Environ. Sci. Technol. 2007, 41, 1635-1640
Lack of Enantioselective Microbial Degradation of Chlordane in Long Island Sound Sediment X I Q I N G L I , †,⊥ L I J I A Y A N G , ‡,§ U R S J A N S , ‡,§ MICHAEL E. MELCER,| AND P E N G F E I Z H A N G * ,†,§ Department of Earth and Atmospheric Sciences, City College of New York, CUNY, New York, New York, 10031, Department of Chemistry, City College of New York, CUNY, New York, New York, 10031, Ph.D. Program in Chemistry, Graduate School and University Center, CUNY, New York, New York, 10016, Department of Math and Science, U.S. Merchant Marine Academy, Kings Point, New York, 11024
Numerous studies have examined the enantiomeric compositions of trans- and cis-chlordane in soils (agricultural, background, and house foundation soils) and in the atmosphere. In contrast, little is known about the enantiomeric compositions of chlordane in sediment. In this work, surficial sediments and sediment cores were collected at various sites in Long Island Sound (LIS) previously surveyed by the National Oceanic and Atmospheric Administration’s (NOAA) National Status and Trends (NS&T) Program. Archived surficial sediments at selected sites were acquired from the NS&T Specimen Bank. The chlordanes were racemic or nearly racemic in most archived and recently collected sediments, indicating that the enantiomeric compositions of the sources of chlordane to LIS sediment did not change in the past two decades, and that house foundation soils are likely the major source of chlordanes to LIS. Invariant enantiomeric compositions temporally in surficial sediments and at different depths in sediment cores clearly indicate the lack of enantioselective biodegradation in LIS sediment, in striking contrast to the widely observed enantioselective biodegradation of chlordanes in soils.
Introduction Technical chlordane was used in the U.S. (1948-1988) and worldwide as a pesticide for farmlands, home lawns and gardens, and as a termiticide for house foundations (1, 2). Commercially available technical chlordane is a mixture of over 140 compounds. Many of the chlordane components and metabolites are toxic (2), are suspected to be carcinogenic (3), and may have estrogenic activities (4). Technical chlordane, along with many other organochlorine pesticides, has been phased out from the market under the UN-ECE (United Nations Economic Commission for Europe) and UNEP * Corresponding author phone: (212) 650-5609; fax: (212) 6506482; e-mail:
[email protected]. † Department of Earth and Atmospheric Sciences, City College of New York. ‡ Department of Chemistry, City College of New York. § Graduate School and University Center, City University of New York. | U.S. Merchant Marine Academy. ⊥ Current Address: College of Environmental Sciences, Peking University, Beijing, 100871, P.R. China. 10.1021/es062125v CCC: $37.00 Published on Web 01/30/2007
2007 American Chemical Society
(United Nations Environmental Program) POPs (persistent organic pollutants) protocol in 1997 (5, 6). Nevertheless, chlordane is still detected in soils (e.g., refs 7, 8), the atmosphere (e.g., refs 9-12), vegetations (e.g., ref 8), sediments (e.g., ref 13), and tissues of marine species (e.g., ref 14). The two major constituents of technical chlordane, transchlordane (TC, ∼13%) and cis-chlordane (CC, ∼11%), are chiral, and each is manufactured as a racemic mixture of two enantiomers. The two enantiomers are non-superimposable mirror images of one another and have identical physicochemical properties. Hence, physical processes (e.g., volatilization, leaching, and deposition) and chemical breakdown (e.g., hydrolysis and photolysis) do not change the racemic composition of chlordanes (15, 16). In contrast, because of their different molecular configurations, the enantiomers may have different ability to bind to structure-sensitive biological receptors (14, 17, 18). As a result, microbial degradation and biological metabolism can be enantioselective and, therefore, change the enantiomeric composition. Numerous studies have demonstrated nonracemic chlordane signatures in agricultural soils (7, 12, 19-25) and in most background soils (26), indicating that enantioselective biodegradation of chlordanes has taken place in these soils. In contrast, chlordanes