A Review of the Fate and Transport of Crude Oil Based Naphthenic Acids in the Aquatic Environment

John V. Headley¹ and Dena W. McMartin^2
1National Water Research Institute, Environment Canada, Saskatoon, Canada
²Division of Environmental Engineering, University of Saskatchewan, Saskatoon, Canada

Abstract

Naphthenic acids are comprised of a large collection of saturated aliphatic and alicyclic carboxylic acids found in hydrocarbon deposits (petroleum, oil sands bitumen and crude oils). Naphthenic acids enter surface water systems primarily through effluent discharge, but also through groundwater mixing and erosion of riverbank oil deposits. Of the possible environmental receptors (i.e., air, soil, and water), the most significant is water due to direct contact with oil sands material. Ambient levels of naphthenic acids in northern Alberta rivers in the Athabasca Oil Sands are generally below 1 mg/L. However, tailings pond waters may contain as much as 110 mg/L. The complexity of natural naphthenic acids in petroleum deposits poses an analytical challenge as reflected by the several techniques reported for quantitation of naphthenic acids in the environment. Although naphthenic acids are known to be persistent biomarkers used in identification of oil source maturation, little is established regarding their relative degradation pathways in aquatic environments. Other than a general knowledge of environmental persistence, the fate and transport of naphthenic acids has been sparsely studied. Investigation of the potential for photolytic and biological degradation as well as adsorption to typical Athabasca Oil Sands soils reveal that naphthenic acids are likely to persist in the water column and, with prolonged exposure, accumulate in sediments.