Banned DDT Lingers in Bangladesh’s Dried Fish, but Health Risks Stay Low, Nationwide Study Finds

Dried fish, known locally as Shutki, occupies a cherished place on the Bengali table and in the national economy of Bangladesh. Sun-dried Bombay duck and ribbon fish are exported by the thousands of metric tons each year, earning the country millions of dollars, while at home they serve as an affordable protein source for low-income families. Yet for decades a shadow has hung over the product: the suspicion that some processors illegally treat their fish with DDT, an insecticide banned in Bangladesh since 1997, to ward off the insect infestations that flourish in the country’s humid monsoon climate. Vendors have even taken to displaying posters reading DDT-Free Dry Fish to reassure nervous customers. A new nationwide study, published in Food Science & Nutrition, has now delivered the most comprehensive picture to date of DDT contamination in Bangladeshi dried fish, and its findings are largely reassuring, with a few important caveats.

The research team, funded by the International Science Programme at Uppsala University, Sweden, purchased 96 dried fish samples from 44 stations across 32 districts, spanning all eight administrative divisions of the country. Half the samples were Bombay duck, Harpadon nehereus, and half were ribbon fish, Trichiurus lepturus, the two most widely marketed dried marine species in Bangladesh. Sampling took place during the monsoon seasons of 2022 and 2023, a deliberate choice: consumer demand for dried fish peaks when fresh fish becomes scarce, and the season’s humidity and rainfall raise the risk of insect infestation, creating conditions in which illegal pesticide use would be most likely. Dhaka, the largest consumer market, contributed the most samples, followed by Chattogram, a hub of dried fish production and trade.

Chemically, the analysis targeted not just the parent pesticide but its two principal breakdown products, 4,4′-DDE and 4,4′-DDD, which had been largely overlooked in earlier Bangladeshi surveys. The researchers ground each fish sample into powder, extracted the lipophilic contaminants with ethyl acetate using a solid-phase dispersion technique, and cleaned up the extracts through acid sulfonation, which destroys fats and lipids while leaving chlorinated pesticides intact. Quantification was performed by gas chromatography with an electron capture detector, a pairing prized for its sensitivity to halogenated compounds because chlorine atoms have a strong affinity for electrons. The method showed excellent linearity, detection limits below 0.4 micrograms per kilogram, and recoveries between roughly 82 and 97 percent, comfortably within international acceptance criteria.

The headline result is striking: the parent compound 4,4′-DDT was detected in only 10 of the 96 samples, meaning nearly 90 percent were free of the banned insecticide. Where it did appear, concentrations ranged from 1.41 to 11.02 micrograms per kilogram, with the highest level found in a Bombay duck sample from Thatari Bazar in Dhaka. These figures represent a dramatic decline from earlier studies. Work published in 2010 reported total DDT levels in Dhaka market dried fish reaching nearly 11,881 micrograms per kilogram, and other surveys from the 2000s and early 2010s documented residues in the hundreds. The authors attribute the improvement to stricter regulatory control, growing public awareness, and the natural degradation of legacy residues.

The metabolites told a subtler story. 4,4′-DDE ranged from 0.95 to 16.63 micrograms per kilogram, peaking in a sample from Kuakata Shutki Polli in Patuakhali, while 4,4′-DDD reached 17.62 micrograms per kilogram in a sample from Bhola. Total DDTs climbed as high as 29.40 micrograms per kilogram in a Bombay duck sample from Port Road Bazar in Barishal. Statistical analysis revealed significant regional variation, driven almost entirely by a difference between the Barishal and Chattogram divisions, with Barishal, in the lower Ganges-Brahmaputra-Meghna delta, bearing the heaviest burden. The researchers suggest that historical agricultural applications across inland floodplains continue to leach into the delta’s dense network of rivers, which flush legacy residues downstream into estuarine sediments where fish absorb them, a process amplified by monsoonal flooding and runoff.

