Microbiological quality of irrigation water collected from vegetable farms in Sao Paulo, Brazil during the dry and rainy season

Abstract

Irrigation water samples were collected from 69 farms in Sao Paulo during two rainy seasons and one dry season. Levels of culturable microorganisms were analyzed using direct plating technique, while levels of E. coli, Enterococci and Clostridium perfringens were determined using membrane filtration. Agroecosystem features including the incidence of manure stockpile, manure lagoon and livestock grazing, amongst others were observed and recorded. In the study area, groundwater (33%) was the most commonly exploited water resource for irrigating vegetables, while the least utilized resources were potable water (4%), streams (2%), lakes (2%) and domestic wastewater (2%). Other water resources exploited for irrigation in the area were farm ponds (21%), harvested rainwater (15%), canals (10%) and rivers (5%). The microbiological quality of water used to irrigate vegetables in the study area was variable depending on factors including source and treatment (chlorination) applied. The levels of culturable microorganisms recovered from the samples ranged between 11.0 and 1.7 log CFU/mL during the rainy and dry seasons, respectively, while the levels of E. coli, Enterococci and Clostridium perfringens detected in irrigation water samples were in the range of 0–6, 0 – 6.5, and 0 – 5.8 log CFU/100 mL, respectively. Irrigation water collected from farms that utilize surface waters such as canals and farm ponds generally contained higher levels of bacteria. In general, bacterial contamination varied among sources in the following order: surface water > groundwater > municipal water. Levels of bacteria detected in groundwater were comparatively low and in about 60% of the cases, for groundwater, no seasonal fluctuation in levels was observed. At the farms where seasonal fluctuations were observed for the levels of bacteria however, at least one potential source of fecal bacteria such as the presence of manure stockpile or livestock grazing was identified.