Document 5DgQOg5e7q4XdDpQ9m9KQyoXR

Science t August 1986 Volume 233 Number 4763 American iiaaatlailoHIcettoAferaiwmertrtSNanae SawMtmi iiriMnMilmnivMeMMnm tnd ducuiMA (t important Inum rMtitd to th* KMne4 ir+nt qI acianoa. including fee praaanlaCon cf fftfnerty O eenHieing Dona M view, ratter man by puOilantog only matW on union a eonaansua nn been reached. AettMdngty, si v* tttai eublbnM n Science memamg MHarlasa. nawa and cetwtnart. and book reviews--ara signed and railacl fen indi vidual view* or fea aufeora ana noi oflasi points e view adopted By fea AAAS or fea inatHutiona wm vdteri fea aufewa ara atKaiad. BuMahan Wilem 0. Caray t&W. OanM E- KoaMwd, Jr. (taputy Utter*: Phip h. AMson (gnflheerttg indAppSod Sadness); Jotm t. Brauman (PTryactlSeitncmt. Gardner Undiay (Social Sdarwaa) BXTOflUL STAFF Minajlna Edfter. Patricia A Morgan AaalafW Managing MRere: Nancy J. Harfeagal, Jew 6 Rtogia tartar Miaia; Saanena Bult Lawrence I. Qreetman. RuOi KidaiBd Aaaaairta BdNors; Marfea Canto*, Banwa Jaany. Katrtot U Keinar. Sdlirt Mayan UNart SdNan Chriattoe Gifeart Soat Review*: Kafearina Uvfegaton. aOter TMt Waah to Mmmi Run levy Guyar CUM Prcdutflaw EriMar: Ban E. Murpny IdMnp Sepefteenb Lola SchmM, Head: CaiBin Gordon. Mary McOaniaf. Barbara E Rattaracn Copy DaaS: laaballa BcukJto, chW; Lyt* L Own. Sharon Ryan. Bawarty Shield*. Uvi Vlctoteen Rrodualan Manager; Karan School* Qwprtat at Produaborc jqnn Borer, acetmrx manager; Holly ewp. Kafeiaan Coalmano. Baanor Warner Cevera Milan Qrayon Ftoger Mmaortpt fyrtnm Anrtyrt: WMlam Cartar HEWS STAFF Nawa IdHot. Barbara J. CullHon Nawa and Cammerti Coin Norman, deputy ad'ror: Mark K Crawford. Constance Hedan, ESot ManhalL R, Jeffrey Srrain. Mirjoria Sun. John Reaeveh Naaras Rogar Lewto. deputy edffor Oaborah U. Bam**. Richard A Kan. Gina Koiaia. Joan L. Man. Artur L Robfeocn. m Mkcnon Waldrop European Cowtapondarts David Bckaon BUSHESS STAFF UiBCiwa Pubuanarr waatn M, MBar. IJ Bualnaaa BlaP tupanHun Oaboran fkvora Wlanhcld AaoaPoOa suehteae Suparriean Lao Lawia Wiibarahtp Wawidunau: Qwendolyn Huddla Maiabar and tubaartpMn Rnardi: Am Ragland Qaida la PldMUinalapy Prodocrt and meSumerts SdMsrt Richard Q. Sonvnar IBVHTMM REFHE1HTAHVES Dfceetor Earl J. Seharaoo Piadwoban Uaaapon Oonnoflhara Advetdtlnp Brtaa M--aw Rfchatd L CMrtae Marta(ln|ilnaBiPHarbaHL.akiune Waa: Naw York. NV lOOpfe J. Kwrfn Harwfeiy. 181H Broadmy (212-730-1050); SeecnPMint. NJ 07]QS C. Rfcfeard CaMa, 12 Umrrl iWaaTaw *573): Chicago, AIIOB11: JKk Ryan. Room 2107. #11N. Mkdkgan Am. (312-3374P7h San Joan. CA #$112: Bob BiMlay. 310 S. It St we 1680); Donat VT 06281: Frad W. DManbacb. Kant Hfl Rd. (802-407-SStl). Inattueiona Par confebulora appaan on paga d d fea 27 Juna 1964 Mu#. Editortar oorraapondanca, inducing rouaoti tor parmiatidi to raprint and raprint ordart. Would ba wt to 1333 h smat wr. wawington. OC 20008. Tatapnena: 2oe424660a Aferadiing corrtapondanca Would ba tad to Tanfe Floor. ISIS Broadway, NY 10034. Talaohona 212-730-1060. Treatment of Hazardous Wastes ost observers agree chat the past performance of the Environmental Protection MAgency in cleaning up Superfund sires has been uninspired In whar Has called a "shell game," die net result has largely been to move hazardous waste from one spot to another or to cover the waste with a day blanket There has been little net destruction ofthe waste and hence little in the way ofpermanent solutions to a set ofnaity problems. Every waste dump is different in geometry, geology, and content of organic and inorganic chemicals. Organic chemicals are die most feared, most complex substances present. Technology exists so deal with part of the organic wastes (incineration), and research results are pointing die way coward dealing with much of die remainder (biodegradation). Where applicable--for example, wanes in drums--incineration can achieve essentially complete destruction. Even the most stable halogen-containing aromatic chemicals are destroyed at 1260C Major chemical companies have been using this procedure