Co-exposure with copper alters the root uptake, xylem and phloem translocation, and excretion of current-use pesticides (CUPs) by Rice (Oryza sativa L.)

The rhizospheric dynamics governing uptake-translocation-excretion processes of current-use pesticides (CUPs) under metal co-exposure remain mechanistically unexplored. This study investigated the sorption dynamic, xylem and phloem translocation, and root excretion of 16 CUPs when copper (Cu) was present within water-rice ( Oryza sativa L.) system using hydroponic experiments. The sorption dynamic indicated that more moderately and highly hydrophobic CUPs were taken up by fresh and dead rice roots respectively, indicating that moderately and highly hydrophobic CUPs potentially being taken up via symplastic and apoplastic pathways, respectively. The presence of Cu was found to induce damage to root cell membranes of rice which has limited impact on the root absorption of CUPs indicated by the comparable root concentration factors between sole CUPs and CUPs-Cu treatments. However, the presence of Cu enhanced the acropetal translocation of highly hydrophobic CUPs from root to shoot, with significant higher translocation factors being observed. These findings necessitate revision of conventional hydrophobicity driven theory that highly hydrophobic organic chemicals were preferentially restricted to roots. Furthermore, the root excretions of moderately hydrophobic CUPs from roots to external solutions via passive diffusion were promoted in the presence of Cu which have not been elucidated previously. The potential ecological risks associated with the translocation, accumulation, and excretion of CUPs by rice needs careful reconsideration in metals-CUPs co-contamination sites.