Images of turtles trapped in plastic packaging or a fish nibbling on microfibres pull on the heartstrings, yet many scientists studying plastics in the oceans remain open-minded on the long-term effects.
While plastics shouldn’t be in our oceans, they say there is still insufficient evidence to determine whether microplastics – the very tiniest plastic particles, usually defined as being less than 1mm in diameter – are actually harmful.
It is estimated that over 1,000 turtles die each year from plastic waste. Image: NOAA Marine Debris Program
On top of this, there is debate over how much plastic is actually in the sea and why so much of it remains hidden from view. Much of the research carried out to date is in its early stages – and has so far produced no definitive answers.
‘My concern is that we have to provide the authorities with good data, so they can make good decisions,’ says Torkel Gissel Nielsen, Technical University of Denmark (DTU). ‘We need strong data – not just emotions.’
Searching the sea
Plastic shopping bags can be degraded into microplastics that litter the oceans. Image: Wikimedia Commons
Gissel Nielsen leads a team of researchers who discovered that levels of microplastics in the Baltic Sea have remained constant over the past three decades, despite rising levels of plastics production and use.
The study – by researchers at DTU Aqua, the University of Copenhagen, Denmark, and Geomar, Germany – analysed levels of microplastics in fish and water samples from the Baltic Sea, taken between 1987 and 2015.
‘The result is surprising,’ says Nielsen. ‘There is the same amount of plastic in both the water and the fish when you go back 30 years.’ He claims that previous studies of microplastics levels were ‘snapshots’, while this is the first time levels have been studied over a longer period.
The UK introduced a ban in January this year of the sale and manufacture of products containing microbeads. Image: MPCA Photos
‘The study raises a number of questions, such as where the plastic has gone,’ he says. ‘Does it sink to the bottom, are there organisms that break it down, or is it carried away by currents? Some is in the sediment, some is in the fish, but we need to find out exactly how much plastic is there.’
In the study, more than 800 historical samples of fish were dissected and researchers found microplastics in around 20% of them. This laborious process involved diluting the stomach contents in order to remove ‘organic’ materials, then checking the filtered contents under a microscope to determine the size and concentration of plastics. It illustrates the difficulty of quantifying plastics in any sample, says Gissel Nielsen.
‘You must remove the biology to get a clear view of the plastics,’ he says.
Just as rivers supply the sea with water, they also act as a source of pollution. Researchers at the Helmholtz Centre for Environmental Research (UFZ), Germany, found that 10 large rivers are responsible for transporting 90% of plastic waste into the sea.
The team collected pre-published data on plastics in rivers and collated it with upstream sites of ‘mismanaged’ plastics waste – municipal waste that is uncollected.
‘The more mismanaged plastic waste there was, the more you found in the river,’ says Christian Schmidt, UFZ. ‘There was an empirical relationship between the two.’
The Yangtze river (pictured in Shanghai, China) is the main polluter of plastic in the ocean in the world. Image: Pedro Szekely/Flickr
Eight of these 10 rivers are in Asia, while the other two are in Africa. All of them flow through areas of high population.
‘Countries like India and China have seen huge economic growth – and now use large amounts of plastic food packaging and bottles – but have limited waste collection systems,’ he says. The data include both microplastic and ‘macro’ plastics – but microplastics data dominate ‘because scientists are more interested in that’, says Schmidt.
Plastic Ocean. Video: United Nations
While it is important to measure how much plastic is in the environment, Schmidt believes that the next step of his research will be more important – understanding the journey the plastics make from the river to the sea.
For all the uncertainty and debate over how much plastic is in the sea – and what harm it can do – one thing is clear. Future research is likely to focus more on the plastics that we can’t see, rather than the items we can.