Microplastic Pollution In Soil, What Does That Mean To Us?
When we think about microplastic pollution, we often think about the ocean. After all, we usually truck our plastic trash off for recycling or the landfill. That should keep it there, right?
Sadly, recent research studies have found that microplastic pollution is a growing concern in farm soil.
Thanks to these scientists, we’re now aware that microplastic can enter plants and impede the growth of plants. This means that animals that eat plants consume the plastic in these plants too.
Obviously, that includes us. I know it isn’t exactly news, we’re already breathing, drinking, and eating microplastic through seafood. Still, now it confirmed that plastic is EVERYWHERE, even in fruits and vegetables!
In the United States and Europe, we deposit 107,000 to 730,000 tonnes of microplastic on agricultural lands annually, which could be more than two times the amount that enters the ocean (93,000 to 236,000 tons).
Where did all these microplastics come from?
Sources and causes
Sewage sludge
A year ago, I wrote about microfiber pollution and how it’s affecting our marine environment. In my research, I came across how plastic microfibers from our clothes shed when we wash and dry them.
I said clothes but it really includes any type of fabric made with synthetic fibers. Anything polyester, acrylic, nylon, or spandex is plastic in the form of textiles. They’re commonly used to make sweaters, fleece jackets, sheets, quilts, soft toys, rugs, upholstery, and etc.
Every time we wash and dry these things, tiny plastic particles break off and go into the drain. At the water treatment plant, filters catch the bigger microplastics while the rest enters the waterways.
Microplastics are plastic particles smaller than 5mm/0.2 inches. In contrast, microfibers are less than 10 micrometers (0.001 mm/about 0.00004″).
Water treatment plants are mostly unable to catch microfibers, but they can catch microplastic. These microplastics end up in sewage sludge which is commonly used as fertilizer at farms.
In Europe and the US, we apply 50% of sewage sludge as fertilizers on agricultural lands, essentially dumping tons of microplastic onto farmlands year after year. In the US, the annual tonnage dumped is approximately 21249 metric tons.
Slow-release fertilizers, coated seed, and plastic mulches
Besides sewage sludge, we’ve also introduced microplastic directly into farm soils in the form of plastic-encapsulated slow-release fertilizers and plastic-coated seeds. The plastic coatings were meant to protect seeds from bacteria and diseases.
These are significant sources of plastic pollution. A 2019 European Chemicals Agency report placed the annual plastic released onto agricultural lands at 10,000 metric tons for slow-release fertilizers, and 500 metric tons for coated seeds.
In addition, some farmers use plastic mulches in place of mulch to keep moisture and warmth in the soil and to suppress weeds. Since the 1950s, farmers have also started using plastic in place of glass for their greenhouses.
These plastics are difficult to recycle and dispose of. They’re often burnt or piled in a corner of their farms where they slowly break down into smaller bits of microplastic.
Naturally, all these sources of plastic breaks down into microplastic that contaminates whatever grows from the soil.
Rain
It’s raining plastic!
Microplastic has been detected in high concentrations air and rain samples in major cities like London and Paris, but studies have found them in the arctic and remote areas all over Europe and the US too.
To find out the extent of plastic pollution over protected areas in the US, Janice Brahney, an assistant professor at Utah State University, conducted a study. She collected atmospheric dust samples and rainwater from 11 National Parks and Wilderness areas in the western US.
Photo by Mark Boss on Unsplash
They found microplastic in 98% of the samples and estimated the number of plastic particles deposited over the area to be the equivalent of 123 to 300 million water bottles.
The biggest source of this microplastic pollution came from synthetic textiles from clothing, carpet, tents and climbing ropes, etc.
Microbeads accounted for 30% of the observed plastic, but they aren’t the microbeads in personal products. The scientists think they might be broken off from paint and coatings.
Consequences of microplastic pollution in soil
What does plastic pollution in the soil mean to us? We don’t know the full effects of soil contamination, but scientists have been researching on it.
Mary Beth Kirkham, a plant physiologist and professor at Kansas State University, conducted an interesting experiment.
She grew wheat plants contaminated with microplastics, cadmium, and both microplastics and cadmium. Cadmium is a very toxic cancer-causing metal commonly released into the environment through car batteries and tires.
She then compared the growth of these plants to plants grown without these contaminants.
