Background: Germline mutations of the SDHD, SDHB and SDHC genes, encoding three of the four subunits of succinate dehydrogenase, are a major cause of hereditary paraganglioma and pheochromocytoma, and demonstrate that these genes are classic tumor suppressors. Succinate dehydrogenase is a heterotetrameric protein complex and a component of both the Krebs cycle and the mitochondrial respiratory chain (succinate:ubiquinone oxidoreductase or complex II).
Polychlorinated
biphenyls (PCBs) are toxic, persistent, and lipophilic
chemical compounds that accumulate to high levels in harbor porpoises
(Phocoena phocoena) and other cetaceans. It is important
to monitor PCBs in wildlife, particularly in highly exposed populations
to understand if concentrations are declining and how levels relate
to toxicological thresholds and indices of health like infectious
disease mortality. Here we show, using generalized additive models
and tissue samples of 814 U.K.-stranded harbor porpoises collected
between 1990 and 2017, that mean blubber PCB concentrations have fallen
below the proposed thresholds for toxic effects. However, we found
they are still associated with increased rates of infectious disease
mortality such that an increase in PCB blubber concentrations of 1
mg kg–1 lipid corresponds with a 5% increase in
risk of infectious disease mortality. Moreover, rates of decline and
levels varied geographically, and the overall rate of decline is slow
in comparison to other pollutants. We believe this is evidence of
long-term preservation in the population and continued environmental
contamination from diffuse sources. Our findings have serious implications
for the management of PCB contamination in the U.K. and reinforce
the need to prevent PCBs entering the marine environment to ensure
that levels continue to decline.
Polychlorinated biphenyls (PCBs) are a group of 209 persistent and bio-accumulative toxic pollutants present as complex mixtures in human and animal tissues. Harbor porpoises accumulate some of the highest levels of PCBs because they are long-lived mammals that feed at a high trophic level. Studies typically use the sum of a suite of individual chlorobiphenyl congeners (CBs) to investigate PCBs in wildlife. However, toxic effects and thresholds of CB congeners differ, therefore population health risks of exposure may be under or over-estimated dependent on the congener profiles present. In this study, we found congener profiles varied with age, sex and location, particularly between adult females and juveniles. We found that adult females had the highest proportions of octa-chlorinated congeners whilst juveniles had the highest proportions of tri- and tetra-chlorinated congeners. This is likely to be a consequence of pollutant offloading between mothers and calves during lactation. Analysis of the individual congener toxicities found that juveniles were exposed to a more neurotoxic CB mixture at a time when they were most vulnerable to its effects. These findings are an important contribution towards our understanding of variation in congener profiles and the potential effects and threats of PCB exposure in cetaceans.
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