seas
Microplastics: No negative consequences for fish
Fish embryos develop undamaged despite adherent microplastic fibers (arrows). photo
© Thünen Institute/dpa
Plastic waste in the sea is considered a major threat to the environment. Researchers from Bremerhaven have now examined the effects of microplastics on fish. The result surprises.
Environmentalists warn again and again about the dangers of plastic waste in the oceans. Researchers at the Thünen Institute for Fishery Ecology in Bremerhaven have therefore conducted a study on the effects of microplastics on fish.
For nine weeks, they fed sticklebacks a diet that contained as many microplastic fibers as seawater. For comparison, other fish were given a feed with natural cotton fibers. A third experimental group was fed a fiber-free diet.
Surprising conclusion
The conclusion of the researchers: “According to current scientific knowledge, the small amounts of microplastics ingested by fish in the North Sea and Baltic Sea do not lead to any impairment of fish health and do not pose a health risk to consumers.” Even with moderately higher microplastic concentrations in the sea, the scientists do not expect any significant damage to the fish.
The study by the team led by fisheries ecologist Jörn Peter Scharsack was funded by the Federal Ministry of Food and Agriculture and recently published in the journal “Science of the Total Environment”.
According to the researchers, the North Sea is significantly more polluted with macro-waste than the Baltic Sea. In the study areas of the North Sea, the researchers found 70.7 pieces of waste per square kilometer, in the Baltic Sea 9.6. The waste in the North Sea consisted of 91.3 percent plastic, that in the Baltic Sea 62.2 percent. About 80 percent of plastic waste settles on the sea floor. There, due to environmental influences, it breaks down into smaller and smaller parts, most of which are made of polypropylene.
Microplastics can be found in the bodies of all marine animals studied so far, from plankton to fish to large marine mammals, it said. The researchers first determined the levels of microplastics in the digestive tract of wild fish that were trawled twice a year from the North and Baltic Seas. In particular, dabs – a type of flatfish – and herring were examined. The researchers were able to detect microplastic particles in the digestive tract of dabs, but fewer than ten particles per fish.
In another experiment, the offspring of three-spined sticklebacks caught at the mouth of the Weser near Bremerhaven served as test animals. The researchers investigated the influence of microplastics on the fertilization rates of the fish eggs and the development of the embryos and larvae. The scientists also looked at the immune system of the stickleback. The blood count of the animals showed no evidence of inflammation, explained Scharsack.
Where is the ingested microplastic?
The scientists explained: “Efficient excretion of the fibers with the faeces is expected to prevent harmful effects of microplastic fibers on fish – even at fiber concentrations well above current environmental measurements.”
According to Scharsack, the research results can be transferred to other fish species. “I would go so far as to say that it can in principle be applied to all vertebrates,” says the fisheries ecologist. The basic structures of the intestinal system are comparable in all vertebrates.
Other scientists have repeatedly expressed concern that microplastics harm animals. At the beginning of the year, Melanie Bergmann from the Alfred Wegener Institute explained that almost 90 percent of the examined marine species had an impact. “The documented effects are extremely worrying,” Bergmann said at the time when presenting a study commissioned by the environmental organization WWF.
Scharsack said: “Our studies do not show that the increasing pollution of the sea with plastic is unproblematic. Only concrete indications that the intake of microplastics impairs the health of the fish or inhibits their development have not been found.”