The central mechanism the review dissects is bioaccumulation, the process by which fish take up metals from water, sediment, and food faster than they can excrete them. Fish absorb dissolved metals primarily across the gills, which are in constant, intimate contact with the surrounding water, while additional uptake occurs through the skin and the gut. Because metals bind to proteins and are stored in organs such as the liver, kidney, gill, and muscle, concentrations inside fish can exceed those in the ambient water by orders of magnitude. Scientists quantify this with two key indicators: the bioconcentration factor, which compares metal levels in fish to levels in water alone, and the bioaccumulation factor, which also accounts for dietary uptake. On top of bioaccumulation sits biomagnification, the stepwise increase in metal concentrations as contaminated prey is eaten by larger predators up the food web. Mercury is the textbook case—methylmercury, its organic and most toxic form, magnifies so efficiently that apex piscivorous fish can carry concentrations thousands of times higher than the water they swim in.

The five metals chosen for the review each follow distinct chemical routes into aquatic systems. Arsenic enters water through geogenic sources such as arsenic-rich bedrock and through anthropogenic activities including mining, pesticide use, and industrial discharge. Mercury is released by coal combustion, artisanal gold mining, and industrial processes, and once in aquatic environments, anaerobic bacteria convert inorganic mercury into methylmercury, the form that penetrates food webs most effectively. Cadmium arrives via metal smelting, electroplating, phosphate fertilizers, and electronic waste. Chromium contamination stems largely from leather tanning, electroplating, and pigment manufacturing, with the hexavalent form, chromium VI, being far more toxic than the trivalent form. Lead persists from leaded fuel legacies, batteries, paint, and mining runoff. The review emphasizes that both anthropogenic and geogenic origins must be understood together, because background geological contributions can mask or compound industrial pollution in any given watershed.

Inside fish, the toxicological consequences unfold at every level of biological organization. At the molecular scale, metals generate reactive oxygen species, overwhelming antioxidant defenses and damaging lipids, proteins, and DNA. Metals also interfere with essential ions: cadmium, for example, mimics calcium and disrupts calcium transport, with studies showing reciprocal enhancement of cadmium uptake and toxicity in trout liver mitochondria. Fish respond by inducing metallothioneins, small cysteine-rich proteins that sequester metal ions, but this detoxification capacity has limits. At the tissue level, the review catalogs classic histopathological damage: gill epithelial lifting and fusion that impair respiration and ion regulation, liver necrosis and vacuolization, and kidney tubular degeneration. Gill damage is particularly significant because the gill is the first point of contact and a sensitive pollution biomarker.

Physiological and behavioral effects extend the damage beyond individual cells. Chronic metal exposure alters blood parameters, suppresses immune function, and impairs reproduction—recent zebrafish studies reviewed in the paper show that dietary arsenic exposure reduces reproductive output and disrupts offspring development across generations. Behaviorally, metals can scramble the chemical alarm signals fish rely on to detect predators; cadmium-exposed juvenile rainbow trout, for instance, fail to mount normal anti-predator responses. Olfactory toxicity is a recurring theme, with cadmium, zinc, arsenic, and chromium all shown to impair the neurobehavioral pathways that larval fish depend on for finding food and avoiding danger. Such sublethal effects may not kill fish outright, but they erode population fitness in contaminated ecosystems.

For humans, the exposure route of greatest concern is dietary—fish and seafood are the dominant source of methylmercury and a significant source of cadmium and arsenic for many populations. The review draws on decades of epidemiological research, including the landmark Faroe Islands studies that documented cognitive deficits in seven-year-old children with prenatal methylmercury exposure, and the Seychelles Child Development Study, which has followed cohorts for decades. Mercury’s cardiovascular risks have also been documented, with studies in eastern Finnish men linking fish-derived mercury intake to lipid peroxidation and increased risk of myocardial infarction. Cadmium targets the kidneys, damaging proximal tubules and causing chronic dysfunction, a process modulated by metallothionein status. Lead’s neurodevelopmental consequences, particularly through disruption of neurotransmitter systems in early life, remain a global concern even at low exposure levels. Hexavalent chromium is associated with respiratory disease, dermatitis, and carcinogenicity through DNA damage pathways.

To translate contamination data into actionable risk, the review evaluates the standard toxicological toolkit: the target hazard quotient, which compares estimated daily intake to a reference dose; the hazard index, which sums hazard quotients across multiple metals to capture mixture effects; and the cancer risk metric for carcinogenic metals such as arsenic, cadmium, and chromium VI. Applied to fish-consuming populations worldwide—from the Gulf of Guinea to the Ganga basin, from Nigerian markets to Bangladeshi estuaries—these assessments repeatedly flag children as a higher-risk group than adults, owing to lower body weight and higher relative consumption. Notably, the review identifies a critical methodological pitfall: most studies report total metal concentrations rather than chemical species. For arsenic, this matters enormously, because the predominant arsenic forms in marine fish are organic arsenosugars and arsenobetaine, which are far less toxic than inorganic arsenic. Relying on total arsenic can overstate toxicologically relevant exposure by roughly an order of magnitude, distorting risk estimates and consumer guidance alike.

On the remediation side, the review compares the major cleanup technologies by efficiency and scalability. Conventional physicochemical approaches—chemical precipitation, coagulation-flocculation, ion exchange, and membrane filtration—remain workhorses for industrial wastewater, but they generate sludge, consume energy, and struggle at low metal concentrations. Adsorption using engineered materials has surged forward, with metal-organic frameworks, amino-functionalized magnetic nanoparticles, carbon nanomaterials, and nanocomposite membranes demonstrating high capacities for lead, chromium, and mercury removal. Biological options offer lower-cost alternatives: microalgae and bacteria biosorb and biotransform metals, plants phytoextract contaminants from soils and sediments, and genetically modified microalgae have been proposed for mercury bioremediation through combined biosorption and biotransformation. Zero-valent iron nanoparticles can sequester multiple metals simultaneously, even when the metals are complexed with natural organic matter. Yet the review is candid about a gap: field-scale performance data for many nanotechnological approaches simply do not exist, leaving laboratory promise unverified in real waterways.

The review closes with a research agenda that reads as a warning to regulators and consumers alike. Standardized, comparable BCF and BAF datasets are lacking, making cross-study synthesis difficult; speciation analysis should replace total-metal measurements, particularly for arsenic in seafood; epidemiological dose-response evidence in fish-consuming populations remains thin, especially for mixture exposures; and climate change may alter metal cycling and uptake in ways not yet captured by monitoring programs. For the billions of people who depend on fish for protein and micronutrients, the message is not to abandon seafood—fish also deliver essential omega-3 fatty acids linked to neurocognitive benefits—but to demand better monitoring, species-specific and site-specific advisories, and cleanup technologies proven beyond the laboratory bench. Heavy metals, the authors make clear, will not degrade away on their own; managing them is a permanent obligation of industrial society.

Subject of Research: Bioaccumulation of heavy metals in fish and associated human health risks

Article Title: Heavy metals in fish: bioaccumulation, toxicity, and human health risk

Article References: Chauhan, V., Dondiyal, P., & Kumari, K. (2026). Heavy metals in fish: bioaccumulation, toxicity, and human health risk. Environmental Monitoring and Assessment, 198(10), Article 1110. https://doi.org/10.1007/s10661-026-15958-y

Image Credits: AI Generated

DOI: 10.1007/s10661-026-15958-y

Keywords: heavy metals, fish, bioaccumulation, biomagnification, methylmercury, arsenic, cadmium, chromium, lead, human health risk, bioremediation, aquatic pollution