Fries1 observed that, in spite of extensive investigation of the anaerobic degradation of DDT, little has been firmly established except that TDE is a major degradation product. In the present study, the identification of p,p'-DDCN, as an important nitrogen-containing environmental breakdown product of /?,/?'-DDT, was facilitated by the use of combined gas chromatography-mass spectrometry in conjunction with radio-chemical techniques. The incorporation of radiolabelled DDT made it possible to detect the diverse DDT-derived products formed in the complex sewage environment. Our results were obtained within the context of a wider investigation of the fate of DDT and other organochlorine pesticides in estuarine sediments and also in sewage sludge2'3 Hill and McCarthy4 have noted the very rapid transformation of DDT to TDE in anaerobic sewage sludge and Halvorson et aL5 have advocated the use of sewage bacteria to provide a rapid biodegradability criterion for insecticides. Anaerobic sewage sludge (400 ml., 5% w/w solids, pH 8.2) from the 35° C anaerobic digestor, Avonmouth Foul Water Treatment Works, Bristol, was incubated for 88 days at 37° C in a vessel fitted with a fermentation lock, during which a total of 7.45 mg 14C-p,p'-DDT (4.7 jiCi) and 20 g minced beef were added, the latter to enhance microbiological activity. 14C-p,/?'-DDT-(phenyl ring-14C(u), 67 uCi/mg) supplied by the Radio-chemical Centre, Amersham, Bucks, and unlabelled p,p'-DDT (99+ % pure, Aldrich Chemical Company) were used, purity being verified by gas liquid chromatography (GLC) and thin layer chromatography (TLC). Addition of p,p'-DDT in ethanol (200 ul. aliquots) was as follows: 2.82 mg (0 jiCi) on day 0; 0.03 mg (2.35 jnCi) on day 5; 4.60 mg (2.35 ^Ci) on day 42. Minced beef (20 g) was added on day 26. When the incubation terminated, the sludge was centrifuged and the aqueous layer filtered and counted. The filtrate contained 0.4 uCi. The solid residue was extracted rapidly three times in the cold with iso-propanol: heptane (4:1) using a modified procedure of Dole and Meinertz6 and a total of 1.5 uCi (32% total label) was recovered. The residual solid was counted (Nuclear Enterprises NE 221 gel scintillator) and was found to retain a further 1.5 uCi activity. The Dole-Meinertz extract was first examined by GLC ('Perkin-Elmer FIT gas chromatograph with 63Ni electron capture detector (ECD) using on-column injection and 6 foot x 0.25 inch silanized glass column of 1.5% OV-17, 1.95% QF-1 mixed phase on Diatoport S, 80-100 mesh; column temperature 200° C isothermal). Comparison with standards (Analabs, Inc.) revealed only trace quantities (amide-Hiitrile or more directly from p,p '-DDT. p^-DDCN may also be produced in other anaerobic environments possessing similar properties (certain estuarine sediments). Future survey work on pesticide residues in the environment should not ignore the contribution of the more polar degradation products. The importance of these compounds is liable to be underestimated in those cases, where, as with /?,/?x-DDCN, the ECD detector is relatively insensitive. Reactions revealed by such studies, for example the conversion of - CC13 to - CN, should be of general significance in pollution studies. We do not know of studies on the toxicological and related properties of ^,^r-DDCN in the environment. We thank Mr R. Deeney and Mr J. Hall of Avonmouth Foul Water Treatment Works for sample of sewage sludge, Mr R. Cleaver, Mr S. Reid and Mrs J. Hunter for assistance, and the Natural Environment Research Council for a research