The research combined environmental sampling with taxonomic identification and statistical analysis of surface-active soil invertebrates collected in eight gallery-forest sites within the 10,500-hectare ecological station in the Federal District. Each 100-square-metre sampling unit contained 10 pitfall traps, whose combined catches formed one composite sample. Traps were deployed from May through July 2021 and collected weekly during seven campaigns. The organisms were identified, counted, measured, freeze-dried and homogenised, while soil and litter were collected from the centre of each sampling unit. Total mercury was measured by atomic absorption spectrometry, with certified reference materials used to verify analytical accuracy and recovery rates of 81% to 103%.

Mercury was significantly more concentrated in litter than in soil, a difference associated with paired statistical testing that yielded t = 4.402, seven degrees of freedom and p = 0.0032. The authors regarded the forest canopy as a plausible interception surface for atmospheric mercury, allowing mercury captured by vegetation to enter the soil compartment through litterfall. Sampling took place in gallery forests, a Cerrado formation that follows watercourses. Their dense canopies limit direct deposition to the ground, while prolonged leaf exposure, reduced litter leaching and shelter from sunlight can help retain deposited mercury. These mechanisms are consistent with the observed litter enrichment, but the comparison does not by itself identify the precise source or chemical pathway responsible.

Soil organic matter was a significant predictor of mercury concentration, accounting for 45.5% of the observed variation in the regression analysis, with p = 0.039. The estimated slope indicated that soil mercury increased by 0.537 units for each unit increase in organic matter content. Soil pH showed no significant relationship with total mercury. The authors connected the organic-matter association with mercury’s affinity for sulfur-bearing functional groups, including thiol and disulfide sites, which can promote binding of inorganic mercury in soil. They also noted that litter decomposition can transfer captured mercury into the underlying soil. Because only eight paired sampling units supplied the environmental comparison, the regression and soil–litter contrast should be interpreted within the scope of this small, site-specific field survey.

The invertebrate collections spanned 15 orders and included ants, termites, spiders, scorpions, beetles, flies, wasps, crickets and other epigeic fauna. Among orders with enough observations for comparison, termites had the highest mean mercury concentration at 458.11 ± 357.9 nanograms per gram, followed by scorpions at 457.48 ± 264.06 nanograms per gram and spiders at 340.70 ± 184.72 nanograms per gram. Variation was often substantial: for several groups, including harvestmen, flies, Vespidae wasps and ants, the standard deviation exceeded the mean. These broad spreads may reflect genuine differences among taxa, but the study’s relatively coarse taxonomic resolution, together with the analysis of whole animals without prior removal of gut contents, likely added variability.

Bioaccumulation factors were calculated by comparing mercury in each organism with its dry-weight concentration in soil or litter. A factor below 1 was classified as no significant bioaccumulation, 1 to 2 as microaccumulation, and above 2 as macroaccumulation. Overall, 83.75% of the analysed samples had a bioaccumulation factor of at least 1 relative to soil, and 91.4% of those accumulators met that threshold relative to litter. Among samples showing accumulation potential, 80.38% were macroaccumulators when compared with soil and 68.53% when compared with litter. Spiders were macroaccumulators in both comparisons, while ants showed a stronger tendency to exceed the macroaccumulation threshold relative to soil than to litter. The divergence between the two reference compartments reinforces that the surrounding soil may be an important exposure pathway for some animals.

Four mercury concentration classes were then compared with the feeding habits assigned to the organisms. Predator frequency rose from 9.1% in the lowest class, no more than 43.50 nanograms per gram, to 30.1% in the next class, 38.1% in the third and 45.5% in the highest class, above 273.81 nanograms per gram. Phytophagous organisms moved in the opposite direction, declining from 26.1% of the lowest class to 15.0%, 8.2% and 2.3% across the progressively higher classes. Omnivores predominated in the second group, while necrophagous organisms were proportionally more frequent in the highest. This shift is consistent with mercury transfer through feeding relationships, particularly the ingestion of contaminated prey, but the study characterized the inference as a local trophic-network pattern rather than a direct measurement of every trophic pathway.

Multivariate analysis provided additional support for an association between ecological function and mercury burden. The analysis combined organism mercury concentration, the bioaccumulation factor based on litter and mean body size. The first two discriminant functions explained 96.69% of the separation among feeding groups, and their profiles differed significantly at p < 0.0001. Xylophagous and sap-sucking organisms occupied similar positions, whereas detritivores, necrophages, parasitoids and predators showed partially overlapping profiles. Predatory and omnivorous groups lay closer to the centre. The overlap demonstrates that organisms with broadly similar feeding strategies did not all accumulate identical amounts of mercury, indicating that diet is not the only relevant variable. Exposure through soil contact, habitat use, body size, taxonomy and other physiological or ecological traits may also influence tissue concentrations.

