Impacts of photo-oxidized dispersed oil on Phaeodactylum tricornutum

The Deepwater Horizon oil spill spilled 130 million gallons of oil into the Gulf of Mexico. This was followed by an application of 1.4 million gallons of chemical dispersants in an effort to disperse the oil into the water column and promote the biodegradation of oil. Photooxidation of oil is a natural process that causes oxygenation of an oil slick. Although the toxicity of oil on phytoplankton has been extensively studied, the effects of photo-oxidized oil, especially in combination with dispersants is virtually unknown. Phytoplankton vary in their sensitivities to oil and dispersant exposure. Here, we study the effects of photo-oxidized oil in the presence of dispersants on the growth and photo-physiology of oil and dispersant resistant pennate diatom Phaeodactylum tricornutum. We exposed P. tricornutum to two different dilutions of dispersed oil and dispersed photo-oxidized oil and monitored their growth rates and photo-physiological parameters such as photosynthetic efficiency (Fv/Fm), electron transport rates between photosystem II and I (rETRmax), and light harvesting ability (α). Growth rates were unaffected when exposed to dispersed oil and dispersed photo-oxidized oil. Analysis of various photo-physiological parameters revealed no significant differences between any treatments, except for lower rETRmax values in photo-oxidized dispersed oil treatment on the very first day of exposure. Further research are underway to determine the mechanisms behind the resistant nature of P. tricornutum.