Demonstration tests of irrigation water disinfection with chlorine dioxide in open field cultivation of baby spinach

BACKGROUNDTreatments for the disinfection of irrigation water have to be evaluated by demonstration tests carried out under commercial settings taking into account not only their antimicrobial activity but also the potential phytotoxic effects on the crop. The consequences of the treatment of irrigation water with chlorine dioxide (ClO2) used for sprinkler irrigation of baby spinach in two commercial agricultural fields was assessed. RESULTSResidual ClO2 levels at the sprinklers in the treated field were always below 1mg L-1. ClO2 treatment provoked limited but statistically significant reductions in culturable Escherichia coli counts (0.2-0.3 log reductions), but not in the viable E. coli counts in water, suggesting the presence of viable but non-culturable cells (VBNC). Although disinfected irrigation water did not have an impact on the microbial loads of Enterobacteriaceae nor on the quality characteristics of baby spinach, it caused the accumulation of chlorates (up to 0.99mg kg(-1) in plants) and the reduction of the photosynthetic efficiency of baby spinach. CONCLUSIONLow concentrations of ClO2 are effective in reducing the culturable E. coli present in irrigation water but it might induce the VBNC state. Presence of disinfection by-products and their accumulation in the crop must be considered to adjust doses in order to avoid crop damage and chemical safety risks. (c) 2017 Society of Chemical Industry