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Asbestos cement(AC)pipes were commonly installed in the drinking water distribution systems from the mid 1920s to the late 1980s.In recent years,an increase in the number of water main breaks has occurred in the AC portions of some pipe networks,which can be partially attributed to the corrosion of the aged pipes.This study evaluated the potential role that microorganisms may have played in the degeneration and failure of AC pipes.In this study,a fresh AC pipe section was collected from the distribution network of the City of Regina,Canada and examined for microbiological activities and growth on inside surfaces of pipe sample.Black slime bacterial growths were found to be attached to inner pipe surfaces and a distinctively fibrous intal coating(patina)with iron oxides was formed over the time.The microbial populations inside the patina and the black slime were tested with BARTTM testers.Heterotrophic aerobic bacteria(HAB)and slime forming bacteria(SLYM)dominated in both the black growths and inside the patina.Iron related bacteria,denitrification bacteria and sulfate reducing bacteria were also commonly present.Microbial challenge assays were conducted by submerging the cut segments of the AC pipe into selected bacterial cultures for a period of 10 days under both aerobic and anaerobic environments.Weight changes were determined and the surface morphology was examined for each of the assayed pipe segments.Results indicated that acid producing bacteria,SLYM and HAB could facilitate the pipe weight loss under anaerobic environments.