Polycyclic aromatic compounds in gull and tern eggs from breeding sites downstream of Athabasca oil sands mines...

Polycyclic aromatic compounds (PACs) were investigated in gull and tern eggs from breeding sites in receiving environments of the Athabasca Oil Sands Region (Alberta, Canada). Bitumen from natural outcrops and industry emissions of PACs are delivered downstream via the Athabasca River to the Peace-Athabasca Delta and Lake Athabasca. Parent and alkylated PACs were measured in eggs of Caspian Tern (n = 111), Common Tern (n = 53) and Ring-billed Gull (n = 40) from two downstream exposure sites and a reference lake. Total (sum of 47) PAC concentrations in eggs were 1-2 orders of magnitude higher for Caspian Tern (215.9 ± 263.3 ng/g wet weight [ww]) compared to Ring-billed Gull (32.6 ± 28.2 ng/g ww) and Common Tern (6.8 ± 5.8 ng/g ww). Concentrations were comparable in Ring-billed Gull eggs at an exposure and reference site. Eggs of all three species were dominated by alkylated low and high molecular weight compounds, and for Caspian Tern, alkylated dibenzothiophenes. Caspian Tern eggs showed large inter-year fluctuations in total PAC concentrations (2009 to 2022), with yearly means ranging from 2.0 to 661.3 ng/g ww. Carbon stable isotopes partially explained the inter-year variability, suggesting an influence of diet or habitat-specific feeding on Caspian Tern exposure to PACs. Egg PAC composition (particularly the detection of dibenzothiophenes) suggested petrogenic origins for Caspian Tern and pyrogenic or mixed sources for Ring-billed Gull and Common Tern. Future work is warranted to characterize the sources, drivers and toxicological risk of higher petrogenic PAC burdens in Caspian Tern eggs.