Water-soluble petroleum compounds: chemical aspects and effects on the growth of microalgae

Abstract

Fluorescence and high performance liquid chromatographic (HPLC) analyses revealed the relative enrichment of the water-soluble fraction (WSF) of crude oil with mono- and diaromatic hydrocarbons and with highly polar petroleum fractions, including phenolic components. Chemical changes of the WSF were recorded simultaneously with the growth of the diatom Phaeodactylum tricornutum and the chlorophyte Dunaliella tertiolecta in batch cultures. Results confirm the potential phytotoxicity of low-molecular-weight aromatic hydrocarbons and photooxidation by-products. Both stimulation and inhibition of growth were observed with the concentrations tested (from 0.02 to 29.3 mg l −1 WSF). Particularly noticeable was stimulation of the exponential growth phase following reduction of photosynthetic capacity during the lag phase when the chlorophyte was exposed to WSF ranging from 0.2 to 15.3 mg l −1. Significant linear relationships between WSF concentration and the difference in growth between control and test cultures were found for both microalgae during the exponential growth phase, demonstrating differences in their sensitivity to soluble petroleum compounds; the EC 50 (growth reduction) for P. tricornutum and D. tertiolecta was 16.4 and 36.0 mg l −1 WSF, respectively. A significant linear relationship was again found for the most sensitive species, P. tricornutum, when considering only the hydrocarbon fraction of WSF; growth inhibition appeared from 0.04 mgl −1 and the EC 50 was calculated at 0.36 mg l −1 hydrocarbons. The toxicity of the WSF was recorded with and without added phosphorus; no significant WSF-phosphorus interaction (ANOVA, P > 0.05) was observed.