Environ. Sci. Technol. 2003, 37, 4887-4893
Volatilization of Weathered Chiral and Achiral Chlordane Residues from Soil BRIAN D. EITZER,* WILLIAM IANNUCCI-BERGER, AND MARYJANE INCORVIA MATTINA Department of Analytical Chemistry, The Connecticut Agricultural Experiment Station, 123 Huntington Street, New Haven, Connecticut 06511
To mitigate the impact on the environment of persistent organic pollutants (POPs), we must understand thoroughly their environmental fate. Residues of many of these pollutants are still present in soil years after their legitimate uses were banned. In this report, the volatilization of one such persistent pollutant, chlordane, from a field where it was applied approximately 40 years ago, is examined in detail over the course of several years. Ambient air samples were collected at three heights above the treated soil throughout the investigation. Air samples were also collected at several background sites in Connecticut for comparison. Analysis of these samples shows that chlordane volatilization from soil continues to occur long after initial application, at rates dependent on both temperature and cultivation of the soil. Comparison of relative concentrations and enantiomeric profiles for components of technical chlordane in atmospheric samples from a variety of sources suggests a regional, urban input of chlordane to the ambient air over Connecticut, possibly related to the widespread termiticidal use of chlordane in home foundation soils.
Introduction The environmental persistence of a variety of POPs is well established, and soil-bound residues continue to be observed in both agricultural and residential settings (1-4). As persistent organic pollutant residues weather in soil, they become increasingly recalcitrant to extraction and less bioavailable (5), the result of pollutant sequestration. Despite its sequestered condition in soil, chlordane has been found in both indoor and outdoor ambient air (6-10). This begs the question of whether soil may act as a reservoir of POPs for volatilization to the atmosphere long after the use of the particular compound has ceased (11-15). The pesticide chlordane was introduced in the 1940s and widely used in both agricultural and residential settings in the United States until its gradual phase out. In 1978 use on food crops was canceled; by 1983 all above ground use ended; and by 1988 all uses in the United States were canceled (16, 17). International restrictions will be imposed when the Stockholm POPs convention, signed by the United States in 2001, goes into effect. The insecticide was applied as a mixture, known as technical chlordane, of over 140 related compounds. The primary active ingredients of this mixture * Corresponding author phone: (203)974-8453; fax: (203)974-8502; e-mail:
[email protected]. 10.1021/es0343196 CCC: $25.00 Published on Web 09/27/2003
2003 American Chemical Society
were cis-chlordane (CC), trans-chlordane (TC), and transnonachlor (TN) and together they comprised about 25 wt % of the technical chlordane mixture. Two of the three primary active ingredients, CC and TC, are chiral and present as racemates in the technical mixture. Therefore, analysis of the relative concentrations of both chiral and achiral components of the technical mixture contained in the residues from contiguous environmental compartments can differentiate enantioselective processes (such as microbial degradation) from physical-chemical processes (such as volatilization). In the former case, enantiomeric fractions (EF), a measure of the relative amount of each enantiomer, would be expected to change. In the latter case, the relative concentrations of the components would vary, while the EF should remain the same. Furthermore, as biological weathering can be expected to differ from site to site, chiral-based analyses may be useful in determining the input source of a particular residue. Thus, comparison of both chiral and compositional profiles of chlordane in soil with those in ambient air can be used to determine if a particular soil is a local source of the atmospheric pollutant. This paper examines the volatilization of chlordane from a field where the pesticide application was well documented. Technical chlordane was applied as part of a crabgrass control experiment on this site 40 years ago. Volatilization from the field has been monitored since March 2000. The air concentrations at this site will provide insights into the volatilization of weathered, soil-bound POPs residues. Comparison with background sites at other locations in Connecticut permit us to propose a source of atmospheric chlordane attributed to volatilization from prior uses of the pesticide.
