Response of the paddy field cyanobacterium Anabaena doliolum to carbofuran

Assessment of the influence of carbofuran on the nontarget cyanobacterium Anabaena doliolum revealed that this sheathless heterocystous form of cyanobacteria was more sensitive to the insecticide carbofuran. Anabaena doliolum was initially able to utilize low concentrations of carbofuran, whereas higher concentrations and the subsequent formation of hydrolytic breakdown products were toxic. Growth inhibition reached more than 50% by treatment with 80 and 100 ppm of the insecticide. Nitrogenase activity of the cyanobacterium was reduced by 38% after 48 h by treatment with 100 ppm carbofuran with no observed change in heterocyst frequency. Toxicity of the insecticide was the highest at pH 4-6 (46-59%) and the lowest at pH 7-10 (12-27%) due to the persistence of carbofuran and the resulting alkaline-catalyzed hydrolysis associated with the water regime of the rice fields. Doubling the initial population level of the cyanobacterium reduced the toxicity of the insecticide.