in house foundation soils (applied as a termiticide) remain racemic or close to racemic (12). Due to continuous volatilization from soil after initial application, chlordanes in the air immediately above the soil have enantiomeric compositions similar to that found in the soil (12, 27). The enantiomeric compositions of chlordanes in ambient air typically lie between nonracemic signatures found in agriculture soils and racemic mixtures expected from past termite control and/or from more recent chlordane application (28, 29). In contrast to the great number of studies on enantiomeric compositions of chlordanes in soils and the atmosphere, reports on enantiomeric compositions in sediments are scarce. To our knowledge, there is only one published study that examined the enantiomeric composition of TC in two sediment cores collected from a single site in the Canadian Arctic (13, 29). TC was more nonracemic in certain sediment layers than in the archived air samples of the same ages, indicating that enantioselective biodegradation may have occurred upon atmospheric deposition in those layers. The objective of this work was to examine the enantiomeric compositions of TC and CC in Long Island Sound (LIS) sediment in order to determine whether microbial degradation plays an important role in chlordane reduction in the LIS sediment. LIS is one of the largest estuarine systems on the Atlantic coast of the U.S., ranked fourth in population (over 6 million) and 10th in population density among U.S. estuarine drainage areas. The Sound is 150 km long and 30 km across at its widest point (30), and provides vital transportation and rich fishing and shell-fishing grounds for commercial interests. However, LIS has been heavily contaminated by chlordane and other chlorinated pesticides (31). Surficial sediments and sediment cores in LIS were collected at various sites previously surveyed by the National Oceanic and Atmospheric Administration (NOAA). Archived surficial sediments were obtained from the National Biomonitoring Specimen Bank (NBSB) of the National Institute of Standards and Technology (NIST) to examine the potential changes in enantiomeric compositions over time. These archived sediments were collected by NOAA’s National Status and Trends (NS&T) Program (31). Temporal trends in enantiomeric compositions in surficial sediments and the profiles of VOL. 41, NO. 5, 2007 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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FIGURE 1. Sampling sites in Long Island Sound (modified from ref 31). The Sound is 150 km long and 30 km across at its widest point. No sediment was collected at LINH (New Haven) since previous studies showed very low TC and CC concentrations at this site. enantiomeric compositions across the sediment cores would unequivocally reveal whether enantioselective biodegradation of chlordane has occurred in LIS. The chiral signatures of TC and CC would also shed light on the sources of chlordanes to the Sound.
Materials and Methods Sample Collection and Acquisition. Surficial sediments were collected in 2005 and 2006 at 8 LIS sites (LICR, LIHR, LISI, LIMR, LITN, LIHH, LIHU, and LIPJ, Figure 1 & Table 1) that were previously surveyed (1986-1996) by the NS&T Program’s Mussel Watch Project (32). These sites were carefully selected by the NS&T Program to avoid point sources and to represent general contamination conditions in the Sound. Sediment samples were also collected at two additional sites, Little Neck Bay (LILN) and Manhasset Bay (LIMB) (Figure 1), where very high chlordane concentrations (>21 ng/g dry weight) were detected during the 1991 sediment toxicity survey conducted by the NS&T Program (31). Sample collection was performed using a Kynar-coated Van-Veen grab sampler (5-6 grabs per site). The top 1 cm sediments from different grabs at a site were collected using a stainless steel flat-bottom scoop and were mixed in a Teflon beaker. The homogenized samples were frozen in the field by dry ice in a cooler. Sediment cores were collected at four sites that showed highest chlordane concentrations during past surveys (LITN, LIHH, LILN, and LIMB, Figure 1). Core collection followed the methodology established by the U.S. Geological Survey (USGS) (33). Briefly, cores