Experimental Section Sample Collection. Samples were collected from several different locations during the duration of this project. The primary location was the experimental plot on the urban campus of the Connecticut Agricultural Experiment Station (CAES) in New Haven, CT. This plot (approximately 12 m × 21 m in size) was treated with technical chlordane in the early 1960s as part of an investigation of the use of chlordane for the control of crabgrass. From that point forward the site remained under turf cover until 1998 when soil cores were collected for analysis. After collection of the cores, the turf cover over part of the site was removed, and this area was tilled in preparation for planting, as part of a series of experiments on the uptake of weathered pollutant residues by plants (3, 4, 18, 19). As part of these experiments soil samples were collected (including samples of soils from large bins of mixtures containing plot soil and “cleaner” soil used to prepare a dose/uptake experiment, air samples were taken in close proximity to the bins). The data for plot soil reported in this paper represent an average across these soil samples. From June 2000 through September 2002 ambient air samples were periodically collected at three heights (0.5, 1.5, and 2.5 m) above the experimental plot. In addition, air samples were also collected at a single height at a background site, approximately 25 m distant from the treated plot, on the CAES campus (site referred to as “CAES lawn background”). From May 2001 through September 2002 a suburban site, Lockwood Farm in Hamden, CT, the experimental farm belonging to CAES, was monitored. Two additional background sites were monitored from March to September 2002; the first, an urban site in downtown Waterbury, CT and the second, a rural site at a fish hatchery in Burlington, CT. Although soil samples were collected from the Lockwood farm, chlordane concentrations were below the limits of VOL. 37, NO. 21, 2003 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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quantitation. Soil samples were not taken at the other two background sites. All samples were collected with high volume air samplers, fitted with glass fiber filters to remove particulate matter and polyurethane foam plugs (PUF) to trap vapor phase chlordane compounds. In 2000 air was sampled using a Cole-Palmer, catalog #A-07047-10, regenerative blower (Cole-Palmer, Vernon Hills, IL). In 2001 and 2002 samples were taken using CF-901 portable air samplers (Hi-Q Environmental Products, San Diego, CA). Samples were collected for time periods between 20 and 50 h at a rate of approximately 0.35 m3/min (rate measured at beginning and end of sampling period and averaged). Air temperatures were monitored during sampling; the overall temperature ranged from -1 °C to 31 °C, with diurnal changes on the order of 10 degrees. Samples were frozen until analysis. During the first year of the study a second PUF plug was placed behind the front plug and analyzed for breakthrough. These second PUFs were shown to be clean, indicating that breakthrough was not a problem. PUF plugs were cleaned prior to sampling by Soxhlet extraction for a minimum of 16 h with petroleum ether followed by drying in a vacuum oven. All solvents used were Ultra-Resi Analyzed pesticide grade (J. T. Baker, Phillipsburg, NJ). Sample Analysis. Prior to extraction PUFs were spiked with 13C10 trans-chlordane and 13C10 trans-nonachlor (Cambridge Isotope Labs, Andover, MA) which serve as internal standards. The PUF plugs were Soxhlet extracted using 350 mL of petroleum ether. After extraction the solvent was reduced in volume to 10 mL via Kuderna-Danish evaporation and loaded onto a Florisil column for cleanup. A 22 mm i.d. × 34 cm long fritted chromatography column was packed dry with a 12 cm layer of PR grade 60/100 mesh activated (2 h at 160 °C) Florisil (U.S. Silica, Berkeley Springs, WV) and then 2 cm of anhydrous sodium sulfate (Fisher, Pittsburgh, PA). The column was pre-eluted with 50 mL of petroleum ether. The entire extract was loaded onto the column. The column was eluted first with 80 mL of petroleum ether and then with 100 mL of 6% diethyl ether in petroleum ether, collecting this second fraction. The eluate was reduced in volume and solvent exchanged to isooctane for GC/MS analysis. The GC/MS procedures have been described in detail elsewhere (18). In brief, the extract was analyzed on a Saturn 2000 Ion Trap GC/MS (Varian, Sugar Land, TX) system fitted with a 30 m × 0.25 mm i.d. × 0.25 µm film thickness GAMMADEX-120 column (Supelco, Bellefonte, PA) for the separation of chiral compounds. The GC oven was temperature programmed, a 3 µL splitless injection was made, and a MS scan range from m/z 345 to 425 was set. All sample extracts were analyzed twice. Racemic standards