Impact of Chlorine Dioxide Treatment on Irrigation Methods in an Organic Farming System

Contaminated irrigation water has been linked to several produce outbreaks associated with E. coli O157:H7 and Salmonella.  Investigating practices that can reduce risk for irrigation water is important due to proposed regulatory requirements through the Food Safety Modernization Act.  This study evaluated irrigation delivery (overhead and drip) and water treatment (with or without chlorine dioxide) on indicator organism levels within an organic farming system. Water samples were collected from the irrigation water source and 4 plots per treatment (overhead and drip untreated, overhead and drip with chlorine dioxide) for four irrigation events.  For treated plots, chlorine dioxide (ClO2) was applied in the water system prior to irrigation. Samples were subjected to the most probable number (MPN) method for quantification of total coliforms, fecal coliforms and generic Escherichia coli, and examined for detection of E. coli O157 and Salmonella.  MPN of the indicator microorganisms was based on proportion of observed positive samples.  Creek water total coliform, fecal coliform, and generic E. coli levels ranged from 3.3 - 3.5 log cfu/100ml, 2.3 - 3.0 log cfu/100ml, and <1.2 - 2.5 log cfu/100ml, respectively. Treated plots had lower levels of indicator organisms compared to untreated plots.  For both treated overhead and drip irrigation, all samples for indicator organisms were <1.2 log cfu/100ml. For untreated overhead irrigation water samples, total coliforms, fecal coliforms and generic E. coli ranged from 2.52 to 3.41 log cfu/100ml, 1.89 to 3.23 log cfu/100ml, and <1.25 to 1.97 log cfu/100ml respectively. The drip irrigation, untreated water samples ranged from 3.0 - 4.2 log cfu/100ml, 2.3 - 3.5 log cfu/100ml, and <1.2 - 2.1 log cfu/100 ml for total coliforms, fecal coliforms and generic E. coli.  Treated irrigation water (with chlorine dioxide) yielded lower levels of total coliform, fecal coliform and generic E. coli than untreated water.