Microplastics in the marine environment: A review of their sources, distribution processes, uptake and exchange in ecosystems

• Published in: Case studies in chemical and environmental engineering Vol. 2; p. 100010
• Main Authors: Coyle, Róisín, Hardiman, Gary, Driscoll, Kieran O’
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.09.2020; Elsevier
• Subjects: Biofouling; Faecal pellets; Marine aggregate; Microplastics; Uptake; Faecal pellets; Marine aggregate; Microplastics; Biofouling; Uptake
• ISSN: 2666-0164; 2666-0164
• DOI: 10.1016/j.cscee.2020.100010

As the global production of plastics continues to accelerate, the ubiquitous presence of microplastics (μPs) has emerged as a significant marine problem. To comprehend fully the potential impacts and ecological harm caused by μPs it is vital that there is an understanding of their potential sources and sinks; the processes affecting their distribution; and their uptake and exchange in ecosystems. We carried out a comprehensive literature review to test the hypothesis that particle density is a key factor in describing the sinking behaviour and vertical distribution of μPs and to consider the uptake and trophic transfer of μPs. It was found that, whilst polymer density is a key factor in determining the vertical distribution of μPs in the water column, interactions with marine organisms better explain the occurrence of buoyant μPs at great depths. Furthermore, these interactions increase μP availability and uptake, leading to trophic transfer and bioaccumulation within the food chain. •Interactions with marine biota cause μPs to sink, regardless of polymer density.•Biofouling, aggregation and ingestion facilitate surface removal of buoyant μPs.•Fouled μP particles are more readily ingested than pristine particles.•Aggregates and faecal pellets are vectors for μP uptake. Microplastics are widespread and prevalent in the marine environment. Whilst it is thought that polymer density primarily influences their vertical distribution, low-density microplastics are present at depths of thousands of metres, suggesting this is not the case. We reviewed interactions with marine biota which have been suggested as alternate hypotheses and found they offer a feasible explanation for the sinking of buoyant plastics. They also enhance the nutritional value of microplastics and act as vectors for their uptake, leading to the transfer of microplastics to higher levels of the food chain where their toxic effects are magnified.