PHYTOTOXICITY AND EFFECT OF WATER SATURATED FRACTIONS OF HYDROCARBONS ON GROWTH AND PHOTOSYNTHETIC PIGMENT OF MICROALGAE

Phytotoxicity and the effects of water saturated fractions of hydrocarbons on growth and photosynthetic pigments of microalgae was carried out using three species of fresh water microalgae namely Chlorella vulgaris (Chlorophyte), Nitzschiapalea(Diatom)and Anabaena flosaquae(Cyanobacterium). The microalgae were grown separately in ratios 1:9 of 0%, 10%, 25%, 50%, 75% and 100% of water saturated fractions of hydrocarbons (Hexane, Benzene, Toluene and Xylene). Absorbance at 745nm was used to estimate algal growth while 630nm, 645nm, and 665nm were used to evaluate photosynthetic pigments. Phytotoxicity was measured using percentage inhibition. C. vulgaris showed growth stimulation at 10% - 50% concentrations of WSFs of hydrocarbon while 75% and 100% concentrations were inhibitory. A. flosaquae showed growth stimulation in 10% - 50% concentration of WSF of (Xylene), 10% - 75% of WSF of Toluene and Hexane and 10% - 100% in WSF of Benzene.N. palea showed growth stimulation at all concentrations (10% - 100%) of the WSFs of the various hydrocarbons. Photosynthetic pigment (Chlorophyll a, b and c) in A. flosaquae were negatively affected in lower to mid concentration of WSF of Xylene, higher concentrations in WSF of Toluene and Hexane and no effect on all concentrations of WSF of Benzene. C. vulgaris showed adverse effects on these growth parameters only at higher concentrations while N. pale show no negative effects in these parameters in all concentrations. The order of phytotoxicity of WSFs of hydrocarbons to the microalgae follows this pattern: Toluene > Xylene > Benzene > Hexane while the order of growth stimulation or response is N. palea>A. flosaquae>C. vulgaris. Phytotoxicity was higher in WSF of aromatic hydrocarbons (Benzene, Xylene and Toluene) than the WSF of the aliphatic hydrocarbon (Hexane). The results obtained showed mineralization pattern of the four hydrocarbons by the different species of microalgae and thus could be an addition to existing list of indicators microalgae of crude oil hydrocarbon polluted environment and microorganism with hydrocarbon bioremediation potentials.