Mussel power: Scoping a nature-based solution to microplastic debris

Microplastics are a prolific environmental contaminant. Curbing microplastic pollution requires an array of globally relevant interventions, including source-reduction and curative measures. A novel, nature-based solution to microplastics is proposed, in which mussels are deployed in aquatic ecosystems to act as microplastic biofilters, removing waterborne microplastics and repackaging them into biodeposits that are subsequently captured and removed. Blue mussels (Mytilus edulis) were used to establish the feasibility of such an approach. In the laboratory, mussels were exposed to representative microplastics in a flume tank; at an initial concentration of 1000 microplastics L⁻¹, mussels reduced waterborne microplastic concentrations at an average rate of 40,146 microplastics kg⁻¹ h⁻¹. Mussel faeces sank irrespective of microplastic content, with average sinking velocities of 223-266 m day⁻¹. Modelling predicts ∼3 × 10⁹ mussels deployed on ropes at the mouths of estuaries could remove 4% of waterborne microplastics discharged from rivers. Mussels were successfully deployed in a prototype biodeposit collection system in an urban marina, with 5.0 kg of mussels removing and repackaging 239.9 ± 145.9 microplastics and anthropogenic particles day⁻¹ into their faeces. These results provide impetus for further development of nature-based solutions targeting plastic debris.