Long-Term Consequences of High Polychlorinated Biphenyl Exposure: Projected Decline of Delphinid Populations in a Hotspot for Chemical Pollution

Beyond the threshold - Different accumulation of organochlorine compounds in common dolphins (Delphinus delphis) inhabiting continental and insular ecosystems in the Northeast Atlantic

Assessing persistent organic pollutant (POP) levels across regions helps evaluate environmental health and determine ecological risks. As an apex predator, the common dolphin (Delphinus delphis) serves as an excellent model for understanding POP exposure and impact in Eastern North Atlantic marine ecosystems. In this study, we collected biopsy samples of common dolphins in two ecoregions, the pelagic system of Madeira Island (Portugal) (n = 30) and in the continental shelf of Northwest Portugal (n = 14) to analyse organochlorine concentrations (PCBs, DDTs, Mirex, HCB) from their blubber. For both ecoregions, PCBs comprised the largest proportion of the total measured organochlorines (60% in Madeira Island and 85% in Northwest Portugal), followed by DDTs, and lastly, HCB. Considerable differences in the organochlorine profile were identified between samples from Madeira and Northwest Portugal, with common dolphins showing higher PCB loads in Northwest Portugal (53 ± 37 μg g-1 lw) compared to Madeira Island (11 ± 4.8 μg g -1 lw). The high levels of PCBs found in individuals from mainland Portugal - reaching values up to 140 μg g-1 lw - are some of the highest reported for the species worldwide, considerably exceeding toxicity thresholds. This is of particular concern as they may be potentially affecting important physiological processes of the animals. These results highlight the poor habitat quality in one of the studied regions, with potential impacts on ecosystem health, while offering valuable insights into the population structure of a species that remains understudied for effective management and conservation.

The Commerson's dolphin as Subantarctic sentinel of POPs: Insights into the pollutant status in one of the southernmost coastal areas of the globe

Persistent organic pollutants (POPs) are halogenated contaminants found globally. Cetaceans are impacted by these pollutants, and nowadays, it is essential to understand their presence to mitigate their impacts. This study aimed to establish baseline levels of POPs in the blubber of Commerson's dolphins (Cephalorhynchus commersonii) within the Subantarctic ecosystem. A wide range of POPs concentrations were measured among individuals: ΣPCBs from 289.5 to 15264 ng g-1 lw and ΣDDTs from 540.4 to 17657 ng g-1 lw. Levels of HCB and mirex ranged from 48 to 1703.7 ng g-1 lw and 5.1-1917.4 ng g-1 lw, respectively. The predominant POPs were mid-to high molecular weight PCBs (hexa-PCBs), consistent with other findings in cetaceans of the southern hemisphere. The mean ratio of ΣDDT/ΣPCB was 0.44, with p,p'-DDE/ΣDDT at 0.56, indicating p,p'-DDE as the dominant DDT isomer. Furthermore, differences in POP concentrations were observed based on sexual maturity, with mature males exhibiting higher levels of ƩPCBs, HCB, ƩDDT, and mirex. Age and total body length of animals were strongly correlated with POP concentrations. Our study provides valuable insights into the pollutant status of POPs in the Subantarctic population of Commerson's dolphins inhabiting the southernmost coastal regions of South America.

PAHs in franciscana dolphins from the Southwestern Atlantic Ocean: Concentration and maternal transfer assessments

Polycyclic aromatic hydrocarbons (PAHs) are organic compounds ubiquitous in the environment and known for their toxic, mutagenic, and carcinogenic effects. These compounds can bioaccumulate in the biota and be transferred through trophic webs. The franciscana dolphin (Pontoporia blainvillei), as top predators, can be an environmental sentinels. Thus, this study aimed to provide data about PAHs concentration in their hepatic tissue collected on the coast of Espírito Santo (Franciscana Management Area, FMA Ia), Rio de Janeiro (FMA IIa), and São Paulo states (FMA IIb), in Southeastern Brazil. PAHs were detected in 86 % of franciscana dolphins (n = 50). The highest ∑PAHsTotal median concentration was reported in FMA Ia followed by FMA IIb and FMA IIa (1055.6; 523.9, and 72.1 ng.g-1 lipid weight, respectively). Phenanthrene was detected in one fetus and two neonates, showing maternal transfer of PAHs in these dolphins. Evaluating PAHs with potential toxic effects is of utmost importance for the conservation of a threatened species.

