Most controlled toxicity studies use single chemical exposures that do not represent the real world situation of complex mixtures of known and unknown natural and anthropogenic substances. In the present study, complex contaminant cocktails derived from the blubber of polar bears (PB; Ursus maritimus) and killer whales (KW; Orcinus orca) were used for in vitro concentration-response experiments with PB, cetacean and seal spp. immune cells to evaluate the effect of realistic contaminant mixtures on various immune functions. Cytotoxic effects of the PB cocktail occurred at lower concentrations than the KW cocktail (1 vs 16 μg/mL), likely due to differences in contaminant profiles in the mixtures derived from the adipose of each species. Similarly, significant reduction of lymphocyte proliferation occurred at much lower exposures in the PB cocktail (EC: 0.94 vs 6.06 μg/mL; P < 0.01), whereas the KW cocktail caused a much faster decline in proliferation (slope: 2.9 vs 1.7; P = 0.04). Only the KW cocktail modulated natural killer (NK) cell activity and neutrophil and monocyte phagocytosis in a concentration- and species-dependent manner. No clear sensitivity differences emerged when comparing cetaceans, seals and PB. Our results showing lower effect levels for complex mixtures relative to single compounds suggest that previous risk assessments underestimate the effects of real world contaminant exposure on immunity. Our results using blubber-derived contaminant cocktails add realism to in vitro exposure experiments and confirm the immunotoxic risk marine mammals face from exposure to complex mixtures of environmental contaminants.

Following the Deepwater Horizon (DWH) oil spill, the Natural Resource Damage Assessment conducted comprehensive health assessments on common bottlenose dolphins Tursiops truncatus in Barataria Bay (BB), Louisiana, in 2011Louisiana, in , 2013Louisiana, in and 2014, as well as in Mississippi Sound (MS) in 2013, to assess potential health effects from exposure to oil compared to Sarasota Bay (SB), Florida dolphins not exposed to DWH oil. Immune functions demonstrated a consistent increase in T (BB 2011) and B (BB 2011 and lymphocyte proliferation compared to SB. Cytokine concentrations varied considerably in wild dolphin populations, and no significant differences were found; however, interesting trends were observed. The Th1 cytokines IL-2, IL-12, and IFNγ, and the Th2 cytokines IL-5, IL-10, and IL-13, were 2-to 50-fold lower, and IL-4 was 3-fold higher, in BB 2011 compared to SB. Overall, the changes observed were compatible with those documented in other species following exposure to oil or PAHs and were most pronounced in BB 2011, at the place and time most affected by oil. The changes in T cell functions, and the trend towards a cytokine balance tilted towards a Th2, rather than a Th1 response, are compatible with intra-cellular bacterial infections such as Brucella, which has been identified as one of the potential contributory factors to perinatal dolphin mortalities, and changes in B cell functions are compatible with an increase in extra-cellular bacterial infections and primary bacterial pneumonia.

The Deepwater Horizon oil spill resulted in the release of over 640 million L of crude oil into the Gulf of Mexico, affecting over 2000 km of shoreline, including estuaries that serve as important habitats and nurseries for aquatic species. Cyprinodon variegatus (sheepshead minnow) are small‐bodied fish that inhabit northern Gulf of Mexico estuaries, are easily adaptable to laboratory conditions, and are commonly used in toxicological assessment studies. The purpose of the present study was to determine the somatic, reproductive, and developmental effects of an environmentally relevant polycyclic aromatic hydrocarbon (PAH) mixture, the oil high‐energy water accommodated fraction (HEWAF), on experimentally exposed sheepshead minnow (F0) as well as 2 generations of offspring (F1 and F2) without additional exposure. The F0 generation exposed to HEWAF had increased liver somatic indices, altered egg production, and decreased fertilization. Several developmental endpoints in the F1 were altered by F0 HEWAF exposure. As adults, low HEWAF‐exposed F1 females demonstrated decreased weight and length. Both the F1 and F2 generations derived from high HEWAF‐exposed F0 had deficits in prey capture compared to control F1 and F2, respectively. Correlations between endpoints and tissue PAHs provide evidence that the physiological effects observed were associated with hydrocarbon exposure. These data demonstrate that PAHs were capable of causing physiological changes in exposed adult sheepshead minnow and transgenerational effects in unexposed offspring, both of which could have population‐level consequences. Environ Toxicol Chem 2019;38:638–649. © 2018 SETAC

Health assessments were conducted on bottlenose dolphins in Barataria Bay, Louisiana, USA, during 2011 to 2018, to assess potential health effects following the Deepwater Horizon oil spill, compared to the unoiled Sarasota Bay, Florida, USA, reference dolphin population. We previously reported significant increases in T‐lymphocyte proliferation, as well as lower T helper 1 (Th1) cytokines, higher Th2 cytokine IL‐4, and lower T regulatory (Treg) cytokine IL‐10 in Barataria Bay in 2011 compared to Sarasota Bay, consistent with Deepwater Horizon oil exposure. Although values between 2013 and 2016 were more similar to those observed in Sarasota Bay, T‐cell proliferation was again elevated and cytokine balance tilted toward Th2 in Barataria Bay during 2017–2018. In 2018, Barataria Bay dolphins had significantly more circulating Treg cells than Sarasota Bay dolphins. Mice experimentally exposed to oil also had significantly increased T‐lymphocyte proliferation and circulating Treg cell number, including effects in their unexposed progeny. In vitro stimulation resulted in greater Th2 responsiveness in Barataria Bay compared to Sarasota Bay dolphins, and in vitro oil exposure of Sarasota Bay dolphin cells also resulted in enhanced Th2 responsiveness. Evidence points to Treg cells as a potential target for the immunomodulatory effects of oil exposure. The immunological trends observed in Barataria Bay appeared exaggerated in dolphins born after the spill, suggesting the possibility of continued oil exposure or multigenerational health consequences of exposure to oil, as observed in mice. Environ Toxicol Chem 2021;40:1308–1321. © 2021 SETAC

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