of CC and TC together with achiral TN (ChemService, West Chester, PA) were used to prepare a series of calibration standards in isooctane with individual enantiomer concentrations of 5, 12.5, 25, 50, 125, and 250 ng/mL. Each calibration standard also had 100 ng/mL of racemic 13C10 TC (i.e., 50 ng/mL each of 13C10 (+)-TC, 13C10 (-)-TC) and 50 ng/mL 13C10 TN. For each instrumental run the complete set of standards was injected twice, once before and once after the set of sample injections. Enantiomerically pure standards of (+)-TC, (-)-TC, (+)-CC, and (-)-CC (EQ Laboratories, Atlanta, GA) were used to establish the retention order of the enantiomers. Quantitation. Two ions from the most intense chlorine cluster, the (M - Cl)+ ion, of each compound were selected. For TC and CC the ions were m/z ) 373, 375; for TN the ions were m/z ) 407, 409; for 13C10 TC the ions were m/z ) 383, 385; and for 13C10 TN the ions were m/z ) 419, 421. Extracted ion chromatograms were converted into an ASCII text file with ChemSW GC/MS file translator (ChemSW, Fairfield, CA). 4888
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The files were then imported into PeakFit ver. 4 (SPSS, Chicago, IL) for smoothing and integration. The settings for data manipulation in PeakFit were as follows: smoothing via a Fourier transform routine and integrating using the AutoFit Peaks II second derivative parameters. The observed isotope ratio from the selected pair of ions (e.g., m/z ) 373, 375 for CC and TC) for each analyte was determined for standards and for samples. Internal standard calibration curves for each analyte were generated from the sum of the two extracted ions from the (M - Cl)+ cluster. Quality Assurance. To ensure data quality it was required that the height of an analytical peak be 2.5 times the background noise for each ion. In addition it was required that the isotope ratio of the two monitored ions for a given analyte be within 2 standard deviations of the isotope ratio for the standards of that analyte analyzed during the same instrumental run. Typically relative standard deviations across the entire range of concentrations were 5% or less.
Results and Discussion Absolute and Relative Chlordane Concentrations in Air and Soil. Several recent reports regarding ambient air concentrations of pesticides above contaminated agricultural soils have appeared in the literature (11, 12, 20). In all such reports concentrations in the air above the soils are elevated relative to background air, which suggests that weathered pesticide residues can volatilize into the atmosphere, despite their sequestration during weathering within the soil matrix. These cited reports, however, examined the air above the soils for a relatively short period of time. The data in this paper report a long-term study of the ambient air above a contaminated soil. The duration of the study allows additional insight into the volatilization process. Air samples taken at each of three heights directly above the experimental plot clearly differed from each other and from the CAES lawn background samples. These differences can be observed in the total chlordane concentration in the sample (sum of the five components quantified, +TC, -TC, -CC, +CC, TN), component fraction (CF, relative amount of the individual components), and enantiomeric fraction (EF, the relative amount of the enantiomer). CF and EF are defined in eqs 1 and 2
CF )
C(specific component) CTC + CCC + CTN
EF )
C(+) C(+) + C(-)
(1)
(2)
where C represents concentration. EF provides a measure of the extent of enantioselective weathering that has occurred since technical chlordane was introduced into the biosphere as a racemate. Average component fractions and total concentrations are shown in Figure 1, and EFs are provided in Table 1. Several single factor ANOVAs were performed on the data from four sites, plot air at three heights and the CAES lawn background. These ANOVAs compared the total concentrations observed, and both EFs (TC and CC) of the samples collected at each of these locations. In all cases the ANOVA showed that the sites were different at the 0.01 probability level. Note that the total concentration above the plot decreased from 0.84 ng/m3 in air collected at 0.5 m height to 0.34 ng/m3 in the sample collected at 2.5 m above the plot. This latter concentration is quite similar to the CAES lawn background site value of 0.28 ng/m3. The higher concentration closer to the soil surface indicate that chlordane is volatilizing from the plot. Volatilization from the plot soil is confirmed in the analysis of compositional fractions and EFs.
FIGURE 1. Average ambient air component fractions at each height above the plot and total concentration at each height from MarchSeptember 2002 along with CAES lawn background air and average soil component fractions and concentration.