successfully, achieving as much as 99.9999+ percent destruction. Currently, for lack of incinerator capacity, choe is a 2-year backlog of wastes to be burned. To avoid possible problems during transport to incinerators and to increase capacity, EPA should devote some of its funds to the construction ofmobile incinerators to be used at Superfond sites. Much of the organic chemical wastes have been damped into landfill*. Dilution with dirt is such that incineration is often not practical. Field experience and research indicate that biodegradation could come to have an important role. For example, benzene, toluene, xylenes, and other hazardous aromatic chemicals are found in many waste dumps and also in leakage firm gaanline tanks. Thgae ehamlgate and many nltier hydmpwrf**i h# in situ to CO2 and HjO by microorganisms provided that they are furnished with such inorganic nutrients as phosphate and ammonium nitrogen, plus oxygen. Ac the site of a large gasoline spill, accompanying extraction and injection ofwater, nutrients were added and oxygen was provided in the form ofdilute H*Oj. A population oforganisms (2 x 102 per gram ofsoil) capable ofusing gasoline as a caibon ami energy source increased to more than 1G6 per gram ofsoil, and 65 percent of the hydrocarbons disappeared after 164 days. Among the individual organic chemicals most prevalent at Superfimd dumps are trichloroethylene, chloroform, tetrachlorocthylene, and 1,1,1-fxichloroechanc. No orga nisms have been found that can grow using these substances as sole energy and carbon sources. However, the compounds can be degraded by bacteria whose growth is supported by another metabolite. As one example, methanogenic organisms (anaerobes), when supplied acetate, slowly degraded tetrachlorocthylene and 1,1,1-trkhloroethane, as well as chloroform and carbon tetrachloride.* A different set oforganisms has destroyed halogenated hydrocarbons under aerobic condition!. This time, the energy and carbon source was methane, and 12 halogenated aliphatic hydrocarbons were degraded to some extent.t Similar treatment of '^-labeled trichloroethylene showed fairly rapid total destruction. Products included COa and biomass; no halogenated organic compound remainedt In terms ofpractical applications, there is a long history ofuse ofaerobes in oxidizing many hydrocarbons such as those in oil or gasoline. However, the most troublesome components of Superfund dumps are the small halogenated hydrocarbons. Priority should be accorded to expanding laboratory investigations dealing with these substances. In addition, field experiments should be conducted using injection coupled with withdrawal of nutrient streams under both anaerobic and aerobic conditions. The public does not welcome die establishment of waste dumps for toxic chemicals removed from somewhere else. As currently authorized sices are filled, EPA will find that it has no real alternative but to deal with the contents ofmost sices in situ. Prospects are good that multidisciplinary applications ofscience and engineering can be effective. --Philip H. Abelson E. J. Bower and P. L MeCinr, Bittwdmal. Bmtw. 27, 1564 (1985). If. M. Hemon, J. W. Cochran, f. T. WUkxi, R. & Kerr, in pteparsdoe. tM. M. Fogd, A. H Taddeo,}. Fagri, A/fL Carima. MmvHtL 51, 720 I AUGUST 1986 EDITORIAL JO0 AP00009917 Environ. SU ToetooL 1988, 20, 96-99 Sequential Dehalogenation of Chlorinated Ethenes Qladye Barrio-Lege,* Prance* Z. Persona, Raja S. Nasser, and Pedro A. Lerenco Orlnking Water Research Center, Rohde International University, Miami, Florida 33199 4. re* 3/fJ <=- e Reductive dehalogenation of tetra- and trichloroethene to cis- and front-I;2-dicbloroethene in microcosms simu lating; groundwater environment has previously been demonstrated. In this study, anoxic mkrocoems containing organic sediment and water were spiked to contain 5 mg/L of one of the following compounds: 1,1-dichloroethene (1,1-DCE), cis-l,2-dichloroethsne (CIS), or trans-l,2-dichloroethane (TRANS). After incubation in the