Effect of pesticides on blue-green algae and nitrogen-fixation

The effects of the pesticides, amitrol, a derivative of amitrol (viz. 3,5-diamino-1,2,4-triazole), diquat, paraquat, linuron, MCPA, malathion, and monuron, were studied on the nitrogen-fixing algae,Anabaena cylindrica, Aulosira sp.,Calothrix elenkenii, Chlorogloeae fritschii, Cylindrospermum muscicola, Nostoc sp. fromCollema tenax, Nostoc muscorum, Tolypothrix tenuis, andWestiellopsis sp. In general, two types of response were discernible; an initial period of depression succeeded by an increased activity and an initial period of depression followed by a distinct decrease on prolonged incubation. The results indicate that some pesticidal compounds can severely limit the nitrogen-fixing capacities of blue-green algae, thereby affecting the overall nitrogen economy of soils in general.