The authors identified several important limitations, including the inability to identify many specimens to genus or species, large within-group variation and possible contributions from undigested material in whole-body samples. They recommended species-level identification and gastrointestinal depuration in future work. The study also took place in gallery forests inside a peri-urban reserve bordered by urban and agricultural landscapes, where previous research found elevated mercury near roads and attributed it to traffic-related emissions. Regional atmospheric deposition, wildfires and natural geological contributions are also plausible influences on the reserve’s mercury cycle. Accordingly, the findings describe bioaccumulation and patterns consistent with biomagnification in one Brazilian savanna system; they do not establish clinical effects in people, prove a specific mercury source or show that the same concentration gradients occur throughout the Cerrado. Nevertheless, the data demonstrate how litter, soil properties, organism–environment contact and feeding relationships can jointly structure terrestrial mercury transfer in a relatively under-studied soil food web.

Subject of Research: Terrestrial mercury bioaccumulation and trophic transfer in Brazilian Cerrado soil invertebrates

Article Title: Mercury dynamics in surface-active soil invertebrates from an ecological reserve in the Brazilian savanna

Article References: Fernandes, I. O., Monteiro, L. C., de Miranda, V. L., de Souza, J. P. R., Rodrigues, Y. O. S., de Castro Paes, É., Júnior, W. F. A., & Bernardi, J. V. E. (2026). Mercury dynamics in surface-active soil invertebrates from an ecological reserve in the Brazilian savanna. Environmental Monitoring and Assessment, 198(11), Article 1230. https://doi.org/10.1007/s10661-026-16051-0

Image Credits: AI Generated

DOI: 10.1007/s10661-026-16051-0

Keywords: mercury, bioaccumulation, biomagnification, soil invertebrates, Brazilian Cerrado, terrestrial food webs, leaf litter, soil contamination, ecological monitoring, dynamics, surface-active, soil

Sharks sit near the top of marine food webs, a position that makes them efficient accumulators of methylmercury, the organic and most toxic form of mercury. This compound is produced by microbes in aquatic sediments from inorganic mercury and then absorbed by plankton and small organisms. As prey are eaten by predators, the methylmercury climbs each step of the food chain, a process known as biomagnification. Because methylmercury binds strongly to proteins in muscle and other tissues and is excreted very slowly, large, long-lived predatory fish can carry concentrations thousands of times higher than the surrounding seawater. Previous studies of shark populations worldwide, including a systematic review of elasmobranch pollutants published in 2020, have repeatedly documented elevated mercury burdens in shark meat, cartilage, and organs, and earlier Korean research has already linked shark meat consumption among workers in Gyeongsangbuk-do province to higher blood mercury levels.

What makes Doochi unusual as an exposure route is that it uses parts of the shark that most cuisines discard: the skin and the intestine. Local producers boil these by-products, slice them, and serve the resulting chewy, gelatin-rich dish, which has been marketed as a signature specialty of the Gampo coastal area. Efforts to scale up production were reported in Korean media as early as 2009, and the Gyeongju city government has listed Doochi among its local specialty products. In other words, a food traditionally eaten a few times a year by a small community may soon appear on far more plates, which is precisely the scenario that motivates the new risk assessment.

The research team approached the problem in two phases, separated by nearly a decade. In 2013, they purchased 32 servings of prepared Doochi from local markets, along with 32 pieces of raw shark skin sold as the dish’s ingredient, and measured total mercury in untreated fragments of the boiled skin and in the raw material. Total mercury analysis, performed according to Korean food code test methods, captures all forms of the element but does not by itself distinguish methylmercury from less harmful inorganic species. Because established regulations in Korea and the European Union are expressed as limits on total mercury for shark, and as methylmercury limits for deep-sea fish in Korea, the researchers worked with both frameworks, estimating methylmercury content using standard conversion assumptions.

The 2013 data already told a striking story. The geometric mean total mercury concentration in the boiled skin fragments was 0.349 micrograms per gram, while the raw skin measured 0.122 micrograms per gram in its outer layer and 0.137 micrograms per gram in its inner layer. More alarming than the averages, however, was the scatter. Concentrations among individual fragments of boiled skin varied by a factor of 167, and a statistical test of variance, Levene’s test, confirmed that the fragment measurements were far more dispersed than those of the raw skin, with a p-value below 0.001. The authors attribute this extreme patchiness to the nature of the dish itself: a single serving of Doochi is assembled from irregular pieces of skin, so a fragment taken from one corner of a plate might contain vastly more mercury than one taken from another.

Recognizing that analyzing small untreated fragments could either miss or exaggerate the true mercury content of a serving, the team repeated the work in 2022 with a more rigorous design. A fresh serving of Doochi was carefully separated into its skin and intestine components, each of which was fully homogenized into a uniform mixture before analysis. The homogenized samples were then measured in triplicate at an accredited laboratory to ensure the results reflected genuine contamination rather than analytical noise or sampling bias. This approach effectively answers a different and more practical question: if you ate an entire serving of Doochi, how much mercury would you actually ingest on average?

