Fashion fades, microplastics are eternal: a critical systematic literature review to assess microplastic fibre colours in environmental samples

Abstract Microplastic pollution is a growing environmental concern that requires assessment of a range of parameters. Colour remains a largely overlooked parameter in environmental monitoring, yet a potentially important one from a biological perspective. This systematic review covers 80 peer-reviewed studies published between 2000 and 2020, and addresses microplastic fibres colours across diverse environmental compartments: air, water, sediment and biota. Our analysis reveals that transparent/translucent (T&T), blue, black, and white fibres are the most frequently reported colours globally, with notable variation across environmental compartments and geographical regions. Blue fibres were predominant in biota (32.8%) and water (28.3%), while T&T fibres were prevalent in sediments (35.2%), and yellow fibres in air (27.4%). Europe and Asia showed the highest colour variability. Spatial patterns emerged with blue fibres more commonly reported in North and South America and Oceania, and red and green fibres being predominant in the African continent. No link was found between fashion colour trends and fibre colours in the environment. Our findings highlight data gaps in methodologies and reporting, particularly in distinguishing between synthetic and natural fibres. Given the relevance of colour in ecological interactions and in pollutants traceability, employing standardised colour categorisation methodologies can improve the reliability of environmental monitoring efforts.