PAHs detected in orcas, including in utero transfer from mother to fetus

Harmful pollutants found in oil spills, burning coal and forest fire smoke have been detected in orcas in British Columbia waters, including the in-utero transfer of the chemicals from mother to fetus.

A team led by Juan José Alava, principal investigator of the University of British Columbia Ocean Pollution Research Unit analysed muscle and liver samples from six Bigg’s, or transient, killer whales and six Southern Resident killer whales stranded in the northeastern Pacific Ocean between 2006 and 2018. The whales were stranded after mishaps with boats.

The researchers looked for 76 polycyclic aromatic hydrocarbons (PAHs) and found some in all samples, with half the PAHs appearing in at least 50 per cent of the samples.

One compound, a PAH metabolite called C3-phenanthrenes/anthracenes, accounted for a third of total contamination. PAH metabolites, known as alkylated PAHs, stick around longer, are more toxic and bioaccumulate more than their precursor pollutant. Previous research on marine mammals shows PAHs cause cancer, mutate genes, suppress the immune system, have toxic effects and can disrupt endocrine systems.

“Southern Resident killer whales are one of the most endangered marine mammals in Canada, and indeed around the world,” says Alava. “They are our canary in a coal mine, telling us how healthy our waters and marine ecosystems are.”

While he and his team found the orcas’ average level of contamination was lower than previous studies of cetaceans in the Gulf of California, it was almost two times higher than in captive killer whales from Icelandic waters.

The paper, published late last year, is first to look at PAHs in orcas living in BC. However, the lack of baseline information on the whales’ previous exposure to PAHs makes it hard to know if the levels in this study are trending upwards.

Using low resolution mass spectrometry, the researchers say they found the contaminants in Bigg’s killer whales were likely those produced by burning coal and vegetation, as well as forest fires, which have plagued the province in the last few years. In Southern Resident killer whales, they were the kind produced by oil spills and burning of fossil fuels like gasoline.

But University of Toronto environmental chemist Frank Wania takes issue with the team’s use of a diagnostic PAH ratio to infer the sources of PAHs in the whales

“Diagnostic ratios apply to the emission source of PAHs to the atmosphere. There could be some argument made that the measured composition of PAHs in the atmosphere, for example diagnostic ratios, might convey information on the origin of these compounds. However, there is mounting evidence that this is not really the case,” says Wania, citing this study, and this one.

“The composition of PAHs in the whales will definitely not reflect the composition of PAHs at the emission source, because there are so many processes that will change the relative abundance of different PAHs on their ‘journey’ from the emission source to the whales,” he adds.

Alava says his team didn’t measure atmospheric concentrations of PAHs to make comparisons of PAH diagnostic ratios. “Thus we cannot comment on issues related to air levels of PAHs and assessment of PAH ratios in the atmosphere as this is out of the scope of our work,” he says.

However, he points to research from Environment Canada showing forest fires, which release about 2,000 tonnes of PAHs a year, are the single most important natural source of PAHs in Canada.

“Our research was robustly focused on the PAH concentration observed in the liver and skeletal muscle tissues to infer PAH sources via the application of PAH ratios comparing levels of low molecular weight PAHs – for examples, naphthalene, acenaphthene, acenaphthylene, fluorene, phenanthrene – and high molecular weight PAHs – for example, fluoranthene, pyrene, benzanthracene and chrysene,” says Alava.

“This was in tandem with the assessment of specific PAH diagnostic isomer ratios for particular PAH compounds, namely, anthracene, phenanthrene, fluoranthene, pyrene, benzanthracene and chrysene to elucidate PAH source identification.”

Regardless of where they come from, PAHs are a major concern for whale health. “It’s one of many stressors they’re experiencing,” says Alava, pointing to dwindling stocks of the Southern Residents’ prey, chinook salmon, climate change, anthropogenic noise and ship collisions.