Organohalogen compounds in a hotspot for chemical pollution: Assessment in free-ranging Atlantic spotted dolphins (Stenella frontalis)

The assessment of chemical pollution in free-ranging living mammals is viable using remote biopsies and portrays a comprehensive scenario of environmental health. The Southwestern Atlantic Ocean holds incredible biodiversity, but it is under the constant and invisible threat of persistent organic pollutants (POPs) of anthropogenic origin, such as pesticides, brominated flame retardants, and industrial-use compounds (e.g., PCBs). Thus, this study aimed to assess the bioaccumulation of POPs (PCBs, DDTs, HCB, mirex and PBDEs) and natural organobromine compounds (MeO-BDEs) using gas-chromatography coupled to mass spectrometry in biopsy samples of Atlantic spotted dolphins (Stenella frontalis, n = 20) that inhabit and forage both inside and in adjacent areas to degraded (Guanabara Bay) and conserved (Ilha Grande Bay) coastal bays in the Southeastern Brazil. Among the studied compounds, PCBs were predominant in the contamination profile with median concentration of 97.0 μg.g-1 lipid weight (lw), followed by the sum of the p,p' isomers of DDT, DDD, and DDE of 11.0 μg.g-1 lw, the brominated flame retardants PBDEs of 1.6 μg.g-1 lw, and the other organochlorine pesticides mirex of 0.78 μg.g-1 lw, and HCB of 0.049 μg.g-1 lw. The MeO-BDEs were detected with a median concentration of 22.8 μg.g-1 lw. 85 % of the Atlantic spotted dolphins analyzed in this study presented PCB concentration that exceeded even the less conservative threshold limits for adverse health effects (41 μg.g-1 lw). This study shows that despite the conservation status of preserved bays, cetacean species foraging in these locations are still under increased threat. Hence chemical pollution demands local and global efforts to be mitigated.

Back on top: Resuspended by dredging and other environmental disturbances, organochlorine compounds may affect the health of a dolphin population in a tropical estuary, Sepetiba Bay

Organochlorine compounds (OCs) are persistent organic pollutants linked to damaging the immune and endocrine systems, leading to a greater susceptibility to infectious diseases at high concentrations. Sepetiba Bay, in the Southeastern Brazilian coast, historically presents anthropogenic activities and environmental contamination that could negatively impact resident populations. In this context, this study aimed to investigate the temporal trends in the accumulation of organochlorine compounds over a 12-year database in the Guiana dolphins' (Sotalia guianensis) resident population from Sepetiba Bay, including individuals collected before, during, and after an unusual mortality event triggered by morbillivirus (n = 85). The influence of biological parameters was also evaluated. The OCs concentrations in the blubber ranged from 0.98 to 739 μg/g of ΣPCB; 0.08-130 μg/g of ΣDDT; <0.002-4.56 μg/g of mirex; <0.002-1.84 μg/g of ΣHCH and <0.001-0.16 μg/g of HCB in lipid weight. Increased temporal trends were found for OCs in Guiana dolphins coinciding with periods of large events of dredging in the region. In this way, our findings suggest that the constant high OCs concentrations throughout the years in this Guiana dolphin population are a result of the constant environmental disturbance in the area, such as dredging. These elevated OCs levels, e.g., ΣPCB concentrations found above the known thresholds, may impair the response of the immune system during outbreak periods, which could lead the population to a progressive decline.

Organohalogen contaminants threaten the survival of indo-pacific humpback dolphin calves in their largest habitat

As long-lived apex predators, marine mammal adults often accumulate alarmingly levels of environmental contaminants. Nevertheless, the accumulation and risks of these contaminants in the critical calf stage of marine mammals remain largely unknown. Here, we investigated the exposure status and health risks of 74 organohalogen contaminants (OHCs) in Indo-Pacific humpback dolphin calves (Sousa chinensis) collected from the Pearl River Estuary (PRE), China, during 2005-2019. Our findings revealed moderate levels of polychlorinated biphenyls (PCBs), medium-high levels of dichlorodiphenyltrichloroethanes (DDTs) and hexachlorocyclohexanes (HCHs), and the highest levels of polybrominated diphenyl ethers (PBDEs) and alternative halogenated flame retardants (AHFRs) compared to those reported for cetaceans elsewhere. Traditional OHCs like DDTs, PCBs, and PBDEs did not exhibit significant decreasing trends in the dolphin calves despite global restrictions on these compounds, and AHFRs as emerging OHCs showed an increasing trend over the study period. Risk quotients of DDTs, HCHs, PBDEs, and PCBs in most of the dolphin samples were > 1, indicating that humpback dolphin calves may have suffered long-term threats from OHC exposure. The significant correlation observed between the traditional OHC levels and the stranding death number of the dolphin calves suggests these OHCs may impact the survival of this endangered species.

