Assessment of acute and chronic toxicity of unweathered and weathered diluted bitumen to freshwater fish and invertebrates

This paper presents the results of two different studies investigating the acute and chronic toxicity of two blends of diluted bitumens ("dilbit") and weathered dilbit on freshwater fish and invertebrates after exposure to different concentrations of physically-dispersed (water accommodated fraction; WAF) and chemically-dispersed (chemically-enhanced WAF; CEWAF). The first study evaluated the acute and chronic toxicity of weathered, unweathered and dispersed Access Western Blend (AWB) dilbit on Fathead minnow (Pimephales promelas). In the second study, acute and chronic toxicity of weathered and unweathered Cold Lake Blend (CLB) dilbit was assessed on Rainbow trout (Oncorhynchus mykiss), and two invertebrate species, Daphnia (Daphnia magna) and Ceriodaphnia (Ceriodaphnia dubia). For Fathead minnow, unweathered AWB WAF demonstrated a significantly higher acute toxicity (LC50-96 h = 0.628 g/L) compared to the weathered AWB WAF (LC50-96 h = 2.06 g/L). Chronic toxicity tests showed that Fathead minnow lethality was also higher for unweathered AWB (LC50-7 d = 0.593 g/L) compared to the weathered AWB (LC50-7 d = 1.31 g/L) whereas larval growth toxicity was lower for unweathered AWB (IC25-7 d=0.312 g/L) compared to the weathered dilbit (IC25-7 d = 0.096 g/L). Rainbow trout exposed to unweathered CLB demonstrated a significantly higher toxicity (LC50-96 h = 5.66 g/L) compared to the weathered CLB (LC50 > 18 g/L). Lethality (LC50 = 6.43 g/L) was observed in Ceriodaphnia exposed to the CLB WAF while no mortality was observed with the weathered CLB. The reproductive effects on Ceriodaphnia were greater with the CLB (IC25 <1.0) than with the weathered CLB (IC25 = 3.99 g/L). Volatile organic compounds (VOC), polycyclic aromatic hydrocarbons (PAH) and total petroleum hydrocarbons (TPH) increased as the dilbit CLB and AWB WAF concentrations increased. The total VOC and the total PAHs (including the alkylated PAHs) presented similar concentrations in the weathered and unweathered AWB WAF. These compounds seem therefore not be affected by the AWB WAF weathering process. However, VOC and PAH concentrations decreased significantly in the Rainbow trout and Ceriodaphnia toxicity tests using the weathered CLB WAF. VOC and PAH concentrations were also lower in the weathered AWB CEWAF used for Fathead minnow chronic study.