Formation and SpectroscopicInvestigation of TwoHexachlorobornanes from SixEnvironmentally RelevantToxaphene Components byReductive Dechlorination in Soilunder Anaerobic Conditions†

G E R D A F I N G E R L I N G , ‡

N O R B E R T H E R T K O R N , § A N DH A R U N P A R L A R * , |

Department of Analytical Chemistry, University of Kassel,D-34109 Kassel, Germany, Institute of Ecological Chemistry,GSF, D-85356 Freising-Attaching, Germany, andDepartment of Chemical Technical Analysis andChemical Food Technology, TU Munich,D-85350 Freising-Weihenstephan, Germany

Six pure polychlorinated bornanes isolated fromtechnical toxaphene, namely, Parlar 32 (toxicant B),Parlar 42a (toxicant A1), Parlar 42b (toxicant A2),Parlar 49a, Parlar 56, and Parlar 59, as well as thetechnical mixture were investigated as to their fate ina loamy silt under anaerobic conditions by laboratorystudies taking 4 or 6 months. All test substancesshared the geminal dichloro group in the C-2 positionand, additionally, one chlorine atom each in theC-5endo and C-6exo positions, respectively. Reductivedechlorination was the major reaction leading toa sequential removal of a chlorine atom from eachgeminal dichloro group. Generally, in the first stepof transformation, all six compounds lost a chlorineatom from the geminal dichloro group in the C-2position, preferentially from the endo-position. Thedechlorination rate was in the order of nonachlo-robornanes > octachlorobornanes > heptachlorobor-nanes. While the two monodechlorination productsformed from Parlar 32 underwent no furthertransformation, those products with additional geminaldichloro groups lost further chlorine atoms fromexactly these groups. Finally, all six compounds formedtwo very stable end-metabolites in different ratios,which have been isolated and identified as 2-exo,5-endo,6-exo,8c,9b,10a- and 2-endo,5-endo,6-exo,8c,9b,10a-hexachlorobornane. Additionally, one ofthese end-metabolites was identified as the majorproduct of the degradation of technical toxapheneafter 6 months.

Introduction

Toxaphene is a complex mixture of more than 200 poly-chlorinated C10-terpenes, primarily bornane derivatives with6-11 chlorine atoms. Formerly, it has been one of themost thoroughly used organochlorine insecticides in manyparts of the world. More than 106 t have been applied from1947 to 1985 especially for cotton pest control as well as onsoya beans, vegetables, and small grains (1-4).

Due to its persistence in the environment, its extremeaccumulationsespecially in the aquatic food chainsandits toxicity to higher animals, toxaphene has been bannedor restricted in many countries since the 1980s, but it is stillused in developing countries (1). Despite reduced emission,toxaphene continues to be a major organochlorine pesticidecontaminant in the biosphere (2). One of the majorproblems in toxicity evaluation is the diversity of toxiccomponents in the complex mixture of technical toxaphene,whose exact composition is still not known (3). However,it is known that the various toxaphene components aredifferently transformed in the environment; while somecongeners are highly persistent, others are rapidly degraded(1). This implies that the biological recalcitrance of theindividual toxaphene component is obviously related tonumber and, especially, position of the chlorine substit-uents.

Under environmental conditions, the half-life of tox-aphene in well-aerated soils is 10-14 years (5, 6), althoughsoil factors such as temperature, microbial activity, air, andmoisture have a direct as well as an indirect effect on itspersistence. However, when toxaphene-spiked soil issubjected to a reducing environment the complex mixtureis rapidly transformed. The most important reaction isreductive dechlorination, including a two-electron transferwith the release of a chlorine ion and its replacement byhydrogen. The exact mechanism is still not known, butthe participation of transition metal-containing coenzymeshas been stated by several investigators (7, 9). Generally,aerobic soil microorganisms often fail to metabolize higherhalogenated compounds such as polychlorinated bornanederivatives. While the lower chlorinated bornane deriva-tives, like trichlorobornanes, can be oxidized by themicrobial enzymatic systems, the higher chlorinated com-ponents cannot (9). Hence, anaerobic conditions arenecessary for the initial step in the transformation ofpolychlorinated compounds.

Several investigators have examined the degradation oftoxaphene under anaerobic conditions. Laboratory studiesindicated that reductive dechlorination of toxaphene oc-curred with iron(II)protoporphyrin as well as in anoxic saltmarsh sediments (10, 11). Furthermore, it was demon-strated in sewage sludge, in an anaerobic silt loam, and inirrigation drainage ditch sediments, all of which favoredthe formation of lower chlorinated products (12-16).

