Between 2006 and 2018, six Southern Resident killer whales and six Bigg’s killer whales sadly stranded. However, these 12 animals have been a vital source of information for scientists and veterinarians, first to understand why they died and then to assess how contaminants impact these two distinct populations. The team’s latest study focuses on polycyclic aromatic hydrocarbons (PAHs), the chemicals released by burning fossil fuels.
What was the study?
PAH exposure can occur through ingestion, inhalation, and skin contact. The team analyzed muscle and liver tissue from each stranded whale. They looked for evidence of PAH from “petrogenic” sources, such as vessel engines, oil spills, and ship wastewater discharge, and “pyrogenic” sources from burning coal, oil, or wood, including climate change-driven forest fires.
What did they find?
They tested for 76 known PAH compounds and found 38 in half the tissue samples. Three compounds were dominant, accounting for nearly a third of the total, and these three were also detected at the highest concentrations.
Results indicated that “urban” Southern Resident killer whales were exposed to petrogenic or fuel-based PAH sources, whereas more “mobile” Bigg’s killer whales were exposed to pyrogenic PAHs, including forest fires. These results suggested that diet and environment influenced the PAH source.
They found that “all contaminants with significant concentration differences were higher in males.” Studies of other contaminants have shown that female killer whales “offload” chemicals to their calves in the womb and through nursing, which results in higher contaminant “loads” in mature males who have no such outlet.
Maternal transfer
J32 Rhapsody’s calf died during birth, resulting in the death of J32. Tests showed that her unborn calf was exposed to 16 different PAH compounds. These findings revealed that PAH can cross the placental membranes to be absorbed by the calf even before birth. This is the first time scientists have identified the in-utero transfer of PAHs in killer whales. However, a previous study showed that other harmful contaminants move from mom to calf.
Sadly, just like human babies in utero, the authors noted that these marine mammals “are not equipped with mature detoxification systems” to rid their bodies of these compounds as adults can through respiration or excretion.
A previous study suggested that PAH levels only indicate recent exposure because, unlike other contaminants, they are not stored in fat layers, like blubber. Yet in this study, the authors proposed that “persistence of PAH contaminants may occur in those species chronically exposed to PAH pollution.”
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Now it seems that being unable to avoid PAH is just as threatening to Southern Resident killer whale health as accumulated contaminants, as the authors concluded that “the weight of evidence from research has supported PAHs’ carcinogenic, mutagenic, immunosuppressant, and toxic effects, as well as their ability to disrupt endocrine systems [hormones] in marine mammals.”
Of course, these toxic effects of PAH are equally likely in humans, so these whales are raising the alarm present in their environment and ours. How many times must these canaries sing in this coalmine before we take action?
