The seaweed Chaetomorpha linum cultivated in an integrated multitrophic aquaculture system: A new tool for microplastic bioremediation?

Microplastics (MPs) are emerging pollutants with detrimental impacts on ecosystems and human health. Due to their adverse effects, new strategies to mitigate MP pollution in the marine environment need to be developed urgently. In this context, the capability of the seaweed Chaetomorpha linum (Chlorophyta, Cladophorales) to trap MPs, as well as the effectiveness of a simple washing procedure to clean up the harvested seaweed biomass, were investigated. This algal species was grown in an integrated multitrophic aquaculture system (IMTA), where bioremediator organisms such as macroalgae, polychaetes, sponges and mussels were farmed in the vicinity of the fish cages. MPs trapped in C. linum were classified based on shape and size, and representative samples of each shape were analysed by attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy to evaluate their chemical composition. Fibre MPs were the most abundant (97.3 %), while the size ranged from 0.025 to 2.00 mm, with most samples being in the size range 0.80-1.00 mm. MPs were composed mainly of polypropylene, polystyrene, and polyethylene. They were efficiently removed from the cultured seaweeds by a simple density separation procedure, consisting of three extractions with hypersaline solutions of sodium chloride. These results suggest that C. linum cultivated in an IMTA system can be proposed as a bioremediator to capture MPs from the surrounding environment. At the same time, harvested and cleaned green seaweeds may be considered a co-product of the bioremediation process and can find application in several biotechnological fields, including the use as a food source for human consumption.