Fish Livers Reveal Hidden Metal Loads in Pristine Andaman Waters

The Andaman Islands have long been imagined as one of the last pristine corners of the Bay of Bengal, an archipelago of coral reefs and low-impact fisheries far removed from the industrialized coasts of mainland India. A new study challenges that comfortable assumption. Researchers who examined five commercially important fish species landed at markets in South Andaman found that while the edible flesh of these fish remains largely clean, their internal organs carry measurable loads of trace metals, including cadmium and lead, that point to a marine environment in transition. The work, published in Discover Oceans, provides the first comprehensive multi-tissue baseline for trace element bioaccumulation in the region’s finfish and raises uncomfortable questions about long-term seafood safety for communities that eat fish every day.

The research team, led by Ajit Kumar and Akshatha Soratur of Pondicherry University together with colleagues at Indian and Japanese institutions, focused on five species that dominate local landings: the greasy grouper Cephalopholis sonnerati, Bleeker’s grouper Epinephelus bleekeri, the bullet tuna Auxis rochei, the Indian mackerel Rastrelliger kanagurta and the Japanese threadfin bream Nemipterus japonicus. These species were deliberately chosen to span different ecological worlds, from fast-swimming pelagic planktivores to bottom-dwelling carnivores, so that any differences in metal uptake linked to habitat or diet could be detected. Between September and December 2024, the team collected adult specimens from the Junglighat and Wandoor fish landing centres near Sri Vijaya Puram, the island capital formerly known as Port Blair, purchasing fish already caught by local fishermen rather than sacrificing animals specifically for the study.

In the laboratory, the researchers dissected each fish under stringent contamination-control conditions, using acid-washed stainless-steel instruments and laminar flow hoods to avoid introducing stray contamination. They sampled four tissues: gills, liver, intestine and dorsal muscle. Roughly one gram of each tissue was digested in closed Teflon vessels with concentrated nitric and perchloric acids in a microwave digestion system, and the resulting solutions were analyzed by inductively coupled plasma mass spectrometry. Quality control was rigorous: certified fish protein reference material, procedural blanks and triplicate analyses produced recoveries between 93 and 105 percent with analytical precision better than five percent. Of the eleven elements targeted, eight, aluminium, cadmium, copper, iron, manganese, nickel, lead and zinc, were consistently quantified, while chromium, cobalt and mercury fell below detection limits in every tissue examined, a striking absence for a region where mercury biomagnification is often assumed to be a concern.

The most striking finding was how strongly metal accumulation depended on organ identity rather than on which species the fish belonged to. The liver emerged as the body’s primary metal reservoir, sequestering copper, iron and especially cadmium at concentrations one to two orders of magnitude above those found in muscle. Cadmium’s affinity for metallothionein proteins and the liver’s central role in detoxification explain this pattern, and the elevated hepatic cadmium burdens in predatory groupers likely reflect cumulative lifetime dietary exposure through cadmium-rich crustacean prey rather than any recent contamination event. Gills told a different story: they preferentially accumulated manganese and aluminium, elements that adsorb onto suspended particles and settle on gill surfaces, making them sensitive real-time indicators of waterborne exposure. Muscle tissue, protected by physiological barriers, consistently showed the lowest concentrations of nearly every metal measured.

Statistical analyses reinforced this tissue-dominated picture. Kruskal-Wallis tests on the pooled dataset of sixty samples found highly significant organ-level differences for six of the eight metals, and multivariate techniques made the pattern unmistakable. Principal component analysis and non-metric multidimensional scaling both separated samples cleanly by tissue type, with liver samples clustering in one region of the ordination space and gill samples in another, confirmed by PERMANOVA with an effect size explaining 46 percent of the variance. When the same ordinations were color-coded by species, no coherent clusters appeared. The overall abundance hierarchy across all samples ran iron greater than zinc greater than aluminium greater than copper greater than manganese greater than lead greater than cadmium greater than nickel, a signature the authors interpret as strong metabolic regulation of essential elements combined with lithogenic inputs from the islands’ lateritic and ultramafic geology.

