Food safety risks associated with the use of contaminated agricultural water in the production of table grapes

Most agricultural water sources are often considered contaminated, due to poorly maintained sanitation systems, polluted river streams and other water catchment areas. Agricultural water used for irrigation and reconstitution of pesticides is suspected to play a direct or indirect role in the transmission of human pathogens to fresh produce. The contamination of fresh table grapes during pesticide spraying can therefore be seen as a potential risk factor. This study focuses on identifying possible sources and levels of bacterial contamination in a river, holding dam and tank in table grape production areas. In addition, the ability of selected pathogens to attach and survive on table grape surfaces was studied using transmission electron microscopy. Water sources sampled in this study were found to be microbiologically contaminated. Microbial populations varied with season, sampling period within a season and water treatment conditions. No human pathogens were detected under natural field conditions on crops irrigated with contaminated water used for reconstituting agricultural pesticides. This study further showed a wide range of pesticide products that permitted survival and multiplication of most of the tested foodborne pathogens i.e. Escherichia coli 157:H7, Listeria monocytogenes, Salmonella enterica subsp. enterica serovar Typhimurium and Staphylococcus aureus. This information provides insight into the potential risk that may be associated with table grapes due to the use of contaminated water. These findings highlight the importance of considering pesticides used, water quality and spray schedules prior to application. Detailed risk assessment studies on the potential of contaminated irrigation water and the actual link with foodborne disease outbreaks have not been investigated and should in future be determined as well as intervention strategies.