Legacy and emerging contaminants in marine mammals from Argentina

Marine mammals are recognized sentinels of ecosystem health. They are susceptible to the accumulation and biomagnification of pollutants, which constitute one of the greatest threats to their survival. Legacy, such as organochlorine pesticides, and emerging contaminants, like microplastics and pharmaceuticals, may have effects on marine mammals' health at individual and population levels. Therefore, the evaluation of the risks associated with pollutants in this group is of great importance. The aim of this review is to provide information on the occurrence of legacy and emerging contaminants in marine mammals that inhabit Argentine waters. Also, to identify knowledge gaps and suggest best practices for future research. Reports of legacy contaminants referring to organochlorine pesticides and polychlorinated biphenyls were found in five species of cetaceans and two of pinnipeds. With respect to emerging pollutants, the presence of plastics was only evaluated in three species. Reported data was from at least a decade ago. Therefore, it is necessary to update existing information and conduct continuous monitoring to assess temporary trends in pollutants. All the studies were carried out in the province of Buenos Aires and Northern Patagonia indicating a knowledge gap in the southern zone of the Argentine Sea. In addition, pollutants of global environmental concern that have not been studied in Argentina are discussed. Future studies should fill these gaps and a greater effort to understand the relationships between pollutants and their effects on marine mammals is suggested. This issue will make it possible to determine thresholds for all the substances and species evaluated in order to carry out more detailed risk assessments and make decisions for the conservation of marine mammals in Argentine waters.

Brominated flame retardants and natural organobrominated compounds in a vulnerable delphinid species along the Brazilian coast

Guiana dolphins, Sotalia guianensis, are vulnerable to extinction along their distribution on the Brazilian coast and assessing chemical pollution is of utmost importance for their conservation. For this study, 51 carcasses of Guiana dolphins were sampled across the Brazilian coast to investigate legacy and emerging brominated flame retardants (BFRs) as well as the naturally-produced MeO-BDEs. PBDEs and MeO-BDEs were detected in all samples analyzed, whereas emerging BFRs were detected in 16 % of the samples, all in Rio de Janeiro state. PBDE concentrations varied between 2.24 and 799 ng.g-1 lipid weight (lw), emerging BFRs between 0.12 and 1.51 ng.g-1 lw and MeO-BDEs between 3.82 and 10,247 ng.g-1 lw. Concentrations of legacy and emerging BFRs and natural compounds varied considerably according to the sampling site and reflected both the local anthropogenic impact of the region and the diversity/mass of biosynthesizers. The PBDE concentrations are lower than what was found for delphinids in the Northern Hemisphere around the same sampling period and most sampling sites presented mean concentrations lower than the limits for endocrine disruption known to date for marine mammals of 460 ng.g-1 lw, except for sampled from Santa Catarina state, in Southern Brazil. Conversely, MeO-BDE concentrations are higher than those of the Northern Hemisphere, particularly close to the Abrolhos Bans and Royal Charlotte formation, that are hotspots for biodiversity. Despite the elevated concentrations reported for this group, there is not much information regarding the effects of such elevated concentrations for these marine mammals. The distinct patterns observed along the Brazilian coast show that organobrominated compounds can be used to identify the ecological segregation of delphinids and that conservation actions should be planned considering the local threats.

The deep dive of organohalogen compounds: Bioaccumulation in the top predators of mesopelagic trophic webs, pygmy and dwarf sperm whales, from the Southwestern Atlantic ocean

Kogia sima and Kogia breviceps are apex predators of mesopelagic trophic webs being far from most anthropogenic threats. However, chemical pollutants and naturally synthesized compounds may travel long distances. This study aimed to use kogiid whales as sentinels of mesopelagic trophic webs in the Southwestern Atlantic Ocean. Persistent organic pollutants (POPs), e.g., polychlorinated biphenyls (PCBs), dichlorodiphenyltrichloroethane (DDT) and metabolites, mirex, hexachlorobenzene (HCB), polybrominated diphenylethers (PBDEs), pentabromoethylbenzene (PBEB) and hexabromobenzene (HBB), and the naturally produced methoxylated BDE (MeO-BDEs) were determined in the blubber of 16 K. sima and 15 K. breviceps. Among the organochlorine compounds, DDTs were the main group found in K. sima and in K. breviceps (1636.6 and 3983.3 ng g-1 lw, respective medians), followed by PCBs (425.9 and 956.1 ng g-1 lw, respectively), mirex (184.1 and 375.6 ng g-1 lw, respectively), and HCB (132.4 and 340.3 ng g-1 lw, respectively). As for the organobromine, the natural MeO-BDEs were predominant (1676.7 and 501.6 ng g-1 lw, respectively), followed by PBDEs (13.6 and 10.3 ng g-1 lw, respectively) and PBEB (2.2 and 2.9 ng g-1 lw, respectively). In general, POPs concentration was higher in K. breviceps than in K. sima. Conversely, MeO-BDEs concentration was higher in K. sima than in K. breviceps. Differences in concentrations in these sympatric odontocetes were attributed to distinct species, sampling sites, and biological parameters and suggest some level of niche segregation. It is noteworthy the long-range reach and bioaccumulation of these synthetic compounds in an unexplored habitat, that present an increasing economic interest.

