The review, led by Suelen Goulart and colleagues at the Federal University of Santa Catarina in Brazil, followed the PRISMA protocol for systematic reviews, screening 255 articles from the CAPES Periodicals Portal and ultimately including 31 that met strict criteria: original peer-reviewed studies, published in English, using biopsy sampling on live marine mammals to assess environmental contaminants. Because the animals are sampled at sea without capture, restraint, or sedation, biopsies offer something necropsies of stranded animals cannot: a real-time snapshot of contamination in healthy, active populations. Stranded animals, the authors note, are often debilitated or decomposed, underrepresent robust populations, and introduce biases that impede continuous health monitoring. Biopsies also allow effective metabolic quenching, making the samples reliable for metabolomics, and they can be paired with ecological data such as satellite telemetry and stable isotope analysis to build a fuller picture of exposure.

The tissue most often sampled is blubber, which appeared in roughly 74 percent of the studies, followed by skin at about 39 percent. The preference is no accident. Blubber is the energy store and thermal regulator of marine mammals, and it preferentially accumulates lipophilic contaminants, making it the ideal matrix for persistent organic pollutants. Skin, by contrast, is rich in keratin and other proteins with sulfhydryl groups, and it turns out to be the superior target for non-lipophilic inorganic contaminants such as mercury, which bind proteins rather than fats. The choice of tissue, in other words, is dictated by the chemistry of the pollutant being hunted.

Persistent organic pollutants dominated the field: 23 of the 31 studies, or 74.19 percent, focused on them, with polychlorinated biphenyls (PCBs) and dichlorodiphenyltrichloroethanes (DDTs) the most frequently quantified, followed by hexachlorobenzene, polybrominated diphenyl ethers, and chlordanes. Both PCBs and DDTs were banned in the 1970s and 1980s, yet they persist in marine food webs with alarming intensity. In false killer whales from Hawaii, 84 percent of individuals exceeded safety thresholds for total PCBs, with average concentrations reaching 30,000 nanograms per gram lipid weight. In the Gulf of Mexico, bottlenose dolphins showed PCB levels as high as 82,500 nanograms per gram lipid weight and DDTs up to 164,000. Adriatic dolphins carried a DDT metabolite comprising 90 percent of their total DDT burden. The Mediterranean Sea emerged as the single most studied region, accounting for 39.1 percent of the POPs papers, a reflection of its history of industrial contamination, restricted water circulation, and dense coastal urbanization.

The review also reveals a striking biological pattern: in 82.6 percent of the POPs studies, males accumulated higher contaminant loads than females. The explanation lies in maternal offloading. During gestation, pollutants such as PCBs, DDTs, and flame retardants cross the placenta into fetal tissue, and after birth, calves receive further doses through milk, often reaching concentrations that exceed maternal levels. Females effectively shed their toxic burdens with each reproductive cycle, while males have no such outlet. Juveniles, too, showed elevated contamination, with humpback whale calves in the Gulf of Maine reaching 12,000 nanograms per gram lipid weight of PCBs, suggesting that accumulation begins well before sexual maturity and that developing bodies are especially vulnerable.

Trophic position proved to be a powerful predictor of exposure. Apex predators carried 10 to 40 times higher concentrations than species feeding lower in the food web. Killer whales in the Canadian Arctic accumulated total POPs of 216,000 nanograms per gram lipid weight, and sperm whales in the Mediterranean reached 22,849 nanograms per gram of PCBs, while krill-feeding fin whales in the same basin carried only 572. The reason is biomagnification: killer whales prey on contaminated seals and cetaceans, sperm whales consume lipid-rich squid, and each step up the chain concentrates the chemicals further. Filter-feeding humpback whales showed moderate contamination except in pollution hotspots such as the Mediterranean, where they reached 10,477 nanograms per gram of DDTs.