The answer was sobering. The fully homogenized boiled skin contained between 2.667 and 2.882 micrograms of total mercury per gram, a level that clearly exceeds the European Union maximum limit of 1.0 microgram per gram set for shark products. The estimated methylmercury concentration likewise surpassed the Korean limit of 1.0 microgram per gram that applies to deep-sea fish. The intestine, by contrast, contained far less mercury, at 0.295 to 0.333 micrograms per gram, suggesting that mercury is concentrated predominantly in the skin. Because the skin is the main ingredient and the signature component of the dish, its outsized contribution dominates the exposure calculation for anyone eating Doochi in the traditional way.

To translate these concentrations into health risk, the researchers compared estimated mercury intake with the United States Environmental Protection Agency reference dose for methylmercury, the daily exposure level considered likely to be without appreciable harmful effects over a lifetime. Under the traditional pattern of ceremonial consumption, the calculated hazard quotients ranged from 0.15 to 0.57 depending on the assumptions used, meaning that a typical diner eating Doochi a few times a year would remain below the threshold of concern. The intake estimates under this pattern corresponded to 7 to 25 percent of the provisional tolerable weekly intake established by the Joint FAO/WHO Expert Committee on Food Additives. However, the margins shrink rapidly as frequency increases: the hazard quotient would exceed 1, the conventional line separating acceptable from potentially harmful exposure, at somewhere between 10 and 36 servings per year depending on the assumptions, and the provisional tolerable weekly intake would be reached at between 22 and 81 servings annually.

Those numbers may sound like a generous allowance, but the authors caution that the traditional consumption frequency is precisely what may change as Doochi gains commercial traction. A dish once confined to memorial rites in a handful of coastal towns is being positioned as a regional brand, and anyone eating it weekly rather than seasonally could cross into the risk zone. The researchers also emphasize that body weight matters. The reference dose is defined per kilogram of body weight per day, so the same number of servings delivers a proportionally larger dose to lighter individuals. Children, smaller adults, and women who are pregnant or planning pregnancy are the groups for whom methylmercury is most concerning, given its well-documented developmental neurotoxicity and its ability to cross the placenta and accumulate in the fetal brain.

The study carries broader lessons beyond one Korean specialty. It demonstrates that fishery by-products, the skins, organs, and trimmings usually hidden inside processed foods, can carry contaminant burdens as heavy as or heavier than the fillets that dominate regulatory attention. It also highlights a methodological pitfall in food monitoring: analyzing untreated fragments of a heterogeneous dish can produce wildly misleading estimates in either direction, which is why the authors’ shift to full homogenization and triplicate accredited analysis in 2022 matters so much. Under the assumptions of the analysis, traditional levels of Doochi consumption remain below the methylmercury reference dose, and the researchers do not call for a ban on the dish. What they do call for is vigilance, in the form of continued monitoring as availability widens, clearer guidance for frequent consumers and vulnerable groups, and awareness that a cherished local tradition, like the shark it comes from, has been quietly collecting the ocean’s mercury all along.

Subject of Research: Mercury contamination and dietary risk assessment of a traditional Korean shark skin and intestine dish

Article Title: High mercury levels in Doochi, a local shark skin and intestine dish of the Eastern coast of Korea

Article References: Park, J. W., Lee, E.-S., & Baek, K. (2026). High mercury levels in Doochi, a local shark skin and intestine dish of the Eastern coast of Korea. Environmental Monitoring and Assessment, 198(11), Article 1222. https://doi.org/10.1007/s10661-026-16032-3

Image Credits: AI Generated

DOI: 10.1007/s10661-026-16032-3

Keywords: mercury, methylmercury, shark, Doochi, Korea, food safety, seafood contamination, biomagnification, risk assessment, dietary exposure, heavy metals, Environmental Monitoring and Assessment

The research team, led by Juan Zhao and Bigui Lin of the Chinese Academy of Tropical Agricultural Sciences together with colleagues from the South China Institute of Environmental Sciences, assembled one of the more comprehensive multi-media datasets assembled for a Chinese coastal population. They analyzed 284 fish specimens spanning 12 species, 50 rice samples, and 449 human hair samples. Hair is a well-established biomarker for methylmercury exposure because the compound binds strongly to the sulfur-rich proteins in growing hair, providing a time-integrated record of dietary intake over weeks to months. By pairing hair measurements with detailed dietary questionnaires, the researchers could connect contamination in the food supply directly to accumulation in people.

The numbers tell a vivid story of unequal exposure. Fish from the fishing community carried a mean total mercury concentration of 158.9 micrograms per kilogram, while hair from residents of that same community averaged 3,317.6 micrograms per kilogram, substantially higher than levels measured in the urban study areas. Rice, the other dietary staple examined, contributed minimally to mercury exposure, confirming that in coastal China the seafood platter, not the rice bowl, is the dominant pathway for this particular contaminant. That distinction matters because methylmercury, formed when microbes convert inorganic mercury in aquatic sediments, is far more readily absorbed by the human body than the inorganic forms found in terrestrial crops.

