Influence of illumination on phytotoxicity of crude oil

Petroleum products discharged at the water surface are rapidly modified under the effect of physico-chemical and biological transformations, themselves closely dependent on ecological factors. The rôle of some of these, such as illumination, may be particularly significant. This report deals with the effect of this parameter on the phytotoxicity of Kuwait crude oil on the primary production of a microalga: (Phaeodactylum tricornutum) and marine plankton communities.The result of these investigations indicates that the toxicity of extracts made from a crude oil is about two to three times greater when the latter is previously subjected to illumination of sufficient intensity and duration. The incorporation of a chemical dispersant (Corexit 8666) magnifies this phenomenon. In the case of a weathered crude oil mixed in equal parts with the dispersant, illumination raises the toxicity of the extracts by a factor of about 30.