Blue tarps are as much a part of the Maine landscape as pine trees and chickadees. Used for everything from covering stacks of firewood to protecting seasonal machinery, they are a common sight on farms and in yards across the state.
It turns out those ubiquitous sheets of colored plastic could be contributing to the presence of microplastics in the soil. Microplastics are the most abundant form of solid waste pollution on the planet, according to The Shaw Institute in Blue Hill.
Microplastics are loosely defined as any piece of plastic smaller than 5 millimeters across. That’s roughly the size of a small grain of rice. One published study suggests up to 730,000 tons of microplastics end up on agricultural land in the United States and Europe every year.
While no studies have focused specifically on the impact of blue tarps on the problem, there is anecdotal evidence that tiny, blue plastic pieces from tarps are ending up in the environment, including in Maine.
The Maine Department of Environmental Protection did not respond to repeated requests for comment.
One of the indications blue plastic tarp microplastics are affecting Maine was discovered by chance during a University of Maine student research study. Rachel White, a PhD student in ecology and environmental sciences was looking at gastropods — snails and slugs — and the role they play as vectors of parasites on Maine farms. Her research showed that the gastropods’ stomachs contained more than parasites.
White created a synthetic stomach acid that dissolves the gastropods, but left any parasites unscathed. It turns out, the gastropods also contained microplastics.
“We were seeing small microplastics that really piqued our interest,” White said. “They have been ingesting these plastics.”
Much of the microplastic material White was seeing was blue.
Her advisor, Dr. Anne Lichtenwalner, director of the university’s veterinary diagnostic laboratory, said the presence of the plastics was an unpleasant discovery.
“I was surprised and horrified,” Lichtenwalner said. “The process of seeing [the plastics] involved surviving an artificial stomach acid, which suggests they go through the digestive system.”
It also means that whatever eats the gastropods are also ingesting the microplastics they contain, along with any parasites.
“It will work its way up the food chain,” White said. “If the parasites are going into an animal’s body, so are the plastics.”
The digestive system is often where toxic substances such as plastics are broken down and can find their way back into the environment, according to Lichtenwalner.
“If you are going to liberate toxins, the digestive system is a place where it will happen,” Lichtenwalner said.
Microplastics pose a risk to the environment even if they are not broken down.
Once in the soil, studies have shown microplastics can potentially alter soil density, water holding capacity, populations of microbes and influence plant development.
While handy as a temporary cover, blue tarps do not last forever. They eventually degrade and start to fall apart the longer they are exposed to the elements. The older a tarp gets, the more frayed it becomes, with bits of it breaking off and blowing away.
White said she saw a lot of blue tarps and plastics on the farms she visited as part of her study and included questions about them in the research.
“Maine farmers are aware microplastics can be an issue,” said Denise Cole, research assistant on the study. “They want to do something about it.”
Cole said farmers indicated they are open to learning about alternatives to plastics they use on their property. Those include corn- or soy-based products.
“We really don’t know all the kinds of damage these microplastics can do,” White said. “I did find some research that suggests there are negative health impacts so, yes, we need to take notice of them.”