of 11-cm diameter and 41-56 cm in length were collected using polycarbonate tubes by scuba divers from the USGS. The lengths of the cores were approximately the depth of clay layers below the sediment surface at these sites. Care was taken to drain the overlying water (using a hand pump) without disturbing the core surfaces. The capped cores were frozen in the field in an insulated storage box with dry ice. The frozen cores were sectioned in a laboratory into slices approximately 1 cm thick using a core extruder and a stainless steel spatula. The sliced core sediments and surficial sediments were stored in a freezer at -20 °C until analysis. To examine the temporal trends of enantiomeric compositions of TC and CC in surficial sediments, aliquots of archived surficial sediments at five sites (LIHR, LIPJ, LICR, LITN, LIHH) collected by the NS&T Mussel Watch Project were requested from NS&T Specimen Bank. These sites are geographically scattered around a large portion of the LIS (Figure 1). Therefore, comparison of the enantiomeric compositions of TC and CC in archived and corresponding recent sediments is expected to reflect the overall temporal trend of enantiomeric compositions and concentrations of TC and CC in the Sound. Before they were acquired, the 1636
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archived surficial sediments were stored in a liquid nitrogen freezer at approximately -150 °C at the specimen bank (32, 34). The sample collection dates and longitudes/latitudes of the archived and recently collected surficial sediments are provided in Table 1. The size of our sampling vessel prevented access to the exact locations of some archived samples (where water was too shallow for the vessel) (Table 1). Sample Extraction and Analysis. The archived and recently collected sediment samples were extracted following EPA standard method 3540C (35). Briefly, the thawed sediment (approximately 10 g) was mixed with 0.5 mL of surrogate standards and ground with 50 g of anhydrous granular sodium sulfate using ceramic mortar and pestle; the mixtures were extracted with acetone and hexane (1:1 v/v) using a Soxhlet system for 24 h (4 cycles per hour). Activated copper pellets were added to the flask to remove sulfur. The extracts were then reduced to 1-2 mL using a Turbovap 500 rotary evaporator (Zymark, Boston, MA). The extracts were cleaned by passing through columns (2.5 cm diameter) packed with 20 g of activated florisil (Supelco, Bellefonte, PA) that was capped with 3-5 cm (about 20 g) of sodium sulfate. The columns were eluted with three fractions, each consisting of 200 mL diethyl ether/hexane of different volume ratios (sequentially, 6/94, 15/85, and 50/ 50, v/v). Each fraction was concentrated into 1 mL hexane, and fraction 1 was used for concentration and chiral signature analysis. The enantiomeric compositions of TC and CC (fraction 1) were determined using a TRACE GC-DSQ (Thermo Electron Co., Madison, WI) gas chromatograph-mass spectrometer (GC-MS) operated in a negative ion mode (NIMS). A chiral Betadex-120 column (20% permethylated β-cyclodextrin in SPB-25, 30 m × 0.25 mm ID, 0.25 µm film thickness, Supelco) was used to separate the enantiomers. The instrument was operated in the selected ion monitoring mode at m/z 410 and 412. Samples (2 µL) were injected splitless (split opens after 1 min) at an oven temperature of 90 °C. After a 1-min hold, the oven temperature was ramped to 155 °C at 15 °C/ min, to 188 °C at 0.4 °C/min, held for 1 min, ramped to 220 °C at 20 °C/min, and held for 10 min. The temperatures of the injector, the transfer line, and the ion source were set at 220, 220, and 150 °C, respectively. Each sample was injected for 6-9 times to derive the mean and standard deviation, which were used in the two-tailed Student t-test to determine whether two sample means were statistically different. Briefly, a non-negative t-statistic was computed from the observations, and the probability (p) of getting a higher absolute value of the t-statistic under the “same population means” assumption was calculated. A p value of greater than 0.05 was used to indicate that two means are not significantly different (36). Quality Control. Blanks, prepared using the same procedure as for the real