Kasaragod: Microplastics ranging from 90 micrometre to 5 millimetres were found in alarming quantities in the low-lying rice fields of Ernakulam district, posing a threat to future production, according to a study by the Central University of Kerala's Department of Environmental Science.

The study confirmed that two common plastics — polyethene, widely used in carry bags and packaging, and polypropylene, used in durable goods like containers and household items — were present in "high levels" in the surface water of these fields.

The research said microplastics, and the chemicals they release into the paddy fields, were disrupting the ecosystem of phytoplankton—the microscopic floating plants that enhance soil fertility and drive nutrient cycling.

The study, led by Assistant Professor Rishiram Ramanan and his PhD scholar C Amaneesh from the department's Sustainable Resources Laboratory, was published in the latest issue of 'Environmental Monitoring and Assessment', a peer-reviewed journal by Springer.

Amaneesh, a native of Wayanad who works on microplastics, collected and tested water samples from five paddy fields at Kandanad in Ernakulam's Udayamperoor grama panchayat where the 'Uma' variety of rice is grown; and another set of samples from five fields at Kadamakudy grama panchayat, where the 'Pokkali' indigenous variety of rice is grown.

The two places are around 30 km apart but sit on the edge of the Vembanad lake. "We picked the Vembanad region because the lake and its surrounding farmland act as natural buffers against annual floods, which also means they tend to trap plastic waste carried by rain and surface runoff. This makes the region a key area to study emerging pollutants such as microplastics in agriculture," said Dr Ramanan.

On top of it, 'Uma', developed by the Kerala Agricultural University, covers 60 per cent of Kerala's rice fields; and the highly nutritious 'Pokkali' is GI-tagged, salt and flood tolerant, and grown in brackish water fields below sea level, he said. "After the Pokkali rice is harvested, the paddy field is turned into fish farms, which gives us more reasons to study the area," he said, implying that microplastics from the fields could enter the fish, making their way directly into the human body through consumption.

Their study found that microplastic levels were higher during the transplantation stage — 1,370 fragments per cubic metre in 'Pokkali' fields and 1,110 fragments per cubic metre in 'Uma' fields. The numbers translate to around 500 mg per 1,000 litres.

During the harvest season, the levels significantly dropped to 400 and 370 fragments per cubic metre, respectively. "We tested only the water in the fields. The numbers will likely be much higher in the soil sediment. That will be our next phase of research," said Dr Ramanan.

What's the impact on the paddy
To study the impact on rice production, the researchers tested microplastics on two types of phytoplankton. The first, microalgae (Chlorococcum sp.), which helps rice plants by providing growth hormones and essential nutrients. The second, cyanobacteria (Synechococcus sp.), which naturally enriches the soil by fixing nitrogen.

The study found that cyanobacteria's growth fell by 30 per cent, and microalgae's growth shot up by 21 per cent. "The microalgae's ability to adapt to plastic pollution suggests that certain resilient organisms may thrive in plastic-contaminated environments. Over time, these organisms could take over, shifting the balance of life in the water," said Amaneesh. This change might also affect how carbon moves through ecosystems, potentially impacting the environment on a large scale, said Amaneesh.

When the phytoplankton community changes, the beneficial bacteria living around them are also affected, said Dr Ramanan. "This is crucial because certain bacteria, known as plant growth-promoting rhizobacteria (PGPR), are proven to boost rice growth and help plants resist pollution," he said.

In 'Pokkali' rice, for example, microbes in its roots help it tolerate salt. Since plant growth-promoting rhizobacteria are closely linked to phytoplankton, any harm to phytoplankton from microplastic pollution could also reduce rice productivity. "This is especially concerning for climate-resilient crops such as Pokkali," he said.

The first such study on the impact of microplastic contamination on phytoplankton in paddy fields also exposes the problem of unscientific plastic waste disposal in Kerala, said the paper. Given the toxic effects of microplastics on phytoplankton and rice fields, urgent policy intervention is needed to protect food security, it said.