Assessing and Managing the Health Risks of Irrigation Water in the Lower Colorado River Basin

NON-TECHNICAL SUMMARY: Approximately 4.2 million acre feet (5 billion m3) of water are diverted at the Imperial Diversion Dam near Yuma to largely irrigate crops in the lower Colorado River region of southern California and Arizona. This region produces more than 90% of the nation's cool season vegetables during the fall-winter-spring period. All crops grown in the region depend almost exclusively on irrigation water from the Colorado River distributed in open canals. A number of studies have shown that irrigation water is a potential source of microbial contamination to vegetables. However, we have limited information for assessing the microbial risk of irrigation water to food safety. Due to a prolonged drought in the region there is also an increased interest in using treated effluent to irrigate crops in the southwestern desert. However, concerns about pathogens and several abiotic contaminants have presented a barrier to the increased use of treated effluent. This project seeks to develop tools and guidelines for risk management decisions based on the microbial monitoring of surface derived irrigation water and assessing potential risks from using treated effluent for irrigation of food crops in the region. The specific objectives of the project are: (1) determine variation and environmental factors affecting the microbial risks of irrigation water (2) determine relationships among total fecal coliform, generic E coli, and E. coli O157:H7 in irrigation water (3) determine the relationships between total fecal coliform, generic E. coli, and E. coli O157:H7, and Salmonella found in irrigation water, and corresponding levels found in vegetables irrigated with that water, (4) determine field distribution of bacterial contamination as affected by irrigation system and field scale hydrology (5) determine criteria needed to estimate cumulative risk of irrigation water and recommended follow up responses including additional testing of water, testing of produce, or ultimately decisions to forego harvest in the interest of food safety, (6) assess the microbial risk and food chain transfer of contaminants from crops irrigated with treated effluent, and (7) conduct an aggressive outreach program to implement irrigation water risk assessment management practices that significantly reduce the health related risks from vegetables produced in the low desert region of the southwestern United States. <P>APPROACH: We will characterize any relationship between environmental factors and microbial status in irrigation water and corresponding crops (Objectives 1, 2 and 3). To achieve this we will sample water from irrigation canals and will evaluate for bacteria indicators and pathogens. Additionally, we will be sampling birds and determining any connection species-behavior with bacteria profile. Furthermore, we will assess microbial risk of surface irrigation water used in southern California and Arizona (Objective 4). For the latter we will inoculate water with non-pathogenic E. coli in field studies and examine potential contamination through different irrigation systems. In lab setting we will determine the survival of E. coli O157:H7 and Salmonella enterica in water and produce during postharvest storage (Objective 5). To assess the microbial and chemical contamination risks of treated effluents we will analyze water, soil and plant samples for important pathogenic bacteria as well as for pharmaceuticals including azithromycin, methamphetamine, and psuedoephedrine (Objective 6). Finally our information transfer plan will include field days and workshops, in addition to the most common ways such as extension publications and electronic outreach, to disseminate results and provide training in the implementation of the risk assessment and management practices developed within the framework of this project (Objective 7).