Effect of carbonyl cyanide m-chlorophenylhydrazone (CCCP) on microbial activity and polycyclic aromatic hydrocarbons (PAH) degradation in contaminated river sediments

Abstract

Polycyclic aromatic hydrocarbons (PAHs) are of continued interest because of their carcinogenic nature and persistence in the environment. Among volatilization, sorption, and chemical oxidation, microbial degradation is the main path of PAHs disappearance. The majority of degradation studies have used pure cultures, were spiked with added PAHs, or have been performed using single pollutants. Because contaminated aquatic ecosystems retain mixtures of xenobiotics, experiments using environmental samples that incorporate the role of microbes provide more realistic conditions to study degradation. We tested the inhibitory effects of [carbonyl cyanide m-chlorophenylhydrazone (CCCP)] on microbial respiration, which in turn altered PAH degradation. In this study, 3.5 mM of CCCP (two orders of magnitude higher to what was needed to inhibit growth of E. coli in pure culture) was shown to inhibit respiration of indigenous microbes in complex sediment samples by 79 % at 25 °C and 64 % at 37 °C. After 15 days of incubation sediment slurries without CCCP showed higher PAH degradation rates (between 60 and 90 %) compared to sediment slurries with CCCP, which showed much lower degradation rates (<40 %). This study also reported the highest recorded rates of INT reduction (29 nkat/g) due to both short incubation times and the potential to stimulate high microbial activity in the sediments. These data indicated the effectiveness of CCCP as a microbial respiratory inhibitor in sediments, and that indigenous microbes in long-term PAH contaminated anaerobic sediments can be stimulated to degrade PAHs present in their environment.