Not all fish are equal when it comes to mercury, and the study quantified exactly which biological factors matter most. Mercury accumulation in fish was associated with the source of the catch, the habitat the species occupies, its trophic level, and its species identity. Marine wild-caught fish, carnivorous species, and neritic species that live in coastal waters close to shore showed the highest mercury burdens. This pattern reflects a well-known ecological process called biomagnification: methylmercury is absorbed at the base of the food web and becomes progressively more concentrated as it moves up through predatory fish, which eat smaller contaminated prey over long lifetimes. A carnivorous species near the top of the food chain effectively integrates decades of mercury from everything below it.

The human side of the analysis focused on the 207 participants who had complete demographic and dietary data. Using multivariable statistical models, the researchers identified four key factors associated with mercury levels in hair: working in the fishing industry, older age, the frequency of fish consumption, and the daily amount of fish eaten. Together, these variables explained more than 60 percent of the variance in hair total mercury and methylmercury concentrations, a remarkably strong result for an environmental exposure study. In other words, knowing what someone does for a living and how often they eat fish predicts their mercury body burden with considerable accuracy.

A region-level ecological analysis added another layer, linking the mercury profile of fish available in each area to the hair mercury burdens of the people living there. The authors are careful to note that this association should be interpreted at the regional rather than the individual level, since ecological comparisons of aggregated data cannot establish what any single person ate. Still, the finding suggests that the contamination profile of the local seafood supply shapes population-level exposure, meaning that two communities with different fish markets can carry systematically different mercury loads even with similar dietary habits.

The public health implications are most acute for the fishing community itself. Fish consumption accounted for the majority of methylmercury intake across the study population, and a substantial proportion of fishing community residents exceeded the provisional tolerable daily intake for methylmercury, the safety benchmark established by the Joint FAO/WHO Expert Committee on Food Additives. Methylmercury is a potent neurotoxin, and the developing nervous system is particularly vulnerable, which is why women of childbearing age and young children are the focus of most international advisories. Chronic exposure in adults is also a concern, with documented associations between elevated methylmercury and cardiovascular and neurological effects at high intakes.

What makes this study particularly valuable is its refusal to treat fish as a single food category. The species-level and habitat-level analysis provides exactly the granularity needed for practical dietary guidance. Advisories that simply tell people to eat less fish risk discarding the well-documented nutritional benefits of seafood, including omega-3 fatty acids that support cardiovascular and brain health. A smarter approach, the authors argue, is to target advice by species and by population: carnivorous, wild-caught, neritic species carry the highest mercury loads and can be substituted with lower-trophic alternatives, while the fishing community, whose members both catch and consume high-mercury fish at high frequencies, needs tailored guidance rather than generic national recommendations.

The Guangdong findings also fit into a larger global picture. China is both a major emitter of mercury and one of the world’s largest consumers of seafood, and recent research has shown that global fishing patterns can amplify human methylmercury exposure as fleets target different species and waters. The Minamata Convention on Mercury, the international treaty governing mercury pollution, depends on accurate exposure data to evaluate whether emission controls are translating into lower human burdens. Studies like this one, which connect environmental measurements to human biomarkers within the same food system, provide the kind of ground-truth evidence that such evaluations require.

For the residents of Guangdong’s coastal communities, the study’s message is not that fish should leave the table, but that the choice of fish matters enormously. The authors call for species- and population-specific fish consumption advisories built on updated food-contamination monitoring and human biomonitoring data in high-exposure coastal areas. As mercury continues to cycle through marine food webs, the simple act of knowing which species carry the heaviest loads, and which neighbors eat the most of them, may prove to be one of the most effective public health tools available.

Subject of Research: Mercury exposure from fish consumption in urban and fishing communities in Guangdong, China

Article Title: Associations between fish consumption and human hair mercury: a multi-media assessment across urban and fishing communities in Guangdong Province, China

Article References: Zhao, J., Gao, Z., Chen, X., Wang, J., Liu, B., Wei, C., Gou, J., Liang, Z., & Lin, B. (2026). Associations between fish consumption and human hair mercury: a multi-media assessment across urban and fishing communities in Guangdong Province, China. Environmental Geochemistry and Health, 48(16), Article 638. https://doi.org/10.1007/s10653-026-03533-w

Image Credits: AI Generated

DOI: 10.1007/s10653-026-03533-w

Keywords: mercury, methylmercury, fish consumption, hair biomarker, Guangdong, dietary exposure, biomagnification, coastal communities, food safety, risk assessment, public health, China

Mercury is a non-essential, globally distributed toxic metal with no biological function, and its behavior in marine food webs makes it a particular concern for top predators. In aquatic ecosystems, inorganic mercury released from industrial sources, coal combustion, and artisanal gold mining is converted by microbes into methylmercury, an organic form that is readily absorbed by living tissue. Unlike many contaminants that dilute as they move up the food chain, methylmercury bioaccumulates in individual organisms and biomagnifies across trophic levels, meaning that animals at the top of the web, such as marine mammals, can carry body burdens orders of magnitude higher than the water they swim in. Because methylmercury crosses the placenta and the blood-brain barrier, developing fetuses are especially vulnerable to its neurotoxic effects.