Insight into the Mechanism Underlying Dehalococcoides mccartyi Strain CBDB1-Mediated B12-Dependent Aromatic Reductive Dehalogenation

Anaerobic bacteria transform aromatic halides through reductive dehalogenation. This dehalorespiration is catalyzed by the supernucleophilic coenzyme vitamin B₁₂, cob(I)alamin, in reductive dehalogenases. So far, the underlying inner-sphere electron transfer (ET) mechanism has been discussed controversially. In the present study, all 36 chloro-, bromo-, and fluorobenzenes and full-size cobalamin are analyzed at the quantum chemical density functional theory level with respect to a wide range of theoretically possible inner-sphere ET mechanisms. The calculated reaction free energies within the framework of Co^I···X (X = F, Cl, and Br) attack rule out most of the inner-sphere pathways. The only route with feasible energetics is a proton-coupled two-ET mechanism that involves a B₁₂ side-chain tyrosine (modeled by phenol) as a proton donor. For 12 chlorobenzenes and 9 bromobenzenes with experimental data from Dehalococcoides mccartyi strain CBDB1, the newly proposed PC-TET mechanism successfully discriminates 16 of 17 active from 4 inactive substrates and correctly predicts the observed regiospecificity to 100%. Moreover, fluorobenzenes are predicted to be recalcitrant in agreement with experimental findings. Conceptually, based on the Bell-Evans-Polanyi principle, the computational approach provides novel mechanistic insights and may serve as a tool for predicting the energetic feasibility of reductive aromatic dehalogenation.

An additional threat to populations predicted to collapse: Organobromine compounds of natural and anthropogenic sources in rough-toothed dolphins from the Southwestern Atlantic Ocean

Organic contaminants with toxic effects, like the conventional brominated flame retardants (BFRs) and BFRs of emergent concern, and their synergistic effects with other micropollutants, can be an additional threat to delphinids. Rough-toothed dolphins (Steno bredanensis) populations strongly associated with coastal environments already face a potential risk of decline due to high exposure to organochlorine pollutants. Moreover, natural organobromine compounds are important indicators of the environment's health. Polybrominated diphenyl ethers (PBDEs), pentabromoethylbenzene (PBEB), hexabromobenzene (HBB) and the methoxylated PBDEs (MeO-BDEs) were determined in the blubber of rough-toothed dolphins from three ecological populations from the Southwestern Atlantic Ocean (Southeastern, Southern and Outer Continental Shelf/Southern populations, SE, S, and OCS/S, respectively). The profile was dominated by the naturally produced MeO-BDEs (mainly 2'-MeO-BDE 68 and 6-MeO-BDE 47), followed by the anthropogenic BFRs PBDEs (mainly BDE 47). Median ΣMeO-BDE concentrations varied between 705.4 and 3346.0 ng g^-1 lw among populations and ΣPBDE from 89.4 until 538.0 ng g^-1 lw. Concentrations of anthropogenic organobromine compounds (ΣPBDE, BDE 99 and BDE 100) were higher in SE population than in OCS/S, indicating a coast - ocean gradient of contamination. Negative correlations were found between the concentration of the natural compounds and age, suggesting their metabolization and/or biodilution and maternal transference. Conversely, positive correlations were found between the concentrations of BDE 153 and BDE 154 and age, indicating low biotransformation capability of these heavy congeners. The levels of PBDEs found are concerning, particularly for SE population, because they are similar to concentrations known for the onset of endocrine disruption in other marine mammals and may be an additional threat to a population in a hotspot for chemical pollution.