† Dedicated to Prof. Dr. H.-D. Scharf on the occasion of his 65thbirthday.

* Author to whom correspondence should be addressed.‡ University of Kassel.§ Institute of Ecological Chemistry.| TU Munich.

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However, no metabolite was isolated for structure iden-tification. Studies dealing especially with the microbialdegradation of isolated toxaphene components underanaerobic conditions are limited. Only the transformationof 2,2,5-endo,6-exo,8,9,10-heptachlorobornane (Tox B) insewage sludge has been investigated (12).

In this paper, we report on the degradation of sixtoxaphene components as well as technical toxaphene byreductive dechlorination in a loamy silt under anaerobicconditions. The structure of the resulting metabolites havebeen investigated by HRGC-MS, HRGC-FTIR, 1H-NMR, andX-ray analysis.

Experimental SectionMaterials. The toxaphene components 2,2,5-endo,6-exo,8c,9b,10a-heptachlorobornane (Parlar 32); 2,2,5-endo,6-exo,8b,8c,9c,10a-octachlorobornane (Parlar 42a); 2,2,5-endo,6-exo,8c,9b,9c,10a-octachlorobornane (Parlar 42b);2,2,5-endo,6-exo,8c,9b,10a,10b-octachlorobornane (Parlar49a); 2,2,5-endo,6-exo,8b,8c,9c,10a,10c-nonachloroborn-ane (Parlar 56); and 2,2,5-endo,6-exo,8c,9b,9c,10a,10b-nonachlorobornane (Parlar 59) were isolated from technicaltoxaphene as previously described (17, 18). Technicaltoxaphene was obtained from Ehrenstorfer, Germany. Thesoil, a loamy silt (pH 6.7, 1.8% organic carbon) was collectedfrom a field in the surroundings of Kassel. It had beenchosen because of its lack of any detectable organochlorinecontaminants. The soil was air-dried and passed througha 2-mm sieve prior to use.

Incubation of Toxaphene Components with Soil andSample Preparation. Incubation with soil was done withportions of 80 g of soil each placed in a 200-mL Erlenmeyerflask and fortified with 1 mL of acetone containing 400 µgof the toxaphene component. After adding 150 mL of sterile,distilled water to each flask, the flasks were shaken, and thesolved O2 was removed with a stream of nitrogen for 30min. Then the flasks were tightly capped with Teflon-coatedstoppers and kept in the dark at∼30 °C. Two samples wereprepared in this way for each component. Furthermore,two blanks were prepared. In the case of technicaltoxaphene, the total of 800 µg (10 µg/g of soil) was addedto the soil. One series of the spiked soil samples wassterilized by autoclaving (121 °C, 15 psi) for two 1-h periodsat intervals of 24 h before adding the compounds. Anaer-obic conditions were checked by measurements of redoxpotentials (EH) with combination platinum/calomel elec-trodes. The redox potentials were greater than -0.20 V.Gas production was observed but was not further inves-tigated. Samples for analysis were taken weekly during thefirst two months and for the rest of the timesa total of 4and 6 months, respectivelysin intervals of 2 weeks. Theflasks were shaken and then opened under a stream of N2,and 10-mL aliquots of the suspension were taken. Eachsample was acidified with H2SO4 to pH ca. 1 and extractedwith a mixture of 5 mL of petroleum ether (45-65 °C)/acetone (1:1) in an ultrasonic bath for 30 min. Thepetroleum ether layer was separated, and the aqueousmedium was reextracted twice with 2× 5 mL of petroleumether (45-65 °C). Finally, the organic phases were com-bined, dried over sodium sulfate, and concentrated undera gentle stream of N2 to ca. 1 mL. These petroleum etherextracts were directly used for GC analysis. With the helpof measurements of blanks, carried out parallel to thesamples, possible contaminations could be excluded.

Gas Chromatography. All routine analyses were carriedout on a Varian 3400 gas chrornatograph (injection,splitless/split 230 °C); column 30 m DB-5, fused silica, i.d.0.25 mm; thickness 0.32 µm; EC detector 280 °C; carriergas, N2, 1 mL/min; temperature program (column): 120 °C(0 min)-20 °C/min-200 °C (0 min)-5 °C/min-230 °C (1min)-1.5 °C/min-250 °C (15 min).

