Microplastics in Soil Threatening Growth of Earthworms: Study

Microplastic pollution is not only affecting oceans but also endogeic worms that live in topsoil.  Researchers have recently found that the tiny particles of plastic akin to those bags & bottles are made of topsoil and it appears to be causing earthworms to grow abnormally. Earthworms exposed to plastic chemicals from bottles and carry bags have lost their weight about 3.1%, while those without added microplastics had an increment of 5.1% in weight.

According to a new study, microplastics in soil are threatening the growth of earthworms because Soil with a high percentage of microplastics also lowers soil pH, i.e it makes the soil more acidic.

The main task of Earthworms is to ingest dead organic matter and maintain healthy soil as well as contribute towards the availability of nutrients in the soil. They intake and convert organic material into fertilizer in a process called vermiculture. Many times they are referred to "engineers of the ecosystem", as they improve the soil structure by burrowing, and help drain nutrients and water from the surface. This could impact the ecosystem in a big way as their growth can affect the development of plants and functioning of the soil ecosystem. It is for the first to measure the effects of microplastics on endogeic worms in top soil.

To understand in detail, a team of researchers from the Anglia Ruskin University which is in the United Kingdom examined the impact of different types of microplastics present in the soil such as biodegradable polylactic acid, high-density polyethylene and microplastic clothing fibres on Aporrectodea rosea .

For 30 days they examined both the specimens. They planted Lolium perenne, along with the microplastics and also without adding microplastics. Researchers said, “When it was exposed to PLA microplastics, fewer seeds germinated. There was also a reduction in shoot height with PLA”.

The main reasons behind this weight loss need to be analysed, said Bas Boots lecturer at Anglia Ruskin University.

Boots said, “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”.

Moreover, the presence of microplastics in soil reduced its pH value, while the soil containing PLA reduced the shoot height of the ryegrass. Presence of PLA and clothing fibres caused less germination of ryegrass seeds.  The researchers also added that the size distribution of water stable soil aggregates was also altered when microplastics were present in it, suggesting the potential alterations of soil stability.

Connor Russell, a graduate at ARU and a co-author of the study said that these deep-burrowing species, also called as farmers friend and also act as "ecosystem engineers" to help improve soil structure, clean sewage and also prevent erosion, which can have a significant impact on the environmental. He added more by saying that "It’s therefore highly likely that any pollution that impacts the health of soil fauna, such as earthworms, may have cascading effects on other side of the soil ecosystem, such as plant growth".