TABLE 1. Average Enantiomer Fractionsa and Mixing Fractionsb in Air Collected between March-September 2002 sample
EFTCa
plot soil plot air @ 0.5 m plot air @ 1.5 m plot air @ 2.5 m CAES lawn background Lockwood Waterbury Burlington
0.465 ( 0.004 0.465 ( 0.007 0.474 ( 0.008 0.482 ( 0.009 0.489 ( 0.008
EFCCa
fTCb
fCCb
0.538 ( 0.004 0.533 ( 0.015 1.00 0.76 0.527 ( 0.014 0.63 0.48 0.515 ( 0.018 0.29 -0.10 0.517 ( 0.010
0.491 ( 0.012 0.515 ( 0.013 0.495 ( 0.009 0.513 ( 0.012 0.489 ( 0.004 0.507 ( 0.005
Note EFs are the average of measured EFs ( 1 standard deviation of all samples collected at each site during the specified time period. b Mixing fractions of plot air calculated as mixture of inputs from plot soil and CAES lawn background. a
In Figure 1 we see that the component fraction for TN is similar to that for the other four components at 0.5 m, while at the 2.5 m height TN is the component present in highest
relative amount. This later value is most similar to the sample from the CAES lawn background site. In a similar vein, the EFs in air samples collected at 0.5 m above the plot match those in the plot soil; EFs for the air samples approach racemic with increased height above soil. The background air sample is also very close to racemic. EFs from two contributing sources can be used to determine the mixing ratio of a sample composed of contributions from the two sources (21, 22)
f1 ) (EFmix-EF2)/(EF1-EF2)
(3)
where f1 is the mixing fraction contributed by source component 1 for a particular chiral chiral component, EFmix is the enantiomeric fraction of the chiral component in the mixed compartment (air above the plot), and EF1 and EF2 are the enantiomeric fractions of the chiral component in the source compartments (EF1, plot soil; EF2, CAES lawn background). These calculations are performed for the air samples in the plot and are also listed in Table 1. Note differences in the contributions for the TC and CC at each
FIGURE 2. Average experimental plot soil component fractions, predicted air component fractions based on soil component fraction and relative KOA, component fraction observed in 0.5 m air if the average background observations are subtracted, and component fraction actually observed in 0.5 m air. VOL. 37, NO. 21, 2003 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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height. As the height of sample collection increases the fraction of chlordane contributed from the soil decreases. Differential volatilization of individual chlordane compounds from soil may account for the different f1 values for TC and CC. The volatility can be estimated from the soil-air partition coefficient (KSA), as reported by Harner et al. (15)
KSA ≈ φ′SOM KOA
(4)
where φ′SOM is the mass fraction of soil organic matter, and KOA is the octanol-air partition coefficient. Since for a given soil φ′SOM will remain the same (0.05 for the plot soil), relative volatility of the different components can be measured from the ratio of the KOAs. From the recently published KOA values for TC, CC, and TN (23), the relative volatilities of TC, CC, and TN can be computed and are in the ratio of 1/0.89/0.35. If we then multiply the actual plot soil concentrations by these values, we generate a relative component profile in air predicted based solely on volatilization from the plot soil. This profile is shown in Figure 2. For the purpose of comparison we have included in Figure 2 a profile that would result if the average air from the CAES lawn background were subtracted from the average observed air at 0.5 m above the soil. In the figure the TC/CC ratio predicted from relative volatility (0.98) is now close to what is observed in the background subtracted sample (1.03), although TN in the background subtracted air still exceeds the relative amount predicted solely based on volatilization. It may be assumed that the temperature of the soil surface differs significantly from that of ambient air. In the calculations done here, KOA was calculated based on a 19 °C air temperature, chosen for consistency with the equilibrium discussion in a later section. Since volatilities for TC, CC, and TN as a function of temperature differ, predicted volatilization may be incorrectly calculated if the soil temperature is assumed equal to the air temperature; soil temperature was not monitored as part of this experiment. This question remains to be answered, but it is likely that TN actually observed in the air would still exceed the amount predicted based solely on relative volatility. Long-Term Air Monitoring above Experimental Plot. Air above the experimental plot was monitored over a period of 3 years. Total concentrations over time for these air samples are shown in the panels of Figure 3 at each of the three heights above the soil, from the initial monitoring date (day 1 ) June 7, 2000). Note that in all three panels of Figure 3, periods of high concentration correspond to warm monthss late spring through early fallswhile the periods of low concentration correspond to the winter