Chitosan‑coated Green‑synthesized ZnO Nanoparticles Attenuate Heavy Metal Co‑accumulation in Common Carp (Cyprinus carpio, Linnaeus, 1758).

The co-occurrence of engineered nanoparticles and heavy metals in aquatic environments poses critical unknowns. Common carp (Cyprinus carpio) were exposed for 28 days to a Cu/Pb/Cd/Cr mixture alone, with commercial ZnO nanoparticles, or with a chitosan-coated ZnO nanocomposite (CZN). Metal bioaccumulation in gill and liver was quantified. Commercial ZnO markedly enhanced gill‑specific accumulation of Pb, Cr, and Zn versus metals alone. Conversely, CZN substantially lowered these elements and reduced Cd below the detection limit in both tissues. Although tissue‑dependent trends were noted, multivariate analysis showed that treatment type, rather than tissue identity, dominated the overall metal profile. Thus, commercial ZnO exacerbates metal accumulation, while chitosan coating efficiently attenuates this enhancement, highlighting that surface functionalization critically modulates metal-nanoparticle interactions and subsequent bioaccumulation in fish.