Thanks to spectroscopy, scientists are learning more about how microbeads behave in oceans, where they pose harm to marine wildlife and ecosystems
At the beginning of September, the UK government announced plans to ban microbeads in household products by 2017, in a bid to protect the environment, following on from countries such as The Netherlands and the United States.
In several independent studies investigating the distribution and abundance of these particles, Fourier transform infrared spectroscopy (FTIR) was used to analyse micro-plastics in ocean sediment, Arctic sea ice, and UK inland waterways.
The research found that not only are some types of microbeads accumulating in the deep sea, but that increasing quantities are being released into the oceans as Artic sea ice melts at a growing rate.
Microbeads are a type of micro-plastic made up of tiny polymer particles, often used in cosmetic and cleaning products for their abrasive properties. Since most water treatment facilities are unable to process these particles before they are released into the environment, they can pose serious harm to aquatic habitats and wildlife and have the potential to contaminate food chains.
In the UK alone, up to 86 tonnes of microbeads from products such as toothpaste, face scrub and shower gel are washed into the ocean each year, according to the Environmental Audit Committee, and a single shower can result in up to 100,000 plastic particles entering the sea.
In multiple studies conducted in 2014, FTIR was used to analyse samples of micro-plastics using infrared transmission. When IR radiation is passed through a sample, some radiation is absorbed by the sample and some is transmitted. The resulting signal at the detector is a spectrum representing a molecular fingerprint of the sample.
One study found, for the first time, that substantial quantities of micro-plastic debris have accumulated in the deep sea1.
In the study, carried out by researchers from the University of Barcelona and the Natural History Museum in London, 10cm diameter cores of sea-floor sediment from submarine canyons, seamounts, basins and continental slopes were collected. After conducting FTIR spectroscopic analysis, the researchers confirmed that micro-plastics were found in all 12 samples, consisting mostly of 2-3mm length fibres. The results showed that micro-plastics are four times more abundant in deeper regions than on the water surface, inferring that deep-sea sediments are a likely sink for micro-plastics.
In a separate study conducted in several remote locations in the Artic2, cores of sea ice measuring between 1m and 3.5m were taken from various depths. Micro-plastic particles were identified using a Bruker Hyperion 1000 microscope and Bruker IFS66 FTIR spectrometer with a mercury cadmium telluride detector. A Specac DC2 Diamond compression cell (2mm in diameter) was used to allow adequate transmission of IR beam to the detector, and Bruker’s Opus 5.5 spectroscopy software was used for measurement, processing, and evaluation of the spectra.
Between 38 and 234 microbead particles were found per cubic metre of ice – these concentrations were found to be several orders of magnitude greater than those previously reported in Atlantic waters north of Scotland (0.34 particles per cubic metre) and the North Pacific Sub-tropical Gyre (0.12 particles per cubic metre of water).
The study concluded that the Arctic sea ice represents a major global sink for micro-plastic particles, and that when Arctic sea ice melts, synthetic particulates sealed in the ice are released back into the sea. The recent acceleration in the melting of ice caps as a result of global warming is therefore causing an increase of micro-plastics re-entering the ocean.
Research was also carried out in the UK3 to determine the quantity and composition of floating plastic debris entering and leaving the Tamar Estuary in southwest England. Samples were collected from the surface waters and were again analysed with the Bruker spectrometer to indicate the proportions of different polymers.
In total, 204 pieces of suspected plastic were found, 84 per cent of which were confirmed to be micro-plastics (less than 5mm). The most abundant types of plastic were polyethylene (40 per cent), polystyrene (25 per cent) and polypropylene (19 per cent), which are predominantly used in the packaging industry. The study proposed that, because these types of plastics are denser than seawater, the plastics found their way into the shorelines via the sewage system.
1Woodhall et al (2014). The deep sea is a major sink for microplastic debris. Royal Society Open Science. 2(6)
2Obbard et al., (2014). Global warming releases microplastic legacy frozen in Arctic Sea ice. Earth’s Future. 2(6) pp 315–320
3Sadri et al., (2014). On the quantity and composition of floating plastic debris entering and leaving the Tamar Estuary Southwest England. Marine Pollution Bulletin. 81(1)