Effects of petroleum oils and their paraffinic, asphaltic, and aromatic fractions on photosynthesis and respiration of microalgae.

Inhibition of photosynthesis was more severe than that of respiration in Anabaena doliolum exposed to Assam crude oil, furnace oil, petrol, diesel, and kerosene. Variabilities in toxicity of these oils, which seem to be related to their aromatic and asphaltic contents, were observed. Diesel and furnace oil, due to greater concentrations of aromatics, were more toxic than other oils. The toxic effects of asphaltic fractions were similar to those of aromatics. The study showed that the effects of a particular fraction vary from oil to oil. Therefore, toxicity of an oil cannot be correctly predicted by mere estimation of its various fractions. Lower concentrations of Assam crude stimulated photosynthesis and respiration of blue-green algae (cyanobacteria); however, green algae did not show such a response. Stimulation was exerted only by paraffinic fractions of the test oils.