GROWTH-RESPONSE OF THE CYANOBACTERIUM MICROCYSTIS-AERUGINOSA TO HERBICIDES AND PESTICIDES

Growth response of the planktonic cyanobacterium Microcystis aeruginosa to various concentrations of the herbicides and pesticides viz. CuSO4, DCMU (analytical grade Diuron), Karmex (commercial grade Diuron), 2,4-D, Fernoxone, BHC and bleaching powder (CCH) was studied in laboratory culture. The organism was sensitive to very low concentrations of CuSO4, DCMU and Karmex. Lethal concentration of Karmex and CuSO4 were found to be O.1 mu g.ml(-1) and 5.0 mu g ml(-1) respectively. The cyanobacterium could tolerate the other chemicals tested up to a concentration of over 500 mu g.ml(-1). On culturing the organism in the CuSO4 containing media, toxic effect of the chemical was reduced to a significant extent. This indicated that CuSO4 was accumulated or detoxified in the Microcystis cells. Toxic effect of Karmex on the organism was not reduced under similar experimental conditions.