The research team, led by Anaclara Roselli-Laclau of the Universidad de la República in Uruguay together with colleagues from Uruguay and Brazil, focused on two sympatric otariid species that breed side by side at Isla de Lobos but occupy different ecological niches: the South American sea lion (Otaria flavescens) and the South American fur seal (Arctocephalus australis). The researchers quantified total mercury, or THg, in two complementary matrices: hair from adult females and lanugo, the fine natal fur that pups grow in utero and shed in the weeks after birth. Sampling covered 11 mother-pup pairs of sea lions and 46 mother-pup pairs of fur seals, providing an unusually direct way to examine maternal transfer because both members of each pair were analyzed.

The results revealed a striking contrast between the two species. Adult female sea lions averaged 30.5 micrograms of mercury per gram of hair on a dry weight basis, with a standard deviation of 9.3, while female fur seals averaged just 5.7 micrograms per gram, with a standard deviation of 3.4. The pattern was mirrored in their offspring: sea lion pups averaged 25.3 micrograms per gram of lanugo, compared with only 4.4 micrograms per gram in fur seal pups. In other words, sea lions at this colony carried roughly five to six times more mercury than their fur seal neighbors, and the concentrations measured in sea lion pups rank among the highest ever recorded for pinnipeds anywhere in the world.

This interspecies gap is best explained by differences in diet and foraging ecology. Sea lions from Uruguayan colonies are known to feed at higher trophic positions and in waters closer to the Río de la Plata estuary, a system influenced by both natural and anthropogenic metal inputs, while fur seals tend to forage further offshore on prey lower in the food web. Because methylmercury biomagnifies with each step in the food chain, a predator eating larger, older, more predatory fish accumulates substantially more of the metal than one feeding on small pelagic species. Previous work by the same group had already linked trophic habits to bioaccumulation in these two otariids, and the new mother-pup data extend that picture to the earliest stage of life.

Perhaps the most consequential finding is that mercury was detectable in lanugo at all. Lanugo is formed entirely before birth, so any mercury it contains must have been transferred across the placenta from the mother during gestation. The presence of THg in this prenatal fur therefore provides direct evidence of prenatal mercury exposure in both species, confirming that placental transfer, and not only lactation, is a significant route by which these animals hand their contaminant burden to the next generation. This aligns with earlier studies on Baltic grey seals and northern elephant seals, which documented transplacental mercury transfer, but the Uruguayan data add a South Atlantic baseline for two species that had been comparatively understudied.

Statistical modeling showed that pup mercury concentrations were positively associated with maternal concentrations in both species, which is exactly what one would expect if the pup’s prenatal fur faithfully reflects the mother’s body burden during pregnancy. However, the strength of that relationship differed dramatically between the species. In sea lions, the final model explained 75 percent of the variance in pup THg, a remarkably tight fit that suggests maternal levels are the dominant driver of pup exposure in this species. In fur seals, by contrast, the model explained only 20 percent of the variance, indicating that other factors, such as individual variation in foraging behavior, gestation timing, or physiological processes governing mercury mobilization, play a much larger role in shaping how much of the metal reaches each fetus.

The models also uncovered a sex effect that was present in one species but absent in the other. Among sea lions, male pups had lower mercury concentrations than female pups for a given maternal mercury level, a pattern that could reflect sex-specific differences in prenatal growth, body composition, or maternal investment, since male otariid pups are typically larger and may dilute their contaminant burden across more tissue mass. No such sex effect was detected in fur seals. The authors note that this kind of species-specific nuance matters for anyone hoping to use pup fur as a shortcut for monitoring adult contamination, because the relationship between mother and pup is not uniform across species or even between the sexes within a species.

That leads to the study’s central practical message: pup lanugo is not a reliable quantitative proxy for the mercury concentration of an individual mother. The variability in the mother-pup relationship, especially in fur seals, is too great to back-calculate a specific female’s burden from her pup’s fur. But the researchers argue that lanugo remains valuable in a different way. Because it can be collected from pups with minimal disturbance, without immobilizing or even closely approaching adult females, it offers a minimally invasive matrix for characterizing prenatal mercury exposure and for tracking broader species-level and population-level patterns over time and across geography. For colonies that are difficult to sample intensively, this could transform monitoring programs that would otherwise require invasive procedures on protected animals.

The broader implications extend beyond the South Atlantic. Marine mammals are widely regarded as sentinel species for ocean and human health, and elevated mercury in newborn sea lions signals that contamination in the southwestern Atlantic food web is reaching the most sensitive life stages of long-lived apex predators. Mercury exposure in young mammals has been linked in laboratory and field studies to impaired immune function, altered lymphocyte proliferation, and neurodevelopmental deficits, and similar concerns have been raised for harbor seal pups and Steller sea lion calves elsewhere. As mercury continues to enter the ocean from atmospheric deposition and from gold mining in the Amazon basin and beyond, studies like this one provide the baseline data needed to detect change, identify the species and populations most at risk, and inform international efforts, such as the Minamata Convention, to curb the flow of this persistent neurotoxin into marine ecosystems.

