Abstract
The ecological risk assessment has become incleaseingly an important issue of the conservation of biodiversity. Many countries including Japan have introduced the test guideline maintained by OECD, in which the ecological risk of each chemicals is assessed based on the acute toxicity test of the three water organism species, that is algae, water flea, and fish, in the laboratory. However, there is little in the studies regarding whether such toxicity data reflect the ecological impacts of each chemical in the actual field. We have promoted the paddy field masocosm test for assessing how insecticides influence the communities of organisms in paddy fields, which is difficult to predict by laboratory tests. We tested the ecological impacts caused by the 2 systemic insecticides, imidacroprid and fipronyl, widely used in the Japanese paddy fields by the paddy field masocosms sice 2010 to 2012. In each the year, we conventionarily applied the chemical into the experimental paddy fields and researched the occurrence of water organism species. As result, we could detect that the insecticides severely influenced the population dynamics of some species even under the standard concentration for the environmental safety provided by the OECD test guideline. And also it was discovered that the divergence of community components of the insecticide applied paddy fields from those of non-chemical paddy filelds increased as years go by because of accumulation of the insecticides residues. We aim to construct and spread a standard method for mesocosm test to each region in Japan for assessing the ecological impact of pesticide to each regional ecosystem.
