Submitted to: Agricultural Water Management
Publication Type: Peer reviewed journal
Publication Acceptance Date: 7/25/2013
Publication Date: 9/1/2013
Publication URL: http://handle.nal.usda.gov/10113/59951
Citation: Shelton, D.R., Kiefer, L., Pachepsky, Y.A., Martinez, G., Mccarty, G.W., Dao, T.H. 2013. Comparison of microbial quality of irrigation water delivered in aluminum and PVC pipes. Agricultural Water Management. 129:145–151. Interpretive Summary: In the past few years, there has been an increase in the frequency of food-borne illnesses resulting from the consumption of fresh produce. A potential source of contamination is irrigation water, particularly if it comes from untreated surface waters. It is well established that biofilms can form on surfaces in the presence of stagnant water. Consequently, irrigation distribution systems may contribute to produce contamination if pathogens adhere to biofilms in irrigation systems, grow, and then are subsequently released during irrigation events. In previous work, we have documented the fact that biofilms do form in irrigation systems and pathogen surrogates (generic E. coli) can multiply in biofilms. In this paper, we compared aluminum irrigation pipes with plastic pipes with respect to biofilm formation. Biofilm formation was observed in both types of pipe; but there was a greater of amount of biofilm accumulation in aluminum vs. plastic pipes. These results suggest that aluminum pipes are more conducive to biofilm formation. However, it is also possible that biofilms more easily slough from plastic pipes. These results are of interest to other scientists, produce growers and food safety regulatory agencies.
Technical Abstract: Microbial quality of irrigation water attracts substantial attention due to the increased incidence of gastrointestinal illness caused by contaminated produce. Little is known about the changes in microbial quality of water during its delivery to crops. Studies were conducted to compare the biofilm formation and changes in microbial water quality in aluminum and PVC irrigation pipes. Irrigation events were conducted weekly and sections of irrigation pipe (coupons) analyzed for total protein, for total and fecal coliform bacteria, and for E. coli. Coliform and E. coli concentrations along with nitrate, orthophosphate, and total organic carbon were monitored in the intake surface water, output irrigation water, and measured in residual standing water in pipes just prior to each irrigation event. Proteins accumulated to a greater extent in aluminum-associated biofilms than in plastic-associated biofilms. Numbers of total coliforms associated with aluminum coupons increased with time while numbers of total coliforms associated with plastic coupons fluctuated. Nitrates disappeared in standing water after one week in aluminum pipes and remained present in plastic. No detectable E. coli remained in standing water in both types of pipe. There was a high probability that coliform concentrations in output irrigation water were different from the intake concentrations in plastic pipes but not in aluminum pipes. Further research is required to evaluate how pipe material may affect the potential of biofilms in irrigation distribution systems to serve as reservoirs of pathogens that can be disseminated to crops during irrigation.