Effects of polystyrene microplastic on the growth and volatile halocarbons release of microalgae Phaeodactylum tricornutum

Volatile halocarbons (VHCs) are trace greenhouse gases that can damage the ozone layer. Trihalomethanes are one of the most common VHCs and play an important role in global climate change. Due to their steadily increasing abundance, microplastics pollutants have attracted growing concern from scientists. However, their impacts on the growth of marine microalgae and the release of VHCs remain unknown. The influence of polystyrene microplastic (PS, 0.1 μm) at different concentrations (25-200 mg/L) on the growth of P. tricornutum and their release of trihalomethanes were studied over 96 h. The results showed that PS can inhibit P. tricornutum growth. At 200 mg/L PS, cell growth, chlorophyll a concentration and photosynthetic efficiency of P. tricornutum were inhibited by 53.53%, 25.45% and 12.50%, respectively. PS concentrations of 25-50 mg/L promoted the release of the three trihalomethanes by P. tricornutum during the 96 h culture as a response to oxidative stress. However, 100-200 mg/L PS severely altered the physiological state of the P. tricornutum cells after 48 h, which reduced the release of trihalomethanes. Our study also demonstrated that the production and release of trihalomethanes served as a protective mechanism against oxidative stress and the toxic effects caused by PS.