Biodegradability-driven nanoplastic modulation of copper fate and toxicity in wetland plants

Nanoplastics (NPs) are increasingly detected in wetlands and may interact with co-occurring metals, yet the influence of NP biodegradability on metal fate and phytotoxicity remains poorly understood. This study investigated how NP biodegradability modulated copper (Cu) uptake and toxicity in wetland plants, using the mangrove Avicennia marina as a model. Seedlings were exposed to Cu alone and in combination with three types of NPs: non-biodegradable polystyrene (PS), biodegradable polylactic acid (PLA), and polybutylene adipate terephthalate (PBAT) in 30-day sediment microcosms. Biodegradable NPs, particularly PLA, effectively sequestered Cu in sediments, thereby reducing root Cu uptake by up to 58% relative to the Cu-only treatment. Conversely, PBAT facilitated high root Cu accumulation (112.4 mg/kg) while maintaining a low translocation factor comparable to the Cu-only control, thereby restricting Cu movement into leaves. Micro-X-ray fluorescence elemental mapping revealed that co-exposure to Cu with PS or PLA preserved leaf Fe homeostasis, whereas Cu-PBAT co-exposure disrupted root metal (Mn/Fe) balance and interfered with sulfur-assisted detoxification. These findings demonstrate that NP polymer type influences Cu mobility and subsequent phytotoxicity, challenging the assumptions about the environmental safety of biodegradable plastics. This study provides crucial insights into the risk assessment of mixed pollution in wetlands, highlighting the necessity of considering polymer-specific properties in regulatory frameworks.