Isolation of Major Metabolites. The isolation of themajor metabolites formed from all six compounds wascarried out by liquid chromatography. For that purpose,all samples were combined, and the solvent was reducedto ca. 1 mL and afterwards applied to a silica gel column(column 100 × 1.2 cm, 50 g of silica gel 60, 70-230 mesh;mobile phase: petroleum ether, 45-65 °C; flow rate ca. 1.5mL; retention volume ca. 500 mL). Besides other metabo-lites, two hexachlorobornanes were isolated with a purityof more than 98%. During slow evaporation of the solvent,one of them crystallized as colorless needles.

Mass Spectrometry. The MS experiments were carriedout using a HP 5890/5988A GC/MS system (column: 25 mHP-5, i.d. 0.2 mm, film thickness 0.33 µm; carrier gas He,1 mL/min; temperature program: 140 °C (3 min) to 250 °C(20 min) with 4 °C/min, splitless (0.5 min)/split injection;injection block and transfer line 280 °C). The temperatureof the ion source was 100 °C for ECNI/MS, with CH4 as themoderating gas. The emission current was ca. 200 µA. EImeasurements were performed at 70 eV and 200 °C ionsource temperature (mass range: m/z 40-500).

FTIR Spectroscopy. An HP 5890/5965 GC/FTIR systemwas used to record the IR spectra (column: HP-5, i.d. 0.32mm, film thickness 0.52 µm; carrier gas: He, 1 mL/min);temperature program: 140 °C (3 min) to 250 °C (20 min)with 4 °C/min; transfer lines: 250 °C; light pipe: 280 °C).

1H-NMR Spectroscopy. Proton NMR spectra wererecorded with a Bruker AC 400 spectrometer (400.13 MHz)at 303 K in CDCl3 (δ ) 7.25 ppm) using a 5-mm broadbandinverse geometry probe (90°: 8.5 µs). DQF-COSY, NOEdifference spectra (mixing time: 1 s) and phase-sensitiveNOFSY spectra (mixing time: 450 ms) were performed usingBruker standard software, employing 90-deg pulses (8.5µs).

X-ray Analysis. The X-ray measurements were takenwith an Enraf-Nonius CAD4 V 5.0 four-circle diffractometerwith a MoKR radiation of λ ) 71.073 pm (graphitemonochromator). A total of 2639 reflections were collectedin the 2θ range of 3-25°.

Results and DiscussionFigure 1 presents the six toxaphene congeners investigatedin an anaerobic, loamy silt. All of them are rather labileunder these conditions. Preferentially, they were trans-formed by reductive dechlorination. No degradation ofany component occurred in autoclaved soil controls, whichindicates that degradation is mediated primarily by mi-croorganisms. This has also been found by other inves-tigators (13, 16, 20).

All compounds are sucessively dechlorinated by reduc-tive removal of one chlorine atom from each geminaldichloro group, beginning with that in the C-2 position,which is the most labile. The dechlorination rate dependson the chlorination stage (nonachlorobornanes > oc-tachlorobornanes > heptachlorobornanes). In most cases,the chlorine atome in the C-2endo position was removed,indicating stereoselective degradation. The two productsderived from Parlar 32, which are formed in a ratio of 1:2.8

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FIGURE 1. HRGC/ECD chromatogram of technical toxaphene. I-V are the investigated congeners; II includes two coeluting isomers (IIaand IIb).

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(endo/exo), are both lacking a further geminal dichloro groupand therefore stable enough not to be further degradedunder these experimental conditions. Contrary to this, allhigher chlorinated bornane derivatives with geminal dichlo-ro groups except the one at the six-membered ring arefurther dechlorinated so that no exact product ratio can be

determined for the first step. Nevertheless, the exo-productalso seems to be the preferred one here. That the first lossof chlorine really takes place in the C-2 position is shownby the fact that no Parlar 32 can be found as intermediateduring dechlorination of other components, which wouldinevitably be the case if dechlorination started at C-8, C-9,

FIGURE 2. ECNIMS spectra of 2-exo,5-endo,6-exo,8c,9b,10a- and 2-endo,5-endo,6-exo,8c,9b,10a-hexachlorobornane.

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or C-10. The successive loss of a chlorine atom fromgeminal dichloro groups in these positions by secondaryreactions could be seen from the signals of the CHCl2

fragments (m/z 83) in the EIMS spectra, which becamesignificantly smaller with decreasing chlorination grade.