samples, were included for every five samples. No chlordane was found in the blanks. The enantiomeric compositions of TC and CC are expressed as enantiomeric fractions (EFs), defined as A+/(A++A-), where A+ and A- are the peak areas of the (+) and (-) enantiomers, respectively. An EF ) 0.5 indicates a racemic compound, whereas EFs < 0.5 or >0.5 indicates preferential depletion of the (+) or (-) enantiomers, respectively. The (+) enantiomers of TC and CC are eluting earlier relative to the (-) enantiomers on the Bedatex-120 column (26). The enantiomer peaks were automatically integrated using the batch reprocessing function of the software Xcalibur provided by the manufacturer of the GC-MS (Thermo Electron Co.). For the peaks (of a very small number of samples) that were not integrated properly under the batch reprocessing, manual integration was performed. Racemic standards (Ultra Scientific Inc., North Kingstown, RI) were injected at the beginning and the end of a sequence (typically consisting of
TABLE 1. Site Names, Codes, Latitudes, Longitudes, and Collection Dates of Archived Surficial Sediments (Collected Prior to 1990) and Recently Collected Sediments (Collected in 2005 and 2006)a site code
state
collection date
latitude (N)
longitude (W)
LICR
Connecticut River
CT
01-Apr-2006 11-Nov-1986
41°15.59′ 41°15.83′
72°20.55′ 72°20.50′
LIPJ
Port Jefferson
NY
01-Apr-2006 1-Dec-1989
40°57.58′ 40°57.42′
73°05.31′ 73°04.96′
LIHR
Housatonic River
CT
09-Apr-2005 11-Nov-1986
41°10.12′ 41°10.47′
73°06.42′ 73°07.23′
LISI
Sheffield Island
CT
09-Apr-2005
41°03.40′
73°24.71′
LIHU
Huntington Harbor
NY
25-Mar-2006
40°55.07′
73°25.82′
NY
08-Apr-2005 7-Dec-1987
40°51.10′ 40°51.15′
73°40.21′ 73°40.17′
LIHH
a
site name
Hempstead Harbor
LIMR
Mamaroneck River
NY
09-Apr-2005
40°56.48′
73°42.03′
LIMB
Manhasset Bay
NY
08-Apr-2005
40°48.57′
73°42.76′
LILN
Little Neck Bay
NY
09-Apr-2005
40°46.61′
73°45.39′
LITN
Throgs Neck
NY
09-Apr-2005 12-Nov-1988
40°49.15′ 40°49.17′
73°48.01′ 73°48.07′
Archived sediments were obtained from NOAA’s NS&T specimen bank.
12 injections) to determine the reproducibility of the EF analysis. Mean EFs of the standards (10 pg/µL) were 0.501 ( 0.014 for TC (n ) 74) and 0.502 ( 0.017 (n ) 88) for CC. Monitoring endosulfan I (which interferes with the (-) CC enantiomer on Betadex column) using the m/z 404 ion indicated that this compound was not present in fraction 1 of any sample following florisil cleanup. The following criteria were set as a quality control protocol for acceptable EF values: EF values using each of the two monitored ions (m/z 410 and 412) agree within 5%; area ratios of the two monitored ions for samples and standards agree within 5%. Such criteria have been applied in previous studies (e.g., ref 7).
Results and Discussion EFs in Surficial Sediments. The concentrations in the recently collected surficial sediments ranged from 0.46 (LIHR) to 12.97 ng/g dry weight (LIMB) for TC and from 0.35 (LIHR) to 12.04 ng/g dry weight (LIMB) for CC (37). The enantiomeric fractions of TC and CC in the recently collected surficial sediments were between 0.482 and 0.513, with the vast majority between 0.489 and 0.506 (Table 2, Figure 2). Twotailed t-test indicated that the mean EFs of CC in none of the recent surficial sediments were statistically different from the mean EF of the standard (p1 > 0.05 in all cases, Table 2, Figure 2b). The mean EF of TC was statistically different from the mean EF of the standard only in one recent surficial sediment (LIPJ, p1 < 0.05, Table 2, Figure 2a). The mean EFs of TC and CC in the archived sediments were close to 0.500, with the overwhelming majority lying between 0.491 and 0.500 (Table 2, Figure 2). The only outlier was the EF of CC in archived LICR sediment (0.475) and this was the only EF that was statistically different from racemic signature (p1 < 0.05, Table 2, Figure 2). The t-test also revealed that the mean EFs of TC and CC in recently collected surficial sediments were not statistically different from the corresponding EFs of the archived sediments at all sites where such comparison could be made (p2 > 0.05, Table 2, Figure 2). This observation clearly demonstrated that EFs of TC and CC in the surficial sediments did not change significantly in the past two decades in LIS.
