The reuse of treated wastewater, in particular for irrigation, is an increasingly common practice, encouraged by
governments and official entities worldwide. Irrigation with wastewater may have implications at two different
levels: alter the physicochemical and microbiological properties of the soil and/or introduce and contribute to the
accumulation of chemical and biological contaminants in soil. The first may affect soil productivity and fertility;
the second may pose serious risks to the human and environmental health. The sustainable wastewater reuse in
agriculture should prevent both types of effects, requiring a holistic and integrated risk assessment. In this article
we critically review possible effects of irrigation with treated wastewater, with special emphasis on soil microbiota. The maintenance of a rich and diversified autochthonous soil microbiota and the use of treated wastewater
with minimal levels of potential soil contaminants are proposed as sine qua non conditions to achieve a sustainable wastewater reuse for irrigation.
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