels occurred in winter. This seasonality was related with neither minor seasonal changes in temperature nor hydrological seasonal events such as the rainy season or the flooding of the Okavango Delta. Thus, the observed spatial and seasonal patterns are more likely related to pesticide usage pattern than to environmental factors or historical use. High temperature and low organic matter content limit the uptake capacity of most subtropical soils for pesticides. No evidence was found that sorption to dry mineral matter plays a major role. Arid soils in subtropical regions are therefore neither a major reservoir of organic contaminants nor do they constitute a significant long-term source of pesticides to the atmosphere.     

An assessment of air-soil exchange of polychlorinated biphenyls and organochlorine pesticides across central and southern Europe

Estimating the net flux direction of polychlorinated biphenyls and organochlorine pesticides is importantfor understanding the role of soil as a sink or source of these chemicals to the atmosphere. In this study, the soil-air equilibrium status was investigated forvarious soil categories in Central and Southern Europe using an extensive database of coupled soil and time-integrated air samples. Samples were collected from 47 sites over a period of 5 months to assess both site-specific as well as seasonal variations in fugacity fractions, calculated as a potential measure of soil-air exchange. Sampling sites were carefully selected to represent a variety of background, rural, urban, and industrial areas. Special attention was given to sites in the former Yugoslavia, a country affected by recent conflicts, where soils were found to be highly contaminated with polychlorinated biphenyls (PCBs). Industrial soils from the Czech Republic, heavily polluted as a result of previous pesticide production, were also included in the survey. Soil was found to be a sink for highly chlorinated PCBs and for dichlorodiphenyltrichloroethane (DDT); for dichlorodiphenyldichloroethylene (DDE), the status was closer to equilibrium, with a tendency for net deposition during winter and net volatilization during summer. For lower-molecular-weight PCB congeners, as well as for alpha-HCH, soil tends to be a source of pollution to the air, especially, but not exclusively, during summer. Fugacity fractions were found to decrease during the colder seasons, especially for the more volatile compounds, although in both the war-damaged areas and the heavily contaminated industrial sites, seasonal variability was very low, with fugacity fractions close to 1, indicating strong net soil-to-air transfer for all seasons. The original assumption that residents of the Western Balkans are still exposed to higher levels of PCBs due to the recent wars was confirmed. In general, the soil-air transfer of PCBs and organochlorine pesticides was found to be site-specific and dependent on the physicochemical properties of the contaminant in question, the soil properties, the historical contamination record and a site's vicinity to sources, and the local meteorological conditions.     

Chiral source apportionment of polychlorinated biphenyls to the Hudson River estuary atmosphere and food web

The New York/New Jersey Harbor Estuary is subject to significant contamination of polychlorinated biphenyls (PCBs) from numerous sources, including the historically contaminated Upper Hudson River, stormwater runoff and sewer overflows, and atmospheric deposition from PCBs originating from the surrounding urban area. However, the relative importance of these sources to the estuary's food web is not fully understood. Sources of PCBs to the estuary were apportioned using chiral signatures of PCBs in air, water, total suspended matter, phytoplankton, and sediment. PCBs 91, 95, 136, and 149 were racemic in the atmosphere of the estuary. However, the other phases contained nonracemic PCB 95 and to a lesser extent PCB 149. Thus, the predominant atmospheric source of these congeners is likely unweathered local pollution and not volatilization from the estuary. The similarity in chiral signatures in the other phases is consistent with dynamic contaminant exchange among them. Chiral signatures in the dissolved phase and total suspended matter were correlated with Upper Hudson discharge, suggesting thatthe delivery of nonracemic contaminated sediment from the Upper Hudson, not the atmosphere, controls phytoplankton uptake of some PCBs. Thus, measures to control PCB contamination in the Upper Hudson should be effective in reducing loadings to the estuary's aquatic ecosystem.     

