Sublethal hydrocarbon phytotoxicity in the marine unicellular alga Pavlova lutheri Droop

The unicellular marine alga Pavlova lutheri Droop responds to petroleum hydrocarbons by changing its normal pattern of motility. This toxic response occurs at very low concentrations of hydrocarbons (0.1 ppm naphthalene, 0.5 ppm Kuwait crude oil, 0.01 ppm No. 2 diesel fuel), and is diagnostic and consistent. The regularity of this phytotoxic response enabled us to analyze it mathematically by fitting toxicokinetic models to the various responses at different toxicant concentrations and exposure times. The data were fitted to a class of generalized compartmental models of which a cumulative (time-dependent) and a compartmental (concentration-dependent) model are specialized cases. Observations using glucose and tryptophan (10 −3 M) were included in order to distinguish between generalized nonspecific and phytotoxic responses. Contrary to expectations, the phytotoxic response exhibited by this alga to the petroleum hydrocarbons was found to be dependent only on concentration of the toxicant, and not on time. Thus, the cell's vulnerability remains constant in time, and its vulnerability is not influenced by the length of exposure to these toxicants.