Toxicity test using medaka (Oryzias latipes) early fry and concentrated sample water as an index of aquatic habitat condition

The aim of the present study was to show a relationship between toxicity of 100-fold concentrated water and aquatic habitat conditions. Environmental waters are 100-fold concentrated with solid-phase extraction. Medaka early fry was exposed in these waters for 48 h. The number of death and disorder was counted at 1, 2, 3, 6, 12, 24, and 48 h; toxicity was expressed using inverse median effect time and median lethal time (ET ₅₀ ⁻¹ , LT ₅₀ ