TOXICITY OF FURADAN TO SEVERAL N-2-FIXING CYANOBACTERIA FROM THE RICEFIELDS OF COASTAL ORISSA, INDIA

The effect of the carbamate pesticide Furadan (carbofuran, 3%) on grow th and heterocyst frequency of, and N-2-fixation by, nine species of h eterocystous cyanobacteria belonging to the genera Anabaena, Nostoc, a nd Cylindrospermum was examined in test tubes. Two species (Anabaena f ertilissima and Nostoc commune) were most sensitive to Furadan treatme nt; all levels of the pesticide decreased the growth of these two orga nisms. Lower concentrations of the pesticide stimulated growth of the other species. Growth of Anabaena variabilis (An 2) was increased by 1 00% in the presence of 2000 mu g mL(-1) of the pesticide in the medium . The N-2-fixing capacity of all the species, except Anabaena sp. (An 7) and Cylindrospermum sp. (Cy 2), was not decreased by up to 50% in t he presence of LD(50) of the pesticide determined for each species.