The final degradation products of all six componentsare two hexachlorobornanes, one with the remainingchlorine atom in the C-2endo position and the other withthis atom in the C-2exo position; they are formed in varyingratios being 1:3 (endo/exo) in the case of Parlar 42, 1:4.8 inthe case of Parlar 49a, 1:95 in the case of Parlar 59, and 1:98in the case of Parlar 56. Obviously, the ratio depends onthe number of geminal dichloro groups in the parentmolecule; with increasing number an increasing preferenceof the exo-isomer can be seen. Both products seem to bedead-end-metabolites under these experimental conditions.A comparison of retention times and mass spectra provedthe concurrence of the final metabolites of all testedcongeners. Therefore, all samples could be combined toallow the isolation of both metabolites giving enoughmaterial for 1H-NMR and, in the case of the exo-isomer, forcrystallization and X-ray analysis.

Mass Spectrometric Investigation of Two Hexachlo-robornanes. ECNI and EI mass spectra of both metabolitescan be seen in Figures 2 and 3. The parent peak m/z 342in the ECNI spectra shows the presence of hexachlorobor-nane derivatives. The M- ion signal of the endo-isomer israther strong, while that of the exo-isomer is far less intense,which is not typical for hexachlorobornanes where, nor-mally, M- signals are favored (21) as compared to thestronger fragmentation of higher chlorinated bornanes.

With the exo-isomer, the loss of Cl- in the ECNI modus isincreased, so that here the base peak constitutes the [M-CI]-

ion with m/z 307. On the other hand, the spectrum of theendo-isomer shows an unusually strong HCI cleavage; theions M-, [M - CI]-, and [M - HCI]- appear in a ratio of1:1:1.

The EIMS spectra differ only slightly, being typical ofbornane derivatives without dichloromethyl groups. Thelack of this group can be deduced from the absence of thefragment m/z 83, which otherwise would be recorded withrather high intensity and, in the presence of two of thisgroup, would generally form the base peak (22, 24).Presumably, the CHCl2 groups are split off as positive ions,and the remaining neutral skeleton as well as furtherfragmentation products cannot be detected. In both cases,the base peak corresponds to the very stable, monochloro-substituted tropylium cation (m/z 125), which is generallystrong in all spectra of bornane derivatives. However, theEIMS spectrum of the endo-isomer shows an intense signalat m/z 244, which is very small in that of the exo-isomer.This ion cluster originates from Retro-Diels-Alder frag-mentation (RDA) following the elimination of HCl, whoseappearance could be expected already from the strong HClelimination under ECNI modus. Judging from the fragmentC2H3Cl (m/z 62) obtained by the RDA reaction, theelimination of HCl must have taken place between C-5 andC-6. In accordance to this, the neutral fragment shouldcontain C-2 and C-3. This result confirms the rule that HClelimination will occur preferentially between those vicinalring carbon atoms that are substituted with the highestnumber of chloro atoms.

FIGURE 3. EIMS spectra of 2-exo,5-endo,6-exo,8c,9b,10a- and 2-endo,5-endo,6-exo,8c,9b,10a-hexachlorobornane.

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1H-NMR Spectroscopic Investigations. Figure 4 showsthe 1H-NMR spectra of the two metabolites. In each case,12 protons are registered revealing an empirical formula ofC10H12Cl6, which is in accordance with the MS data. Whilethe signals are distinctly separated in the case of the endo-isomer, six protons overlap between 4.15 and 4.45 ppm inthe case of the exo-isomer. Therefore, an definite spectralassignment required two dimensional NMR experiments.COSY spectra established, like NOESY spectra, geminal

proton pairs and furthermore hydrogen connectivitieswithin the six-membered ring (H-2,3,4,5,6) while NOESYspectra revealed interactions between spatially close exoprotons and the protons of the CH2Cl substituents at C-7.

The presence of three CH2Cl groups in each metaboliteis confirmed by appearance of the respective six chloro-methyl protons with the typical geminal coupling constantsof ca. 12 Hz. Two of them are spatially close, and long-range couplings of 2.2 Hz correlating protons at 3.71 and4.43 ppm in the endo-isomer and of 1.2 Hz correlating

FIGURE 4. 1H-NMR spectra of 2-exo,5-endo,6-exo,8c,9b,10a- and 2-endo,5-endo,6-exo,8c,9b,10a-hexachlorobornane.

