Submitted to: Irrigation Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 7/17/2013
Publication Date: 8/5/2013
Citation: Kiefer, L., Shelton, D.R., Pachepsky, Y.A., Blaustein, R.A., Martinez, G. 2012. Coliform retention and release in biofilms formed on new and weathered irrigation pipes. Irrigation Science. 31(5):971-981. Interpretive Summary: Irrigation water is recognized as a probable source of pathogenic organisms that caused illness outbreaks. Biofilms in irrigation water delivery systems are suspected as microbial reservoirs. However, almost no research has been performed to evaluate the impact of biofilms in pipes or other parts of irrigation systems on the microbial quality of water going through the pipes. We performed experiments on a sprinkler irrigation system where water from a creek at the intake, water from the sprinklers, water left in pipes from the previous irrigation, and pipe biofilms were analyzed for concentrations of three types coliforms. The coliform concentration in irrigation water was altered because of the interaction with pipe biofilms. This was more pronounced in new pipes as compared with old pipes. This suggests that biofilms in irrigation pipelines may impact microbial quality of irrigation waters. This information is important for produce preharvest management in that it indicates the need to monitor quality of water coming from sprinklers in addition to the intake and to consider applying practices and technologies that will mitigate the possible pathogen accumulation in pipes and transmission of them to produce with irrigation water. This information should be useful to other scientists and to the produce industry.
Technical Abstract: Irrigation waters have come under increasing scrutiny as a source of pathogenic microorganisms contaminating fresh produce. It is generally assumed that the microbial concentrations entering and leaving irrigation pipe networks are identical. However, this may not be true if biofilms form on the inner surfaces of irrigation pipes. The retention and release of pathogens in biofims is well documented in drinking water distribution systems, but very little data is available for irrigation systems. We examined the attachment and/or incorporation of total coliform, fecal coliform, and Escherichia coli bacteria into biofilms in new and used aluminum irrigation pipe. Water from a local creek in Maryland was used to conduct weekly irrigation events. Prior to each event, removable sections of pipe (coupons) were scraped to determine the extent of bacterial attachment; in addition, bacterial concentrations in residual water were determined. Substantial populations of coliform bacteria were found at the pipe surfaces. Old pipes had fewer attached or biofilm incorporated coliforms, and lower coliform concentrations in the residual water. High probabilities were found for fecal average coliform and total coliform concentrations being different between creek water and sprinkler water. These results have implications for monitoring and control of microbial quality of irrigation waters.