Microplastics found in pond-farmed fish in first-of-its-kind Bangladesh study

Researchers have now detected microplastics in the sediment and fish of Bangladesh's aquaculture ponds. They say the study is important for understanding how these particles accumulate in fish ponds and enter the aquatic food chain through fish.

The researchers claim this is the first integrated study of its kind on sediment and fish in Bangladesh's freshwater aquaculture ponds. The study was published this month in the international scientific journal Environmental Pollution, titled 'Microplastics in Freshwater Aquaculture: Evidence of Sediment–Fish Transfer and Associated Ecological Risk in Bangladesh'.

The fieldwork was carried out in Trishal upazila of Mymensingh. The area is one of the country's freshwater fish-farming regions, where fish are produced commercially through intensive and semi-intensive methods. The researchers collected samples from 25 selected fish farms during the winter.

Microplastics were found in the sediment samples of every pond. The tiny particles were also found in fish samples. The findings have raised fresh concerns about potential risks to fisheries resources, the environment and public health. Questions have also arisen over how microplastics are entering ponds despite fish being farmed in a controlled environment.

The study was led by Professor Badiuzzaman Khan of the Institute of Environmental Science and Disaster Management at Bangladesh Agricultural University. He said this is the first study of its kind on the presence of microplastics in freshwater farmed fish, and that it could play a major role in assessing potential damage to the country's fisheries resources.

The study's main aim was to determine the presence and characteristics of microplastics in pond-bottom sediment and fish. It also examined the relationship between fish body characteristics and microplastic ingestion, the chemical composition of the plastics, and the associated environmental risks.

In pond-bottom sediment, the study found an average of 11.04 microplastic particles per kilogram. The Pollution Load Index used to assess sediment contamination ranged from 1 to 4.5. Based on this index, the researchers classified most sampling sites as moderately to highly polluted.

The picture for fish is no less worrying. The researchers examined a total of 150 farmed fish of six species. A total of 90 microplastic particles were found in these fish samples, an average of 0.60 particles per fish.

The difference in particle intake between species was notable. In sorputi fish, an average of 1.20 microplastic particles were found per fish. For rui and mrigal, the average was 0.68. In contrast, comparatively fewer particles were found in samples of katla, common carp and pangas, the study said.

By habitat layer, 52 percent of all detected particles were found in bottom-dwelling fish. The rate was 35 percent for fish moving between the bottom and the middle layer, and 13 percent for fish living near the surface. In other words, particles accumulate most in fish that stay close to the sediment — reinforcing the idea of transfer from sediment to fish.

How do these particles get into ponds? Professor Badiuzzaman Khan said: 'Fish are fed a lot of feed. I am not saying all feed is bad. But some feeds contain these. Sometimes floodwater carries microplastics from other places into ponds.' The researchers mainly observed their presence in the fishes' digestive tracts.

Polyethylene (PE) and polypropylene (PP) were identified as the main microplastic polymers in the study. Polyethylene is commonly used in plastic bags, wrapping and packaging. Polypropylene is used in various containers, packaging, ropes and other plastic products.

Public health concerns were voiced by Mahbubur Rahman, an associate scientist and public health expert at icddr,b who has long worked on microplastics. He said the situation has reached a point where microplastics have spread everywhere. There is no proper place to dispose of them, and they are barely processed at all. Noting that microplastics have been found in the human body, he said there is no guarantee that they will not reach the human body from fish.

Those concerned believe more research is needed on what effect microplastics found in fish may have on human health. For now, the message of this study is clear — plastic pollution is no longer just a problem of rivers and seas; it has entered the food chain through pond-farmed fish as well.