Issue link: https://read.dmtmag.com/i/696150
22 JULY 2016 Good Fruit Grower www.goodfruit.com growers to monitor irrigation water for the presence of generic Escherichia coli (E. coli), which indicates the presence of fecal contamination, if it could come into contact with the harvestable portion of a crop. It doesn't matter if that water is being applied through sprinkler irrigation, overhead cooling or other means. Growers who use drip or micro jet irrigation may think they are exempt, Partyka said, but if they use irrigation water in their pesticide sprayers, then the water could come into contact with the crop and monitoring is required. (For tips on how to properly take a water sample, see "Water sampling 101" on next page.) Understanding the rule The Produce Safety Rule requires untreated surface water that could come into contact with produce to undergo a minimum of 20 samples, collected as close as feasible to harvest, over the course of two to four years. The initial fi ndings are used to calculate a geometric mean (GM) and statistical threshold (STV), which together create the microbial water quality profi le for that source. A single positive sample can't be seen as a "hit" — a word researchers would like to remove from the lexicon, said Ronald Bond, water quality researcher at WCFS. In TMDL (total maximum daily load) water sampling for environmental purposes, a "hit" requires continued testing until the problem is cleared up, he said. In this case, growers will take 20 samples over the sampling period. Each year thereafter, fi ve more samples will be added and the oldest fi ve will be dropped, creating a rolling geometric mean. For untreated ground water that is directly applied to growing produce, growers are required to do an initial survey using a minimum of four samples, with a minimum of one new sample each year thereafter. One sample with high levels doesn't necessarily mean a grower has a water quality problem, Partyka said. The series of samples are needed to understand the variability of the water quality, and not everyone's variability is going to be the same. "Variability at the start of the season is likely to be different by the end of the season, and you need to understand what makes your system unique," she said. Understanding the math Partyka and Bond, joined by researcher Jennifer Chase of WCFS, conducted a training seminar for irrigation district personnel and packing house food safety compliance offi cers at several sites in Washington in May. The hope is that those who have been trained will help to initially spread the word and offer guidance to growers. More training seminars are planned for growers in the coming months. However, a key point the researchers made during the training was that a late rule change by the U.S. Food and Drug Administration could affect the method or laboratory a grower might choose to analyze samples. Most probable number (MPN) and colony-forming units (CFU) are both estimates of fecal indicator bacteria concentration and are common measures of water quality in aquatic environments. CFU is a count of bacterial colonies grown on a petri dish, while MPN is based on a statistical estimation. MPN methods for indicators have yet to be adequately vetted scientifically for epidemiological use, or for human contact, Bond said, and the FDA has ruled it is not acceptable for use under FSMA. That means growers must ensure that they use — or that the laboratory they hire to analyze their sample — uses a CFU analysis instead of an MPN analysis. Specifi cally, the FDA has stated that EPA Method 1603 is the only currently acceptable method for analyzing your samples. Any other method requires scientifi c verifi cation. Under the Produce Safety Rule, the geometric mean of a grower's samples must be 126 CFU or less of generic E. coli per 100 milliliters of water (2.1 log10 E. coli). The statistical threshold of samples is 410 CFU or less of generic E. coli in 100 milliliters of water (2.6 log10 E. coli). Several tools have been developed to make it easier to calculate the geometric mean and statistical threshold to determine if water meets standards for unrestricted application before harvest. UC-Davis (WCFS) has created Excel tools both for those using untreated surface water or untreated ground water. In addition, the University of Arizona Cooperative Extension has developed an online calculator and ag water app to aid growers. Visit the Western Center for Food Safety online for links to those sites at wcfs.ucdavis.edu. • During the workshop, Melissa Partyka of the University of California-Davis pointed out several environmental factors that can impact water quality, such as runoff, changes in canal banks, nearby animals and, as seen in the background, alterations to neighboring orchards and land. ONLINE THE MATH: A calculator or spreadsheet program are necessary to �ind the averages of your test results. Find out more at goodfruit.com "We want to clarify some of the things in the rule that are vague, but also demystify it and empower growers with information — let them know it doesn't have to be as scary as it seems." —Melissa Partyka