Akiakane (Sympetrum frequens), a Japanese common meadowhawk, is widely distributed in Japan. The larvae hatch in paddy water in a season of rice planting. In recent years in Japan, insecticides for nursery-box application are widely used. As these insecticides include a long-acting type, it is concerned about affecting the growth of S. frequens larvae. The objective of this study is to develop acute toxicity test method for 2^nd instar larvae of S. frequens to some typical insecticides for nursery-box application (Fipronil, Imidacloprid) and compare the sensitivity of these insecticides. A 48-hour acute toxicity test method using a 48-well plate was established. Susceptibility to 2^nd instar larvae of S. frequens was 48 times higher for fipronil than for imidacloprid. For effective hatching of larvae, it was necessary to treat the eggs at low temperature for at least 4 weeks. The temperature during the acute toxicity test was preferably 21°C. rather than 26°C.

In the present study, we have examined whether the predicted bioavailability for heavy metals in sediments obtained through chemical analysis reflected the actual accumulation by the polychaete, Perinereis nuntia. In this study, P. nuntia was exposed to sediments collected from two sites of Kagoshima Bay, Japan, for 28 days. The polychaete adsorbed metals such as copper (Cu) and zinc (Zn) from sediments. Biomagnification factors from sediment to polychaete for Cu and Zn were 0.002–0.052 and 0.062–0.066, respectively, and Zn tended to be in higher concentrations in polychaete than Cu. Additionally, we measured metal content in geochemical fractions to predict the bioavailability through chemical analysis and was found to be 2–4% for Cu, and 16–21% for Zn. The prediction of bioavailability through chemical analysis could roughly reflect the actual absorbance of metals in the polychaete. Therefore, we conclude that the prediction of metal bioavailability through geochemical speciation is useful to reliably estimate actual bioaccumulation in the benthic organism.