Testing agricultural water

by Sally Colby

As growers become more familiar with the Food Safety Modernization Act (FSMA) and the Produce Safety Rule (PSR), it’s important they understand the meaning of and regulations pertaining to testing agricultural water used for irrigation and other areas of production.

The PSR defines agricultural water as “water used in covered activities on covered produce where water is intended to, or is likely to, contact covered produce or food contact surfaces, including water used in growing activities (including irrigation water applied using direct water application methods, water used for preparing crop sprays and water used for growing sprouts) and in harvesting, packing and holding activities (including water used for washing or cooling harvested produce and water used for preventing dehydration of covered produce).”

Dr. Don Stoeckel, Produce Safety Alliance Midwest regional Extension associate, said produce growers are testing water to meet buyer requirements or regulatory requirements. “Although the water requirements, unless you’re growing sprouts, aren’t being enforced under the Produce Safety Rule,” he said, “a farm still has to sell their produce and many of the buyers have an understandable interest in knowing that the water used is of a certain quality.”

The role of outreach teams, primarily Extension, is to help farmers understand water testing requirements and locate suitable testing labs. Stoeckel said most labs that provide commercial water analysis services were not set up specifically to meet the needs of farms and aren’t aware of agricultural water or regulatory requirements. “There’s potential for inappropriate recommendations,” he said, “and potential they might be doing tests using unacceptable methods if their main business is serving recreational water or waste water treatment plant discharge water quality.”

Stoeckel explained that the PSR proposed compliance dates for water (other than sprouts) is under enforcement discretion until at least 2022. The delay is due to concern within the regulated community about the practical implementation of compliance and the regulatory burden in meeting those requirements.

During a water summit in early 2018, the FDA collected input from the regulated and industry community as one of the steps in addressing the compliance timeframe. “The proposed extension of compliance dates has been described in a PowerPoint presentation that the PSA put together,” said Stoeckel. “It’s on the PSA’s main page under ‘trainer resources.’”

The PSR currently includes core requirements, including an annual inspection of the agricultural water system, a testing requirement for generic E. coli for untreated surface and ground water used in certain ways, and maintenance of agricultural water quality during use, which is intended to maintain its safety and adequate sanitary quality. Stoeckel reminded growers that requirements may change prior to the 2022 proposed implementation date, and that agricultural water is only some of the water used on the farm.

Stoeckel outlined water sampling requirements for growers. “For untreated agricultural water used during or after harvest, it’s a four-year data set, but the goal is to determine that there’s no detectable generic E. coli,” he said. “There is no allowance for untreated surface water in post-harvest, even if it tests negative for generic E. coli under the current rule – which may change.” The exception regarding sampling requirements is public water supplies where the grower must have testing records from the public water supply provider.

The PSR specifies aseptic technique for water sample collection. Stoeckel said aseptic means the water sampled is the only source of generic E. coli in the sample. “It’s a matter of keeping dirty fingers out of the bottles and using sterile bottles,” he said. “It’s ensuring that the analysis done at the laboratory and the only source of E. coli in that sample is the water itself, not from the environment.”

After the sample is collected, it should be refrigerated or kept on ice. Stoeckel suggested that the bottle containing the labeled sample should be placed in a plastic bag so wet ice doesn’t cause the label to peel off. Avoid using blue ice (reusable freezer packs) because some are designed to maintain freezer temperature rather than refrigerator temperature and may result in a frozen sample. “If you freeze the water sample, you’ve killed some of the bacteria in the sample,” said Stoeckel. “The water sample should be chilled but not frozen during holding and delivery.”

Hold time requirements, or the time between sample collection and lab analysis, can be a stumbling point. “Some methods list hold time requirements,” said Stoeckel.

“If the method does not list hold time requirements, one of the industry standards is the book ‘Standard Methods for the Examination of Water and Waste Water’ (provision 9060B) and it states that ‘non-potable water (from rivers, ponds) for quantitative tests have six hours from collection to delivery, and sampling within eight hours.’” For drinking water, or tests that use a presence/absence test, samples must be analyzed within 30 hours.

The two test methods for agricultural use water include production water criteria or postharvest water criteria. “If you’re using agricultural water in a way that it needs to meet production water criteria, it has to be done using a quantitative method,” said Stoeckel. “If agricultural water is being used postharvest, it can be either quantitative or presence/absence because the criterion is no detectable E. coli.”

The EPA created a list of equivalent (water testing) methods in 2017 and updated the list in 2018. The FDA website includes a comprehensive list of test methods and criteria for postharvest uses (plus sprouts) and production uses. However, some farms are not covered, qualify for exemptions or will have modified requirements.

Different methods are expressed in various formats, including Colony-Forming Units (CFU) per 100 ml. “That’s the unit used in the Produce Safety Rule criteria,” said Stoeckel. “Most Probable Number (MPN) per 100 ml results are only for some of the methods. Then there are the presence/absence methods in 100 mls.” Stoeckel explained that presence/absence is used in the PSR by implication when the result is expressed as “no detectable generic E. coli in 100 ml.” Results expressed as “not detected” means the same as absent, and means the same as less than one CFU or less than one MPN per 100 mls – as long as the laboratory is using a full 100 ml sample.

For clarification, Stoeckel explained CFUs as a count of the colonies formed on the surface of a gel agar plate. “The water sample is poured into a funnel on top of a filter,” he said. “Everything bigger than one-half micron in that sample gets stuck on the filter. The filter is transferred to a plate, and that plate is incubated. Anywhere one or more cells was on that filter, if it’s a target cell, it can grow a colony.”

For reliable results, Stoeckel urged producers to complete lab forms as accurately as possible. Details such as collection site, hold time, time of sampling, ground or surface water and whether there was a significant rain event prior to sampling are critical in obtaining the most accurate results.

2019-04-08T18:03:46-05:00April 8, 2019|Grower Midwest|0 Comments

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