Achyut Adhikari and Marlene E. Janes
Agricultural water is the water that is likely to contact the edible portion of fresh produce during growing, harvesting, processing or packing. Water quality is critical, especially when dealing with food that is consumed raw.
Agricultural water is considered a potential source for foodborne pathogen contamination. Recent outbreaks of Escherichia coli O157:H7 and Salmonella spp. point to irrigation water as the vector in the production environment of fresh fruits and vegetables. Once introduced, it is difficult to remove the pathogens from fresh produce because rough surfaces hinder the release of microorganisms during washing. Even with vigorous washing, there may be enough pathogen left to cause serious health hazards.
Proposed Requirement for Agricultural Water
With the recent enactment of the Food Safety Modernization Act produce safety rule, “all agricultural water must be safe and of sanitary quality for its intended use.” Water used for pre-harvest practices of high-risk fruits and vegetables must meet the Escherichia coli requirements as proposed by the U.S. Environmental Protection Agency. Farmers with agricultural water that does not meet the proposed microbial standard would be required to take one or more of the following actions: 1) change the irrigation system, 2) establish an irrigation-to-harvest or harvest-to-end-of-storage interval to allow time for potentially dangerous microbes to die off, or 3) treat the water to reduce the microbial food safety risk.
Microorganisms exposed to environmental conditions, such as ultraviolet light from the sun or limited availability of nutrients, may die. Studies show that waiting after irrigation until harvest will reduce the levels of bacterial pathogens. This factor is considered as an option in the FSMA agriculture water quality requirement. The rule allows growers to calculate a microbial die-off rate from the last day of irrigation until harvest. After each day, you can assume a roughly 67 percent reduction in generic E. coli compared to the previous day.
In some cases, growers may not be able to wait for harvest because of adverse environmental conditions such as heavy rain or floods. In such situations growers can harvest their crops without waiting after the last day of irrigation but must apply a time interval in days between harvest and the end of storage, using an appropriate microbial die-off or removal rate. Washing or other antimicrobial treatments during post-harvest processing are also considered as microbial removal, which will reduce the waiting period.
There are three main sources of agricultural water: the municipal water supply, well water and surface water. The food safety risk associated with agricultural water varies depending on the source of water. Municipal water supplies potable water, but it is available in limited volume and locations. Vegetable production is water-intensive, and producers meet the production requirements usually by drawing water from ground and surface sources.
Well water is relatively safer than surface water. However, several factors affect the quality of well water. These include location, proximity to a sewage system, the well condition and soil porosity. Routine inspection and maintenance of the well will ensure that it is functioning properly to avoid possible contamination.
Surface water is regarded as high risk and should not be used for high-risk activities such as post-harvest processing, unless it is treated and converted to potable water. There are many environmental factors that affect the quality of surface water, runoff being the important one. Even for pre-harvest activities producers must take steps to minimize the risk of produce contamination with surface water.
Routine inspection and monitoring of an irrigation water source will help to determine possible adverse environmental conditions affecting water quality. Most standards related to agricultural water require frequent water testing during the growing season. The number of tests and frequency of testing depend upon the source of water. It is recommended that water be tested at least quarterly if using surface water and at least annually if using well water for agricultural production.
Federal and state regulations and some buyers require producers to perform generic E. coli testing of their agricultural water rather than direct pathogen testing. Common foodborne pathogens may be present at low numbers in water but may go undetected during testing. Even at low numbers, some pathogens can cause serious health hazards. Human and animal fecal material is the main source of generic E. coli and other common bacterial pathogens. Thus, generic E. coli testing is performed to indicate potential fecal contamination.
The LSU AgCenter has a water testing laboratory in Baton Rouge to provide affordable and reliable water testing services for Louisiana producers. AgCenter extension agents and specialists also provide consultation services to producers if their water testing results do not meet the regulatory or buyers’ requirements. Growers also can buy a water sampling kit from their local AgCenter parish extension office.
Research and Outreach
LSU AgCenter researchers and extension specialists are developing best practices for water treatment suitable for Louisiana producers. These practices include the use of ultraviolet light inactivation of microorganisms and modifying filtration systems to remove microbial contaminants from irrigation water. Louisiana producers have numerous opportunities to attend workshops and meetings to learn how to manage food safety risk associated with agricultural water. During 2015, the LSU AgCenter has been hosting a series of Good Agricultural Practices (GAPs), Good Handling Practices (GHPs) and food safety workshops. The workshops are presented in collaboration with LSU, the Louisiana Department of Health and Hospitals, the Louisiana Department of Agriculture and Forestry and the Southern University Agricultural Research and Extension Center.
Achyut Adhikari is an assistant professor in the School of Nutrition and Food Sciences and is in charge of training and education about the Food Safety Modernization Act. Marlene E. Janes is a professor in the school and an expert in food safety.
The summer 2015 issue of Louisiana Agriculture magazine includes articles on a variety of topics that affect Louisiana’s agriculture industry and the environment – water management at Catahoula Lake, 4-H youth wetland programs, artificial reefs for water conservation, corn nitrogen management in saturated soil conditions, and more. 36 pages