months. Clearly, as is expected, volatilization from soil is highly dependent on temperature. However, another interesting observation may be made with regard to the data in Figure 3. Some of the concentration spikes within a period of elevated concentration correlate with dates of destructive harvest of the crops grown in the plot as part of a different series of experiments reported elsewhere (18, 19). For example, the jump between dates 418 and 430 during the summer 2001 correlated with harvesting during this period. In our experiments, harvesting consists of digging up the entire plant root system so that we can collect the entire root ball for analysis. Thus, harvesting can bring soil from as far as a foot beneath the surface to the surface. In 2002 we carefully monitored this phenomenon by taking samples on two successive days. Date numbers 762 and 763 show data prior to and after a harvest of plants grown in bins of contaminated soil. At the 0.5 m height the concentration almost doubles between these dates, though the average air temperature is approximately the same (20.4 °C on day 762; 18.9 °C on day 763). Obviously, cultivation in the plot brings contaminated soil to the surface from where its chlordane burden can be more easily volatilized. This 4890
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FIGURE 3. Total concentration (sum of all five components) plotted versus sampling date. day 1 ) June 7, 2000 at 0.5 m, 1.5 m, and 2.5 m above the plot. cultivation effect could be of importance in agricultural fields contaminated with chlordane and other POPs, with both planting and harvesting easily bringing fresh soil to the surface, promoting volatilization from these fields. The influence of cultivation practices on volatilization of applied pesticides has been reported by others (15, 24, 25). It is useful to examine the soil/air equilibrium after soil cultivation has occurred. The cultivation process mixes the soil, exposing a fresh soil surface containing weathered residues to the air. A 1-day air sample taken immediately after cultivation can be compared to the soil concentration to provide a field-estimated, dimensionless soil-air partition coefficient, kSA (eq 5)
kSA ) CS/CA
(5)
where CS is the bulk soil concentration in mg/mL, and CA is the 1-day average air concentration in mg/mL. These estimated kSA values can be compared to the KSA at equilibrium calculated from the laboratory-measured KOA at equilibrium reported by Shoeib and Harner (23) and eq 4, with φ′SOM ) 0.05 for the CAES plot soil. This laboratorymeasured KOA at equilibrium was adjusted for temperature using eq 6 (soil temperatures were not monitored, the average air temperature (T ) 18.9 °C) on the post cultivation day was used for this adjustment)
Log KOA ) A + B/T
(6)
where T is the temperature in K, and A and B are experimentally derived parameters reported by Shoeib and Harner (23).
TABLE 2. Comparison of Estimated Partition Coefficients (kSA) Post Cultivation (Day 763) with Calculated Partition Coefficient (KSA) at Equilibrium component +TC -TC +CC -CC TN a
Log KOAa (eq 6)
KSA (eq 4)
kSA (eq 5)
kSA/KSA
9.22 9.22 9.27 9.27 9.68
8.35 × 8.35 × 107 9.40 × 107 9.40 × 107 2.37 × 108
2.19 × 2.23 × 109 2.59 × 109 2.52 × 109 2.46 × 109
26.2 26.7 27.5 26.8 10.4
107
109
KOA - octanol-air partition coefficient, temperature corrected.
It can be seen in Table 2 that for all components the field-estimated partition coefficient (kSA) is greater than the equilibrium partition coefficient (KSA) by a factor of 10-30. Therefore, the air concentration in the field is lower than would be expected at equilibrium, although we note with interest that TN values are much closer to an equilibrium condition than either TC or CC. This agrees with the prior observation that TN in air above the plot is higher than predicted based solely on relative volatility. It should be mentioned that as pointed out by Hippelein and McLachlan (13, 14) KSA is also dependent on relative humidity which was not measured during this study. The concentration vs date profiles shown in Figure 3 permit us to calculate the yearly loss of chlordane from the soil. We begin by constructing a box model representing the air directly above a 1 m square portion of the plot. This air is broken into three 1-m high segments; thus, each segment contains one cubic meter of air. For simplicity, it is assumed that the background air is well mixed and has the same concentration at all heights and that any air higher than 3 m above the plot is the same as background. These assumptions are reasonable given the similarity in both concentration and profile for the sample collected at the 2.5 m height and the CAES lawn background (shown in Figure 1). This model is depicted in Figure 4. The chlordane in the air in any of the three boxes above the plot is a sum of chlordane inputs minus chlordane outputs. These three
(0.5 m) C + G ) F + H
(7)
(1.5 m) B + H ) E + I
(8)
(2.5 m) A + I ) D
(9)
equations can be summed and rearranged to solve for the total volatilization from the soil, “G”.