Influence of pH on the stereoselective degradation of the fungicides epoxiconazole and cyproconazole in soils

Many pesticides are chiral and consist of two or more enantiomers/stereoisomers, which may differ in biological activity, toxicity, effects on nontarget organisms, and environmental fate. In the last few years, several racemic compounds have been substituted by enantiomer-enriched or single-isomer compounds ("chiral switch"). In this context, the stereoselective degradation in soils is an important part of a benefit-risk evaluation, but the understanding of the environmental factors affecting the chiral preferences is limited. In this study, the stereoselective degradation of the fungicides epoxiconazole and cyproconazole was investigated in different soils, selected to cover a wide range of soil properties. The fungicides were incubated under laboratory conditions and the degradation and configurational stability of the stereoisomers were followed over time using enantioselective GC-MS with a gamma-cyclodextrin derivative as chiral selector. In alkaline and slightly acidic soils, the degradation of epoxiconazole was clearly enantioselective, whereas in more acidic soils, both enantiomers were degraded at similar rates (overall half-lives 78-184 d). The enantioselectivity, expressed as ES = (k(i) - k(j))/ (k(i) + k(j)), ranged from -0.4 in alkaline soils (faster degradation of enantiomer j) to approximately 0 in acidic soils (non-enantioselective), and showed a reasonably linear correlation with the soil pH. The four stereoisomers of cyproconazole (overall half-lives 5-223 d) were also degraded at different rates in the various soils, but only the stereoselectivities between epimers showed some correlations with pH, whereas enantioselectivities did not. Both fungicides were configurationally stable in soils, i.e., no enantiomerization or epimerization was observed. Correlations between pH and ES have previously been reported for other pesticides (metalaxyl, dichlorprop, mecoprop), but the presence or absence of such correlations is not obviously linked to the pathways of degradation. It can be assumed that different microorganisms and enzymes are involved in the primary degradation of these compounds, but on which level soil pH has an influence on ES remains to be investigated.     

Evidence of enantioselective degradation of alpha-hexachlorocyclohexane in groundwater

In the fall of 2000, 34 groundwater samples were collected from beneath an active pesticide reformulating and packaging facility in coastal northeastern Florida to measure the enantiomer fractions (EFs) of alpha-hexachlorocyclohexane (alpha-HCH) as an indicator of biodegradation of this chlorinated pesticide in groundwater. Concentrations of alpha-HCH as high as 500 microg/L were observed beneath the historical source area and decreased with distance downgradient. Seventy-eight percent of the EF values were greater than 0.504 and ranged up to 0.890, indicating that the (-)-alpha-HCH enantiomer is preferentially degraded relative to the (+)-alpha-HCH enantiomer at this site. Samples taken from the groundwater that flows north from the historical disposal facility to a local discharge point at a creek did not indicate enantioselective degradation (EF values ranged from 0.495 to 0.512). The acidity (pH 3.7-4.6) and short flow path to the creek for this lobe of the groundwater plume likely preclude biodegradation of alpha-HCH. In contrast, the neutral lobe of the groundwater plume, which flows eastward from the historical source area, demonstrated enantioselective degradation (EF values ranged from 0.500 to 0.890 and increased with distance from the source area). Groundwater conditions beneath this portion of the site are conducive to biodegradation of HCH owing to anaerobic reducing conditions and lengthy travel times, and the chiral signatures for alpha-HCH provide evidence that biological degradation is occurring beneath this portion of the site.     

