Does Salmonella move through the irrigation systems of mixed produce farms of the southeastern United States?

Does Salmonella move through the irrigation systems of mixed produce farms of the southeastern United States?

Jan. 1, 2014 - Dec. 31, 2015

2014-300

$371,782.00

/George Vellidis, Ph.D.
University of Georgia

Michele Jay-Russell, Ph.D.

Final Report

Our goal is to develop knowledge which will allow vegetable producers who rely on untreated surface sources of irrigation water to effectively address proposed FDA rules.  These rules may require that all agricultural water, including irrigation water, be safe for its intended use.  In a small pilot study we conducted in the southeastern United States, we found that Salmonella is present in irrigation systems using water from ponds to irrigate vegetables.  These findings are intriguing but preliminary and a more comprehensive study is needed to draw defensible conclusions.  With that in mind, our objective is to understand if Salmonella moves through irrigation systems of mixed produce farms of the southeastern United States; if it persists on the crop until harvest; and if chlorine dioxide treatment of the water prevents produce contamination.  We will measure Salmonella concentrations in ponds and wells, irrigation systems (pivot, sprinkler, drip), and produce (cantaloupe, tomatoes, peppers, leafy greens) irrigated by these systems on five farms in southern Georgia to answer these questions. Knowledge resulting from this project will allow vegetable producers that rely on untreated surface sources of irrigation water to effectively address new rules the FDA may implement on safe agricultural water.

Technical Abstract

The overall goal of this proposal is to develop knowledge which will allow vegetable producers who rely on untreated surface sources of irrigation water to effectively address recently proposed FDA rules.  In January 2013, the FDA proposed that all agricultural water must be safe for its intended use (proposed § 112.41.)  FDA’s definition of agricultural water is water that comes into direct contact with produce and includes irrigation water that is applied using direct water application methods such as overhead sprinkler irrigation.  FDA also proposed that agricultural water be considered safe if test results do not exceeded 235 CFU per 100 mL generic E. coli.  Companion CPS-funded studies conducted in the southeastern United States by members of our project team have consistently found measurable concentrations of Salmonella and other pathogens in ponds used to irrigate fruits and vegetables.  Members of the project team also conducted a pilot study to assess the presence of Salmonella in irrigation water in four different irrigation systems on one farm.  Salmonella and generic E. coli were found in samples collected from all three irrigation systems fed by pond water.  Generic E. coli concentrations in all samples from the irrigation systems containing Salmonella were below the proposed threshold of 235 CFU/100 mL.  In contrast, no Salmonella or generic E. coli were found in samples collected from an irrigation system fed by a deep groundwater well.  These preliminary findings are intriguing but the sample sizes were small and a larger and more comprehensive study is needed to draw defensible conclusions.

With that in mind, our objective is to understand if pathogenic organisms, and specifically Salmonella, move through the irrigation systems of mixed produce farms of the southeastern United States and if so, do they persist on the crop until harvest.  We have developed a research plan which will measure Salmonella and generic E. coli concentrations in source water (ponds and wells), irrigation systems (pivot, sprinkler, drip), and produce (cantaloupe, tomatoes, peppers, leafy greens, and others) irrigated by these systems on five farms in southern Georgia.  We will also evaluate if chlorine dioxide treatment of irrigation water drawn from ponds effectively removes pathogens.  Finally, we will assess the validity of measuring generic E. coli as an indicator for Salmonella serovars. 

The expected outcome of our proposed project is information on whether Salmonella moves through the irrigation systems of mixed produce farms of the southeastern United States and if so, does it persist on the crop until harvest.  We will also provide information on whether treatment of the irrigation water after it is withdrawn from the pond eliminates the pathogen threat.  This knowledge will allow vegetable producers that rely on untreated surface sources of irrigation water to effectively address new rules the FDA may implement on safe agricultural water.  If our assessment of the validity of measuring generic E. coli as an indicator for Salmonella serovars produces highly significant results, then these results could potentially be applied to the entire country and multiple fresh produce commodities.