dark at 25 C for up to 6 months, contents were analyzed by gas chromatography and verified by gaa chromatography/mass spectrometry in an attempt to identify sequential steps in the transformation process. Vinyl chloride (VC) was produced after 1-2 weeks of incubation in all striked mi crocosms, but none was observed in sterile and unspiked controls. Chloroethane (CE) was produced only in mi crocosms spiked with CIS, indicating isomer specificity and the occurrence of mechanisms other than reductive de chlorination. Kinetic parameter* associated with the microbistl dehalogenation of 1,1-DCE, CIS, and TRANS were calculated. Introduction Previous studies of transformations of chlorinated alkenes in microcosms simulating underground environ ments (1,2) indicated that tetrachloroethene (PCE) and trichloroethene (TCE) undergo reductive dehalogenatioa to form cis- and tran*-l,2-dichloroetheae (CIS and TRANS, respectively). This was recently verified with TCE isotopically labeled with one l3C atom (3). Further transformation to vinyl <*h1on*rf was indicated (4) but not proven. It was reported (2,4) that microcosms spiked to contain 6 mg/L of a chlorinated alkene produced com pounds with one leu chlorine than the parent aubetrate in quantities less than 10% of the original compound, in 8 weeks of incubation. This means that if cm- and tpons-1,2-dIchloroethene were transformed to vinyl chlo ride, the resulting concentration of vinyl chloride was too amail for detection by the methods used (1,4). Horowits et aL (5) and Suflita et aL (6) reported sw quential reductive dehalogenation of halogenated bea coatee with 100% of the dichiorinated benxoates trans formed to monochlorhaated bensoates in approximately 1 month. v Bouwar and McCarty (7,8) studied the biotransforma- tlon of several 1* and 2-carbon halogenated aliphatic compounds tinder methanogenlc and denitrification con ditions. They observedthat removal of chlorine by bio oxidation ox hydrolysis can occur simultaneously with reductive dehalogenation, thus causing a greater oonfusion in determining the mechanistic steps involved in the complete removal of halogenated compounds. Chlorinated ethenes transform very slowly, and appar ently with several simultaneous removal reactions. All of the intermediate products of biotransformation between PCE and vinyl chloride, including vinyl chloride itself; that were observed in laboratory studies have been found in groundwater. The processes involved and rates at which these changes occur are Important in assessing risk from use of affected waters. This study was made to further elucidate the behavior and fate of these toxic environ mental contaminants by each intermediate step of the transformation of PCE to VC. The specific objective of this research was to study the biotransfonnaiion of CIS, TRAMS, and 1,1-DCE to vinyl chloride and to measure the rate of depletion of these substrates in microcosms simulating groundwater envi ronments. Experimental Procedures Chemicals. 1,1-Dichloroethene (99%) (1,1-DCE), cts1,2-dichloroethene (97%) (CIS), and frans-l,2-dich]oroethene (98%) (TRANS) were purchased from Aldrich Chemical Co., Milwaukee, WL Vinyl chloride (0.2 mg/mL methanol) (VO was obtained from Supelco, Inc., Bellefonte, PA. Chloroethane (CE) was purchased from Eastman Chemical Co., Rochester, NY. Preparation of Microcosms. Natural organic sedi ment collected from the Everglades, s graminoid wetland that is the recharge basin for the Biscayne Aquifer in southern Florida, waa used to construct microcosms. Muck samplesfrom two sites in the same area were obtained: rite "A", which was the bottom ofa shallow canal, and rite "B', which was near the surface. Sites previously uncontaminated by chlorinated organic compounds were chosen for sediment sources to prevent selection of adapted mi croorganisms, which may yield different and variable re sults depending on quantity, nature, and age of contam inant Fjirh mdlmant sample wu thoroughly mixed and pewied through a 6.34-mm sieve and then weighed (wet) into 50mL septum bottles. Care was taken to prepare microcosms as uniformly as possible. The sediments were used in their natural state. Average dry weight was determined for purposes of comparison and to determine uniformity on a separate aet of aubeamplea and amounted to 4 g dry weight per 50-mL bottle. After addition of sediment, the bottles were completely filled with water taken from the sample site. The water wu purged with nitrogen prior to use to eliminate any highly volatile contaminants and to purge oxygen entrapped by sampling. Microcosms were prepared in sets that included the following controls: sterile, no-spike, and distilled water. Distilled water controltconieined the orgaafosediment, but nitrogen-purged distilled water wu substituted for rite water. Sterile controls were prepared by autoclaving the organic sedi ments and the site water for 20 min on two consecutive days. After the materials were cooled, microcosms were constructed under aseptic conditions and sealed with sterile Teflon-lined septa, preventing headspace formation. Spiking solutions were prepared in 50-mL serum bottles that- were autoclaved along with the distilled water, mag netic stirrers, pipets, and the microsyringe used to prepare solutions. Accurately measured amounts of the three compounds, CIS,TRANS, and 1,1-DCE, were injected into separate, sterile bottles containing 50 mL.of sterile, ni trogen-purged water and allowed to stir overnight. The final concentration of each compound in the spiking so lutions was 500 mg/L. Half milliliter of each solution was spiked into each 50-mL microcosm to yield a final con centration of 5 mg/L in the microcosms. The microcosms wars spiked 2 weeks after construction to allow equili bration and oxygen depletion to occur inside the test &mf control bottles and thus simulate the original conditions of the sample rite. All microcosms and controls were al- 99 Eiwkon. Sci. Teehnot. VoL 20. No. 1.1986 0013-939X/88/0920-0098S81.80/0 C 1988 American Cherried Society AP00009918 lowed to incubate in the dark at 25 C for measured time periods of up to 6 months. Repeated sampling of a single microcosm in preliminary studies caused contamination and a change in the volume of the contents and introduced a gas phase (headspace). For this reason, duplicate mi crocosms were constructed as described above, for each scheduled test period, so that each microcosm was used only once in an analysis. Replicate microcosms were provided for concurrently measuring pH and redox po tential (Eh). Although tha microcosms were prepared homogeneously, variability of activity was accounted for by calculating the mean of replicate runs. Sterility of sterile controls and spiking solutions was determined by streaking these materials on plates of RjA medium (2,9), incubating the plates, and observing them for growth. Instrumentation. A Tracor Model 222 gas chromato graph with a 244 cmXifi mm i.d. stainless-steel column, packed with 60/80 mesh Tenax GC, and a Hell electrolytic conductivity detector, Model 700, were employed for analysis. Nitrogen carrier gas at 40 xnL/min and hydrogen reaction gas at 50 mL/min were supplied. The column oven was programmed to hold isothermal for 6 min at 40 *C while 5 mL of microcosm contents or standards were purged with N2 directly on the head of the column (JO). The column temperature was then increased from 40 to 220 C at 8 6C/min. The temperature of the detector was kept at 650 de 20 C. Hu three isomers were successfully separated under the stated working conditions as follows: 1.1- DCE at 15.03 min of retention time and TRANS and CIS at 16.21 and 17.53 min, respectively. Gas chromatography/mass spectrometry (GC/MS) data were obtained on a Finnigan 4500 GC/MS system inter faced to a Tekman LSC-2 purge*end-trap system. The gas chromatographic column was a 6 ft X 2 mm i.d. 0.2% Carbowax 1500 on 80/100 Carbop&ck B. The data system was standardized for the dlcMaroethenes and the purgeahla gases (vinyl chloride, bromoethane, chloromethane, and