Effect of insecticide fenamiphos on soil microbial activities in Australian and Ecuadorean soils.

The effect of fenamiphos, a widely used organophosphorus pesticide, on important soil microbial activities such as dehydrogenase, urease and potential nitrification in four soils from Australia and Ecuador were studied. The results showed fenamiphos in general was not toxic to dehydrogenase and urease up to 100 mg/Kg soil. However potential nitrification was found to be highly sensitive to fenamiphos with a significant inhibition recorded even at 10 mg/Kg soil. In general, the nitrification activity in soils was decreased with an increase in fenamiphos concentration. The calculated EC(50) values for nitrification in all the tested soils ranged between 19 and 56 mg fenamiphos/kg dry soil. This study suggests that fenamiphos is likely to be detrimental to nitrification at field application rates.