Underweight earthworms — two words you probably didn’t expect to read much less expect to care about — are about to make you deeply concerned. Microplastics in soil can stunt the growth of earthworms essential to soil health and plant growth, a new study out of the U.K.’s Anglia Ruskin University has found.
Microplastics are defined as plastic particles 5 mm or smaller. Previous reports have found microplastics polluting soil, polluting drinking water and food, rainwater, and Arctic snow, and of course, polluting the Pacific Ocean in the form of the Great Pacific Garbage Patch.
In other words, microplastic pollution is everywhere, but we’re only starting to explore whether it has effects on biodiversity (including humans). While according to the World Health Organization, the current level of microplastics in our environment is unlikely to affect humans negatively, this latest study suggests our tiny, annelid relatives may not be so well protected from microplastics in soil.
The researchers explored the effect of three common microplastics on rosy-tipped earthworms, soil pH levels, and the health of ryegrass plants. The first type, high-density polyethylene, or HDPE, comes from plastic bottles and bags. Exposed to HDPE in their soil environment for 30 days, the earthworms lost 3.1% of their body weight.
By contrast, earthworms living in healthy, control soil, gained 5.1% of their body weight in that same period.
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HDPE also reduced soil pH. Soil polluted with the microplastic polylactic acid, or PLA, a biodegradable form of plastic, grew shorter stalks of ryegrass; and in soil contaminated by acrylic and nylon clothing microfibers, fewer ryegrass seeds germinated.
Researchers say the precise reason for earthworm’s weight loss still requires exploration. But they speculate the mechanism by which microplastics affect earthworms could be similar to the mechanism by which their more-studied aquatic cousins, the lugworm, is affected: via “the obstruction and irritation of the digestive tract, limiting the absorption of nutrients and reducing growth,” the study’s lead author, Bas Boots, PhD., a lecturer in Biology at the university, said in a statement.
The findings hold implications for crop production — already under assault from climate change — as well as the maintenance of ecosystems and their biodiversity.
“Earthworms can be called ‘ecosystem engineers’ as they help maintain a healthy soil. They do this through ingesting dead organic matter, therefore contributing to the availability of nutrients,” Connor Russell, a graduate of the MSc Applied Wildlife Conservation course at the university and a co-author of the study, said in the statement. “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.”