chloroethane). Ac internal standard mix of fLuorobenzene and p-bramofluorobanzene at the 25 pg/L level was added to each sample on die basis of volume of extractant water available. Redox potentials (Eh) and pH were measured with a Censing Model 7 meter by using a Coming glass electrode for pH measurement* and a Fisher platinum combination electrode for redox measurements. For pH measurements the Instrument was calibrated at pH 4 and 7 with Scientific Product! reference buffer solutions. For Eh measurements the instrument was calibrated at 180 and 0X3 mV by using pH 4 and 7 buffer solutions supersaturated with hydro* quinone crystals-..'' ` Standard Solutions- Stock aqueous solutions of 1,1- DCE, CIS, andTRANS waitprepared at 500 mg/L (ppm), by volumetric dilution, similar to the spiking solutions. Working standard of the five chlorinated compounds, 1.1- DCE, CIS, TRANS, VC, and CB were prepared by diluting aliquots of the stock solutions with water and stirring overnight to achieve solutions of the desired con centrations. All bottles were wrapped in aluminum foil frt ftwirt phpfeyWrmprtMtinw and fewpfcat X C_ Thesystem was checked daily against standard solutions and was re calibrated when the deviation was greater than 3%. Result* and Di$cturion Evidence for Dehalogenatlon. The organic com pounds produced when 1,1-DCE, CIS, and TRANS were incubated with oxygen-depleted sediment were identified by gas chromatography/mass spectrometry. Vinyl chloride - was detected in all microcosms (Figures 1-3). VC was not Figure 1. Pattern of anaerofcfe depaCaSon et t,t-OCE by eeefcnent and water microcosm*. (A) Depletion of t.i-OCE in tedmsnt end water from sK* B. (O) Oeplstlon of 1,1-OCE h asUfcitwS *M water from Me A. (O) Formation ef VC hi sedhwnt and water from site B. (O) Formation of VC in sedknsnt and watar from sK* A. Flgura 2. Pattern of anaerobic degradation of TRANS lrt secimsnt and water microcosms. Site A muck sample. (A) Depletion of TRANS. (O) Formation of VC. detected in the no-apike and sterile controls. A peak identified as chloroethane was observed to increase with Environ. Soi. TeehnoL. Vol. 20. No. 1.1960 S7 AP00009919 \ ,< v ri `i i i: A Flgwt *. Pattsm of anaarobta dayadstton of CIS in sethiiwit and water microcosm*. Site A mucJc sampta (A) Doptotion of CIS. (O) Fo matter of CE. (O) Formation of VC. Figures. MIchsoH Menten ftt of the data (eg 1) from the depUttcn of TRANS in aeflmant and water from site B. time in all microcosms spiked with CIS (Figure 3). Sam ple! spiked with 1,1-DCE and TRANS did not produce CE, nor did the sterile microcosms spiked with CIS. Analyses were made only for the intermediate compounds VC and CE and not for the complete mineralization of the spike. Only the intermediate steps were sought to dem onstrate the stepwise nature ofthe transformation process. Dechlorination of the three compounds under study did not occur in sterilized microcosms. In microcosms spiked with 1,1-DCE and TRANS (Figures 1 and 2), only the formation of vinyl chloride was observed. When CIS was the parent substrate (Figure 3), however, CE also was produced. In microcosms spiked with CIS (Figure 3), the concentration of VC remained low end nearly constant after 2 weeks of Incubation, white chloroethane increased slowly. Microcosms spiked with TRANS (Figure 2) showed production ofVC similarto the transformation of CIS; i.e., low mid nearly Constant concentration after 2 weeks, butCEwsinot produced in this ease. Figures 1 igacQfilhow that the depletion of the parent substrate was frequently preceded by an apparent Initial increase In concentration. This was caused by an initial physical equilibration time and adaptation of the microbiota to the microcoem end assimilation ofthe introduced substrate. The microcosms were shaken vigorously upon spiking to distribute the chlorinated substrate. 