Fate of brominated flame retardants and organochlorine pesticides in urban soil: volatility and degradation

As the uses of polybrominated diphenyl ethers (BDEs) are being phased out in many countries, soils could become a secondary emission source to the atmosphere. It is also anticipated that the demand for alternative brominated flame retardants (BFRs) will grow, but little is known about their environmental fate in soils. In this study, the volatility and degradation of BFRs and organochlorine pesticides (OCPs) in soil was investigated. A low organic carbon (5.6%) urban soil was spiked with a suite of BFRs and OCPs, followed by incubation under laboratory condition for 360 days. These included BDE- 17, -28, -47, -99; α- and β-1,2-dibromo-4-(1,2-dibromoethyl)cyclohexane (TBECH), β-1,2,5,6-tetrabromocyclooctane (TBCO), and 2,3-dibromopropyl-2,4,6-tribromophenyl ether (DPTE), OCPs: α-hexachlorocyclohexane (α-HCH) and (13)C(6)-α-HCH, trans-chlordane (TC), and (13)C(10)-TC. The volatility of spiked chemicals was investigated using a fugacity meter to measure the soil-air partition coefficient (K(SA)). K(SA) of some spiked BFRs and OCPs increased from Day 10 to 60 or 90 and leveled off afterward. This suggests that the volatility of BFRs and OCPs decreases over time as the chemicals become more strongly bound to the soil. Degradation of alternative BFRs (α- and β-TBECH, β-TBCO, DPTE), BDE-17, and α-HCH ((13)C-labeled and nonlabeled) was evident in soils over 360 days, but no degradation was observed for the BDE-28, -47, -99, and TC ((13)C-labeled and nonlabeled). A method to separate the enantiomers of α-TBECH and β-TBCO was developed and their degradation, along with α-HCH ((13)C-labeled and nonlabeled) was enantioselective. This is the first study which reports the enantioselective degradation of chiral BFRs in soils. Discrepancies between the enantiomer fraction (EF) of chemicals extracted from the soil by dichloromethane (DCM) and air were found. It is suggested that DCM removes both the sequestered and loosely bound fractions of chemicals in soil, whereas air accesses only the loosely bound fraction, and these two pools are subject to different degrees of enantioselective degradation. This calls for caution when interpreting EFs obtained from DCM extraction of soil with EFs in ambient air.     

Can physicochemical and microbial soil properties explain enantiomeric shifts of chiral organochlorines?

Enantiomeric fractions (EF) of PCB 95, 132, 149, and 174, alpha-HCH, o,p'-DDD, and o,p'-DDT were analyzed in 112 soil samples using two-dimensional gas chromatography and triple-quadrupole mass spectrometry. To assess the soil conditions that facilitate enantioselective fractionation of chiral compounds, EF values of selected PCBs were further correlated with a wide range of physicochemical and microbial soil parameters in an attempt to identify the influential factors and their mutual relations. It was evident that soils where nonracemic ratios of investigated compounds were found were more carbon rich but they also contained significantly more humic and fulvic acids and total nitrogen. These specific physicochemical properties were accompanied by significantly increased values of all key biotic variables, the amount of microbial biomass, and its respiration activity (both basal and substrate-induced). Therefore, the shifts from racemic ratios appeared to be associated with more sustainable and active soil microflora. Among other abiotic characteristics, most significant differences were detected in the soil texture. Soil samples with significant shifts contained increased amount of clay component and correspondingly decreased proportion of sand fraction. These differences can also be associated with more intensive microbial activity, because clay content and texture with an increased amount of microaggregates are known to be favorable for soil microflora and its viability.     

