A critical scientific and policy opinion on reuse and reclamation of contaminated wastewater for agriculture and other purposes

Contaminants of emerging concern and other chemicals are widespread in the environment. While their effects are ambiguous, a wealth of literature now illustrates their ability to induce various effects at concentrations/ doses smaller than the toxicological threshold, leading to hormetic biphasic responses. Such responses are increasingly understood, can be positive or negative, and present an issue for wastewater reuse and reclamation for agriculture and other purposes. Considerable efforts have been placed by stakeholders at multiple levels to address the issue of low-dose effects, but there is more that can be done. To effectively address the low-dose issue, treatment/remediation sites for pollutant elimination should be improved, the number and amounts of chemicals released to the environment should be better controlled/prevented, and citizen-science approach with the involvement of NGOs and other organizations should be employed to expand the coverage of assessing pollution and its effects. This Opinion paper summarizes the main challenges introduced by the continuous discovery of emerging contaminants in the environment and the low-dose effects, discusses what has been done by stakeholders to address low-dose effects, and proposes a path forward.