Comparative studies on the green algae Chlorella homosphaera and Chlorella vulgaris with respect to oil pollution in the river Nile

The effect of oil pollution on growth and metabolic activities of the fresh water algae Chlorella homosphaera and C. vulgaris was studied. The study was conducted on two locations in the river Nile, one is oil polluted and the other is not polluted. The assemblage of the different algal groups was monitored in both locations. Chlorophyta was more dominant than Cyanophyta and Bacillariophyta in both locations during all seasons except in winter when Bacillariophyta is the most dominant group. The presence of crude oil or its refinery products (solar and lubricating) in the culture media of algae markedly influenced their growth, proteins and nucleic acid contents. The toxicity of oil was a concentration dependent. The low concentrations stimulated growth, protein content and nucleic acids, whereas high concentrations had an inhibitory effect. Although DNA and RNA responded similarly to crude oil in the two tested organisms, DNA showed more sensitivity than RNA to solar oil. Lubricating oil had a little phytotoxic effect on nucleic acids. Different species of algae response differentially to oil pollution; Chlorella vulgaris can be referred to as oil-sensitive, while Chlorella homosphaera can tolerate relatively higher concentrations of oil.