Effects of salinity and temperature on the bioavailability of dispersed petroleum hydrocarbons to the golden-brown algae, Isochrysis galbana

Comparative studies were done to determine the influence of a dispersant on the bioavailability of naphthalene from crude oil to the unicellular golden-brown algae, Isochrysis galbana, under changing temperature and salinity conditions. Conditions were selected to represent a range (two temperatures, 12 and 20 degreesC, and two salinities, 22 and 34 per thousand) encountered in Pacific waters, where extensive crude oil transport and refining occurs. Cells were exposed to laboratory preparations of either the water-accommodated fraction (WAF) of Prudhoe Bay crude oil (PBCO) or a dispersed oil (DO) mixture of PBCO and Corexit 9527(R) spiked with [U-14C]naphthalene. Uptake increased by as much as 50% in DO, 20 degreesC exposures run at 22 per thousand (0.24 µmol naphthalene/g algae in WAF, 0.37 µmol naphthalene/g algae in DO) compared with comparable exposures at 34 per thousand (0.23 µmol naphthalene/g algae in WAF, 0.37 µmol naphthalene/g algae in DO). A 24-h bioaccumulation factor (BAF) calculated in the absence of steady state indicated increasing bioaccumulation with decreasing temperature. No significant variation in relative metabolite composition occurred under the different experimental conditions. Results of these experiments showed that the use of dispersants enhanced the uptake of naphthalene by microalgae under a variety of temperature and salinity conditions, independent of aqueous concentration.