FIGURE 5. Molecular structure of (1S,2R,4R,5R,6R)-2-exo,5-endo,6-exo,8c,9b,10a-hexachlorobornane.

TABLE 11H-NMR Data of 2-exo,5-endo,6-exo,8c,9b,10a-and 2-endo,5-endo,6-exo,8c,9b,10a-Hexachloro-bornane

chemical shifts (ppm), coupling constants (Hz) in parentheses

protons 2-endo 2-exo

H-2endo 4.28 dd (9.0; 4.7)H-2exo 4.97 dd (10.7; 4.7)H-3endo 2.44 dd (14.9; 4.7) 3.0 dd (15.5; 9.0)H-3exo 2.54 dddd (14.9; 10.7;

4.5; 2.0)2.19 dddd (15.5; 4.7;

4.6; 2.1)H-4 2.60 dd (4.5; 4.5) 2.68 dd (4.6; 4.6)H-5exo 4.58 ddd (4.5; 4.5; 2.0) 4.57 ddd (4.6; 4.3; 2.1)H-6endo 4.85 d (4.5) 3.99 d (4.3)H-8a 3.71 dd (12.2; 2.2) 4.27 dd (12.1; 1.2)H-8b 4.43 d (12.2) 4.18 d (12.1)H-9a 4.43 dd (12.1; 2.2) 4.33 dd (12.1; 1.2)H-9c 4.13 d (12.1) 4.23 d (12.1)H-10b 3.60 d (12.4) 3.94 d (11.9)H-10c 4.34 d (12.4) 4.18 d (11.9)

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protons at 4.27 and 4.33 ppm in the exo-isomer indicate asubstitution of a single carbon atom with two CH2Cl groupseach. The remaining CH2Cl group displays geminalcouplings of 11.9 Hz (exo-isomer: 3.94 and 4.18 ppm) and12.5 Hz (endo-isomer: 3.60 and 4.34 ppm), respectively. Asno other coupling of these protons are observed, the CH2Clgroups must be isolated, indicating a location of two CH2Clsubstituents in C-7 and another at a bridgehead position.

Of ring protons, six signals each are present (Table 1).As all parent compounds lack chlorine only in the C-3position, the rather large coupling constants of 14.9 and15.5 Hz (endo- and exo- isomer), which are characteristicof geminal ring-protons, can belong only to the protons inthe C-3 position. Generally, ring protons of bornanes inexo-orientation are shifted to lower δ-values by about 0.4ppm as compared to those in endo-orientation (18).

FIGURE 6. HRGC/ECD chromatograms of technical toxaphene before (above) and after degradation in soil under anaerobic conditions(below).

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Besides, according to Karplus, the coupling constants ofvicinal protons are small for a dihedral angle of Φ ≈ 90°and large for Φ ) 0° or 180° and, in the last case, larger for180° than for 0°. H-2endo (4.28 ppm) interacts with H-3endo

with a vicinal cis-coupling constant of 9.0 Hz and with H-3exo

with a vicinal trans-coupling of 4.7 Hz, whereas theconstants are 4.7 Hz for the H-2exo (4.97 ppm) interactionwith H-3endo and 10.7 Hz for that with H-3endo. Similarrelations have been found with other bornane derivatives(22, 23). As for the protons H-4 and H-5exo, the δ-values arealmost the same for both isomers, while there is a significantdifference between the δ-values of H-6endo.

X-ray Analysis. The structure of the exo-isomer couldbe confirmed by X-ray analysis too. Figure 5 shows themolecular structure (1S,2R,4R,5R,6R)-2-exo,5-endo,6-exo,8c,9b,10a-hexachlorobornane. The crystallographic dataare summarized as follows: C10H12Cl6, formula wt ) 444.90,monoclinic space group Cc, a ) 823.5(5) pm, b ) 1277.1(8)pm, c ) 1276.7(7) pm, R ) 90°, â ) 93.22(5)°, γ ) 90°, z )4, density (calculated) 1.69 g cm-3.

