The bacterial quality of salad crops drip and furrow irrigated with waste stabilization pond effluent: an evaluation of the who guidelines

Field- and glasshouse-grown lettuces and radishes were drip- and furrow-irrigated with waste stabilization pond effluent and with trickling filter effluent diluted with clean water. Crop contamination levels varied considerably. Under dry weather conditions they were at worst of the orders of 10³ and 10⁴E. coli per 100 g (fresh weight) for radishes and lettuces, respectively; salmonellae were always absent. The bacterial quality of experimental lettuces was similar to those of lettuces on sale in local markets. When rainfall occurred E. coli numbers increased and salmonellae were isolated from lettuce surfaces. These results are interpreted as partially, substantiating the current World Health Organization bacteriological guideline for unrestricted wastewater reuse, but suggest the need for further assessment on the variation in crop contamination caused by climatic conditions.