Physiological and structural responses of the seagrass Cymodocea nodosa to titanium dioxide nanoparticle exposure

Abstract

The extensive application of titanium dioxide nanoparticles (TiO2 NPs) has raised concern about its environmental risks. The present study aims to elucidate TiO2 NP ecotoxicity, by assessing effects on seagrasses at environmentally relevant concentrations. Changes in physiological and structural cell traits of Cymodocea nodosa leaves, treated with TiO2 NPs at 0.0015–1.5 mg l-1 for eight consecutive days, were investigated. Intracellular levels of hydrogen peroxide (H2O2) increased significantly, even early during the lowest exposure, despite an up-regulation of H2O2-scavenging enzyme activity. Actin filaments (AFs) and endoplasmic reticulum (ER) were affected in a concentration- and time-dependent pattern, while no changes in microtubule organization and cell ultrastructure were detected. The lowest effect concentrations for AF and ER impairment were 0.15 and 1.5 mg l-1, respectively; for cell death, these were 0.15–1.5 mg l-1, depending on leaf age, and for leaf elongation inhibition 0.15 mg l-1. Thus, elevated H2O2 level can be considered as an early warning biomarker for TiO2 NPs, while leaf elongation, AF and ER impairment are also reliable indicators. A risk quotient greater than 1 was estimated; thus, TiO2 NPs might present a significant potential environmental risk. Our findings can be utilized for monitoring pollution levels in coastal environments.