G)D+E+F-A-B-C
(10)
A-F are all advection terms and can be calculated from the observed concentration multiplied by the observed wind speed. These equations hold for any given time period. To determine the annual values of each advection term requires integration of the concentration versus time plots of Figure 3. This is done by importing each data set (including the CAES lawn background concentration versus time plot not shown) into PeakFit, ver. 4. Each data set was smoothed via Fourier transform and integrated to produce three separate peaks. Thus, the entire data set consists of 12 peaks; one peak per year at each of three heights within the plot and one peak per year for the CAES lawn background site; each peak area is expressed as ng-day/m3. These resultant areas are multiplied by average annual wind speeds at the sampled height (m/day) to yield the advection terms in ng/ m2. The CAES lawn background site area is used with the three wind speeds (from different heights) to generate the three separate advection input terms A, B, and C. All six annual advection terms are then summed via eq 10 for the annual
loss of chlordane from one square meter of plot soil. From these calculations we were able to determine that 17.3 mg of chlordane was lost from a square meter of plot soil in 2000, 12.8 mg in 2001, and 9.4 mg in 2002. These yearly losses decrease at an exponential rate
Y ) Y0e-kt
(11)
where Y is the annual chlordane lost, Y0 is the chlordane lost during the first year, k is exponential rate constant, and t is time in years (the constant k ) -0.3043 yr-1 and t1/2 ) 2.3 years). Using this loss rate the volatilization loss from the soil was projected forward 7 years, allowing estimates of the loss amounts for each year over 10 years, a time period equivalent to a total of 4 half-lives. The sum of these 10 yearly losses should therefore represent 94% of the amount which might be expected to volatilize from this soil. This 10-year total chlordane loss was found to be 63 mg. This loss amount can be compared to the original amount of chlordane in the soil. The original average soil total chlordane concentration in the plot was 4 µg/g dry weight. Assuming that the field soil was 10% wet weight with a field density of 1.3 g/cm3, we calculate that originally there were 47 mg of chlordane in a slice of field plot 1 cm deep × 1 m long × 1 m wide. From these calculations over a 10-year period the entire amount of chlordane volatilized over 1 square meter of cultivated soil would be equivalent to the amount of chlordane present in the topmost 1.3 cm of the one square meter area. We stress again that cultivation of the soil has enhanced the amount of chlordane outgassing from the plot. Thus, the total calculated volatilization loss from an uncultivated soil would be somewhat less, and the depth from which chlordane volatilized would also be less. It is interesting to compare this calculated loss depth with the soil-air exchange model proposed by Harner et al. (15). These authors propose a soil-air exchange layer of 0.1 cm depth, a buffer layer from 0.1 to 1.0 cm and a soil reservoir below this level. The data reported here, therefore, would correspond to the surface exchange of chlordane with replenishment of the surface from the buffer and the reservoir. As the annual total loss is decreasing over the 3 years examined in the studies presented here, it appears that the surface exchange and replacement of chlordane from the buffer layer takes place more rapidly than the replenishment of the buffer layer from the reservoir is occurring. This would again emphasize the importance of the cultivation process, which mixes the soil and replenishes both the soil-exchange and buffer layers. Concentration in Background Connecticut Air. The average total concentration of the five monitored components for the four background sites during the spring and summer of 2002 ranged from 0.13 to 0.28 ng/m3. A single factor ANOVA indicated that during this time period these total concentrations were statistically different at the 0.05 probability level. Higher concentrations were observed in the urban sites, while the suburban and rural sites showed lower concentrations of chlordane. Average air component fractions from the four sites during the summer of 2002 are presented in Figure 5, along with the average total concentration observed for each site. Note the consistency of the compositional profiles across these sites. At all sites TN was approximately 25% of the total, and both TC components were present in higher concentrations than the CC components. Principal components analysis of the component fractions observed in the samples taken from these four sites would seem to indicate that the pattern is consistent throughout. This consistency was confirmed with a single factor ANOVA for each of the TC or CC enantiomeric fractions. In both cases there were no significant differences between the EFs at these four sites. The four sampling sites in this study are not more than 35 VOL. 37, NO. 21, 2003 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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FIGURE 4. Model of volatilization from the plot. A - advection in at 2.5 m; B - advection in at 2.5 m; C - advection in at 0.5 m; D advection out at 2.5 m; E - advection out at 1.5 m; F - advection out at 0.5 m; G - volatilization from soil to air at 0.5 m; H - advection from 0.5 m to 1.5 m; I - advection from 1.5 m to 2.5 m.
