Amazon river basin.

Plastic pollution evidence found in Amazon basin freshwater fish

BRAZIL
Monday, November 19, 2018, 09:00 (GMT + 9)

A team of scientists has found the first evidence of plastic contamination in freshwater fish in the Amazon, highlighting the extent to which bags, bottles and other waste dumped in rivers is affecting the world’s wildlife.

As part of the study, these researchers conducted tests on the stomach contents of fish in Brazil’s Xingu River, one of the major tributaries of the Amazon and revealed plastic particles in more than 80 per cent of the species examined, including the omnivorous parrot pacu, herbivorous redhook silver dollar, and meat-eating red-bellied piranha.

Analysis of the fish’s stomach contents identified a dozen distinct polymers used to manufacture plastic items, including bags, bottles, and fishing gear.

Cluster and shade plot showing diet similarity among 16 serrasalmid species (fish figures from top to bottom): Pristobrycon cf. scapularis, Serrasalmus manueli, Serrasalmus cf. altispinis, Serrasalmus rhombeus, Pristobrycon eigenmanni, and Pygocentrus nattereri (▬ depicting the carnivore species); Myloplus rhomboidalis, Acnodon normani, Ossubtus xinguense, Tometes kranponhah, and Tometes ancylorhynchus (▬ depicting the omnivore species); Myloplus rubripinnis, Myloplus schomburgkii, Metynnis cf. guaporensis, Myloplus asterias, and Metynnis luna (▬ depicting the herbivore species). (For interpretation of the references to colour in this figure legend, the reader should refer to the Web version of this article.)

“It was a sad surprise because in the initial stage of our research the main objective was to understand the feeding ecology of fish, but when we started analysing the stomach contents we found plastic,” said Tommaso Giarrizzo, who studies aquatic ecology at the Federal University of Pará in Brazil.

Violin plot showing the length of plastic particles ingested by the serrasalmid fish from the Xingu River, Brazil ►

In their analysis, published in the journal Environmental Pollution, the scientists describe how 13 of the species had consumed plastics, regardless of whether they were herbivores that fed on river plants, carnivores that survived primarily on other fish, or omnivores.

The herbivores may mistake pieces of plastic for seeds, fruits and leaves, while the omnivores are likely to ingest plastics caught in the feathery river plants, called macrophytes, which make up much of their diet. Meanwhile, carnivores such as piranha are likely to consume plastics when they eat contaminated prey.

Overall, 96 pieces of plastic were recovered from stomachs of 46 fish. Tests showed more than a quarter were polyethylene, a material used in fishing gear that is often discarded in rivers and oceans. Others were identified as PVC, polyamide, polypropylene, rayon and other polymers used to make bags, bottles, food packaging and more.

Summary of trophic network showing plastic debris intake pathways by three species of serrasalmid fish in the lower Xingu Basin

Rivers are responsible for up to a fifth of the plastic waste found in the oceans. Much of the pollution is caused by poor waste management or by rubbish intentionally being dumped in water courses.

Over 90 per cent of the plastic debris that reaches open water comes from 10 rivers, eight in Asia and two in Africa.

Giarrizzo said more research was needed to understand the origin of the plastic in rivers in the Amazon and to assess the impact it may have on human health.

Plastic debris from stomachs of serrasalmid fish from the Xingu Basin. Examples of fragments (AeE) and filaments (F), and of black (A), blue (B), red (C), white(D), and transparent (EeF). Scale bar ¼ 1 mm. (For interpretation of the references to colour in this figure legend, the reader should refer to the Web version of this article.)

One concern, he said, is that hazardous chemicals can bind to the plastics found in fish, and so eating them may lead to a build-up of dangerous chemicals in the body.

"Even though the effects of human consumption of microplastics are largely unknown, our findings are a public health concern since the Amazon has the world’s highest per-capita consumption of fish,” the scientist concluded.


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