Microplastics Found in Commercially Farmed Fish in Trishal Ponds, Raising Food-Safety Concerns
Microplastics — the tiny plastic particles harmful to the environment — have now been found even in commercially farmed fish, one of the country's main sources of protein. Researchers detected the particles in bottom sediment and in 150 fish of six species collected from 25 commercial fish ponds in Trishal upazila of Mymensingh, raising fresh concerns about aquatic environmental quality and food safety.
The findings come from an international joint 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 'Microplastics in Freshwater Aquaculture: Evidence of Sediment-Fish Transfer and Associated Ecological Risks in Bangladesh', has been published in the international science journal Environmental Pollution.
As part of the research, bottom sediment and fish samples were collected from 25 commercial farms in Trishal. The six species were rui, catla, pangas, mrigel, common carp and sarpunti; 25 fish of each species, 150 in total, underwent chemical and microscopic analysis.
The analysis found a total of 90 microplastic particles in the fish digestive tracts — an average of 0.60 particles per fish. Rates varied by species: sarpunti had the highest average at 1.20 particles per fish, while rui and kalibaus averaged 0.68 each.
The proportion of fish containing microplastics also differed by species: pangas was highest at 40 percent and rui 36 percent, while catla and mrigel were 20 percent each and common carp and sarpunti 16 percent each.
Microplastics were found in the bottom sediment of all 25 ponds tested, averaging 11.04 particles per kilogram of sediment. The researchers used the Pollution Load Index (PLI) to measure sediment contamination; values ranged from 1 to 4.5, with some samples showing extremely high levels of pollution.
Particle intake was also linked to the layer of the pond where fish live and to their feeding habits. Bottom-dwelling fish had an intake rate of 52 percent, mid-layer fish 35 percent and surface fish 13 percent. By feeding habit, omnivorous fish showed a 58 percent rate and herbivorous fish 42 percent.
Chemical analysis of the particles revealed several types of polymer. 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 sediment, polyethylene was most common at 39 percent, followed by polypropylene at 27 percent.
Most particles were between 1 and 5 millimetres in size; fragmented and irregular particles and fibres were the most common shapes, and black particles were the most frequent colour at 33 percent. Microplastics are generally defined as plastic particles smaller than five millimetres, formed as plastic waste breaks down in the environment.
The researchers identified plastic bags and packaging from fish feed, nylon and polyester fishing nets, plastic tarpaulins used on pond banks and the erosion of plastic pipes used for irrigation as likely sources. In their view, pond-bottom sediment can act as a long-term reservoir for these particles, which then enter fish digestive tracts through feeding.
Lead researcher Professor Dr Md Badiuzzaman Khan said: 'The study examined the digestive tracts of fish, but did not directly measure how much microplastic accumulates in the muscle of fish that people eat. So this research cannot say with certainty how much microplastic may enter the human body from eating these fish, or what the health effects might be.'
He added that future research must examine microplastics in fish muscle and their combined effects with heavy metals and other harmful chemicals. He also urged proper collection and recycling of plastic bags, nets and equipment used on farms, an end to dumping plastic waste in ponds, the use of eco-friendly materials, and regular monitoring of pond water and sediment quality.
