Abstract
The ecological risks to aquatic organisms posed by insecticide use were compared using species sensitivity distribution (SSD) to determine if nursery-box application is ecologically safer than surface-water application. The targeted insecticides were imidacloprid and fipronil for nursery-box application and fenitrothion as a reference for surface-water application. Ecological risks were quantified as the potentially affected fraction (PAF) of species calculated using SSD and the pesticide concentration in river and paddy water. The PAF value was the highest for fenitrothion in both river and paddy water, indicating that substituting nursery-box for surface-water application reduces the ecological risk. The validity of our SSD approach for risk quantification was confirmed with comparisons in mesocosm studies. The comparisons suggest that the PAF values successfully correspond to the magnitude of the pesticide effect on ecosystems. The actual ecosystem appeared to have strong recovery potential, even when more than 50% of the species were affected.
