Heavy metals in farmed fish and feed raise exposure concerns in Bangladesh
Farmed fish from a major aquaculture region in Bangladesh carried a chemical burden that reached beyond nutrition and into toxicology. In samples drawn from fifteen fish farms and three upalizas in Mymensingh district, investigators measured twelve heavy metals in fish and feed and found a pattern that places feed quality at the center of the exposure pathway. Fe dominated across nearly all samples, but the broader signal came from the repeated appearance of metals with established health concern, especially Ni, Cr, Pb, and As.
The study collected forty-five fish samples and thirty feed samples between June and August 2022. After acid digestion, the samples were analyzed by ICP-MS, a method suited to trace-level metal detection in complex biological material. Three farmed species formed the core of the analysis: Pangasius, Rui, and Tilapia. Across these species, the highest concentrations repeatedly involved Fe, Ni, Zn, and Cr. In Pangasius, the reported values for those four metals were 20.84, 9.4, 6.60, and 1.86 mg/kg, respectively. Rui showed 25.8, 13.82, 8.91, and 2.00 mg/kg. Tilapia carried 27.58, 7.08, 7.92, and 2.09 mg/kg.
Tilapia carried the heaviest overall contamination burden.
Feed quality emerged as the most direct route of contamination
The fish were not the only concern. Feed samples from farmers and commercial suppliers exceeded WHO/EU standard limits for Cr, Mn, Ni, and Pb. In aquaculture, feed is not a passive input. It is the engine of growth, and when it contains metals above accepted limits, it becomes a direct route by which contaminants enter the food chain. Metals can move from feed into fish tissue through digestion and assimilation, then persist long enough to matter at the consumer level, especially in communities with regular fish intake.
The study also assessed bioaccumulation behavior using a bioaccumulation factor approach. Tilapia showed a strong tendency to acquire As, Co, and Ni from farmer-supplied feed, and As and Se from commercial feed, with BFAF values above 1. In plain terms, the fish were not simply reflecting what was present in the water or feed; they were concentrating certain elements beyond baseline environmental levels. The species comparison placed contamination at Tilapia first, then Rui, then Pangasius.
Risk estimates stayed below intake thresholds but not below concern
The exposure calculations split into two different messages. Mean estimated daily intake for the heavy metals stayed below the recommended daily allowance. For a casual reader, that might sound reassuring. It is only part of the story. Toxicology does not end with daily intake alone, especially when multiple contaminants appear in the same food source and accumulate over time.
For THQ, or target hazard quotient, all values were below 1 except for Fe. A THQ below 1 generally suggests that non-carcinogenic risk from a single element is not expected to be substantial on its own. Yet the combined hazard index told a different story: HI was above the allowable threshold of 1 in all species. This matters because combined exposure can create a cumulative toxic burden even when individual elements remain under their separate thresholds. At the bedside of public health, mixed exposure is often the more realistic problem.
The carcinogenic-risk analysis added another layer. Risk from Ni and Pb consumption was present in all fish species. The study does not provide a cause-and-effect clinical outcome in human consumers, and it does not claim that illness has already occurred. It does show that the exposure profile contains agents with carcinogenic potential, which is enough to warrant regulatory attention and a closer look at upstream contamination controls.
Antibiotic residues suggest a second layer of aquaculture exposure
Heavy metals were not the only residues detected. Antibiotics, especially oxytetracycline and tetracycline, appeared in various fish samples. Their presence points to a separate management problem that sits alongside metal contamination: the broad use of farm inputs without sufficient control over residue carryover. Antibiotic detection does not change the heavy metal findings, but it does deepen the picture of farm-level exposure risk. Fish consumers in the region may be confronting a mixture of chemical residues rather than a single isolated contaminant.
In environmental health terms, this is a feed-chain problem as much as a fish-chain problem. The fish act as sentinels because they integrate what enters the aquatic system through water, sediment, and commercial inputs. When feed contains excess metals, and when fish tissue reflects that excess, the aquaculture system stops functioning as a clean protein source and starts behaving like a vector for low-dose chemical exposure.
Aquaculture oversight now looks like a food safety issue
The findings point toward a practical regulatory priority: feed quality control. Screening feed ingredients, checking commercial formulations against metal standards, and monitoring farm inputs would address the contamination pathway more directly than downstream testing alone. The study comes from a renowned fish-growing district, which makes the signal harder to ignore. High-output aquaculture regions can scale food supply quickly, but they can also scale contamination if oversight is weak.
For consumers, the concern is not one metal in one fish on one day. It is repeated intake over time from a product that is widely eaten and often trusted as a healthy protein source. For regulators, the relevant question is whether feed sourcing, manufacturing, and farm use are being monitored closely enough to keep Cr, Mn, Ni, and Pb below accepted limits. This study suggests that at least some feeds are not meeting that standard.
The work is limited to samples collected in one district over one season, and it does not establish human disease outcomes. Even so, the combination of elevated feed metals, bioaccumulation in fish, HI values above 1, and carcinogenic risk signals for Ni and Pb makes the exposure problem concrete. The remaining gap is not whether the pathway exists; it is how widely it extends across the aquaculture supply chain and how quickly feed oversight can close it.