Polycyclic Aromatic Compounds in Rivers Dominated by Petrogenic Sources after a Boreal Megafire

Area of Science:

• Environmental Chemistry
• Ecotoxicology
• Boreal Ecosystems

Background:

• Aquatic ecosystems face threats from polycyclic aromatic compounds (PACs).
• Oil sands mining in northeastern Alberta has increased PAC delivery into freshwaters.
• Natural PAC sources include bitumen erosion and wildfire inputs.

Purpose of the Study:

• To quantify petrogenic (oil sands) and pyrogenic (wildfire) PAC inputs into Alberta's freshwaters.
• To distinguish between industrial and natural PAC sources in an industrialized region.
• To understand the impact of increasing wildfire frequency and severity on PAC pollution.

Main Methods:

• Characterized river water PACs before and after the 2016 Fort McMurray wildfire.
• Analyzed wildfire ash and outcropping bitumen to identify PAC sources.
• Quantified PAC concentrations ranging from tens to thousands of ng/L.

Main Results:

• Petrogenic PACs were dominant throughout most of the post-wildfire period.
• Short-term episodes of pyrogenic PAC signatures occurred in burned watersheds due to ash wash-in.
• Wildfire events caused exceptional PAC concentration increases, sometimes exceeding background petrogenic levels.

Conclusions:

• This study provides the first quantification of petrogenic and pyrogenic PAC sources in this industrialized region.
• Petrogenic PACs remain a significant background pollutant, even after major wildfires.
• Increasing wildfire frequency and severity may exacerbate PAC pollution in Boreal Forest ecosystems.