Toxicity of crude oil and crude oil plus dispersant mixtures on the marine diatom Phaeodactylum Tricornutum

Abstract

The effects of six different oil dispersants of the third generation on the toxicity of crude oil emulsions to the marine diatom Phaeodactylum tricornutum were investigated. Cultures were exposed to five different concentrations of oil or oil plus dispersant mixtures for 24 h and the algal cell counts relative to controls are presented. The higher concentrations of total petroleum hydrocarbons in the test mixtures changed from 145 to 48 ppm, while the lower concentrations changed from 2.7 to 1.7 ppm over the 24 h test period. Generally, the oil plus dispersant mixtures were more toxic than the oil alone especially for three particular dispersants at the higher concentrations. The effects of different temperatures (12°, 16°, 20° and 25° C) on the toxicity of one particular dispersant are reported, indicating that enhancement of the toxicity of crude oil by the dispersant is even more pronounced at the higher temperatures. The ecological significance of these results is discussed.