Microplastics are everywhere, from the tips of the Arctic to the bottom of your bowels. However, their effects on the health of Earth’s inhabitants are still relatively unclear. 

Now, new research has shown that the presence of microplastics in the soil can stunt the growth of earthworms and even cause them to lose weight. Given the huge importance of worms to the wider ecosystems of the world, this is very bad news.

Reporting in the journal Environmental Science & Technology, scientists led by Anglia Ruskin University (ARU) in the UK studied the impact of different forms of microplastics on rosy-tipped earthworms living in a lab. Along with a control tank containing soil and no microplastics, they set up a series of identical tanks that also contained biodegradable polylactic acid (PLA), microplastic clothing fibers, and high-density polyethylene, a material used in the production of plastic bottles and carrier bags. 

Within just 30 days, the worms in the microplastic tank lost an average of 3.1 percent of their weight, while the earthworms living in the control conditions saw their weight rise by 5.1 percent.

While hanging out with microplastics appears to have a notable impact on the worms’ bodyweight, it’s not exactly understood how or why this effect occurs. 

"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 need unraveling,” explained lead author Dr Bas Boots, lecturer in Biology at ARU, in a statement.

"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."

As touched on earlier, the humble earthworm is an important “ecosystem engineer” that plays a fundamental role in the maintenance of healthy soil. Earthworms, along with bacteria and fungi, decompose organic material, which helps to unlock nutrients like phosphorus and nitrogen held within dead lifeforms for others to use. Their burrowing also helps to modify soil structure, allowing for greater aeration and water infiltration, which is crucial for plant growth. 

It’s not yet known how earthworms losing weight could affect these processes, however, given their cornerstone role, it could have knock-on effects right up the food chain and through the ecosystem. 

"Their burrowing activity improves soil structure, helping with drainage and preventing erosion," added co-author Connor Russell, a graduate of the MSc Applied Wildlife Conservation course at ARU. "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."