Single and combined effects of microplastics and copper on the population growth of the marine microalgae Tetraselmis chuii

As the accumulation of microplastics continues to rise in the marine environment, more knowledge on their potential toxic effects on marine organisms is needed to assess their risks to environmental and human health. Thus, the goal of the present study was to investigate the effects of fluorescent red polyethylene plastic micro-spheres 1–5 μm diameter (used as microplastic model and hereafter indicated as MP), alone and in mixture with copper, on the population growth of the marine microalgae Tetraselmis chuii . Two null hypotheses were tested: (H 01 ) Exposure to MP concentrations in ppb range does not affect the average specific growth rate of T. chuii ; (H 02 ) MP do not interact with the toxicity of copper to T. chuii . In laboratory bioassays, T. chuii cultures were exposed for 96 h to MP concentrations ranging from 0.046 to 1.472 mg/l), concentrations of copper alone ranging from 0.02 to 0.64 mg/l, and the same concentrations of copper in the presence of 0.184 mg/l of MP in test media. No significant effects of MP on T. chuii population growth were found (p > 0.05), leading to the acceptance of H 01 . Copper alone significantly decreased the population growth of T. chuii with EC 10 , EC 20 and EC 50 of 0.009, 0.023 and 0.139 mg/l, respectively. The corresponding values in the presence of MP were 0.012, 0.029 and 0.145 mg/l, respectively. Moreover, the study found no significant differences between the toxicity curves of copper in the presence and absence of MP (p > 0.05), leading to the acceptance of H 02 . Despite these findings, because microplastics are known to adsorb and accumulate copper, aged pellets more than virgin ones, and the toxicity of smaller particles may be higher, further studies on the combined effects of copper and microplastics on microalgae should be performed, especially under long-term exposures to nano-sized aged microplastics.