Nanoplastics influence on toxic metal bioaccumulation and antioxidant responses in Lactuca sativa L. irrigated with treated wastewater

Freshwater scarcity has increased interest in circular water-use strategies, including the reuse of treated wastewater (TWW) for crop irrigation. While TWW contains nutrients beneficial for plant growth, it may also carry contaminants such as toxic metals (TM), which can be taken up by plants and pose risks to both crop and food safety. This field study investigates the influence of nanoplastics (NP), an emerging pollutant commonly found in waters, on TM bioaccumulation and antioxidant compound production in lettuce (Lactuca sativa L.), one of the most widely cultivated and consumed leafy vegetables in Western countries. Lettuce plants were grown under greenhouse conditions and irrigated throughout the entire growth cycle with TWW, either alone or supplemented with NP, TM, or both. The results indicate that the interaction between NP and TM leads to a decreased TM bioaccumulation (24%, 50%, and 79% for Cr, Ni, and Cd, respectively) and reduced phytotoxicity, although with negative impact on plant growth (ca. 60% reduction in biomass production). To the best of our knowledge, this is the first study to investigate the effects of nanoplastics and co-existing contaminants present in treated wastewater on crops. These findings provide new insights into plant responses under irrigation with TWW and highlight potential implications for crop safety within the context of circular water use.