More than two weeks later, the plants grown with microplastic turned yellow and wilted. Plants grown only with cadmium-contaminated soil did better, so the plant growth problem was due to microplastics.
Worse, plants grown with soil contaminated with both cadmium and microplastic contained a higher level of cadmium. This is an indication that microplastics act as a vector for cadmium to enter the plant.
The experiment demonstrated three effects of microplastic in soil.
- altered soil characteristics
- impeded plant growth
- contaminated plants – not just with microplastic, but it worsened contamination of whatever chemicals may be lurking in the soil
These effects have been observed by scientists all over the world.
Alters soil characteristics
In a study conducted in Germany, researchers added different types of microplastic to the soil in different concentrations. Then they studied the microplastics’ effect on soil structure and function, water holding capacity, and microbial activity.
They used 4 different types (polyacrylic fibers, polyamide beads,
polyester fibers, and polyethylene fragments) of microplastic commonly found in the environment. And added them in different amounts up to just 2% in concentration. (Plastic has been detected in soil in concentrations up to 7%.)
Though the full impact of microplastic soil contamination still needs to be studied, the results from this study show that microplastic affects fundamental soil characteristics.
In the words of the scientists, “microplastics are relevant long-term anthropogenic stressors and drivers of global change in terrestrial ecosystems.”
Contaminates vegetables and fruits
A group of Italian researchers have detected the presence of microplastic in a variety of supermarket produce like apples, carrots, and lettuce. Apples were the most contaminated, while lettuce were the least contaminated.
The scientists think that the perennial nature of fruit trees allow more plastic to accumulate.
Another study done by Chinese researchers found that plants contaminated with nanoplastics don’t grow as well and have lower chlorophyll content.
They found evidence of nanoplastics bioaccumulating in plants and concluded that microplastic pollution can affect agricultural sustainability and food safety.
Bioaccumulation
The natural question at this point is, what happens to animals (and humans) that consume these plants?
In studies conducted on rats, scientists learned that microplastics can accumulate in the gut, liver, and kidneys, disrupt the metabolism of energy and fat, and cause oxidative stress.
The smaller the microplastic, the quicker and easier it passed into the rat’s tissues and organs. The horror!
Consider Professor Kirkham’s experiment which demonstrated that microplastic can increase the chemical contamination of plants, and the problem becomes worse.
Owing to the characteristic of plastic, it’s easy for microorganisms and pollutants (like lead and pesticides) to bind to its surface.
While we don’t understand the full effects of these contaminated particles on the human body yet, both microplastic and its contaminants can bioaccumulate as we go up the food chain.
For instance, the microplastic enters the plants, cows eat the plant in copious amounts. Over time, microplastics and toxins that entered the plant bioaccumulates. By the time we consume the beef, the plastic and toxin content would be elevated.
As mentioned, it’s not clear what this would do to us, but it can’t be positive.
Now what?
The more I read about plastic pollution, the more evident it is that what I know is just the tip of this nasty iceberg. I’m grateful for hardworking scientists studying climate change and plastic pollution.
The solution to microplastic pollution, if there’s even one, has to be a collective effort. No single country, individual, or profession can solve this problem. Absolutely everyone has to chip in.
As a consumer, there are limits to what we can do, but as usual, I’ll suggest the following:
- Vote for leaders who know about and propose comprehensive climate change solution (a comprehensive solution will include plastic pollution too)
- Listen to and learn from the scientists
- Talk about the plastic and climate issues to everyone who’s willing to listen
- Make lifestyle changes to reduce plastic use
A note about synthetic fibers
Previously, I was in two minds about synthetic fibers. Surely recycled polyester clothes are fine? Plastic down-recycled into stuffings and rugs seems to be a good use of plastic too, but now I’m thinking twice about it.
After all, microplastic from synthetic textiles (including stuffings and rugs) are polluting land, water, air, and even rain.
However, suggesting a wardrobe change is extremely irresponsible if we don’t address our overconsumption of clothes. People may start buying too many natural-fiber clothes and that would tax natural resources.
A better way is to buy secondhand natural-fiber clothes, reduce our polyester clothes use, and go for a high-quality capsule wardrobe rather than a tonne of plasticky clothes.
Microplastics in the soil are irrecoverable and extremely persistent. It’s also a source of marine plastic pollution. So, we need to address our plastic crisis immediately. For all we know, the soil beneath our feet has already begun to change, just as the oceans have.
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