Environ. Scl. Technol. 1982, 16, 130
CORRESPONDENCE Correspondence On: Anaerobic Degradation of Halogenated 1- and 2-Carbon Organic Compounds SIR: We are writing in regard to your article “Anaerobic Degradation of Halogenated 1- and 2-Carbon Organic Compounds” (ES&T 1981,15,596). The article stated that no aerobic conditions were found under which chloroform in the 10-100 pg/L range could be degraded after 25 weeks of incubation in the dark at 20 “C. For the study, a primary sewage bacterial inoculum in chloroform-mineral salts medium was used. In July 1980,a 20 OOO-gal chloroform spill occurred which contaminated both soil and groundwater. This spill created a unique situation with regard to the enrichment of chloroform degraders. Using a chloroform-contaminated soil inoculum collected in April 1981 from the spill site, our laboratory recently completed a 27-day study using an electrolytic respirometer which demonstrated chloroform reduction under aerobic conditions. The electrolytic respirometer is a closed system with oxygen generated within the system. For the study, duplicate l-L respirometer vessels containing chloroform-mineral salts medium were each inoculated with 50 g of chloroform-contaminated soil. In addition, one of the two vessels received a suspension of commercially available selected microbial strains. A third vessel was prepared which served as an uninoculated control. The soil contained a chloroform concentration of 490 mg/L and a microbial aerobic heterotroph population of lo6 colony-forming units/g. For the purpose of the study, the chloroform concentration in each of the respirometer vessels was adjusted to approximately 500 mg/L on day 3. The degradation rates were determined from day 9 to day 27. On day 9, chloroform concentrations in the vessels were 580 and 560 mg/L. On day 27, the chloroform concentrations were 190 and 180 mg/L, respectively, thus demonstrating 67 % and 68% chloroform reductions. The uninoculated control had an initial chloroform concentration of 530 mg/L as determined on day 9 and did not show a decrease throughout the study period. Other laboratories have also aerobically degraded chloroform at other concentration levels, We thought that this observation might be of interest to your readers.
SIR: A finding that chloroform is biodegraded under aerobic conditions is an important one that should be well documented and reported. As our article mentions, we were unable to find aerobic conditions under which chloroform could be biodegraded when present at sub-mg/L concentrations, and a survey of the literature revealed no evidence for aerobic biodegradation of chloroform. However, we think that better documentation of the experiments by Flathman and Dahlgran is needed before positive confirmation of aerobic biodegradation can be claimed. Listed below are four significant problems with the report of Flathman and Dahlgran. (1)The large amount of soil in the test apparatus (50 g/L) complicates interpretation because of possible sorptive or catalytic effects. Since the control apparently contained no soil, the results could have been related solely to the soil and not the bacteria. The problem is compounded because the report does not differentiate between dry and wet soil, between clayey and sandy soil, or between organic-rich and organic-poor soil. (2) The relationships among the 490 mg/L of chloroform in the soil, the theoretical 500 mg/L at the start of the test, and the 560-580 mg/L after nine days are unclear. (3) Despite being carried out in an aerobic respirometer, microanaerobic zones could have existed in the soil/water medium. This would have been especially likely if the soil had not been well mixed. (4)The amount of oxygen utilized was not reported. Biodegradation of about 380 mg/L of chloroform aerobically would result in a significant and predictable oxygen consumption. Was oxygen consumption observed or observable in the experiments? Also, was chloride released and measured to confirm degradation? Our reply does not imply that Flathman and Dahlgran’s claim is necessarily incorrect. Instead, we stress that confidence in such an important claim can only rest on data from well-controlled and fully documented research. We encourage Flathman and Dahlgran, or others, to submit such a report. Edward J. Bouwer, Bruce E. Rlttmann Perry L. McCarty Environmental Engineering and Science Department of Civil Engineering Stanford University Stanford, California 94305
Paul E. Flathman, James R. Dahlgran
Received September 8, 1981
0. H. Materials Company Findlay, Ohio 45840
Received June 16, 1981
130 Environ. Sci. Technol., Voi. 16, No. 2, 1982
0013-936X/82/0916-0130$01.25/0
0 1982 American Chemical Society
