Is the aquatic macrophyte Landoltia punctata tolerant to high concentrations of polystyrene nanoplastics?

Nanoplastics (NPs), arising from the degradation of plastic waste, are emerging environmental contaminants with high adsorptive potential for hydrophobic pollutants. Despite their recognized risks, knowledge of their effects on living organisms under natural environments remains limited. This study aims to evaluate the adverse effects and toxicological mechanisms of polystyrene nanoplastics (PSNPs) in the aquatic macrophyte Landoltia punctata. To this end, PSNPs were synthesized and characterized, followed by in-depth toxicological assessments. L. punctata was exposed to six concentrations of PSNPs (50, 100, 200, 400, 800 and 1600 mg L^-1), and a control, under standardized conditions (ISO DIS 20079, 2005), followed by a second exposure phase using EC₅₀ (682.5 mg L^-1), LOEC (50 mg L^-1), and the highest concentration at which growth was still observed (800 mg L^-1). This exposure aimed to identify the factors underlying the observed effects on plant growth and to enhance understanding of plant response mechanisms. Morphological, functional, and ultrastructural modifications, alongside alterations in photosynthetic pigment profiles and oxidative stress biomarkers were analyzed, to elucidate the mechanisms underlying nanoplastic toxicity. The results demonstrated alterations in the plant's growth rate, enzymatic activity, and tissue structure, alongside evidence of PSNP adsorption and cellular internalization. Nevertheless, metabolic activity remained unaffected, allowing sustained plant development even at elevated concentrations. These findings indicate that, despite physiological and structural impacts, the organism displays resilience to PSNP exposure. Consequently, it presents promising potential for use in bioremediation strategies targeting environments contaminated by this pollutant, underscoring its significance as a biological agent for environmental restoration.