TABLE 2. Mean Enantiomeric Fractions (EFs) and Standard Deviations (SD) of Archived and Recently Collected Surficial Sedimentsa TC site LIHR
EF
0.502 0.491b LIHH 0.495 0.498 LITN 0.491 0.500 LICR 0.485 0.495 LIPJ 0.482 0.497 LISI 0.503 LIMR 0.483 LIHU 0.497 LILN 0.493 LIMB 0.491
CC
SD
p1
0.007 0.020 0.020 0.008 0.009 0.014 0.031 0.014 0.016 0.014 0.025 0.028 0.014 0.017 0.014
0.81 0.43 0.43 0.39 0.14 0.85 0.21 0.35 0.03 0.48 0.86 0.22 0.53 0.28 0.14
p2 0.40 0.73 0.20 0.45 0.13
EF
SD
p1
0.493 0.498 0.506 0.495 0.498 0.489 0.490 0.475 0.498 0.498 0.489 0.499 0.501 0.513 0.490
0.011 0.024 0.024 0.016 0.022 0.021 0.022 0.021 0.020 0.016 0.012 0.017 0.008 0.019 0.015
0.41 0.54 0.71 0.31 0.29 0.22 0.33 0.04 0.57 0.58 0.08 0.63 0.78 0.30 0.10
p2 0.64 0.34 0.47 0.34 0.99
a p represents the probability (associated with the two-tailed t-test) 1 between the mean EFs of the sediment samples and the standard, whereas p2 represents the probability between the mean EFs of archived sediments and those of the recently collected surficial sediments. A p-value greater than 0.05 indicates that the two means are not significantly different. b Values in the second row (italic) of a site are for the archived sample of that site.
EFs in Core Sediments. Every fifth core slice was extracted and analyzed to determine EFs of TC and CC. Each slice was 1.1 cm thick and the interval between two adjacent extracted slices was therefore approximately 4.4 cm. The total lengths of the cores were 41, 51, 51, and 56 cm at LIHH, LILN, LIMB, and LITN, respectively. For the LITN core slices with depths greater than 36 cm, TC and CC concentrations were too low to allow reliable determination of EF values. The EFs of TC and CC are presented in Figure 3 and Tables S1-S4 (Supporting Information). Note that the EFs of the surface slice (∼1.1 cm thick) are not exactly the same as the EFs of the surficial sediments at the same site (Tables 2, S1-S4), VOL. 41, NO. 5, 2007 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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FIGURE 2. Enantiomeric fractions (EFs) of (a) TC and (b) CC in archived and recently collected surficial sediments. Arrow indicates that the EF of the sample is statistically different from the mean EF of the corresponding racemic standard (same notation also applies to Figure 3). since the surficial sediments and the sediment cores were collected separately (a few to a few tens of meters apart). A student t-test indicates that the EFs of the surface slice were not statistically different from those of the surficial sediments. cis-Chlordane. The averages of the mean EFs of CC across the core lengths were 0.500 ((0.017), 0.505 ((0.014), 0.498 ((0.017), and 0.498 ((0.015) for LIHH, LILN, LIMB, and LITN, respectively. Except at one sediment slice (depth 39.4 cm) of LIMB, the mean EFs of CC were not statistically different from the mean EF of the standard (p1 > 0.05, Figure 3b, Table S3). To examine whether EF values of CC varied significantly across the core lengths, a t-test was performed to compare the EFs of the sediment slices. For illustration purposes, the probabilities associated with the two-tailed t-tests between each slice and the middle slice (p2) and between each slice and the surface slice (p3) are presented here (Tables S1-S4). The middle slice depths were 21.6, 28.3, 28.3, and 18.1 cm for LIHH, LILN, LIMB, and LITN, respectively. Statistically different EF of a particular slice from the EFs at the two reference slices occurred only at one slice in one core (39.4 cm, LIMB) (Tables S1-S4). Even for this slice, the mean EF value (0.488) differed from the average EF of the entire core (0.498) by only 0.010, indicating that EFs of CC were virtually invariant with depth in all the sediment cores. trans-Chlordane. The averages of the mean TC EFs across the core lengths were 0.495 ((0.017), 0.495 ((0.013), 0.491 ((0.012), and 0.492 ((0.011) for LIHH, LILN, LIMB, and LITN, respectively. Mean EFs of TC were not statistically different from the mean EF of the racemic standard across the LILN core (p1 > 0.05, Figure 3a, Table S2). Statistically different EFs from the EF of the racemic standard were found at three slices (5.0, 32.7, and 39.3 cm) for the LIHH core (Figure 3a, Table S1), six slices (17.2-44.9 cm) for the LIMB core (Figure 3a, Table S3), and three slices (1.8, 6.4, and 35.6 cm) for the 1638