Enantiomer fractions of chiral Perfluorooctanesulfonate (PFOS) in human sera

Perfluorooctane sulfonate (PFOS) is the most prominent perfluoroalkyl contaminant in humans and wildlife, but there is great uncertainty in exposure pathways, particularly with respect to the importance of PFOS-precursors (PreFOS). We explored the hypothesis that nonracemic proportions of chiral PFOS in serum are qualitative and semiquantitative biomarkers of human PreFOS exposure. A new chiral HPLC-MS/MS method was developed for alpha-perfluoromethyl branched PFOS (1m-PFOS, typically 2-3% of total PFOS) and applied to enantiomer fraction (EF) analysis in biological samples. In blood and tissues of rodents exposed subchronically to electrochemical PFOS, 1m-PFOS was racemic (EF = 0.485-0.511) and no evidence for enantioselective excretion was found in this model mammal. 1m-PFOS in serum of pregnant women, from Edmonton, was significantly nonracemic, with a mean EF (±standard deviation) of 0.432 ± 0.009, similar to pooled North American serum. In a highly exposed Edmonton family (mother, father, and 5 children) living in a house where ScotchGard had been applied repeatedly to carpet and upholstery, EFs ranged from 0.35 to 0.43, significantly more nonracemic than in pregnant women. Semiquantitative estimates of % serum 1m-PFOS coming from 1m-PreFOS biotransformation in both subpopulations were in reasonable agreement with model predictions of human exposure to PFOS from PreFOS. The data were overall suggestive that the measured nonracemic EFs were influenced by the relative extent of exposure to PreFOS. The possibility of using 1m-PFOS EFs for assessing the relative contribution of 1m-PreFOS (or PreFOS in general) in biological samples requires further application before being fully validated, but could be a powerful tool for probing general sources of PFOS in environments where the importance of PreFOS is unknown.     

Resuspension of soil as a source of airborne lead near industrial facilities and highways

Geologic materials are an important source of airborne particulate matter less than 10 microm aerodynamic diameter (PM10), but the contribution of contaminated soil to concentrations of Pb and other trace elements in air has not been documented. To examine the potential significance of this mechanism, surface soil samples with a range of bulk soil Pb concentrations were obtained near five industrial facilities and along roadsides and were resuspended in a specially designed laboratory chamber. The concentration of Pb and other trace elements was measured in the bulk soil, in soil size fractions, and in PM10 generated during resuspension of soils and fractions. Average yields of PM10 from dry soils ranged from 0.169 to 0.869 mg of PM10/g of soil. Yields declined approximately linearly with increasing geometric mean particle size of the bulk soil. The resulting PM10 had average Pb concentrations as high as 2283 mg/kg for samples from a secondary Pb smelter. Pb was enriched in PM10 by 5.36-88.7 times as compared with uncontaminated California soils. Total production of PM10 bound Pb from the soil samples varied between 0.012 and 1.2 mg of Pb/kg of bulk soil. During a relatively large erosion event, a contaminated site might contribute approximately 300 ng/m3 of PM10-bound Pb to air. Contribution of soil from contaminated sites to airborne element balances thus deserves consideration when constructing receptor models for source apportionment or attempting to control airborne Pb emissions.     

Chiral PCB signatures in air and soil: implications for atmospheric source apportionment

Enantiomeric fractions (EFs) of chiral PCBs 95, 136, and 149 were measured in samples of topsoil and outdoor air at one urban and one rural location in the U.K. West Midlands between early 2001 and early 2002. While EFs in air were essentially racemic, those in topsoil indicated appreciable enantioenrichment of the second eluting enantiomer for PCB 95 and the (+) enantiomer for PCBs 136 and 149. This suggests (i) that essentially all atmospheric PCBs at both sites arise from racemic (i.e, primary) sources, rather than volatilization from soil and (ii) that appreciable enantioselective degradation of the monitored PCBs in topsoil occurs. This is one of only two reports of enantioselective degradation of PCBs in soil worldwide and is particularly noteworthy as it is occurring at PCB concentrations (e.g., 5.9 pg g(-1) for PCB 136) that are typical of the U.K. and other industrialized countries. The extent of enantioselective degradation in this study for PCBs 95 and 136 is consistent with those reported for soils in the Greater Toronto area (GTA). In contrast, enantioselective degradation of PCB 149 observed in this study is--while consistent with that reported for U.K. lacustrine sediments--in excess of that observed in either the GTA soil study or in U.S. lake sediments.     

