Toxicity of Oil Sands Plant Wastewaters and Associated Organic Contaminants

Abstract

Abstract Acute toxicity testing using rainbow trout (Salmo gairdneri Richardson) was conducted on two wastewater streams from an oil sands extraction and upgrading plant. The main effluent stream from the upgrading plant was non-acutely toxic in flow-through bioassay while the construction drainage from the tailings pond dyke was acutely lethal in static bioassay with an extrapolated LC50 of 11% (by volume). With no obvious toxicant present, trace organic analysis was undertaken based on the high indeterminate organic carbon content of the sample. Analysis by GC-MS of the sample was able to identify four compounds: 2, 6-di-tert-butyl-p-cresol, (BHT); di-n-butyl phthalate, (DBP); bis (2-ethylhexyl) adipate, (BEHA); and bis (2-ethylhexyl) phthalate, (BEHP). Toxicity testing of the compounds required the evaluation of various schemes for the preparation of the test mixtures. Direct emulsion of the test compounds in water was ultimately adopted. Ninety-six hour static bioassays with rainbow trout indicated LC50 values of 540 mg/l for BEHP, 3 mg/l for BHT, 1.2 mg/l for DBP, and an approximate range of 54–110 mg/l for BEHA. Loss of emulsified components from the test mixture during the bioassays suggested that calculated LC50 values likely underestimate the actual toxicity of the compounds. The contribution by BEHA and BEHP to the whole effluent toxicity was likely minor while BHT and DBP indicated sufficient acute lethal toxicity to warrant further consideration. The feasibility of trace organic analysis and component toxicity testing as a means for conducting longer term research on oil sands wastewaters was demonstrated.