Micro-nanoscale polystyrene co-exposure impacts the uptake and translocation of arsenic and boscalid by lettuce (Lactuca sativa)

The influence of micro-nanoplastics (MNPs) on the fate and effects of other pollutants present in the environment is largely unknown. This study evaluated if the root exposure to MNPs (polystyrene, PS; 20 or 1000 nm) had an impact on the accumulation of arsenic and boscalid (As and Bos) in lettuce (Lactuca sativa). Under hydroponic conditions, plants were co-exposed to MNPs at 10 or 50 mg/L, and to 1 mg/L of each environmental pollutant (EP). For soil-like media, plants were exposed to MNPs at 50 and EPs at 10 mg/kg. Phytotoxicity was enhanced by PS under both growth conditions, particularly by nanoscale PS (nPS), although impacts were less in potting mix-grown plants. Nanoscale PS had a greater impact than microscale PS (μPS) on As fate; the As translocation factor from roots to the edible shoots was increased 3-fold in plants exposed to nPS (50 mg/L) and EPs. PS dose and size had a variable impact on Bos uptake and translocation. Fluorescent microscopy analysis of lettuce co-exposed to MNPs and EPs suggests that nPS is entering the roots and translocating to the leaves, while μPS mostly remains in the roots. Pyrolysis-GC/MS showed that in solid media, the presence of EPs significantly increased the translocation of nPS to lettuce shoots from 4.43 ± 0.53 to 46.6 ± 9.7 mg/kg, while the concentration of μPS in the shoots remained the same regardless of the presence of EPs (ranging between 13.2 ± 5.5 to 14.2 ± 4.1 mg/kg). These findings demonstrate that co-exposure of MNPs with other EPs can significantly impact co-contaminant accumulation and toxicity, presenting an unknown risk to humans and other receptors.