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Microplastic modulates cadmium toxicity in duckweed: Insights into metal uptakes and oxidative stress in the plant
Summary
Researchers found that microplastics in water reduced duckweed's uptake of toxic cadmium by adsorbing the metal onto plastic fibers and causing it to settle into sediments rather than enter plants. While this may seem protective, it highlights a troubling dual role: microplastics can redistribute heavy metals through aquatic systems in ways that affect long-term contamination patterns.
Microplastic (MP) are widespread in aquatic environment alongside other toxic pollutants, potentially impacting the uptake and toxicity in aquatic organisms. This study investigated the effect of MP (1,500 ± 50 particles/L) on the removal of Cd (0.5, 1.0, and 2.0 mg/L) using a duckweed (DW)-based batch setup over 24 days. The setup without MP served as an experimental control. Results showed that Cd exposure significantly hindered DW growth (2.0–3.33 g/d), whereas in the presence of MP, growth slightly increased (2.60–3.70 g/d) (t-test: p < 0.05). Visible signs of Cd toxicity, such as frond discolouration, decay, and necrosis, were observed. The MP-spiked setups resulted in a 1.89–2.0fold decrease in Cd uptake by DW. Oxidative stress enzyme analysis indicated enhanced tolerance of DW to Cd in setups with MP. Meanwhile, Cd bioaccumulation in DW decreased (35.65–55.30%), while its deposition in the bottom sediments increased (30.60–57.15%). The reduced Cd sensitivity of DW in the presence of MP could be due to mechanisms such as the adsorption of Cd onto MP fibers, leading to sedimentation and decreased bioavailability, and the deposition of MP on DW fronds and roots, which might limit metal transfer. These findings suggest that MP can significantly modulate Cd behaviour in aquatic environment by lowering its toxicity and availability to DW through adsorption and enhanced sedimentation, indicating a dual role in reducing metal stress while raising concerns over microplastic accumulation and associated ecological risks. Nonetheless, nano-sized MP bioaccumulation and its toxic effects in such systems warrant further research.