Prospect member Tim Wilkinson talks about microplastics in marine samples for Marine Week 2017. Tim works for the Centre for Environment Fisheries and Aquaculture Science (Cefas).
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Analysis of microplastics in marine samples
The presence of tiny plastic particles or fibres (commonly termed microplastics), from diverse sources such as disintegration of larger items, washing machine cycles, urban runoff and flaking paint, is an emerging cause for concern in the marine environment.
The potential of microplastics to cause harm is related to several important characteristics. They are extremely persistent, and their small size makes them available for ingestion by diverse small animals such as zooplankton, shellfish and sediment worms. Such small creatures are often abundant and include drivers of ecosystem function.
A related concern is that hydrophobic (water hating) contaminants in seawater tend to adsorb to the hydrophobic surface of plastics. Adsorbed substances, such as PCBs and pesticides have been recorded on plastic litter at concentrations many times higher than those in the surrounding water.
The extent to which adsorbed chemicals can be transferred to the fatty tissues of animals that consume plastic is an important topic for research.
Innovative solutions are needed to survey, in a cost effective manner, the distribution and composition of microplastics, and provide information about sources, fate and impacts.
Cefas has developed automated sampling equipment for surveying suspended particles, and, in a recent collaboration with the University of East Anglia (UEA), a novel fluorescent labelling technique to distinguish synthetic particles from natural ones.
The new method, published in Scientific Reports by the Nature Publishing Group, employs a dye that adsorbs to the surface of plastics. When excited by intense blue light, stained microplastics emit shades of bright yellow, orange or red fluorescence, making them stand out among the bits of shell, organic debris, clay and sand that often comprise marine sediments.
Fluorescing particles or fibres measuring just a few micrometres (thousandths of a millimetre) can be recorded using ordinary digital photography, while automated image analysis speeds up the otherwise tedious work of counting them. By enabling a relatively high sample throughput, this technique has the potential to measure microplastic concentrations in diverse matrices from water, sediment and biota, to seafood, sewage and cosmetics.
Additionally, Cefas has a well-established vessel based monitoring programme for seafloor litter, generating data that feed into national and international policy, such as the OSPAR Commission’s Regional Action Plan, and measures to combat terrestrial sources of marine litter, including the introduction of the carrier bag charge.