One important result of the X-ray analysis was that thestructure originated from only one enantiomer of the chiralhexachlorobornane. The absolute structure of this enan-tiomer could be settled. Unfortunately, the isolated amountwas too small for chiroptic investigations, and GC separationwith chiral columns is still going on. Therefore, whetherenantioselective degradation has taken place in additionto the stereoselective one cannot be decided at present.Enantioselective degradation has been demonstrated forseveral chiral organochloro compounds (25-27), whereasthe loss of one enantiomer by total degradation seems ratherimprobable; until now, only one case has been reported(28). Nevertheless, it may be that a separation occurredduring crystallization as has been observed in rare cases(29). Palmer et al. (30) also reported separation of chiral2,2,5-endo,6-exo,8,9,10-heptachlorobornane (Tox B) intoits antipodes during crystallization. Perhaps this unusualprocess is more frequent with chiral chlorobornanes. Thiscan be settled only by additional X-ray investigations.

All these results show the geminal dichloro group in theC-2 position of the six-membered ring of chlorobornanesto be the most labile under anaerobic conditions. There-fore, all toxaphene components possessing this groupshould be rapidly transformed in anaerobic soils. The sameseems to be true for other experimental conditions, as hasbeen found with Parlar 32 (12). During photodegradation,too, chlorine loss takes place exactly from the geminaldichloro group in C-2 position (31, 32). As toxaphene issynthesized by photoinduced chlorination of camphene,preferentially under the formation of a geminal dichlorogroup in the 2-position as the primary step, a highpercentage of components containing this group shouldbe produced. This could explain the low stability of higherchlorinated toxaphene congeners, which can be derivedfrom the shift of the GC peak pattern to shorter retentiontimes after anaerobic degradation, as has been observedby several investigators. Geminal dichloro groups in otherpositions, being labile also, obviously contribute to thiseffect.

The common dead-end-metabolite of all pure parentcongeners (2-exo,5-endo,6-exo,8c,9b,10a-hexachlorobor-nane) was formed also after 6 months of degradation oftechnical toxaphene. The partial degradation of thetechnical mixture under anaerobic conditions results in acharacteristic shift of the GC peak pattern to shorter

retention times. During the first 2 months, no significantreduction in peak number could be observed, only after ca.4 months the peak pattern gradually became more simpletogether with an accumulation of certain degradationproducts. After 6 months, finally, only few products couldbe detected (Figure 6), with 2-exo,5-endo,6-exo,8c,9b,10a-hexachlorobornane as the major one, whereas the portionof 2-endo,5 endo,6-exo,8c,9b,10a-hexachlorobornane wasvery small and could be identified only by comparison ofGC/ECD retention times. Analogous to the single conge-ners, degradation of the higher chlorinated componentspreferentially leads to the exo-isomer. As in technicaltoxaphene, octa- and nonachlorobornanes dominate; thisdegradation path prevails here as well.

In sediments from toxaphene-treated lakes, hexachlo-robornanes and heptachloro compounds were also foundto be the dominant transformation products (33), althoughnone of the metabolites could be isolated and have itsstructure determined. The situation differed in marinemammals where mainly an octa- and a nonachlorobornanederivative have been found (34, 35). Here, the majority ofcomponents must have been either totally degraded oreliminated, while only these highly chlorinated, persistentcompounds could accumulate (36). Contrary to this, liveroil samples contained small amounts of the same hexachlo-robornanes formed by successive dechlorination (37),indicating the occurrence of reductive dechlorination inmammals also.

As has been shown, polychlorinated bornane derivatives,which amount to 75% of technical toxaphene, are partiallydechlorinated under anaerobic conditions, mainly byreductive dechlorination. Where the loss of chlorine takesplace depends on the individual substitution of thecongener. Generally, all geminal dichloro groups are labile,but most of all those at the C-2 atom, as the first reactionstep involves the elimination of chlorine exactly in thisposition. The higher the total number of chlorine, thehigher is the degradation rate. The same mechanismprobably applies to technical toxaphene. Here also chlorinefrom geminal ring dichloro groups is preferentially elimi-nated, followed by reductive dechlorination of otherdichloro groups. The continuous decrease in chlorinecontent can be seen in the GC peak pattern, whereas thechange in intensity of the CHCI2

+ ion peak (m/z 83) in theEIMS spectra shows the loss of one chlorine atom eachwith successive reduction of the dichloro groups. Thefavored formation of 2-exo,5-endo,6-exo,8c,9b,10a-hexachlo-robornane from technical toxaphene suggests that most ofthe bornane derivatives in technical toxaphene possess thesame chloro substitution at the ring, thus being precursorsfor this final metabolite.

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Received for review December 29, 1995. Accepted May 28,1996.X

ES950957F

X Abstract published in Advance ACS Abstracts, August 1, 1996.

2992 9 ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 30, NO. 10, 1996

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