'As the microcosm contents were allowed to settle in the dark at room temperature, most of the added organic compound was trapped, and some was adsorbed in the interstices of the solid phase, Le., muck. Equilibrium between solid and liquid phases was established in about 2-weeks incubation time. Other authors have reported lag periods of up to 6 months (ff), caused by the adaptation of die mlooblota to utilize one specific substrate. The Inconsistency ofthis initial equilibration time made it impossible to measure the initial velocities that are valuable in calculating the true order of reactions. Figure 3 is a typical plot of a consecutive reaction where the concentration of the intermediate (VC) rose to a maximum and then decreased or stayed constant, and the concentration of the iast product (CE) rose to a maximum. However, VC ia not believed to be an intermediate species between CIS and CE because chloroethane was not ob served in samples spiked with 1,1-DCE end TUANS where VC was detected First-order kinetic models were attempted to depict the decay of 1,1-DCE, CIS, and TRANS. In every case, how ever, we found that semilogarithmic plot# of the data de viated from linearity usually after 3-4 months of incuba tion. Horowitz et aL (4) observed that when S-chlorobenzoate wea tile initial substrate, the data followed first-order deplstioirkinetics. If the parent substrate was 3,5-di- chlorobenzoata (6), the dichlorinaied substrate competi tively inhibited of substrate, causing a deviation from first-order kinetics. These authors (6) found that debalcgenation ofmono- and dichlorinated benzoates exhibited Michaelis-Menten ki netics. Good linearity was obtained when our data was fitted to the linearized form of the Michaelie-Menten equation which was also used by Suflita et al. (6) t/[ln (S0/5)l - (1/V)[(50 - S)/In (50/S)]+ Km/V (1) where t is time, S9 ia the initial substrate concentration, S is the substrate concentration at time t, V is the max imum rate of substrate depletion, and Km is the half-sat uration constant. Michael!s-Menten kinetics only de scribes bacterial substrate when this process is unlinked to growth of microbial, biomasa figure 4 shows the Michaelie-Menten lit of the data for the depletion of TRANS in microcosms with sediment M rtm ra irg r Enwon. Set Technoi, VoJ. 20, No. 1, 1986 j AP00009920 f \ Tibi* I. Kinetic Paranatart Describing the Dshalogsaatlon af the Isomers af Dichloroethen# by Anoxic Sediment dehalofsastum VL. mol lubstrate nude am 1?h* *t, h-`* 1,1-DCE its B 43.4 0.0155 3.57 X 10* . { ' site A 36.7 0.0061 1.67 X 10* CIS tits B 66.3 Q.0214 8.28 X 10* sits A 41.8 0.0096 0.869 x 10* TRANS site B 35.8 0.0076 2.19 X 10* its A 29.6 0.0068 1.97 x 10* * First-order rata constant obtained by V__/AL Fleur# 8. Summary pathway* for dechlorination of tetra- and H- from ait# B. 1,1-DCE ghowsd tha largest deviation from ehtaroethena h anorobtc emtonrnenta. Step* a-c from Parsons and Lag# (9). the Michaelii-Menten model with correlation coefficients between 0.75 to 0.91. This may be due to 1,1-DCE pro environmental organic sediments, under anoxic conditions, ducing the largest amounts of VC, and an inhibition factor undergo reductive dechlorination leading to the formation from the consecutive depletion of VC may be important of vinyl chloride. Mechanisms of transformation other in this case. than reductive dechksinatkm also occur because the sum I Table I summarizes the kinetic parameters associated with dehalogenation ty tto sediment microflora. Km and of the products observed doee not account for alt of the substrate that is removed. Isomers undergo different V^.. values reported in Table I were attained from a linear tranformations; CIS led to the formation of CE and only regression analysis of the MichaeHs-Menten fit of the data trace* of VC; 1,1-DCE yielded greater concentrations of and subsequently divided by the microcosm volume to VC and no CE; TRANS produced VC only. obtain the reported values. As it can be seen, the Ka Kinetic parameters associated with the microbial de values for the dehalogenation of the three isomers in the halogenation of 1,1-DCE, CIS, and TRANS were calcu