Chiral signatures show volatilization from soil contributes to polychlorinated biphenyls in grass

Enantiomer fractions (EFs) of PCB 95 and concentrations of PCBs 28/31, 52, 101, 118, 138, 153, and 180 were determined in air. Samples were taken at ~14 day intervals on a vertical gradient at an urban background site in Birmingham U.K. in summer 2009 (114 days) and spring 2010 (84 days). EFs in air at 3 cm height were nonracemic (average 0.453 (2009) and 0.468 (2010)) and differed significantly (p < 0.05) from the racemic EFs in air at 10, 40, 90, and 130 cm. EFs in soil (average 0.452 (2009) and 0.447 (2010)) closely matched those in air at 3 cm, while those in grass (average 0.468 (2009) and 0.484 (2010)) were intermediate between those in soil and the racemic EFs in air at ≥ 10 cm. This implies that at the study site, PCBs volatilize from soil to an extent discernible only at the soil:air interface, and that PCBs in grass arise due to foliar uptake of volatile emissions from soil. Atmospheric concentrations of ΣPCBs increased significantly (p < 0.05) with increasing height. Combined with the chiral signature data, this suggests the influence of PCB emissions from soil on airborne concentrations decreases with altitude, while that of emissions from the built environment increases.     

Chlordane enantiomers and temporal trends of chlordane isomers in arctic air

A 14-year data set (1984-1998) for chlordane compounds in arctic airwas examined to discern temporal trends. trans-Chlordane (TC), cis-chlordane (CC), and trans-nonachlor (TN) declined significantly (p < 0.001-0.02), with apparent times for 50% reduction of 4.9-9.7 y. The isomer fraction of TC = (TC/(TC + CC) also declined significantly (p < 0.001 -0.014) over the same time period. The enantiomeric composition of TC and CC was determined in air samples collected at arctic stations in Canada (1993-1996), Russia (1994), and Finland (1998), and a temperate station on the Swedish west coast (1998). Enantiomer fractions, EF = (+)/[(+) + (-)], were significantly different from measured EFs of racemic standards (0.498-0.501) at all stations for TC (p < 0.001) and two stations for CC (p < 0.001 to <0.05). These observations suggest changing source composition of chlordane in arctic air, with a greater proportion of weathered residues in recent years, possibly derived from soils. Identification of nonracemic (mean EFs = 0.662-0.703) heptachlor exo-epoxide (HEPX) at the four air stations further exemplifies contributions of soil emissions to long-range transport of chlordane-related compounds.     

Organochlorine compounds in Lake Superior: chiral polychlorinated biphenyls and biotransformation in the aquatic food web

The enantiomeric composition of seven chiral PCB congeners was measured in the Lake Superior aquatic food web sampled in 1998, to determine the extent of enantioselective biotransformation in aquatic biota. All chiral PCB congeners studied (CBs 91, 95, 136, 149, 174, 176, and 183) biomagnified in the Lake Superior aquatic food web, based on biomagnification and food web magnification factors greater than unity. PCB atropisomers were racemic in phytoplankton and zooplankton, suggesting no biotransformation potential toward PCBs for these low trophic level organisms. However, Diporeia and mysids had significantly nonracemic residues for most chiral congeners studied. This observation suggests that these macrozooplankton can stereoselectively metabolize chiral congeners. Alternatively, macrozooplankton obtained nonracemic residues from feeding on organic-rich suspended particles and sediments, which would imply that stereoselective microbial PCB biotransformation may be occurring in Lake Superior sediments at PCB concentrations far lower than that previously associated with such activity. Widely nonracemic PCB residues in forage fish (lake herring, rainbow smelt, and slimy sculpin) and lake trout suggest a combination of both in vivo biotransformation and uptake of nonracemic residues from prey for these species. Minimum biotransformation rates, calculated from enantiomer mass balances between predators and prey, suggest metabolic half-lives on the order of 8 yr for CB 136 in lake trout and 2.6 yr for CB 95 in sculpins. This result suggests that significant biotransformation may occur for metabolizable PCB congeners over the lifespan of these biota. This study highlights the potential of chiral analysis to study biotransformation processes in food webs.     

