River ecosystems and microplastics
We are used to linking the problem of microplastics to the oceans and seas. Our first thought goes to the fish that eat these plastic microparticles, bringing them to our tables and our stomachs. It’s because of this that we get surprised to know that the problem is going up the food chain of ecosystems that we thought were far from the invasion of plastic pollutants.
A British study recently published in Global Change Biology by a team of researchers from the universities of Cardiff and Newcastle, in collaboration with the Greenpeace Research Laboratories of the University of Exeter, opens our eyes to the real impact of the issue. The research entitled "Food-web transfer of plastics to an apex riverine predator" shows, unfortunately leaving little room for doubt, how plastic has reached the top of the river ecosystem food chain. And yes, even the predatory birds that populate the banks of the rivers ingest large quantities of plastic every day.
The research carried out on dipper
According to the researchers, this would be the first scientific evidence of how plastic has now reached most of the wildlife making its way along the food chain. It was already known that small plastic fragments (up to 5 mm) also polluted the waters of rivers. What was not clear was the impact on the animals that inhabit this ecosystem. Scientists then studied the microplastics found in the Eurasian dipper or golabianca dipper (Cinclus cinclus), discovering that these animals eat hundreds of them a day, also transferring them to their chicks.
This animal lives by diving into streams and rivers to hunt aquatic insects. Previous research on Welsh river insects had already shown that more than half of these were contaminated with polypropylene, nylon or polyester particles. It was therefore widely predictable, even if not proven so far, that plastic was making its way into the freshwater food network: fish, birds and small mammals have now been reached by this growing plastic "wave" that passes from insects to all components of the ecosystem, from animals to animal and from parent to cub, without sparing anyone.
The team of researchers analyzed excrements and boluses regurgitated by this small river bird in about fifteen sites between Brecon Beacons (South Wales Natural Park) in Severn Estuary, estuary of the longest English river. Out of the 166 samples examined, both from adult specimens and from nestlings, about half had plastic particles. The concentration of fragments was greater in urban areas and the particles were mainly attributable to textile and construction material.
According to what scholars have calculated, each specimen of dipper gets to swallow 200 plastic particles every day.
From rivers to seas, to oceans: nobody is spared
The study in question represents another worrying step in the dramatic awareness of the impact of plastic on natural ecosystems. We knew that these microscopic but lethal pieces of plastic were now also present in the ocean depths and from there they had gone up the marine food chain up to whales, dolphins, crustaceans and sea birds. It was quite probable that rivers and their small inhabitants were not exempt from this plague since the water cycle is clear: before reaching the sea, the water passes right there. And the particles of textile fibers, tire powders and other microplastics inexorably follow the same path, threatening the health and existence of all living beings that inhabit these environments.