Toxic effects of pollutants on methane production in sediments of the River Rhine.

Abstract

High numbers of bacteria are found in Dutch river sediments, which have a large capacity for the biodegradation of organic compounds and play an important role in the cycling of nutrients and elements. The bacteria are of vital importance in the functioning of river ecosystems. The methanogenic bacteria are responsible for the production of methane. Methanogenesis is the last stage of the anaerobic decomposition of organic matter. Without methanogen activity the degradation of organic matter cannot be carried out completely and acetic acid (and other organic acids) would accumulate. In anaerobic freshwater sediments acetate is the substrate used in about 70% of the methane production. An inhibitory effect on any of the processes carried out by the microbial consortium degrading organic matter, can lead to a decrease of methane production. The 5 toxicants used in this study are priority pollutants in the Rhine Action Programme, which are produced in high quantities and are relatively toxic and persistent. Benzene is an organic toxicant without a specific mode of action and thus exhibiting minimum toxicity. Chloroform is not very toxic under aerobic conditions. Van der Heijden quotes a value for initial reduction of cell multiplication of a Pseudomonas putida strain under aerobicmore » aqueous conditions at 125 mg/L chloroform. Under anaerobic conditions however, toxic free radicals can be formed during the reductive dechlorination of chloroform. Therefore anaerobic bacteria might be more sensitive to chloroform. The mode of action of 1,2-dichloroethane might be similar to chloroform. Pentachlorophenol is an uncoupler of the proton motive force. Zinc is known to be relatively toxic to microbial processes. Monitoring the effect of these very different pollutants on the methane production give information about the effect of these compounds on the microflora decomposing organic matter in a particular methanogenic ecosystem. 17 refs., 1 fig., 1 tab.« less