FIGURE 5. Average ambient air component fractions and total concentration from March-September 2002 for each of the four ambient background sites. air miles apart. Although the chlordane component profiles are similar among the sites, the chlordane concentrations were higher in the urban settings, suggesting that there is local urban input of chlordane to Connecticut air. Such a local, urban source may likely be mixing with background chlordane transported from longer distances, but the similarity in profile and enantiomer fraction between the rural and the urban sites suggests that chlordane transported into the state and chlordane from the local urban source present similar component and enantiomer fractions. We have reported previously a survey of the chlordane concentrations in soils throughout Connecticut (3, 4). In that survey we found that some of the soils taken from areas near home foundations had concentrations of chlordane which were much higher, often by several orders of magnitude, than the concentrations observed in other residential or agricultural soils, see Table 3. Furthermore, EFs in the lower concentration residential and agricultural soils were often far from racemic, while in the high concentration home foundation soils the EFs were racemic. Comparison of these soil EFs with those we report for our background air samples suggest that one possible urban source of chlordane to Connecticut ambient air is the volatilization of chlordane from soils around home foundations. These soils have the highest concentration and, presumably, greater outgassing 4892
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TABLE 3. Connecticut Soil Concentrations and EFs ( 1 Standard Deviation (4) soil
concn range (ng/g)
EFTC
home foundations 5000-94000 0.500 ( 0.006 residential (other) ND-5000 0.467 ( 0.028 farm 1 200-700 0.0502 ( 0.006 farm 2 30-700 0.467 ( 0.004 farm 3 30-40 0.405 ( 0.545
EFCC 0.500 ( 0.004 0.527 ( 0.022 0.504 ( 0.002 0.538 ( 0.004 0.545 ( 0.011
potential and EFs close to those observed. It should be pointed out that the termiticide usage of chlordane has also resulted in elevated and racemic chlordane levels in indoor air (9). It would be difficult to discriminate between outgassing of soils adjacent to treated homes with release of indoor air from treated homes. In any case, chlordane was used in many locations throughout the country as a termiticide, and it is likely that the component profile of this source (either from indoor air or soil outgassing) could be both transported into Connecticut from out of state and arise from home foundations within the state of Connecticut. It is useful to compare the concentrations observed in this study with those reported by other workers. In urban
settings, Basu and Hites (26) have observed the sum of CC, TC, and TN in Chicago to average approximately 0.17 ng/m3 in the summer of 2001; Bidleman et al. (8) reported concentrations in South Carolina to be 0.31 ng/m3 during 1994-1995. Jantunen et al. report Alabama air at 0.095 ng/ m3 in a region abutting both urban areas and agricultural fields (10). Ambient air from rural, nonagricultural regions of the United States Midwest were reported by Leone et al. (12) to be between 0.01 and 0.20 ng/m3 depending on site. Clearly the background concentrations observed in the current study fall within the range reported by other researchersshigher concentrations in urban settings and lower concentrations in rural settingsswhich is consistent with nonagricultural, atmospheric sources of chlordane, i.e., home residential use. It is interesting to note the scatter in TC/CC ratios in ambient air; the ratio was 1.1 in the technical mixture available from Velsicol, a chlordane manufacturer. The ratio has been reported to be as high as 1.78 in the Alabama air (10) and as low as 0.89 in the rural agricultural air from the Midwest (12). In the latter case, the researchers attribute the lower ratio in the ambient air samples to TC degrading faster photochemically. In our previous survey of Connecticut soils we observed that residential home foundation soils, those with relatively high concentrations of chlordane and low biological activity (EFs racemic), had a TC/CC ratio on average of 1.08. This would translate to a TC/CC ratio in ambient air of approximately 1.22 when the relative KOAs are considered. The actual observed TC/CC ratio for the ambient air background samples from the current study is 1.14, a value in good agreement with the expected amount, supporting the idea that home foundation soils are a primary source of chlordane to ambient background air in Connecticut. Interpretation of the TC/TN ratio is not so straightforward. Based on an average TC/TN ratio in foundation soils of 1.30 and the relative KOAs, a ratio of 3.42 would be expected in the Connecticut ambient air. The observed value of 1.54 is quite different, with an overabundance of TN observed in the air. This overabundance of TN is similar to the result observed over the CAES experimental plot. It is interesting to note that Jantunen et al. (10) also tried to predict ambient Alabama air TC/CC and TC/TN ratios based on soil concentration in Alabama (using relative vapor pressures rather than relative KOA). They also observed TC/CC ratios close to expected values (predicted range 1.32-1.69, observed value 1.79) but TC/TN ratios much further apart (predicted range 1.231.53, observed value 1.92), an underabundance of TN as opposed to our overabundance of TN. This inability of the model to correctly predict the relative amount of TN requires further study.