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FIGURE 3. Enantiomeric fractions (EFs) of (a) TC and (b) CC in core sediments collected at LIHH, LILN, LIMB, and LITN. LITN core (Figure 3a, Table S4). Except at one slice of the LIMB core (depth 11.6 cm), mean TC EFs were not statistically different from the EFs at the surface and middle slices in any cores (Tables S1-S4). At this depth of the LIMB core, the EF value (0.497) differed from the average EF across the core length (0.491) only by 0.006, indicating that EFs of TC were also virtually invariant across the depth in all the sediment cores. Lack of Enantioselective Biodegradation in LIS Sediment. In a previous study that examined TC EFs in sediment cores (13, 29), enantiomeric degradation was inferred by comparing the EFs in the air samples and those in the core layers of the same ages. This approach was feasible because the sampling site was in Arctic (where atmospheric deposition was the sole input of TC) and the sediment cores were annually laminated (which allowed accurate age-dating using radionuclides 210Pb and 137Cs). Such an approach could not be adopted in this work, even though EFs of TC and CC in the atmosphere nearby are available in the literature (12) and 210Pb and 137Cs isotope analysis was performed. One reason is that there may be multiple sources of chlordane to LIS, including atmospheric deposition, runoff from urban and agricultural applications, etc. The other reason is that temporal resolution of EFs across the cores may well be obscured due to sediment mixing in estuaries caused by bioturbation and/or storm events. Bioturbation refers to the enhanced transport processes of particles, solutes, sorbed species in bed sediment by daily activities of benthic organisms, such as feeding, burrowing, excavation, tube construction, and irrigation (38). Bioturbation can transport newly deposited material and conceivably the associated contaminants to depths of tens of centimeters (39). Preliminary 210Pb and 137Cs data from the LILN core indicate that significant sediment mixing did occur at this site, as evidenced by the lack of a sharp peak on the 137Cs concentration-depth profile (Figure 4). 137Cs in sediments is derived from the global fallout that resulted from the atmospheric
FIGURE 4. 137Cs and excess 210Pb concentrations in the LILN core sediments. testing of nuclear weapons that commenced in 1952 and peaked in 1963. A sharp peak in the 137Cs concentrationdepth profile is characteristic of sediments that are not significantly mixed (13, 40). In general, excess 210Pb concentration in the core decreased with increasing depth (Figure 4). This observation does not rule out sediment mixing (41), however. 210Pb and 137Cs data from the LIMB core also indicated sediment mixing, albeit at a lesser degree (37). Sediment mixing can potentially lead to constant contaminant parameters (such as EFs of chlordanes) at different depths of sediment cores. Therefore, the observed depthinvariant EFs alone do not necessarily ensure the lack of enantioselective biodegradation of chlordanes. Likewise, temporally invariant EFs in surficial sediments alone do not guarantee the lack of enantioselective biodegradation either, because without sediment mixing, surficial sediments (in depositional environments) are deposited recently, and EFs in these sediments would largely reflect the EFs of the source which could be temporally constant. However, our findings that EFs were virtually invariant both temporally in surficial sediments and across the lengths of core sediments and that chlordane in the vast majority (>95%) of the sediment samples were racemic or nearly racemic (EFs between 0.49 and 0.51) clearly demonstrate the lack of enantioselective biodegradation of chlordane in LIS sediment. Implications. Upon entry into the atmosphere, chiral pesticides such as chlordane only undergo abiotic processes (e.g., photolysis, atmospheric deposition) and their distinctive chiral signatures are preserved. For this reason, enantiomers of pesticides have been