Degradation of Fibrous Microplastics in the Marine Environment

This chapter describes the sources of microfibres in the marine environment, different degradation mechanisms and the knowledge on biodegradation for specific polymers. Input from outside and fragmentation of plastic items contribute to their ubiquitous presence. Most conventional plastic polymers are used for fibre applications and biodegradable plastics are still rare in the marine environment. Physical and chemical processes lead to macroscopic and molecular degradation, whereas biodegradation requires the action of either extracellular enzymes to attack the intact polymer or the abiotic degradation of the polymer to result in intermediates small enough to be taken up by microorganisms. Mechanisms of biodegradation of unweathered or otherwise pre-treated, most-used conventional plastic grades are unknown. The biodegradation rate of plastic depends on the conditions in the receiving environment and environmental biodegradability of plastic should be seen as a system property. There is a ‘cellulose enigma’ with the discrepancy of good biodegradability of the natural polymer cellulose on the one hand and the dominance of cellulosic fibres on the other hand. Biodegradability as an engineered property and the natural preservation of polymers in the marine environment are illustrated. The role of biodegradable plastics on material development and the assessment of environmental biodegradation and of risk and benefit is shown.