Effects Of Heavy Metals On Growing Cultures Of Chlorella emersonii

This work evaluates the effect of some metals on a green alga Chlorella emersonii , under continuous and batch culture conditions with added metal and another, batch culture with no added metal but where organism had been exposed to metal for 18 hours prior to growth. It was found that Chlorella growth under continuous culture was reduced in the presence of silver at levels as low as 0.1 mg/l and ceased altogether at silver concentration of 1.0 mg/l. Under batch culture conditions no growth occurred with any of the silver concentrations tested. Chlorella that had been exposed to silver (1.0 mg/l) prior to cultivation without added metal showed growth. Above concentrations of 1.0 mg/l exposure there was no growth. Copper stimulated growth of Chlorella under continuous culture conditions up to levels of 0.5 mg/l but became severely toxic at levels of 1.0 mg/l and above. Under continuous culture conditions cadmium inhibited Chlorella growth at cadmium levels of 0.05 mg/l with no growth occurring at 0.5 mg/l. However under batch culture conditions Chlorella growth was not affected at levels below 1.0 mg/l. Chlorella that had been exposed to cadmium up to 20 mg/l. prior to cultivation without added metal showed growth This study indicates that for short periods some microorganisms can tolerate elevated levels of heavy metal contamination, although environment can be seriously affected if contamination persists over long periods. Key Words: Heavy metals, Chlorella, continuous culture, batch culture, environment. Global Journal of Environmental Sciences Vol.3(1&2) 2004: 21-26