Interaction between macroalgae and microplastics: Caulerpa lentillifera and Gracilaria tenuistipitata as microplastic bio-elimination vectors

The pollution of microplastics (MPs) in the ocean has become a serious matter of concern. The farmed seaweeds ( Caulerpa lentillifera and Gracilaria tenuistipitata ) were selected to study their ability of adsorption with two typical classes of MPs (polyamides and polystyrene), thereby revealing the interaction between MPs and macroalgae and exploring novel methods of removing MPs from macroalgae. The results demonstrate that polyamides (PA) fibers had no effect on the various physiological parameters of both seaweeds (e.g., relative growth rate, photosynthetic oxygen evolution rate, the contents of malondialdehyde and extracellular polymeric substances) after 7 days of exposure, except for the chlorophyll- a concentration. However, the effects of polystyrene (PS) particles on the algae were strongly associated with the concentration of MPs exposure. Exposed to the high concentration (100 mg/L) of PS particles, the relative growth rate of C. lentillifera and G. tenuistipitata decreased by 54.56% and 30.62%, respectively, compared to the control, while no significant ( P >0.05) harmful effect of PS particles on seaweeds was observed in an environment with a low content of PS particles (25 mg/L). The PS particles in concentration of 100 mg/L significantly ( P <0.05) inhibited photosynthetic oxygen evolution rate and extracellular polymeric substances (EPS) contents in both seaweeds, but increased malondialdehyde (MDA) contents. When exposed for 72 h, the MPs adhesion rate of G. tenuistipitata is higher than that of C. lentillifera , which might be due to the higher EPS content of G. tenuistipitata . The MPs desorption experiment indicated that the combination of dewatering and washing had the highest desorption rate of MPs which could reach to 91.45% and 87.23% for C. lentillifera and G. tenuistipitata , respectively. This research demonstrates the potential of macroalgae as a vector for MPs in aquatic environment and provides methodological insights into decontamination procedures for removing the MPs from macroalgae.