Toxic Effects of Tire Wear Particles on Microcystis aeruginosa

Tire wear particles (TWP), generated by the friction of vehicle tires against the road surface during driving, accelerating, and braking, are transferred to aquatic ecosystems via rainfall runoff. These particles exhibit toxicological effects on aquatic organisms and have become the focus of research in environment and health. Microalgae, as primary producers in the marine food web, play a crucial role in aquatic ecosystems and are inevitably affected by TWP. However, the toxic mechanisms by which TWP influences microalgae's normal physiological activities remain unclear. Given this, Microcystis aeruginosa, a common species in freshwater ecosystems, was selected as an experimental species in this study to investigate the effects of different concentrations of TWP (5, 25, 50, 100 mg/L) on its growth, chlorophyll a content, photosynthetic activity, extracellular polymer secretion (EPS), and oxidative stress. The results showed that TWP had a concentration-dependent inhibitory effect on the growth, chlorophyll content, and photosynthetic activity of Microcystis aeruginosa, with maximum inhibition rates reaching 89.4%, 98.44% and 92.9%, respectively. TWP stimulated the secretion of the EPS of Microcystis aeruginosa, and the secretion of the EPS increased with the increase of the concentration of TWP. TWP also promoted the polysaccharide-to-protein ratio in the EPS with a rise of 27.3-38.5%. Meanwhile, the three-dimensional fluorescence-area-integral analysis indicated that the ratio of the protein-like component was generally higher than the one of the humic-like component in the EPS of Microcystis aeruginosa. The significant increase in superoxide dismutase (SOD) activity under 50 and 100 mg/L TWP exposure predicted a substantial activation of oxidative stress. In contrast, the significant increase in the malondialdehyde (MDA) content indicated the overproduction of reactive oxygen species (ROS) and may lead to lipid peroxidation damage. These findings will help us better understand the toxic mechanisms by which TWP induces effects in microalgae.