The relative abundance of the metabolites offers a chemical fingerprint of contamination’s age. DDE forms under aerobic conditions through dehydrochlorination, while DDD arises from anaerobic reductive dechlorination in oxygen-poor sediments. In this study, DDE exceeded DDD in 42 samples, DDD exceeded DDE in only 13, and the two were equal in 41, a pattern indicating that aerobic degradation dominates in the regions investigated. Moreover, the ratio of parent DDT to total DDTs fell below 0.5 in seven of the ten DDT-positive samples, a threshold commonly used to distinguish aged, historical residues from recent inputs. Collectively, these signatures point to legacy contamination cycling through aquatic food webs rather than widespread ongoing application of the pesticide.

There were exceptions, however. Three samples showed parent DDT either alone or with ratios approaching unity, hinting at limited degradation and therefore possible recent introduction. Given that this pattern appeared in only about 3 percent of samples, the authors conclude it reflects sporadic illicit use rather than a systematic practice, echoing findings from coastal China where a small minority of bivalves similarly indicated localized recent inputs. The study’s authors caution that without confirmatory mass spectrometry, which was unavailable to them, the GC-ECD results rest on retention-time matching and validated quantification alone, though the method’s performance parameters support the reliability of the measurements.

On the question consumers care most about, the health risk assessment delivered good news. Using U.S. Environmental Protection Agency models, the team calculated estimated daily intakes based on an average Bangladeshi adult consumption rate of 15 grams of dried fish per day and a body weight of 60 kilograms. Hazard quotients for all three compounds remained far below the safety threshold of 1, with the highest cumulative value, 0.1497, recorded for the Bhola sample, indicating no meaningful non-carcinogenic risk. Incremental lifetime cancer risks were predominantly in the negligible range below one in a million; seven samples exceeded that threshold, all still well within the acceptable band of one in a million to one in ten thousand defined by the EPA. Notably, three of the highest-risk samples all originated from Barishal Division, mirroring the contamination hotspot identified in the residue data. No sample came close to the U.S. Food and Drug Administration action level of 5,000 micrograms per kilogram for fishery products.

The findings place Bangladesh in a favorable position internationally. Comparable low levels have been reported in South Korean seafood, and long-term monitoring in Zhejiang, China, shows declining DDT in coastal bivalves. By contrast, smoke-dried fish in Nigeria has shown concentrations above 700 micrograms per kilogram, and Canadian brook trout still carry legacy residues from aerial spraying in the 1950s and 1960s, a reminder that DDT’s environmental half-life of 4 to 30 years, and far longer in aquatic sediments, means historical contamination can persist for generations.

The authors emphasize that the acceptable risk profile at current consumption rates does not eliminate the need for vigilance. DDT is lipophilic and bioaccumulative, and heavier consumers of dried fish could face greater exposure, while the pesticide’s links to cancer, endocrine disruption, reduced fertility, and developmental disorders justify continued scrutiny. The team recommends intensified monitoring of fish-drying practices, strict enforcement of the pesticide ban, training for processors and retailers in safe preservation methods, and public awareness campaigns. They also call for routine surveillance of other food-chain items, including poultry and dairy, to build a national residue database capable of tracking contamination trends over time. For now, the millions of Bangladeshis who rely on Shutki can take measured comfort in the science: the ghost of DDT still haunts the delta’s waterways, but it is fading from the dinner plate.

Subject of Research: DDT and metabolite residues in dried marine fish from Bangladesh and associated consumer health risks

Article Title: DDT and Its Metabolites in Two Marine Dried Fish Species From Bangladesh: Residue Levels, Distribution Patterns, and Health Risk Assessment

Article References: Ghosh, O. K., Islam, M. M., Nesa, F., Hasan, M. S., Abid, A. A., Arham, S. A. A., Shoeb, M., & Mamun, M. I. R. (2026). DDT and Its Metabolites in Two Marine Dried Fish Species From Bangladesh: Residue Levels, Distribution Patterns, and Health Risk Assessment. Food Science & Nutrition, 14(9), Article e72286. https://doi.org/10.1002/fsn3.72286

Image Credits: AI Generated

DOI: 10.1002/fsn3.72286

Keywords: DDT, dried fish, Bangladesh, pesticide residues, food safety, organochlorine pesticides, DDE, DDD, health risk assessment, Bay of Bengal, GC-ECD, bioaccumulation