Biofouling Promotes Higher Concentration of Heavy Metal on Disposable Face Masks than Microplastic Films and Particles in Seawater: Mechanisms and Potential Ecological Risks

The insufficient control of waste associated with personal protective equipment (PPE) resulted in a large influx of disposable face masks (DFMs) in marine environments. Herein, we investigated the biofilm colonization on three types of polypropylene microplastics (MPs, i.e., DFMs, films, and particles) as well as the potential risks of MP-associated heavy metals (HMs) in seawater. Compared to conventional MP particles and films, DFMs were conducive to colonization by microorganisms and minerals, resulting in the formation of a typical spatial network biofilm structure. This triggered more HM adsorption by the biofilm-developed DFMs through surface complexation with the organic components in the biofilm. By BCR sequential extraction analysis, we found that organic and mineral components comprised 70.2-85.6% and 14.4-29.8% of the HM concentration in the biofilm-developed DFMs, respectively. In an in vitro gastrointestinal tract model, biofilm-developed DFMs had a much higher desorption capacity for HMs than MP particles and films. Moreover, the ecological risk index of biofilm-developed DFMs was significantly higher than that of biofilm-developed films and particles. Considering the potential ecological risk of biofilm-developed DFMs, we advocate that the reasonable recycling and environmentally friendly treatment of PPE MP pollutants should be considered as a bursting challenge for sustainable coastal development.