Origin of Polycyclic Aromatic Hydrocarbons in Lake Sediments of the Mackenzie Delta

Abstract

The concentrations and distribution of polycyclic aromatic hydrocarbons (PAHs) were assessed in sediment cores from among 14 lakes from three regions comprising a transect across the central Mackenzie Delta. PAHs were consistently found in the lake sediments, with parent concentrations in the 20-200 ng/g range. Concentrations were generally independent of depth in the sediment cores and this pattern was similar among the 3 regions of the delta. Concentrations increased in a westerly direction among the regions. For some lakes, the concentration of PAHs decreased with decreasing flooding frequency, and decreasing sedimentation rates. For the latter, maximum concentrations occurred at shallower depths within the sediment cores as flooding frequency among the lakes decreased. The distributions of C0-C4 alkylated 2- and 3- ring PAHs were consistent with a petrogenic origin, while the corresponding distribution of 4-ring PAHs appears to be more consistent with a biogenic or pyrogenic origin. Based on relative contributions to the overall PAH budget, a petrogenic source appears to be dominant. However, the pyrene/fluoranthene ratio is more consistent with a source derived from peat. The alkylated PAH profiles are inconsistent with those in the Athabasca River system, and supports a previously published hypothesis that the contribution of PAHs from the Athabasca oil sands to the lower Mackenzie River is minimal. A double ratio plot of chrysene vs dibenzothiophene, diagnostic of weathering, suggests most weathering occurred before the sediments were deposited in the lakes, while a double ratio plot of dibenzothiophene vs phenanthrene suggests a common source of PAHs across the delta, despite differing water sources from east to west across the delta. PAH inputs to the delta appear to mirror sediment inputs documented in previous work, where high sediment input from the Mackenzie mainstem during high floods dominates the delta sediment influx and masks any influence of the Peel River.

Has Alberta Oil Sands Development Altered Delivery of Polycyclic Aromatic Compounds to the Peace-Athabasca Delta?

“…This occurs because moving river-ice and high river flow velocities can mobilize and transport naturally occurring bitumen-rich materials in the riverbanks and in localized depositional accumulations downstream to the delta [62]. Similarly, studies at the Mackenzie Delta have identified that naturally occurring petrogenic PACs eroded from the mainstem of the Mackenzie River are carried with the sediment loads during the spring freshet [18] and that concentrations of PACs in floodplain-lake sediments are positively related to flood frequency [55].…”

Levels of polycyclic aromatic hydrocarbons and dibenzothiophenes in wetland sediments and aquatic insects in the oil sands area of Northeastern Alberta, Canada

“…These trends were evident in experimental, oil sands and reference wetlands. The dominance of alkylated over parent PAHs is indicative of a petrogenic source, typically associated with oil deposits (Steinhauer and Boehm 1992;Yunker et al 2002;Sauer and Uhler 1994;Headley et al 2002) and is a pattern that has been observed throughout much of the Athabasca oil sands area (Headley et al 2001;Akre et al 2004). In experimental and oil sands ponds the petrogenic source was most likely unrecovered bitumen from the mining and/or extraction processes.…”

Toxicokinetics and bioaccumulation of polycyclic aromatic compounds in wood frog tadpoles (Lithobates sylvaticus) exposed to Athabasca oil sands sediment

“…Although PACs are ubiquitous in the environment and can be formed naturally from forest fires, volcano eruptions, and diagenesis, the majority of these hydrophobic compounds are released by anthropogenic sources (Zhang and Tao, 2009). Anthropogenic PACs can be pyrogenic or petrogenic, depending on the condition under which they are formed (Lima et al, 2005 (Zhang et al, 2015b), snow (Kelly et al, 2009, Manzano et al, 2016, sediment (Headley et al, 2002, Kurek et al, 2013, and biota (Wayland et al, 2008, Lundin et al, 2015.…”