Gas Chromatography-Mass Spectrometry Analysis of Organohalogen Compounds in Remote Bottlenose Dolphin Populations

The Saint Peter Saint Paul archipelago (SPSPA), situated in the central Equatorial Atlantic, approximately 1000 km from the northeastern coast of Brazil, has become the habitat of choice for a small population of common bottlenose dolphins (Tursiops truncatus) that exhibit a strong site loyalty to the remote archipelago. Due to these dolphins being the apex predators in this environment, they can act as sentinels for the transport and bioaccumulation of organohalogen compounds in isolated marine environments.

Acting upon that presumption, a research team set out to analyze chemical markers in remote biopsies of free-ranging bottlenose dolphins sampled in the SPSPA. Blubber samples from nine of the dolphins were analyzed for polychlorinated biphenyls (PCBs), organochlorine pesticides (OCPs), brominated flame retardants (BFRs), and naturally produced methoxylated organobromines (MeO-BDEs), using gas chromatography (GC) coupled with electron capture detection (ECD) or mass spectrometry (MS). Additionally, dolphin skin samples were analyzed in an isotopic ratio mass spectrometer. A paper presenting their findings was published in Marine Pollution Bulletin.¹

A widely dispersed species, bottlenose dolphins are mostly found in the inner continental shelf of tropical and temperate oceans, but also dwell in lagoons, rivers, bays, channels, and oceanic habitats.² Around oceanic islands such as SPSPA, dolphins exhibit low population density and low genetic diversity, and share genomic variants with the North Atlantic offshore population, suggesting a degree of gene flow between them.³ The dolphins inhabiting SPSPA are characterized by strong site fidelity and limited movement, which ensures geographical and genetic isolation from other populations of the species in the Southwestern Atlantic.^4,5 “Thus,” report the authors of the paper,¹ “assessing the bioaccumulation of natural and anthropogenic organohalogen compounds in free-ranging bottlenose dolphins inhabiting oceanic islands can provide valuable information regarding their transport to the oceanic domain.”

The researchers collected remote biopsies from nine individual dolphins to investigate pollutant exposure, and report that the samples show coastal-like pollutant profiles, revealing long-range transport of high molecular weight compounds and enhanced biotransformation of lighter ones. Their benthic-linked MeO-BDEs suggest limited coastal-oceanic movement. Elevated POPs in these isolated dolphins demonstrate pollution's far reach and biomagnification in nutrient-poor waters, making them pollutant reservoirs. This highlights threats to remote ecosystems and underscores the need for chemical monitoring to support ocean conservation and UN sustainability goals.¹

“These findings,” write the authors of the study,¹ “suggest the efficient transport of man-made pollutants to isolated locations and the key role of apex predators, such as bottlenose dolphins, as POPs reservoirs in oceanic zones.”

The authors go on to point out that the patterns observed and presented in their study are based on a small dataset and should be carefully interpreted. In addition, their work provides the first assessment of organohalogen compounds from both natural and anthropogenic sources in this geographically isolated population. “Assessing pollutant levels in remote areas,” they state, “poses substantial logistical challenges, making these data extremely valuable to account for the stocks of pollutants that reach locations far from their sources.” Still, they believe that their findings highlight that “while local and biological factors influence pollutant bioavailability, chemical pollution remains a global concern, as the transport of these compounds transcends geographic boundaries.”¹

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References

1. de Oliveira-Ferreira, N.; Hoffmann, L. S.; Manhães, B. M. R. et al. Long-Range Transport of POPs to the Central Atlantic Ocean: Using a Resident Population of Bottlenose Dolphins (Tursiops truncatus) as Sentinel Species. Mar Pollut Bull. 2026, 226, 119371. DOI: 10.1016/j.marpolbul.2026.119371
2. Jefferson, T. A.; Webber, M. A.; Pitman, R. L. et al. Marine Mammals of the World: A Comprehensive Guide to Their Identification; 2^nd Ed.; Elsevier, 2015.
3. Alexandre, B. G.; Cruz, M. M.; do Amaral, K. B. et al. Exploring mtDNA Databases to Evaluate the Population Structure and Genetic Diversity of Tursiops truncatus in the Atlantic Ocean: Implications for the Conservation of a Small, Offshore Population. Ecologies 2024, 5, 170-187. DOI: 10.3390/ecologies5020011
4. Milmann, L. C.; Danilewicz, D.; Baumgarten, J. et al. Temporal–Spatial Distribution of an Island-Based Offshore Population of Common Bottlenose Dolphins (Tursiops truncatus) in the Equatorial Atlantic. Mar. Mamm. Sci. 2017, 33, 496-519. DOI: 10.1111/mms.12380
5. de Oliveira, L. R.; Fraga, L. D.; Ott, P. H. et al. Population Structure, Phylogeography, and Genetic Diversity of the Common Bottlenose Dolphin in the Tropical and Subtropical Southwestern Atlantic Ocean. J. Mammal. 2019, 100, 564-577. DOI: 10.1093/jmammal/gyz065