Assessing multigenerational exposure of an extract of naphthenic acid fraction components derived from oil sands process-affected water in Daphnia magna.

Naphthenic acids (NAs) naturally occur in bitumen deposits and surrounding waters, particularly within the Athabasca oil sands region in Alberta, Canada. Bitumen extraction produces large volumes of oil sands process-affected water (OSPW), which contains elevated concentrations of bitumen-derived chemicals, including NAs and other soluble organics. Although NAs are among the most acutely toxic component of OSPW to aquatic biota, there is limited understanding of chronic or multigenerational effects. To understand the effects of multigenerational exposure from an OSPW-derived NA fraction component (NAFC) extract, the model cladoceran Daphnia magna was used. Four generations (F0-F3) were each reared under continual NAFC exposure (0, 6.9, 15.8, and 31.1 mg/L) for 21 days in their exposure solution. The F0 and F2 generations experienced high mortality at 31.1-mg/L NAFC, with only 65% and 55% of the population surviving, respectively. Survivors showed significant growth and reproductive effects occurring at 31.1-mg/L NAFC exposure. Daphnia mass decreased by up to 43%, and delays in reproduction resulted in fewer broods within the 21-day period, with high reproductive failure (i.e., nonviable neonate production increased in all generations by up to 27-fold). The F2 generation was the most vulnerable to the NAFC exposure out of all the generations tested. Individual survival was highest in the F3 generation, although growth and reproduction were still negatively affected. These results suggest that exposure to NAFCs can considerably affect D. magna by causing individual mortality and affecting growth and reproduction, beyond the first generation exposed. This study provides novel insight into NAFC toxicity following long-term exposure, emphasizing the need for further multigenerational toxicity testing.