proposed to trace the soil-air and water-air exchange processes and to identify the sources of pesticides in the atmosphere (19, 42). For example, racemic or nearly racemic chlordane in the ambient air of northern Alabama indicates that little airborne chlordane in this region comes from volatilization of chlordane in agricultural soils, which contain nonracemic chlordane (22, 42). Since chiral signatures of chlordanes were also preserved in LIS sediments (due to the lack of enantioselective biodegradation), chiral signatures in LIS sediments can also help to provide insights into the sources of chlordane. Chlordanes in agricultural soils near LIS have been demonstrated to be greatly nonracemic (EF ) 0.464 for TC and 0.538 for CC) in at least one study (12). The observed racemic or nearly racemic signature in surficial sediments at most sampling sites in this study suggests that runoff from agricultural soils constitutes, at most, a minor fraction of the recent input into LIS. Since chlordanes in house foundation soils remain racemic, racemic or nearly racemic chlordanes in LIS sediment suggest that house foundation soils are likely the major source of chlordane input into the Sound, at least for more recent
input. It is estimated that 24 million homes were treated with chlordanes for termite control (43). It is conceivable that a tremendous amount of chlordanes has been used as a termiticide in the heavily populated area around LIS. Possible pathways of chlordane transport into LIS include runoff from house foundation soils and volatilization of chlordanes from the soils followed by atmospheric deposition into the Sound. Since biodegradation is the sole possible enantioselective removal mechanism of chlordane, racemic or nearly racemic chlordane signatures may indicate that biodegradation is inhibited in LIS sediment. The lack of biodegradation suggests that chlordane might be more persistent in LIS sediment than in agricultural soils where biodegradation occurs. An important distinction between soil and sediment is that the former is aerobic and the latter is anaerobic. The lack of biodegradation in sediments but not in soils indicates that biodegradation of chlordane may be inhibited under anaerobic conditions. This is consistent with the previous observation that chlordane does not degrade in the anaerobic conditions in flooded soils (44). Alternatively, lack of enantioselective removal of chlordanes may suggest that biodegradation of chlordanes in LIS sediment is non-enantioselective. Hence, the observation of enantioselective degradation of TC in the Canadian Arctic (13) and the lack of enantioselecctive degradation of chlordanes in LIS may indicate that enantioselectivity of biodegradation of chlordane (and presumably other organochlorine compounds) is site specific.
Acknowledgments This work was supported by a STAR grant from the United States Environmental Protection Agency (USEPA, RD83221501-0). Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the USEPA. We thank NS&T/NOAA and NIST/NBSB for providing the archived sediment. Special thanks go to Dr. Barbara Porter of NIST for aliquoting the archived samples and Dr. Gunnar Lauenstein with NOAA for his coordination during the sample request process and for his suggestions on field sampling procedures. We express our gratitude to Rick Rendigs and Dann Blackwood from the USGS for diver coring operations, the U.S. Merchant Marine Academy for providing the vessel “Storm”, and the Stony Brook Marine Sciences Research Center for providing the grab sampler. We also thank Drs. Terry Bidleman and Tom Harner for their help with the method development for chiral analysis.
Supporting Information Available Enantiomeric fractions of cis- and trans-chlordane in four sediment cores as well as associated t-test results (Tables S1-S4). This material is available free of charge via the Internet at http://pubs.acs.org.
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(6)
(7)
(8) (9)
(10)
(11) (12) (13)
(14) (15)
(16)
(17) (18) (19) (20) (21) (22) (23)
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Received for review September 6, 2006. Revised manuscript received November 29, 2006. Accepted December 18, 2006. ES062125V
