Scientists: Plastic mulch sheets deliver microplastics to the food we eat

Scientists have found that plastic mulching sheets used by farmers lead to microplastic pollution, and the particles find their way into the human body through the food we eat.

Toxics Link, an environmental non-profit organisation in India, tested soil samples in agricultural belts in Karnataka and Maharashtra states.

Experts 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 researchers say.

Experts define microplastics as tiny plastic materials less than five millimetres in diameter.  

“The soil samples were tested at the Manipal Academy of Higher Education and microplastics were detected in all of them,” the study observes.

“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 use of plastics in modern agriculture is jeopardising the overall sustainability of our ecosystem, said Priti Banthia Mahesh, chief programme coordinator at Toxics Link. The plastic used for mulching, she said, is relatively thin and the removal and recycling of these plastic films from agricultural fields 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,” she said.

In Kenya, Mr Rafael Wabuge, a large-scale farmer in Kitale, told the Nation that microplastics are a big issue.

“Root crops like carrots and potatoes have a tendency of growing around stones and plastics, which nowadays make their way to farms due to the careless nature of humans,” he said.

“When rain falls, microplastics jump to bean pods and other foods growing and when we harvest them we carry them along unknowingly.

Fruits and fruit juices

“In Kitale, however, I have seen fellow farmers go back to using saw dust and dry grass for mulching purposes and so it is the big farms owned by companies that process, for example, fruits and fruit juices for export and greenhouse farmers mostly that love using mulching sheets.”

Griffins Ochieng, the executive director at the Centre for Environmental Justice and Development in Nairobi agrees with Mr Wabuge.

“Plastics are fossil fuels made of polymers and different types of toxic chemicals. When some people look at mulch sheets as a solution, they do not realise the impact their ‘solution’ has to our health,” he said.

It takes more than 300 years for polythene plastic, which is mainly used as mulching film, to break up in the soil into microplastics that pose a greater danger to nearly all life forms, said Kevin Lunzalu, the co-founder of the Kenyan Youth Biodiversity Network and a 2022 Aspen New Voices fellow.

“While the use of plastics as essential farming products has gained popularity across Kenya, many farmers do not understand that several generations down the line will suffer from the environmentally harmful effects of commodities currently in use,” he said.

“Globally, about 454 million kilograms of plastics are used on farms each year. Of these, mulching materials contribute the third-highest percentage. As a country whose economy is largely supported by agriculture, Kenya’s use of plastic in the farming sector is significant, which calls for targeted plastic waste management systems and policies.”

Various processes

He added: “With a size as small as a grain of rice, microplastics are transported to agricultural lands through various processes, including on-site and off-site activities. Fertilisers, mulching materials, seed coatings, and single-use agro-chemical packages are a few examples of farm-based sources of microplastics.”

Other sources include rainwater runoff, windblown plastics and sewage sludge.
“Yes, that pit latrine located next to the maize plantation could be slowly releasing microplastics to the adjacent lands and in the soil, microplastics reduce soil productivity by curtailing aeration and proper flow of nutrients by limiting the performance of soil microorganisms,” he said.

“The chemical and biological characteristics of microplastics make it possible for them to be transported up the plant through the water absorption process by the plant roots.”

Once absorbed by the plant, Mr Lunzalu said, these tiny bits of plastic then go to various parts of the plant, including the food storage areas that are usually harvested by humans.

“For root vegetables such as carrots, the fruit itself could be the main store. It is, hence, possible that the plastics you feed the farms could be coming right back to your plate and form part of your diet,” he said.

“The phrase ‘garbage in, garbage out’ rings home for microplastics.”

Earlier this year global researchers who took blood samples from anonymous, healthy adults and looked for plastics that were between 700 and 500,000 nanometres – around 140 times smaller than the width of a human hair – found plastic in the blood of 17 of 22 study participants, about 77 percent of them.

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