Studies on risk assessment procedure of rice herbicides for microalgae in river ecosystem

The sensitivities of 4 unicellular microalgal strains to 14 rice herbicides were determined. After comparing the hazard and exposure data of herbicide concentration in rivers, it was clear that certain amide, triazine and sulfonylurea herbicides pose a relatively high ecological risk to Japanese aquatic ecosystems. To investigate in further detail the adverse effects of triazine herbicides on riverine native algal growth and to discover the relation between the diatom community and the use of herbicides, we compared the sensitivities of native attached diatoms (ADs) to triazine herbicides. Consequently, it became apparent that diatoms unresponsive to triazine herbicides were widely distributed in Japanese rivers.