Subject of Research: Maternal-to-pup transfer of total mercury in South American sea lions and fur seals measured through maternal hair and pup lanugo

Article Title: Maternal–Pup Mercury Relationship in South American Sea Lions and Fur Seals

Article References: Roselli-Laclau, A., García-Alonso, J., Valdés, A., Freitas-Souza, M., Almeida, M. G., de Rezende, C. E., & Franco-Trecu, V. (2026). Maternal–Pup Mercury Relationship in South American Sea Lions and Fur Seals. Archives of Environmental Contamination and Toxicology, 91(3), Article 23. https://doi.org/10.1007/s00244-026-01227-z

Image Credits: AI Generated

DOI: 10.1007/s00244-026-01227-z

Keywords: mercury, South American sea lion, South American fur seal, pinnipeds, lanugo, prenatal exposure, biomagnification, ecotoxicology, marine mammals, Uruguay, maternal transfer, heavy metals

The study was carried out during the 2023 breeding season by Mohammadreza Ahmadi, Rasool Zamani-Ahmadmahmoodi, Seyed Mehdi Amininasab and Atefeh Chamani, researchers affiliated with Shahrekord University, Sari Agricultural Sciences and Natural Resources University and Islamic Azad University. The team deliberately selected three species with distinct ecological roles: the common tern (Sterna hirundo), a fish-eating predator near the top of the aquatic food chain; the black-necked grebe (Podiceps nigricollis), an intermediate feeder on invertebrates and small fish; and the Eurasian coot (Fulica atra), a largely herbivorous omnivore feeding low on the chain. By comparing metal burdens across this trophic gradient, the researchers could test whether contamination accumulates as it moves upward through the ecosystem, a pattern known as biomagnification.

Eggshells are an unusually convenient biomonitor. As the shell mineralizes inside the female, calcium is drawn from her body and deposited as calcium carbonate, and any lead circulating in her blood can hitch a ride on that process. The mechanism behind this is ionic mimicry: the lead ion Pb2+ is close enough in size and charge to the calcium ion Ca2+ that the biological machinery building the shell cannot reliably tell them apart, so lead substitutes for calcium in the crystal lattice. Cadmium, by contrast, enters the egg through different physiological routes and is generally present at lower levels. Because shells are abandoned naturally after hatching, sampling them leaves breeding colonies undisturbed, a major advantage over studies that require tissue collection from live or dead birds.

Metal concentrations in the collected shells were quantified with an Agilent 240FS AA atomic absorption spectrometer, a workhorse analytical instrument that atomizes a digested sample and measures how much light of a characteristic wavelength each metal absorbs. The results were stark. Lead concentrations exceeded cadmium in every species examined, and mean values for both metals surpassed widely used hazard thresholds of 4 milligrams per kilogram for lead and 2 milligrams per kilogram for cadmium. In other words, every one of the three species is carrying shell metal burdens associated in the ecotoxicological literature with potential reproductive and developmental harm.

The trophic pattern was unmistakable. The common tern, the high-trophic-level piscivore, showed the highest mean concentrations by a large margin: 424.29 milligrams of lead per kilogram of shell material and 23.39 milligrams of cadmium per kilogram. The black-necked grebe recorded intermediate values of 174.60 milligrams per kilogram for lead and 1.75 milligrams per kilogram for cadmium, while the low-trophic Eurasian coot carried 44.58 milligrams of lead and 2.38 milligrams of cadmium per kilogram. The tern’s lead burden was nearly ten times that of the coot, a difference consistent with the idea that predatory fish-eaters integrate contamination from every link below them in the food web. Each step up the chain concentrates the pollutant further, so a tern eating contaminated fish effectively eats the accumulated exposure of the smaller organisms those fish consumed.

Statistical analysis backed up the visual pattern. A one-way analysis of variance confirmed that the differences among species were significant at the conventional P < 0.05 threshold, supporting the trophic-level hypothesis of bioaccumulation in this system. Interestingly, Pearson correlation analysis found no significant relationship between lead and cadmium concentrations across samples. That statistical independence matters, because it suggests the two metals are not arriving from a single shared source. The authors point to likely distinct origins: industrial effluents for lead, and agricultural runoff for cadmium, which is a common contaminant of phosphate fertilizers and can wash from farmland into wetlands during irrigation and rainfall.

Gandoman Wetland sits in Iran’s Chaharmahal and Bakhtiari province and is recognized under the Ramsar Convention as a wetland of international importance, valued for its bird diversity and its role as a stopover and breeding site for waterbirds. Previous work has already documented heavy metal contamination in its sediments, and recent studies have flagged climate-driven vegetation change and other pressures on the wetland’s bird populations. The new eggshell data add a biological dimension to that picture, showing that contamination is not merely present in the substrate but is actively moving through the food web into the reproductive tissues of the birds themselves, with the potential to affect hatching success and chick development.

