Interactions of polychlorinated biphenyls and organochlorine pesticides with sedimentary organic matter of retrogressive thaw slump‐affected lakes in the tundra uplands adjacent to the Mackenzie Delta, NT, Canada

Abstract Using a comparative spatial analysis of sediment cores from eight lakes in tundra uplands adjacent to the Mackenzie Delta, NT, we examined how the presence of retrogressive thaw slumps on lake shores affected persistent organic pollutant (POPs, including polychlorinated biphenyls and organochlorine pesticides) accumulation in lake sediments. Sediments of slump‐affected lakes contained higher total organic carbon (TOC)‐normalized POP concentrations than nearby reference lakes that were unaffected by thaw slumps. Mean focus‐corrected inorganic sedimentation rates were positively related to TOC‐normalized contaminant concentrations, explaining 58–94% of the variation in POP concentrations in sediment, suggesting that reduced organic carbon in slump‐affected lake water results in higher concentrations of POPs on sedimentary organic matter. This explanation was corroborated by an inverse relationship between sedimentary POP concentrations and TOC content of the lake water. Inferred chlorophyll a , S2, and S3 carbon fluxes to sediment were not significantly correlated to POP fluxes. Higher POP concentrations observed in sediment of slump‐affected lakes are best explained by simple solvent switching processes of hydrophobic organic contaminants onto a smaller pool of available organic carbon when compared to neighboring lakes unaffected by thaw slump development. Key Points Sediments in thaw‐affected lakes had higher pollutant concentrations Inorganic sedimentation rates were related to sediment contaminants Contaminants explained by “solvent switching” to organic carbon