57% of Species: Startling Numbers of Small Mammals Are “Plastic Positive”

Microplastic on Finger

A new study reveals the impact of microplastics on small mammals.

More than half of the species investigated had traces of plastic in their excrement, according to researchers looking into how much plastic small mammals in England and Wales were exposed to.

More than half of the species whose feces were analyzed had evidence of plastic in them, according to researchers looking into how much plastic small mammals in England and Wales were exposed to.

Researchers from the University of Sussex, the Mammal Society, and the University of Exeter claim in a study that was published in Science of the Total Environment that the concentrations of plastic excreted were equal to those found in human studies.

Fiona Mathews, Professor of Environmental Biology at the University of Sussex, states, “Much is known about the impact of plastic on aquatic ecosystems, but very little is known about the same with terrestrial systems. By analysing the droppings of some of our most widespread small mammals, we’ve been able to provide a glimpse of the potential impact plastic is having on our wildlife – and the most commonly found plastics leaking into our environment.”

Graduate Emily Thrift, Professor Fiona Mathews, Dr. Frazer Coomber, and the Mammal Society, together with Dr. Adam Porter and Prof. Tamara Galloway of the University of Exeter, wrote the paper. It identifies plastic polymers in four of the seven species for which they obtained fecal samples. The brown rat, field vole, wood mouse, and European hedgehog were all discovered to be plastic positive.

Researchers discovered that plastic ingestion was occurring across locations and across different dietary habits, from herbivores, insectivores, and omnivores, contrary to their expectations that samples from urban areas would have higher plastic concentrations and samples from herbivorous species would have lower plastic concentrations.

Emily Thrift, a graduate of the University of Sussex, says “It’s very worrying that the traces of plastic were so widely distributed across locations and species of different dietary habits. This suggests that plastics could be seeping into all areas of our environment in different ways. We’re also concerned that the European hedgehog and field vole are both species suffering declines in numbers in the UK.”

Using equipment at the Greenpeace labs at the University of Exeter, the team analyzed 261 fecal samples, with 16.5% containing plastic. The most common types identified were polyester, polyethylene (widely used in single-use packaging), and polynorbornene (used mainly in the rubber industry). Polyester accounted for 27% of the fragments identified and was found in all the plastic positive species, except the wood mouse. Widely used in textiles and the fashion industry, the paper explains that microfibres can enter the wastewater system through household washing and subsequently end up on the land through the use of sewage sludge as fertilizer.

Over a quarter of the plastics found in the study were also ‘biodegradable’ or bioplastics. The authors warn that while these types of plastics may degrade faster than polymers, they can still be ingested by small mammals and further research is needed to investigate their true biological impacts.

The authors believe that the microplastics found in the study are likely to have entered species’ guts as a result of the consumption of contaminated prey or through direct ingestion. With ingestion, researchers believe species could be mistaking plastics for food or chewing macroplastics used as nesting material or to escape entanglement.

The potential impact of plastics on the food chain is another issue the authors are concerned about, and urging further study into.

Prof. Fiona Mathews adds, “We really need to get a deeper understanding of the implications of plastic ingestion on land mammals – and the potential impacts this has on their conservation status. In our study, droppings from European hedgehogs carried the highest quantity of plastic polymers. As a species, they are already in decline in the UK for reasons that are largely unknown, and they are classified as Vulnerable to Extinction on the IUCN-compliant regional Red List.”

He continues, “European hedgehogs consume earthworms and previous studies have found these to contain microplastics. So we really need further research to establish the scale and route of exposure more precisely, and to assess prevalence in predatory species that consume small mammals, so that we can take adequate steps to try to protect our declining wildlife from plastics.”

Andy Bool, CEO of the Mammal Society states, “The Mammal Society is proud to have helped and part-funded this research as it represents an important step into the study of the impact of plastics on terrestrial mammals. With a number of small mammal species experiencing worrying declines in numbers it highlights one of the challenges they face. We can all make a difference to help protect them from this threat by reducing the amount of single-use plastic we use and reusing and recycling what we do use properly.”

Dr. Adam Porter, NERC Post-Doctoral Research Fellow at the University of Exeter says, “In the UK, plastic pollution can often seem like a problem somewhere else when most images are of polluted shorelines of tropical landscapes, or charismatic organisms like turtles or sea lions. This study brings the focus home, into our lands and in some of our much-beloved mammal species. Further, it demonstrates that the amount of plastic waste we produce is having an impact. We must change our relationship with plastic altogether; moving away from disposable items and moving towards replacing plastic for better alternatives and establishing truly circular economies.”

Reference: “Ingestion of plastics by terrestrial small mammals” by Emily Thrift, Adam Porter, Tamara S. Galloway, Frazer G. Coomber and Fiona Mathews, 24 June 2022, Science of The Total Environment.
DOI: 10.1016/j.scitotenv.2022.156679

The study was funded by the Natural Environment Research Council, The Mammal Society, the University’s Fund for Animal Welfare (UFAW), and the Jubilee Trust.

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