The purpose of my project was to model how motor oil released to a lake impacts the organisms that live there. Whole effluent toxicity (WET) testing is used by regulatory agencies to determine how clean an effluent must be before release to the environment. In a WET test, aquatic animals are exposed to an effluent to determine if the effluent harms the animals.
I conducted eight experiments using the organism Daphnia magna. I added oxygenated, dechlorinated water to sample containers, then added varying concentrations of motor oil. For each experiment, two replicates were prepared. To each sample, I added Daphnia magna and then recorded the number of organisms alive after 24 and 48 hours. Great care was taken to properly maintain the Daphnia magna culture for the experiments. I maintained optimal temperature and lighting and followed the appropriate schedule for feeding and water changes.
I initially tested motor oil concentrations of 0.2% and higher. When all the Daphnia magna neonates died, I conducted two experiments using NaCl, since their response to NaCl is known. When the Daphnia magna reacted as expected, I continued the experiments, eventually using motor oil concentrations as low as 0.00017%. Using data from Replicate #1 Experiment #8 24-hour observations, I was able to generate a graph which revealed a motor oil LC50 of 30 mg/l. This is the concentration at which 50% of the organisms die. This very low concentration confirms how only a little bit of oil can cause serious damage to the environment.