Environmental behavior of the chiral triazole fungicide fenbuconazole and its chiral metabolites: enantioselective transformation and degradation in soils

Fenbuconazole is a widely used systemic agricultural fungicide of the triazole class with one chiral center. In the present study, the enantioselective degradation of fenbuconazole and its chiral metabolites, RH-9129 and RH-9130, in two soils under aerobic and anaerobic conditions were investigated using a chiral OD-RH column on a reversed-phase liquid chromatography-tandem mass spectrometry system. Under aerobic or anaerobic conditions, the results showed the occurrence of enantioselectivity with (-)-fenbuconazole preferentially degraded in both soils. Further enantioselective analysis of converted products showed that the concentrations of four RH-9129 and RH-9130 stereoisomers were different from each other under both aerobic and anaerobic conditions. The four stereoisomer concentrations followed the order (-)-RH-9129 > (+)-RH-9129 > (-)-RH-9130 > (+)-RH-9130 in Langfang alkaline soil. However, in the case of Changsha acidic soil, different RH-9129 and RH-9130 stereoisomer patterns were produced in the order (-)-RH-9129 > (+)-RH-9129 > (+)-RH-9130 > (-)-RH-9130. The (-)-RH-9129 stereoisomer had the highest concentration formed by transformation of fenbuconazole in both soils. The degradation of RH-9129 and RH-9130 in the two soils is also stereoselective under both aerobic and anaerobic conditions, the results indicating that the (+)-RH-9130 enantiomer degraded faster than the (-)-RH-9130 enantiomer and the (+)-RH-9129 enantiomer degraded faster than the (-)-RH-9129 enantiomer. In addition, the (-)-RH-9129 isomer exhibited the slowest degradation rate in both soils. This study provides the first experimental evidence of stereoselective degradation and transformation of fenbuconazole as well as its chiral metabolites in the environment.     

Production of toxaphene enantiomers by enantioselective HPLC after isolation of the compounds from an anaerobically degraded technical mixture

Enantiomers of 12 chlorobornanes were separated on a chiral stationary HPLC phase. The investigated compounds included relevant chlorobornanes in technical toxaphene (Toxicant A and an unknown hepatachlorobornane), anaerobically mediated media such as sediment, soil, and sewage sludge (B6-923, B7-1001), as well as eight persistent compounds of technical toxaphene (CTTs) frequently detected in biological samples (B7-1000, B7-1453, B8-1412, B8-1413 or P-26, B8-1414 or P-40, B8-1945 or P-41, B8-2229 or P-44, and B9-1679 or P-50). Sufficient amounts of these 12 CTTs were not commercially available and had to be produced in our lab. Eight CTTs were obtained from sewage sludge that was spiked with technical toxaphene and kept under anaerobic conditions for four weeks. The samples were extracted with hexane followed by RP-HPLC fractionation. The resulting toxaphene pattern was significantly simpler than that of the technical mixture. CTTs that showed intense fragmentation in GC/ECNI-MS were preferably metabolized. Moreover, only one of the diastereomers that make Toxicant A (B8-806/B8-809 or P-42a/b) resisted degradation in sewage sludge. We found that the persistent component of Toxicant A is 2,2,5-endo,6-exo,8,9,9,10-octachlorobornane (B8-809 or P-42b). B9-1679 (P-50), B7-1453, and B8-1412 were earlier isolated from biological samples, and B7-1000 was isolated from naturally contaminated sediments. The fractions obtained after these procedures were suitable for enantioselective HPLC separations. The first eluting enantiomer was usually obtained as an enantiopure standard whereas the second eluting enantiomer also contained the other enantiomer. Attempts to determine the optical rotation with the help of a chiral HPLC detector failed. Elution orders of the enantiomers were established on three GC chiral stationary phases. Only the enantiomers of B7-1453 and B8-1945 (P-41) eluted in the same order from all CSPs while the others showed different enantiomer elution orders or were not resolved on one of the chiral GC stationary phases. The knowledge and consideration of these results is important for the interpretation of enantiomer ratios found in biological samples and comparison of literature data.