The effect of oxygen and storage conditions on the metabolic activities, measured by volatile fatty acid (VFA) degradation and methane production, and by the dechlorinating activity of methanogenic polychlorinated biphenyl (PCB) granules, were studied. Incubation of the granules in air for different periods did not result in significant inhibition in volatile fatty acid degradation and methane production activities. The inhibitory effect of oxygen increased with increased length of exposure. The overall methanogenic activities, however, recovered after a 10-day incubation period in the absence of oxygen. Oxygen exposure did not cause any significant effect on the dechlorinating activity of the granules tested with a PCB mixture, Aroclor 1254. In 6 months, approximately 80% [based on the concentration (mu M) of chlorine removed] of the Aroclor 1254 was dechlorinated even by granules exposed to oxygen for 168 h. Granules stored at room temperature (20 degrees C) appeared to be more active compared to the granules stored at 4 degrees C or -20 degrees C. Similarly, granules stored with a nutrient mixture, containing methanol, glucose and yeast extract showed higher metabolic activities. Our results demonstrate that the effect of oxy gen exposure was not significant and was reversible. PCB granules could be stored at room temperature with an auxiliary carbon source in the presence of PCB without significant loss of activity. These properties make methanogenic PCB granules suitable candidates for practical use in PCB dechlorination and biodetoxification.