tested environment varied by a factor of about 2 (3CHJ5 lated. The first-order rate constant ku for the depletion nM), whereas the V-r values varied by a factor of 8 of the parent substrate ranged from 0.853 x 10* to 3.67 I (0.0036-0.0214 /umoi IrUr1). The first-order rate constant x 10* h*. of dehalogenation ranged from 0,853 x 1CT4 h~l for CIS In sediment to 3.57 X 10* h-1 for 1,1-DCE in site *B* sedi Acknowledgments ment, indicating a very slow rate of dehalogenation. The mast spectrometry analysis of Garmon B. Smith, pH ofail microcosms was measured and found to remain Jr., and the help of John Wilson, both of the U.S. EPA, constant at 7.0 0.6. Redox potential data (Eh) changed Ada, OK, are gratefully acknowledged. drastically in the first 2 week* of incubation while equi librium was attained, after which time it remained almost Registry No. 1,1-DCE, 78-35-4; CIS, 156-59-2; TRANS, 156-60-5; VC, 75-01-4; CE, 7540-3; PCS, 127-104;TCE, 79-01-6. constant between -20 and -130 mV. Not all the substrate that was depleted was transformed Literature Cited I to VC (Figures 1-3), indicating that mechanisms of (1) Parsons, P. Z4 Wood, P. ft; DeMarco, J. J.--Am. Water transformation other than reductive dechlorination were Work* iUm. 1964,76,66-S& taking place. Transformation ofsubstrate by biooxidation (2) Panona, F. Z4 Lags, G. B. J.--Am. Water Workt Assoc. (7) or hydrolysis (8) are possible removal mechanisms. The appearance of CE (Figure 3) in microcosms spiked with CIS indicates isomer specificity and a different pathway 1945, 77, 52-59. (3) Klaopfer, R. D4 Eaalay, D. M4 Haas, B. B., Jr.; Doth], T. G.; Jackson, D. 84 Wurrey, C. J. Environ. SeL Teehnol. 1985,19, 277-260. of transformation in the sequential dechlorination. (4) PazKXts.F. Z4Lege, G.B4Rice, R.rwraii. 7bxieol.C/tem^ Figure 6 shows a summary oftransformations that may m prase. ' occur to tetra- and trichloroethene in oxygen-depleted (5) Horowitz, A.; Suflita, J, M4 Tisdje, J. M. AppL Environ. sediment. Steps a-c were reported previously (2). Step d was suspected to occur but never reported because of possible interference from contaminants (2).. Recently ft was repotted (SfthAtthia isomer did not result from the biotransfoRnatibn of isotopfoalbrlabeled trichloroethene. Steps e-h are reported inIbis paper. It is not known whether step* and t occur Independently or are inter related. Microbiol. 1983,46,1459-1485. (6) Suflita. J. M4 Robinson, J. A4 Tisdje, J. M. AppL Environ. Microbiol. 1988, 46,1469-1473. (7) Bouwer,* B. J.; McCarty, P. L'Appt Environ. Microbiol. 1983, 45,1286-1294. .1 * (8) Bouwer, B. J.; McCarty, P. L. AppL Environ. Microbiol. 1983,45,1295-1299. (9) Rsaaonar, D. J4 Qddmteh, R. R. AppL Environ. Microbiol. 1985, 49,1-7.. Depletion of these substrates, similar to that reported (10) Mehran, ^"Abstract* ofPapon", 189th National Meeting for trichloroethylene (9), required longer periods of time than other chlorinated slVnnts reported by different au of the American Chemical Society, Miami, FL, 1965; Amarican Chemical Sodit^ Washington, DC, 1985; ENVR thors (5-8). Most probably the slow biotransformation of such compounds caused Bouwer et aL (If) to report ob serving no appreciable anaerobic degradation of tetra- and 21 111) Bouwer, E,J.;Rittauui,B.B4 McCarty, P.K Environ. Sci. TechnoL 1981,16,696-599. trichloroethylene. Figures 1-3 show that only 50-80% of 1,1-DCE, CIS, and TRANS was depleted in 8 months of incubation. Received for review March 89,1986. Accepted August 6,1985. This work was supported by the U.S. Environmental Protection Agency, Ground Water Research Branch, under Contract . Conclusion* CR809994-02 40 Florida State University.and Subcontract 281908-600 tojlorida International University. Tha content* This study has shown that 1,1-DCE, CIS, and TRANS, do not nccestarify'refleet the views orpolicies ofthe Agency nor subjected to the indigenous microbiota at uncontaminated doee mention of trade names constitute endorsement. Envtoe. 3d. Teehnol., VoL 20, No. 1. 1966 99 AP0000992I