The concentrations reported are striking by any comparative standard. Lead levels in the tern shells, at over 400 milligrams per kilogram, are orders of magnitude above the 4 milligram per kilogram hazard threshold cited in the study, and even the coot, the cleanest of the three, exceeded both the lead and cadmium benchmarks. Eggshell metal burdens reflect the maternal body burden during egg formation, so these figures indicate that female birds at Gandoman are carrying substantial internal loads of lead and cadmium during the breeding season. Chronic lead exposure in birds is associated with neurological impairment, anemia and reduced reproductive output, while cadmium accumulates in the kidney and can disrupt calcium metabolism and eggshell quality, creating a feedback loop in which contamination may itself weaken the shell’s structure.

The non-invasive eggshell approach has grown into a respected tool in ecotoxicology, with studies of herons, egrets, gulls, cranes, terns and even flamingos using shell residues to trace environmental metal pollution across Europe, Asia and the Americas. What the Gandoman study adds is a clean demonstration of trophic structure within a single wetland, using three co-occurring species that share the same water but occupy different feeding niches. Because the three species forage at different levels, their shells function like a set of nested barometers, each reading the contamination of its own slice of the food web. The strong species-level differences, and the divergence between lead and cadmium, give managers a way to distinguish pollution pathways rather than just measuring a generic toxic load.

The authors describe Gandoman as a high-risk environment and argue that stringent pollution control is urgently needed to protect its wetland-dependent birds. Practically, that means addressing the two suspected sources separately: controlling industrial discharges that carry lead into the watershed, and managing agricultural runoff that delivers cadmium from surrounding farmland. The study also underscores the value of continued eggshell monitoring as a low-cost, repeatable surveillance method that can track whether remediation is working without ever handling a live bird. For a Ramsar site whose international designation rests on its birdlife, the message written into these fragile calcium shells is hard to ignore: the contamination that begins in factory outfalls and farm fields is ending up, concentrated and measurable, in the very animals the wetland was designated to protect.

Subject of Research: Lead and cadmium bioaccumulation in waterbird eggshells at Gandoman Wetland, Iran

Article Title: Trophic drivers of lead and cadmium bioaccumulation in waterbird eggshells: a non-invasive assessment at Gandoman Wetland, a Ramsar site in Iran

Article References: Ahmadi, M., Zamani-Ahmadmahmoodi, R., Amininasab, S. M., & Chamani, A. (2026). Trophic drivers of lead and cadmium bioaccumulation in waterbird eggshells: a non-invasive assessment at Gandoman Wetland, a Ramsar site in Iran. Environmental Monitoring and Assessment, 198(11), Article 1159. https://doi.org/10.1007/s10661-026-15984-w

Image Credits: AI Generated

DOI: 10.1007/s10661-026-15984-w

Keywords: heavy metals, lead, cadmium, eggshells, waterbirds, biomagnification, Gandoman Wetland, Ramsar site, ecotoxicology, biomonitoring, Iran, common tern

The research team, led by Danielma Silva Maia and Guilherme Sgobbi Zagui of the University of Ribeirão Preto together with colleagues at the University of Barcelona, screened 255 articles from PubMed, Scopus, SciELO, and Web of Science using the PRISMA framework. After removing duplicates and studies focused on marine species, 52 investigations met the eligibility criteria. The analysis reveals a striking geographic imbalance in the science itself: 26 of the studies come from Brazil’s Northern region, concentrated in the states of Pará and Amazonas, while the Northeast contributed only a single study. That uneven distribution, the authors note, may leave less-studied basins effectively unmonitored even as contamination pressures grow.

The regional pattern of contamination tells its own story. In the Amazon, mercury dominates, driven largely by artisanal and small-scale gold mining, which uses the metal to amalgamate gold, and by deforestation. Forest fires add a second, less obvious source: Amazonian soils are naturally enriched in mercury, and the rainforest acts as an atmospheric sink, so burning vegetation volatilizes mercury accumulated over decades and allows it to travel long distances before redepositing on soils and waterways. In the Southeast, the picture is shaped by catastrophic mining dam failures at Mariana and Brumadinho, which released metal-rich tailings into the Doce and Paraopeba rivers, compounded by industrial effluents, tanneries, and urban sewage. In the Pantanal and Cerrado of the Central-West, agricultural expansion, pesticide use, and pasture conversion emerge as the leading drivers, while the South and Northeast show primarily industrial and agricultural signatures.

Which metals end up in which fish is not random. The review found that trophic level, feeding strategy, and position in the water column strongly shape bioaccumulation. Carnivorous and piscivorous species such as peacock bass (Cichla spp.), trahiras (Hoplias spp.), and piranhas (Pygocentrus spp.) sit at the top of the food chain and accumulate the highest mercury loads, because mercury is the one trace element with consistent evidence of biomagnification across ecosystems. In Indigenous communities of the Tapajós region, piscivorous fish carried mercury levels roughly four times higher than non-piscivorous species. One study found that 70 percent of analyzed samples exceeded recommended mercury guidelines for consumption, and another reported liver concentrations in Cichla reaching 26.7 milligrams per kilogram dry weight.

