Effect of Ultraviolet-B Radiation on Growth and Pigments of Chlorella Vulgaris

Ultraviolet radiation (UV) is known to affect the biological processes and thereby production of metabolites and overall growth of organisms including phytoplankton. Algal responses to UV radiations are broadly species and dose specific. The impact of artificial UV-B light from the source to cultures has been studied in Chlorella vulgaris. The cultures of C. vulgaris were exposed at two distances (50 and 100 cm) from the radiation source for different periods and cultured under laboratory conditions. The effect on growth and pigment contents were studied after irradiation and compared with untreated control cultures. The exposure of UV-B at short distance (50 cm) with increasing the duration from 1 to 10 min showed decreasing trend of growth (optical density, cell count and dry weight) and photosynthetic pigments (chlorophyll-a, b and carotenoids) as compared to the controls. Chlorophyll-b was found more sensitive to radiation. Growth and pigment contents were found increased up to 5 min exposure at long distance (100 cm) thereafter reduction was observed on subsequent exposures as compared to unexposed cultures. The UV-B exposure for 2 min had maximum growth and pigment content. These experiments revealed that the growth and pigment contents of C. vulgaris was inversely proportionate to the exposure time and directly proportionate to distance of source.