Are free and coated silver nanoparticles from sugarcane bagasse safe nanomaterials for freshwater organisms?

In this study, we evaluated the toxicity of silver nanoparticles synthesized from sugarcane bagasse (AgNPsBCA) and those coated with polyethyleneimine (AgNPsBCA-PEI) in three freshwater invertebrates: Daphnia magna, Cypricercus centrura, and Palaemon pandaliformis. AgNPsBCA-PEI exhibited up to ∼100× greater toxicity than AgNPsBCA (LC50: 5–105 µg/L vs. 2,240–13,070 µg/L in C. centrura), with D. magna showing the highest sensitivity (LC50: 0.28–0.71 µg/L). In P. pandaliformis, AgNP exposure reduced oxygen consumption (−67.7% for AgNPsBCA; −72.4% for AgNPsBCA-PEI) and ammonia excretion (−68.3 to −90.1%), likely linked to gill dysfunction and impaired ion regulation. All reductions were statistically significant (p < 0.05) relative to controls. These toxicity levels are markedly higher than those reported for biogenic and commercial AgNPs. The enhanced toxicity of AgNPsBCA-PEI is likely associated with the strong cationic surface charge imparted by PEI, which promotes electrostatic interactions with negatively charged cell membranes, increases cellular uptake, and may facilitate greater Ag+ release. Collectively, these results underscore the critical role of surface functionalization in shaping the ecotoxicological profiles of AgNPs and emphasize that even eco-friendly synthesis approaches must account for potential environmental risks associated with nanoparticle modifications.