Microbiological assessment of wastewater irrigated peach trees

Water scarcity is an important challenge that agriculture needs to address. Irrigation with treated wastewater can be a strategy to reduce the use of fresh water while extending its availability during drought periods. Unfortunately, wastewater quality could be characterized by the content of human pathogens (e.g., E. coli) that could create human and environment risks. The aim of this research is to assess the microbiological contamination in soil, shoot and fruit tissues of peach trees irrigated with secondary treated wastewater (SW), compared to peach trees irrigated with fresh water (FW). Trees were grown in pots and subjected to drip irrigation; water was supplied directly by the local urban wastewater treatment plant. A high bacterial load was found in SW. E. coli and total coliforms (TC) were detected only in soil samples and not in vegetative tissues. Shoots and fruits were surface-sterilized, and the bacterial internal concentration was evaluated. Total bacterial count (TBC) was detected in shoots and fruits of both SW and FW irrigated plants, although with significantly higher concentrations in SW-irrigated plants. These results confirmed the microbiological safety (E. coli) of fruits irrigated with SW when a drip irrigation system is used. The adoption of these alternative water resources could be a valid and safe support for fruit tree crops irrigation, where the risk of food contamination can be furtherly reduced by the lack of a direct contact between the water source and the edible part of the plant.