At the other end of the ecological spectrum, detritivorous species such as the curimbatá (Prochilodus spp.) face a different hazard. These fish feed on organic detritus in constant contact with river sediments, which act as long-term reservoirs for chemical contaminants. As a result, they tend to accumulate lead and chromium rather than mercury. Omnivorous species such as the mandi (Pimelodus maculatus) and piau (Leporinus spp.) occupy an intermediate position but can still build up significant metal loads when they consume benthic organisms or contaminated sediment. The review also notes that metal concentrations vary dramatically among organs: metabolically active tissues like liver, gills, and kidneys accumulate far more than muscle, although muscle is what humans typically eat.

The metals of greatest toxicological concern identified across the studies were lead, cadmium, chromium, and mercury, with arsenic appearing less frequently but still exceeding limits in specific cases. Cadmium stood out for its extraordinary bioconcentration factor, reaching levels in fish up to ten times higher than in the surrounding water. In one alarming study from urban Amazonian waters, cadmium exceeded the maximum limit permitted by Brazilian legislation in all ten species evaluated; another found eight of eleven species above the legal threshold. Lead exceeded Brazilian limits in multiple investigations, with one study reporting concentrations above 2 milligrams per kilogram and another finding 41 percent of samples over national standards. Chromium, whose toxicity depends heavily on chemical form, showed a trophic biodilution pattern, with higher concentrations in herbivorous and detritivorous fish than in predators.

What does this mean for human health? The review’s risk assessments paint a sobering picture, particularly for Amazonian riverine and Indigenous communities. While the global average fish consumption is about 20.5 kilograms per person per year, Amazonian riverine populations can consume 100 to 550 grams daily, roughly 148 to 169 kilograms annually. At those intake levels, estimated daily intake of mercury exceeded reference doses in nearly all Amazonian scenarios studied. Hazard quotient values above 1.0, indicating potential harm, were reported for methylmercury across all fish species in one study, and for lead with values ranging from 1.75 to 3.60 in another. Children appear especially vulnerable, with mercury intake reaching or exceeding safety thresholds in multiple assessments. Cadmium and lead also produced hazard quotients above 1 in several studies, suggesting possible carcinogenic risk from chronic consumption.

The authors are careful to note an important caveat: total metal concentrations do not necessarily translate directly into human exposure. For a metal to cause systemic toxicity, it must first be released from the food matrix during digestion and then cross the intestinal barrier, a property known as bioaccessibility. Incorporating bioavailability and bioaccessibility measurements into risk assessments could refine exposure estimates and reduce overestimation. The review also flags a frequently overlooked variable: cooking. Most studies analyze raw fish, yet recent work found that elemental concentrations, particularly aluminum, copper, and mercury, tended to increase after cooking, meaning risk calculations based on fresh tissue may understate real-world exposure.

Hydrology adds another layer of complexity. Seasonal flood pulses mobilize contaminants and alter their bioavailability, and hydroelectric reservoirs act as sinks where altered water stratification promotes metal accumulation. Evidence from extreme events raises further concern: after the May 2024 floods in the Sinos River Basin, researchers found soil chromium concentrations ranging from 2,400 to 107,560 milligrams per kilogram, and during the extreme Amazon drought of 2023, shifts in temperature, oxygen, and pH in the Negro and Solimões rivers were linked to increased fish mortality. Studies from the Paraíba do Sul basin found that drought itself elevated total mercury and methylmercury in most fish species evaluated, and climate change is expected to make such events more frequent.

The review closes with a call to action that goes beyond monitoring. The authors argue that national and international safety limits, including those set by Brazil’s ANVISA and aligned with European Union standards, may be fundamentally insufficient to protect communities whose lifetime fish consumption far exceeds the national average, and they urge the development of regional regulatory limits reflecting local dietary realities. They also identify persistent research gaps: too few studies distinguish between the chemical forms of metals, such as the far more toxic hexavalent chromium or methylmercury, which makes up more than 80 percent of the mercury in fish muscle, and the reproductive and nervous systems of neotropical fish remain rarely investigated. Until enforcement of mercury controls strengthens and monitoring expands to neglected basins, the fish that sustain Amazonian communities will continue to carry an invisible load, and the people who eat them will keep absorbing it.

Subject of Research: Trace metal contamination in Brazilian freshwater fish and associated human health risks

Article Title: Trace metals contamination in freshwater fish in Brazil: related factors, environmental impacts, and risks to human health

Article References: Maia, D. S., Sierra, J., Martí, E., & Zagui, G. S. (2026). Trace metals contamination in freshwater fish in Brazil: related factors, environmental impacts, and risks to human health. Environmental Monitoring and Assessment, 198(11), Article 1163. https://doi.org/10.1007/s10661-026-15977-9

Image Credits: AI Generated

DOI: 10.1007/s10661-026-15977-9

Keywords: heavy metals, freshwater fish, Brazil, mercury, bioaccumulation, biomagnification, Amazon, mining, food safety, risk assessment, water pollution, ecotoxicology

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