Photo: Colourbox

The oceans are overflowing with plastic

Monday 08 Sep 14
Plastic waste in the world’s oceans is an environmental problem that is gaining increasing global attention. At DTU, researchers are investigating the problem.

By Lotte Krull and Line Reeh

This spring, the media was full of stories about lakes of waste the size of Spain, Texas or even Africa, floating about the world’s oceans. Some of this waste consists of plastic, and as yet, no one knows the impact on the marine ecosystem, marine life and thus our food. However, researchers are now investigating the problem further.

According to the National Oceanic and Atmospheric Administration in the USA, most of the plastic consists of microwaste—i.e. fibres and particles smaller than half a centimetre. The smallest particles are invisible to the naked eye. Bags, bottles and personal care products such as soap and creams are among the contamination sources.

This is what DTU is working on:  

How much plastic is in the oceans?
Plastic is prevalent everywhere. A literature review conducted by Professor Torkel Gissel Nielsen, DTU Aqua, shows that plastic waste is present in all of the world’s oceans.
During the research vessel Dana’s eel expedition to the Sargasso Sea in the Atlantic Ocean in spring 2014, two PhD students collected water samples using a special filter that captured microplastic particles as minute as 0.01 mm. DTU Aqua is now analysing these water samples under the microscope. Once completed in the autumn of 2014, the analyses will provide new unique data on the concentration of microplastic from the Danish coast across the open Atlantic Ocean to the Caribbean. 
Sources: Professor Torkel Gissel Nielsen, DTU Aqua and PhD students Kristina Enders and Robin Lenz, DTU Aqua.

What happens to the plastic?
It is highly probable that the copepod inadvertently swallows microplastic waste because it is the same size as the plant plankton on which it feeds. Thus, the plastic either continues further up the food chain when the copepod is consumed by fish or it sinks down to deeper water strata as part of the copepods’ excrement.
But that does not mean that the plastic has disappeared: it may be absorbed into the ocean floor, consumed by deep-sea marine life or recirculated with seawater. Professor Torkel Gissel Nielsen’s group at DTU Aqua is currently conducting laboratory tests to determine the extent to which water fleas eat microplastic and where it ends up in the food chain.
Sources: Professor Torkel Gissel Nielsen, DTU Aqua.

Photo: Colourbox

Is plastic present in fish stocks?
“Yes!” In autumn 2013, DTU Aqua conducted a pilot study in the Great Belt. Approximately 100 herring and whiting were captured and examined. About 30 per cent showed evidence of microplastic in their stomachs, suggesting that fish in Danish waters swallow plastic waste.
International studies have shown that the same is true for fish in the North Sea and the English Channel, the Baltic Sea and the Clyde Sea in Scotland. Lobsters, mussels, herring and several examined species contain plastic waste.
DTU Aqua recommends that Denmark examine a wider range of fish species and sizes with an extended geographical spread in order to gain a more detailed assessment of the scope of the problem. The studies could be included in existing fishery monitoring.
Sources: Senior Officer Thomas Kirk Sørensen and Associate Professor Colin Stedmon, DTU Aqua

Does this mean the fish are inedible?
Nobody knows. The plastic may constitute two potential problems for fish as a food source:
• The microscopic plastic waste can be absorbed by the fish, so that plasticizers, for example, accumulate in the meat.
• Large plastic particles can bind chemicals and environmental toxins, which are then absorbed by the fish.

DTU Aqua and DTU Food are working together under the auspices of the European research programme EC Safe Seafood to identify the impact of plastic waste on fish as a food source.
In the coming year, DTU Aqua in Hirtshals will give salmon and bream feed containing microplastic and different chemicals, including brominated flame retardants, methylmercury and perfluorinated chemicals.
The fish meat will be examined for chemicals to determine whether the substances accumulate in the fish or whether they are eliminated. 500 fish of each species will take part in the research study. Initial results will be published in 2015.
Sources: Senior Researcher Professor Bodil Katrine Larsen, DTU Aqua and Senior Researcher Professor Kit Granby, DTU Food

 Article from DTUavisen No. 7, September 2014.
17 APRIL 2021