Acknowledgments The authors would like to thank Terry Bidleman for the loan of an air sampler during 2000 and the Connecticut Department of Environmental Protection for the use of sampling
sites in Waterbury and Burlington. This paper was supported in part by EPA STAR Grant no. R828174.
Literature Cited (1) Falconer, R. L.; Bidleman, T. F.; Szeto, S. Y. J. Agric. Food Chem. 1997, 45, 1946-1951. (2) Aigner, E. J.; Leone, A. D.; Falconer, R. L. Environ. Sci. Technol. 1998, 32, 1162-2268. (3) Mattina, M. J. I.; Iannucci-Berger, W.; Dykas, L.; Pardus, J. Environ. Sci. Technol. 1999, 33, 2425-2431. (4) Eitzer, B. D.; Mattina, M. J. I.; Iannucci-Berger, W. Environ. Toxicol. Chem. 2001, 20, 2198-2204. (5) Kelsey, J. W.; Alexander, M. Environ. Toxicol. Chem. 1997, 16, 582-585. (6) Louis, J. B.; Kisselbach, K. C., Jr. Bull. Environ. Contam. Toxicol. 1987, 39, 911-918. (7) Ulrich, E. M.; Hites, R. A. Environ. Sci. Technol. 1998, 32, 18701874. (8) Bidleman, T. F.; Alegria, H.; Ngabe, B.; Green, C. Atmos. Environ. 1998, 32, 1849-1856. (9) Leone, A. D.; Ulrich, E. M.; Bodnar, C. E.; Falconer, R. L.; Hites, R. A. Atmos. Environ. 2000, 34, 4131-4138. (10) Jantunen, L. M. M.; Bidleman, T. F.; Harner, T.; Parkhurst, W. J. Environ. Sci. Technol. 2000, 34, 5097-5105. (11) Finzio, A.; Bidleman, T. F.; Szeto, S. Y. Chemosphere 1998, 36, 345-355. (12) Leone, A. D.; Amato, S.; Falconer, R. L. Environ. Sci. Technol. 2001, 35, 4592-4596. (13) Hippelein, M.; McLachlan, M. S. Environ. Sci. Technol. 1998, 32, 310-316. (14) Hippelein, M.; McLachlan, M. S. Environ. Sci. Technol. 2000, 34, 3521-3526. (15) Harner, T.; Bidleman, T. F.; Jantunen, L. M. M.; MacKay, D. Environ. Toxicol. Chem. 2001, 20, 1612-1621. (16) Dearth, M. A.; Hites, R. A. Environ. Sci. Technol. 1991, 25, 245254. (17) United States Environmental Protection Agency. 2003, USEPA Persistent Bioaccumulative and Toxic (PBT) Chemical Program; Chlordane Fact Sheet. www.epa.gov/opptintr/pbt/chlordane.htm. (18) Mattina, M. J. I.; Iannucci-Berger, W.; Dykas, L. J. Agric. Food Chem. 2000, 48, 1909-1915. (19) Mattina, M. J. I.; White, J.; Eitzer, B.; Iannucci-Berger, W. Environ. Toxicol. Chem. 2002, 21, 281-288. (20) Bidleman, T. F.; Leone, A. D.; Van Vilet, L.; Szeto, S.; Ripley, B.; Harner, T.; Shoeib, M. Abstract Book SETAC 23rd Annual Meeting, Salt Lake City, Utah, Nov 16-20, 2002, SETAC, Pensacola, FL, 336. (21) Bidleman, T. F.; Falconer, R. L. Environ. Sci. Technol. 1999, 33, 2299-2301. (22) Harner, T.; Wiberg, K.; Norstrom, R. Environ. Sci. Technol. 2000, 34, 218-220. (23) Shoeib, M.; Harner, T. Environ. Toxicol. Chem. 2002, 21, 984990. (24) Whang, J. M.; Schomburg, C. J.; Glotfelty, D. E.; Taylor, A. W. J. Environ. Qual. 1993, 22, 173-180. (25) Wienhold, B. J.; Gish, T. J. J. Environ. Qual. 1994, 23, 292-298. (26) Basu, I.; Hites, R. A. Integrated Atmospheric Deposition Network; Indiana University, 2002.
Received for review April 9, 2003. Revised manuscript received August 12, 2003. Accepted August 19, 2003. ES0343196
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