Site-specific ecological effect assessment at community level for polymetallic contaminated soil

Current ecological risk assessment (ERA) is based more on book-keeping than on science especially for terrestrial ecosystems due to the lack of relevance to real field. Accordingly, site-specific ecological effect assessment is critical for ERA, especially at high tiers. This study developed procedures to assess ecological effect at community level based on field data. As a case study, we assessed ecological effect of polymetallic contamination in soil in the surrounding of an abandoned mining and smelting site in Hunan, China. Firstly, Zn was identified as the dominant contaminant in soil and slope gradient (SG) and pH as environmental impact factors using distance-based redundancy analysis(db-RDA). Secondly, sensitive endpoints were screened using correlation analysis between Zn and parameters of plant community composition and functional traits. Thirdly, exposure-effect curves between Zn and screened endpoints were developed by taking SG and pH as covariates using Bayesian kernel machine regression analysis (BKMR), based on which half-effect concentrations (EC₅₀s) and 10 %-effect concentrations (EC₁₀s) of soil Zn for each endpoint were calculated. Finally, site-specific hazardous concentrations (HC₅₀s) of Zn were estimated. It was revealed site-specific EC₅₀s and EC₁₀s for soil Zn ranged 80.5-201 mg kg^-1 and 342-893 mgkg^-1, respectively, and HC₅₀s based on EC₁₀s and EC₅₀s ranged 104-110 mg kg^-1 and 595-612 mg kg^-1, respectively, which are more specific and inclusive than those obtained based on crop and vegetable seed germination and seedling growth toxicity experiments.

Interspecies differences in mammalian susceptibility to legacy POPs and trace metals using skin fibroblast cells

The susceptibility to trace metals and legacy POPs is different between terrestrial and marine mammals. In this study, we established the first cell line from Indo-Pacific finless porpoises and compared the cellular responses of skin fibroblast cells from Pygmy killer whales, Pantropic spotted dolphins, Indo-Pacific finless porpoises, mice, and humans following exposure to copper, methylmercury, cadmium, PCB126, PCB153, and BDE47 to better understand the interspecies sensitivities of mammals to chemical pollutants. We conducted a risk assessment by comparing no-observed effect concentrations (NOEC), lowest-observed effect concentrations (LOEC), and half maximal effective concentrations (EC50) from cell viability assays and previously reported pollutant body burdens in mammals. Based on the in vitro data, Indo-Pacific finless porpoises were more sensitive to copper and methylmercury than other mammals. PCB153 exposure reduced cell viability in all mammals except humans, while PCB126 was more potent, with 13.33 μg/mL exposure reducing cell viability in all mammals. In contrast, BDE47 exposure reduced cell viability only in terrestrial mammals in addition to pantropic spotted dolphin. Based on the in vitro data and the natural context of metal concentrations, both methylmercury and cadmium posed a higher risk to cetaceans than human, while copper posed a lower risk to cetaceans. All three legacy POPs (PCB126, PCB153, and BDE47) posed minor risk to cetaceans for short-term exposure. This study demonstrated that a species-specific in vitro model may provide more accurate information on the potential risk of pollutants to mammals. However, due to the bioamplification of POPs and their potential impact on the endocrine system and immune system of cetaceans, risk assessment with long-term exposure with more in vitro models should be further studied.

Franciscana dolphins, Pontoporia blainvillei, as environmental sentinels of the world's largest mining disaster: Temporal trends for organohalogen compounds and their consequences for an endangered population

On November 5th, 2015, the Fundão dam collapsed in Minas Gerais, southeastern Brazil, releasing millions of cubic meters of mud containing mining residue into the Doce River. Two weeks later, the mud arrived to the marine environment, triggering changes in franciscana dolphin habitat, Pontoporia blainvillei, from Franciscana Management Area Ia. This is an isolated population of the most endangered cetacean species in the South Atlantic Ocean. Organohalogen compounds (OHCs) may pose a threat to this endangered population because of their endocrine disrupting properties. Hence, this study sought to determine if there were differences in the bioaccumulation profile of OHC (PCBs, DDTs, Mirex, HCB, HCHs, PBDEs, PBEB, HBBZ and MeO-BDEs) in franciscana dolphins before and after dam collapse and to build a temporal trend. Blubber of 33 stranded individuals was collected in Espírito Santo state for organohalogen assessment between 2003 and 2019. Differences were found between franciscana dolphins collected prior to and after the disaster. Additionally, significant temporal trends for organochlorine pesticides and natural and anthropogenic organobromine were detected. The increase in pesticide concentrations after 2015 is suggestive of their reavailability in the environment. The decline in organobromine over time could be due to their debromination in the marine environment and alterations in the composition of their natural producers. PCBs remained stable during the period of the study. Our findings show an increase in endocrine disruptor concentrations, which is of great concern for this endangered population.