M11 AM Using Stable Isotopes in Ecotoxicology
Monday, 14 November 2005: 8:00 AM - 11:40 AM in 343-344

(VID-1117-248940) Using stable isotopes to monitor the bacterial degradation of naphthenic acids and polycyclic aromatic hydrocarbons.

Videla, P¹, Farwell, A¹, Butler, B¹, Dixon, D¹, ¹ University of Waterloo, Waterloo, Ontario, Canada

ABSTRACT- Large amounts of process-affected water (tailings) are generated from the extraction of bitumen from the oil sands in Alberta. The tailings consist of sand, clay, unrecovered bitumen, and large quantities of naphthenic acids (NAs) and polycyclic aromatic hydrocarbons (PAHs). NAs are complex mixtures of carboxylic acids that have been analytically characterized by C numbers (C5-C33) and Z families (Z=0, linear; Z=-12, 6 rings). The PAHs associated with oil sands are primarily alkylated PAHs, dominated by substituted dibenzothiophenes and phenanthrenes/anthracenes. NAs are of concern for their acute toxicity effects, PAHs for their carcinogenic and mutagenic potential. A "zero-discharge" policy prevents the release of tailings to receiving waters. As such, prior to reclamation, the tailings are placed into settling basins. To some extent the NAs and PAHs are biodegradable which could potentially reduce their toxicity. Biodegradation of NAs and PAHs in reclaimed aquatic environments is important in determining the structure and function of the mature aquatic ecosystems. To improve our understanding of energy sources and trophic level interactions, stable carbon and nitrogen isotopes have been analyzed for food web components of various oil sands reclaimed systems. Previous studies of benthic invertebrates indicated changes in stable isotope values (¹³C depletion and ¹⁵N enrichment) associated with elevated levels of NAs and PAHs in reclaimed systems. To gain a better understanding of the cycling of carbon and nitrogen sources at the base of the aquatic food web, laboratory studies have been initiated to examine the levels of isotope fractionation associated with the biodegradation of NAs and PAHs. Oil-sands derived bacterial cultures were supplied oil sands-extracted and commercially prepared NAs and PAHs of varying profiles and concentrations. At various time intervals, microbial growth, concentrations of NAs, PAHs, CO₂, DIC, DOC and NA profile, as well as ¹³C and ¹⁵N for the biomass, CO₂, DIC, DOC were characterized.

Key words: oil-sands, process-affected water, degradation, stable isotopes