Microplastics Found in Farmed Fish in Bangladesh

Microplastics—tiny plastic particles that can persist in the environment—have been detected in commercially farmed fish, a major source of protein in Bangladesh. Researchers examined bottom sediment from 25 commercial fish ponds in Trishal, Mymensingh, and 150 fish representing six species. They found 90 microplastic particles in the fish digestive tracts, while sediment from every sampled pond also contained the particles. The findings raise concerns about aquatic environmental quality and the need to assess food safety, although the study did not determine how much microplastic may enter the human body through eating fish.

The findings come from an international collaborative study led by Professor Dr Md Badiuzzaman Khan of the Institute of Environmental Science and Disaster Management at Bangladesh Agricultural University (BAU). The study, titled “Microplastic in Freshwater Aquaculture: Evidence of Sediment–Fish Transfer and Associated Ecological Risks in Bangladesh,” was published in the international scientific journal Environmental Pollution. It assessed the presence, characteristics and potential environmental risks of microplastics in pond sediment and fish samples from freshwater aquaculture systems in Bangladesh.

90 particles found in 150 fish

Researchers collected bottom sediment and fish samples from 25 commercial aquaculture farms in Trishal. The six species listed in the study were rohu, catla, pangas, mrigal, common carp and sarputi. Twenty-five fish were sampled from each species, bringing the total to 150. The samples underwent chemical and microscopic analysis.

The analysis identified 90 microplastic particles in the fish digestive tracts, an average of 0.60 particles per fish.

The level of microplastic ingestion varied by species. Sarputi had the highest reported average, at 1.20 particles per fish. The average reported for rohu and kalibaus was 0.68 particles per fish each. However, the study’s list of six sampled species names common carp rather than kalibaus, an inconsistency in the source information.

The reported detection rates also varied by species. Pangas had the highest rate at 40 percent, followed by rohu at 36 percent. The rates for catla and mrigal were 20 percent each, while common carp and sarputi each recorded 16 percent.

Bottom-dwelling fish showed greater exposure

Microplastics were found in the bottom sediment of all 25 sampled ponds. The average concentration was 11.04 particles per kilogram of sediment.

The study also found differences associated with fish habitat and feeding habits. The reported ingestion rate was 52 percent for bottom-dwelling fish, 35 percent for fish inhabiting the middle water layer and 13 percent for surface-dwelling fish.

By feeding habit, omnivorous fish accounted for 58 percent of the reported microplastic ingestion, compared with 42 percent for herbivorous fish.

Researchers also analysed indicators of fish condition. The Fulton condition factor, or K value, was highest in sarputi at 2.27. The corresponding values for catla and pangas were 0.35 and 0.37, respectively.

Sediment pollution index reached 4.5

Researchers used the Pollution Load Index (PLI) to assess plastic pollution in pond sediment. The index values ranged from 1 to 4.5, with some samples showing very high levels of pollution.

According to the researchers, pond-bottom sediment can act as a long-term reservoir for microplastics. Fish may ingest the particles while feeding on or near the sediment. Habitat and feeding behaviour could therefore play important roles in determining fish exposure.

Plastic bags, nets and pipes identified as possible sources

Chemical analysis of the fish and sediment samples identified several types of polymers.

In the particles detected in fish digestive tracts, polypropylene accounted for 24 percent, polystyrene 21 percent, polycarbonate 19 percent, cellulose acetate 15 percent, polyethylene terephthalate 13 percent and polyethylene 8 percent.

In pond sediment, polyethylene was the most prevalent polymer at 39 percent, followed by polypropylene at 27 percent.

The researchers identified several possible sources of microplastics: plastic bags and packaging used for fish feed, nylon and polyester fishing nets, plastic tarpaulins used along pond banks, and the degradation of plastic pipes used for irrigation.

Particles measuring 1 to 5 millimetres were prevalent in the fish digestive tracts. The most common shapes were fragments and irregular particles, along with fibres. Black particles were the most common colour, accounting for 33 percent.

More research needed to assess human health risks

Microplastics generally refer to plastic particles smaller than five millimetres. They can form as plastic waste breaks down in the environment. Particles accumulated at the bottom of water bodies may enter fish digestive tracts during feeding.

The detection of microplastics in commercial aquaculture ponds highlights the need to assess aquatic environmental quality and food safety. However, finding particles in the digestive tract does not establish that edible fish muscle contains them at the same level.

Lead researcher Professor Dr Md Badiuzzaman Khan said: “Although the study examined the digestive tracts of fish, it did not directly measure the accumulation of microplastics in the muscle tissue of fish intended for human consumption. Therefore, this study cannot conclusively determine how much microplastic may enter the human body through eating these fish or what the health effects might be.”

He added: “Future research should focus on examining the presence of microplastics in fish muscle and their combined effects with heavy metals and other harmful chemicals. At the same time, plastic bags, nets and other equipment used on fish farms should be properly collected and recycled. Plastic waste should not be dumped into ponds, environmentally friendly materials should be used, and the quality of pond water and sediment should be monitored regularly.”

//DBTech/ARBCN/MSI/MVNO//