That geological signature matters for interpreting the contamination profile. The Andaman-Nicobar ridge is built from iron- and aluminium-rich formations, and intense monsoonal weathering naturally flushes these elements into coastal waters, where sediment resuspension during storms drives particulate metal fluxes. The Bay of Bengal also acts as a regional sink for atmospheric pollutants carried from South and Southeast Asia, including metal-bearing aerosols from coal combustion. Against this natural backdrop, the consistent detection of cadmium and lead across all species signals a measurable but low-level anthropogenic influence, likely diffuse inputs from maritime transport, antifouling coatings, harbour activity and long-range atmospheric deposition rather than any single point source. Muscle lead concentrations were comparable to those reported from moderately urbanized Indian coasts such as Visakhapatnam, yet far below levels documented in heavily industrialized systems like Thane Creek near Mumbai.

The human health risk assessment produced a genuinely paradoxical result. Based on muscle tissue concentrations, a conservative regional fish consumption rate of 24 grams per day and a 70-kilogram adult body weight, the estimated daily intakes of all eight metals fell well below FAO/WHO provisional tolerable daily intake thresholds and USEPA reference doses. Target hazard quotients for every metal in every species remained below 1.0, and the cumulative hazard index peaked at just 0.425 in the Indian mackerel, indicating no appreciable non-carcinogenic risk for average consumers. By conventional toxicological standards, Andaman fish are safe to eat.

Yet when the team calculated lifetime cancer risk for cadmium and lead, the only two metals analyzed with established oral carcinogenic potency slope factors, the picture changed. Total carcinogenic risk values exceeded the USEPA benchmark of one excess cancer case per 10,000 individuals in all five species, ranging from 1.28 times ten to the minus three in the bullet tuna to 2.77 times ten to the minus three in the greasy grouper, roughly 13 to 28 times the acceptable limit. The authors are careful to contextualize this: the carcinogenic model assumes linear, no-threshold dose-response relationships and continuous lifetime exposure, deliberately precautionary assumptions that tend to inflate risk estimates at low concentrations. The exceedance does not imply imminent harm, but it does flag a genuine long-term concern for high-frequency consumers, particularly subsistence fishing communities that may eat 100 to 300 grams of fish daily, several times the global average, and for those who favor long-lived, high-trophic predators like groupers, which accumulate more cadmium through trophic transfer.

The study’s broader message is methodological as much as environmental. Reliance on muscle tissue alone, the standard practice in most seafood safety monitoring, would have missed nearly all of the signal documented here, since muscle is precisely the compartment where fish physiology keeps metal concentrations lowest. The liver, by contrast, integrates chronic exposure over an animal’s lifetime, while gills track immediate waterborne conditions, and together these non-edible tissues offer the ecological resolution needed to distinguish natural geochemical background from emerging anthropogenic contamination. The authors recommend a multi-tissue monitoring framework for the Andaman Islands, complemented by otolith microchemistry, which can archive a fish’s metal exposure history in chronological layers, and by paired sediment and water chemistry to strengthen source attribution.

As tourism, inter-island shipping and coastal development accelerate around Sri Vijaya Puram, the transitional contamination profile documented in this study may represent a baseline captured just in time. The absence of mercury, chromium and cobalt in all tissues suggests the region still benefits from limited point sources and efficient open-ocean flushing, but the same open access that keeps the archipelago clean today makes it vulnerable tomorrow. For the coastal communities whose diets depend on these waters, the findings argue for nuanced risk communication that distinguishes acute toxicity from probabilistic lifetime cancer risk, and for consumption advisories tailored to species, trophic position and local eating habits rather than generic safety thresholds. The Andaman fish on the dinner plate remain, by most measures, safe. The fish livers, however, are quietly keeping score.

Subject of Research: Organ-specific trace metal bioaccumulation in commercial marine finfish from the South Andaman Islands and associated human health risks

Article Title: Organ-specific bioaccumulation of trace elements in commercial marine finfish from the South Andaman Islands and associated human health risk assessment

Article References: Kumar, A., Soratur, A., Kumar, S., Sarkar, A., Krishna, S. S. S., Kiruba-Sankar, R., Jha, D. K., & Venmathi Maran, B. A. (2026). Organ-specific bioaccumulation of trace elements in commercial marine finfish from the South Andaman Islands and associated human health risk assessment. Discover Oceans, 3(1), Article 35. https://doi.org/10.1007/s44289-026-00150-4

Image Credits: AI Generated

DOI: 10.1007/s44289-026-00150-4

Keywords: trace metals, bioaccumulation, marine finfish, Andaman Islands, cadmium, lead, liver, gills, food safety, health risk assessment, Bay of Bengal, seafood contamination