Microplastics in Topsoil Stunt the Growth of Earthworms

Worms exposed to topsoil with microplastics lost weight after thirty days.
Donna Fuscaldo

Here's another way plastics are harming the earth: they are stunting the growth of worms. 

That's according to a new study by academics at Anglia Ruskin University, which was published in Environmental Science & Technology.  


First study to measure microplastics impact on earthworms 

The study, which is the first of its kind to measure the impact of microplastics on endogeic worms that live in topsoil, found that after 30 days living with high-density polyethylene or HDPE, which is used to make plastic bottles and bags, earthworms lost about 3.1% of their weight on average.  Earthworms living in topsoil without the microplastic increased their weight by 5.1% in the same time period.  

In addition to harming the earthworms ability to gain weight, researchers found the soil with the microplastics had decreased soil PH. Spoil that included polylactic acid or PLA, which is a biodegradable plastic, resulted in the reduction of the height of ryegrass. When HDPE and microplastic clothing fibers were introduced the number of ryegrass seeds that germinated declined. 

 "The earthworms lost weight overall when certain microplastics were present and grew significantly in weight in soil without added microplastics. However, the specific reasons for this weight loss needs unraveling," wrote Dr. Bas Boots, Lecturer in Biology at Anglia Ruskin University and lead author of the study in a press release. "It may be that the response mechanisms to microplastics may be comparable in earthworms to that of the aquatic lugworms, which have been previously studied. These effects include the obstruction and irritation of the digestive tract, limiting the absorption of nutrients and reducing growth."

Worms play an important role in maintaining healthy soil

So why was studying the impact of microplastics on worms so important?

According to Connor Russell, a graduate of the MSc Applied Wildlife Conservation course at Anglia Ruskin University (ARU) and a co-author of the study earthworms should be viewed as "ecosystem engineers" since they play a role in maintaining healthy soil by ingesting dead organic matter. That, in turn, increases the availability of nutrients in the soil. 

"Their burrowing activity improves soil structure, helping with drainage and preventing erosion. It's therefore highly likely that any pollution that impacts the health of soil fauna, such as earthworms, may have cascading effects on other aspects of the soil ecosystem, such as plant growth," he said in the press release. 

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