Black microplastic in plastic pollution: undetected and underestimated?

Plastic pollution includes microplastics. The environmental ubiquity of microplastics (< 5 mm) is evident and the leak of microplastics into the environment is projected to increase globally. Microplastics in the environment possess high heterogeneity in polymer composition, particle size, shapes, and surface chemistry, which sometimes result in contradictory toxicological findings. However, much less attention is paid to the color of microplastics, particularly black plastics that are the least recycled and account for a significant proportion of total plastic waste and environmental microplastics. In the present perspective article, based on 50 field-based research articles on microplastics published from 2014 to 2022 and our own research experience, we raised specific environmental concerns about black microplastics and emphasized the challenges posed by black microplastics in multiple aspects. Future prospects were also discussed for better mitigating black microplastics in the context of plastic pollution.