Assessment of three plant-based biodiesels using a Daphnia magna bioassay

Biodiesel is an alternative fuel that is gradually replacing petroleum-based diesel use. Although biodiesel is considered friendlier to the environment, the potential toxic effects of biodiesel to aquatic organisms are still uncertain due to the wide range of feedstocks used to generate the fuel. The aquatic cladoceran Daphnia magna (D. magna) has been commonly used as a lethal and/or sub-lethal toxicological model organism in ecological risk assessments for contaminated water environments. In this work, we evaluated whether significant differences exist in the sensitivity of freshwater aquatic life to different biodiesels. The acute toxicity of three plant-based biodiesels was investigated using D. magna over a 96-h period. In addition, diesel fuel was tested as a reference. Increased immobility was observed as time progressed following exposure. Testing revealed of the four fuel products, diesel proved most toxic to D. magna, with half maximal effective concentration (EC₅₀) values of 4.7 μg/mL (24 h) and 3.4 μg/mL (72 h). Among the biodiesels, safflower methyl biodiesel was most toxic, with EC₅₀ values of 1026 μg/mL (24 h) and 71 μg/mL (48 h). Our data indicate that although not all biodiesels were toxic, the short-term exposure of D. magna to sub-lethal concentrations of biodiesels affects their mobility and thus decreases their reproductive potential. Overall, this research provides insights into the sub-lethal effects of biodiesels on an aquatic organism.