Bacteriological and physico-chemical analysis of irrigation water, soil and lettuce (Lactuca sativa L.)

Abstract The contamination of greenery by pathogenic microorganisms is directly related to the quality of irrigation water used in agriculture and to the soil where the greenery is located. In order to verify the conditions surrounding lettuce (Lactuca sativa L.) production at three small properties of Rio Grande do Sul State, Brazil, we evaluated the physico-chemical conditions of irrigation water as well as the microbiological condition of water, soil and lettuce leaves. Bacteriological analyses of the irrigation water, greenery and soil were performed using the multiple tubes or plate-counting techniques, and the total coliforms, thermo-tolerant coliforms, and presence or absence of Escherichia coli, Salmonella sp. and Listeria sp. was evaluated. The irrigation water was analyzed to determine pH, turbidity, dissolved oxygen, biochemical oxygen demand, total organic carbon and total nitrogen. Bacteriological analysis on the irrigation water indicated the absence of Salmonella sp. and Listeria sp.. However, we detected the presence of E. coli and higher thermo-tolerant coliform levels than that established by current legislation. Thus, these water samples do not conform to the standards established by the CONAMA n° 357 Resolution. Our analyses also showed the presence of E. coli, Salmonella sp. e Listeria sp. on the irrigated greenery, suggesting that the source of the Salmonella sp. and Listeria sp. contamination must be the soil, rather than the irrigation water. Physico-chemical analyses showed that only one of the analyzed properties conforms to the standards established by current legislation for Class 1 fresh water. Therefore, only one of the properties presented the physico-chemical conditions appropriate for lettuce irrigation, although no property presented hygienic sanitary conditions for such use.