Study shows plastic used for mulching leading to soil contamination

Plastic sheets being used for mulching — a practice of covering the soil to retain temperature and moisture to facilitate higher crop production are leading to microplastic pollution in agricultural soil, according to a new study.

Microplastics are tiny plastic materials less than 5 mm in diameter and are regarded as a major source of plastic pollution in the environment.

NGO Toxics Link tested soil samples in agricultural belts in Karnataka and Maharashtra under the study titled Plastic Mulching: Microplastics in Agricultural Soils and found tiny plastic particles at various depths, indicating soil contamination due to the rampant use of plastic mulch sheets.

A total of 30 samples were collected from mulched and un-mulched fields and dumpsites — areas being used by farmers to dump used plastic sheets, other plastic waste and waste material — from varying depth in the selected regions.

The soil samples were tested at the Manipal Academy of Higher Education and microplastics were detected in all of them.

The abundance of microplastics in the mulched soil samples was much higher than the un-mulched soil samples. This clearly points towards a possible contamination of soil due to the usage of plastic mulch sheets, the report read.

The highest microplastic contamination — 87.57 pieces per kg of soil — was found at a dumpsite in Maharashtra. This was almost double the abundance in mulched soil, indicating that plastic mulch sheets dumped around the agriculture area cause pollution, the researchers said.

In case of all mulched soil samples, the highest concentration of microplastics 40.46 pieces per kg of soil was found at a depth of 15 cm in Badgaon in Maharashtra, whereas the lowest concentration of 8.45 pieces per kg of soil was found at a depth of 30 cm in Khanapur in Karnataka.

Among all un-mulched sites, Aurnol in Maharashtra recorded the highest concentration (20.54 pieces per kg) of microplastics at a depth of 15 cm, while Hukkeri in Karnataka had the lowest concentration (2.83 pieces per kg) at the same depth.

Use of plastic in modern agriculture is jeopardising the overall sustainability of our ecosystem. The plastic used for mulching is relatively thin, and the removal and recycling of these plastic films from the agricultural field is labour intensive, costly, and challenging.

Consequently, it remains in the field or is dumped nearby and ultimately disintegrates into micro-particles (microplastics), accumulating in the soil. The microplastic contamination in the soil can also result in their uptake by plants or crops, affecting the environment and human health, said Priti Banthia Mahesh, Chief Programme Coordinator, Toxics Link.

Mulching has been in use globally for centuries, using dry leaves, straw, trash, etc. for water conservation. The use of plastic film in mulching is a recent development worldwide, and in India, it has been around only for a few decades. The idea of using polyethylene film as mulch in plant production saw its beginnings in the mid-1950s and plastic mulch was first noted for its ability to increase soil temperature.

A recent study detected microplastics in human blood for the first time, with scientists uncovering the tiny particles in nearly 80 per cent of the people tested.

A study conducted by Toxics Link in 2020 detected microplastics in the Ganga at Haridwar, Varanasi and Kanpur. Another study conducted by Toxics Link had found microplastics in tap water samples collected from different parts in Goa.