Microplastics In The Food Chain: A Cross-Generational Look
Eurasian dippers (Cinclus cinclus), live and breed in freshwater areas. They eat aquatic invertebrates, including small shrimp and fish, and bring food to their offspring for the first thirty days of their lives. Because transporting food in their beaks over long distances is risky, dippers use a regurgitative feeding strategy: they throw up small amounts of food in the beaks of their young. This is a natural process for many birds, but what happens if what they eat is not entirely natural?
We know that plastic is abundant in the natural world. Recently, a group of ecologists found that free-living Eurasian dippers in South Wales (U.K.) eat plastic indirectly (through their prey) and feed it to their offspring.
The researchers measured the presence of plastics in dippers by collecting samples of fecal and regurgitated pellets from rocks at fifteen different river sites. Over a period of six months (Winter and Summer), they collected 166 samples in which they counted and identified suspected plastic particles. About half of the plastic particles were then analyzed using Fourier transform infrared (FT-IR) spectroscopy to confirm the type of plastic. To limit the contamination of the samples (e.g. from fibers of their own clothing) the researchers took a variety of preventative measures, such as using as few plastic materials as possible.
The researchers found that plastics are indeed transferred in food webs, with about 50% of dipper regurgitate samples containing plastic. The feed of young dippers was also contaminated by plastic: 45% of fecal pellets of both adults and chicks contained particles. Finally, the concentrations of plastics in these pellets was higher in the most urbanized areas along the river.
Fibers of polyester and polymer mixtures fibers were the most common (94.8%) plastic particles found in the dipper pellets. These types of plastic are found most frequently in textiles, reinforced concrete, and fishing lines. Wastewater treatment, urban drainage, and increased road density, as well as the large amount of everyday plastic used by locals, are main causes of plastic pollution in river catchments.
The study is based on the assumption that the dippers did not eat plastic directly. It is supported by the fact that the invertebrates the dippers typically eat are known to be contaminated by microplastics, similar in shape and size to those found in this study. Furthermore, the plastic particles found in the pellets were so tiny that the dippers could not have confused them with their usual prey and accidentally eaten them.
All in all, the researchers’ calculations suggest that a single dipper ingests and excretes an average of 200 plastic particles each day, some of which are transferred to their young. Not all ingested plastic stays in the dipper’s body (or that of their offspring). However, the fact that some of the plastic leaves the body does not take away from the ingestion itself. Lab studies have shown that the consumption of plastics has negative consequences for growth, development, reproduction, and even survival, for various water organisms. The authors of the present study urge that more research be done to properly assess what the consequences of consuming microplastics are on the ecosystem more broadly, and for animal advocates, the study shows yet another example of how animal welfare and the environment are linked.