The health consequences documented in the review are severe. Concentrations above 9,000 nanograms per gram lipid weight are considered a critical threshold for immunosuppression in aquatic mammals, and 65.2 percent of the POPs studies reported levels exceeding known toxicity thresholds. Populations of long-finned pilot whales and Cuvier’s beaked whales in the Mediterranean, bottlenose dolphins in the Atlantic, Gulf of Mexico, and Indian Ocean, and false killer whales in Hawaii all surpassed the 17,000 nanogram threshold associated with reproductive impairment. At the molecular level, more than half of the POPs studies documented disrupted detoxification, endocrine, and neurological systems. In one innovative study, researchers cultured skin fibroblasts from biopsy samples of Norwegian killer whales and exposed them to a mixture of the ten most abundant pollutants at environmentally relevant concentrations, observing significant downregulation of the detoxification gene CYP1A1 and deregulation of lipid metabolism pathways. In Florida dolphins, high DDT levels were associated with reduced testosterone in males and suppressed cortisol in females, impairing reproduction and stress responses.

Inorganic contaminants received far less attention, with only eight studies, yet the findings were no less concerning. Mercury appeared in six of the eight papers, and the Mediterranean pilot whales carried the highest concentrations recorded, at 33,028 nanograms per gram. Resident bottlenose dolphins in Ecuador’s Gulf of Guayaquil all exceeded immunotoxic mercury thresholds. In Australia, stranded Burrunan dolphins from industrialized regions carried blubber mercury levels nearly three times higher than live individuals from less impacted waters, with hepatic concentrations reaching 840,000 nanograms per gram, evidence that long-term dietary accumulation eventually overwhelms the body’s detoxification capacity. The review also highlights chromium-induced genotoxicity in fin whale skin cells, which showed dose-dependent cytotoxicity and DNA damage in laboratory exposures. Perhaps most striking is how little is known about emerging contaminants: only two studies examined phthalates, yet the plasticizer DEHP was detected in every sample from three cetacean species, reaching an extreme outlier of 4,697 nanograms per gram in a bottlenose dolphin near Madeira.

Geographically, the science is strikingly lopsided. North America accounted for 38.1 percent of the continental study occurrences and Europe 28.6 percent, while Africa and South America contributed just 7.1 percent each and Antarctica and Australia 4.8 percent each. Cetaceans, particularly bottlenose dolphins, which appeared in 11 of the 31 studies, dominated the literature, while pinnipeds were nearly absent, largely because sampling seals requires capture, restraint, or sedation, making the procedure far more stressful than a remote dart. The authors argue that this bias leaves regions facing intense plastic disposal and chemical contamination, including Brazil’s so-called Blue Amazon and the coasts of Uruguay and Argentina, dangerously under-monitored, a concern amplified by recent regulatory shifts such as Brazil’s new pesticide law, which replaces stringent danger criteria with more flexible risk assessments.

The review closes with a call to action that extends well beyond marine mammalogy. The authors urge standardization of collection, storage, and analytical protocols, noting that differences in chromatographic methods have produced discrepancies in PCB measurements of up to 40 percent between studies, and they propose global biobanks and certified reference materials modeled on the United States National Institute of Standards and Technology. They advocate integrating biopsies with multi-omics approaches, stable isotope analysis, satellite telemetry, and machine learning to map pollution hotspots and identify resilient populations. Framed within the One Health paradigm, the message is that the contaminants accumulating in whale blubber and dolphin skin are the same ones moving through the seafood that coastal and Arctic communities depend on. In a warming ocean where climate change may remobilize legacy pollutants, the small dart sample retrieved from the wake of a diving whale may prove to be one of the most important early-warning systems humanity has for the health of the sea, and of itself.

Subject of Research: Biopsy-based contaminant monitoring in free-ranging marine mammals as a measure of ocean health

Article Title: Assessing oceans’ health through biopsy sampling in free-ranging marine mammals: a systematic review (2014–2024)

Article References: Goulart, S., Galani, G., Lima, L. F. D., Piccinin, I. N. L., Valente, F. D. S., Nunes, A., Renault-Braga, E. P., & Maraschin, M. (2026). Assessing oceans’ health through biopsy sampling in free-ranging marine mammals: a systematic review (2014–2024). Environmental Science and Pollution Research, 33(28), 14055-14085. https://doi.org/10.1007/s11356-026-38163-3

Image Credits: AI Generated

DOI: 10.1007/s11356-026-38163-3

Keywords: marine mammals, biopsy sampling, persistent organic pollutants, PCBs, DDTs, mercury, phthalates, cetaceans, ocean health, ecotoxicology, One Health, pollution monitoring