Study finds high level of microplastics in salt

A recent study has found a surge in harmful microplastics in sea salt produced over the last couple of years in the country.

Researchers from Noakhali Science and Technology University (NSTU) have detected 560 to 1,253 plastic particles per kilogram of raw salt collected from 12 salt-producing sites in Cox's Bazar and Chattogram.

The study, published in the acclaimed Amsterdam-based Regional Studies on Marine Science journal in June this year, has found 9, 640 microplastic particles from 12 kgs of raw salt. It has also revealed that offshore salt pans are more contaminated with microplastics than those onshore.

The study was conducted by a group of researchers from the oceanography department and the environmental science department of NSTU.

The presence of microplastics in the recent study was much higher than that of another study conducted in 2021 when researchers found 78 to 137 particles per kg of raw salt.

The previous study was jointly conducted by Bangladesh Oceanographic Research Institute (BORI) and the fisheries and marine science department of NSTU. Titled "Microplastics pollution in salt pans from the Maheshkhali Channel, Bangladesh", it was published in the peer-reviewed, multidisciplinary Nature Journal in November 2021.

Salt, composed of sodium chloride, is produced in the south-eastern coastal belt of the country. It is an essential part of our diet and an inevitable mineral for the human body.

Experts believe the increased presence of microplastics in salt may pose threats to public health.

The contamination in raw salt is caused mostly by toiletries products like soap, facewash, cleanser, and different kinds of packaging and single-use plastics, according to researchers.

Sultan Al Nahian, scientific officer of BORI and a part of the research team that conducted the 2021 study, told The Daily Star that the findings of the recent study suggested an alarming development.

"As the recent study has found more microplastics in salt than ours, I find it alarming that our sea is now more polluted given its exposure to transboundary and domestic plastic waste. We should take urgent action to rein in the microplastic pollution," he said.

The 2023 study has found the highest concentration of microplastics in Kutubdia, an offshore island. For each kg salt, the pan in South Kutubdia had 1,253 particles while North Kutubdia had 1,026 particles, reads the study.

24 percent of the particles were black followed by 17 percent transparent and 15 percent yellow. Dominance of black perhaps is explained by black threads and ropes used by the fishermen and also by black plastic cover, which farmers use to preserve salt, according to the study.

The size of the plastic particles ranges from 0.3 to 1.5 micrometres, most of which are fibres and foams, the researchers have found.

The 12 sites that were chosen for collecting samples for the study were Napitkhali, Maheskhali, Badarkhali, Chanua, Ilishia, Darbeskhata, South Kutubdia, North Kutubdia, Rajakhali, Puichari, and Gurakhali from Cox's Bazar; and the only salt pan from Chattogram district was selected from Dulahazara.

Concentration of microplastics in salt pans varies from one place to another depending on the level of pollution of sea waters.

The average of microplastics found in Bangladesh is 803 per kg of salt while it is 1,690 in Sri Lanka, 1,500 in China, 1,200 in Korea, 900 in Vietnam, and 700 in Thailand, says the study.

In India, the average of microplastics is 35 to 575 per kg of sea salt, according to a study jointly conducted by the Centre for Environmental Science and Engineering and the Indian Institute of Technology.

Mohammad Abdul Momin Siddique, assistant professor of the department of oceanography at NSTU, told The Daily Star that their study suggests surface seawater in the south-eastern coast of Bangladesh is highly contaminated by microplastics.

He said the study demonstrates that the coastal waters of Bangladesh have been polluted with plastic particles, and that the sites which are located offshore have higher concentration of microplastics.

"Filtering out seawater at the mouth of the dyke, through which the seawater flows into the salt pans, can reduce the presence of plastic particles including microplastics," he said.

A study done by the department of environmental sciences at Jahangirnagar University (JU) last year confirmed the presence of microplastics in commercial salt. They collected several packets of salt manufactured/produced by ten different brands, as well as three samples of raw salt.

The samples the JU researchers studied contained microplastics between 370 and 7,400 per kg of salt. The study concludes that each year a person's intake of microplastics is 13,088.

Fahmida Parvin, assistant professor of the department of environmental sciences at JU told The Daily Star that among the different sizes of microplastics they extracted from the samples, higher concentration has occurred in commercial salt with a diametre less than 0.5 mm and transparent colour.

"That's why it may be difficult to remove the microplastics from salt during the purification process," she added.

Public health expert Dr Lenin Chowdhury told The Daily Star that gradual intake of microplastics could harm the human body at multiple stages.

"It primarily impedes the digestive enzyme in the human body, which may lead to the dysfunction of the stomach. Not only that, at one stage, it will prevent the liver and kidney from functioning normally," said Lenin.

"Policymakers must take it seriously, as it poses a huge threat to our public health," he noted.

Sarwar Hossen, deputy general manager (Salt Cell) of Bangladesh Small and Cottage Industries Corporation, told The Daily Star that they wrote several letters to the research team, requesting them to outline a course of action to contain microplastic contamination in seawater. But they didn't receive any reply.

"We will treat the matter seriously as it's appearing as a public health crisis", he said.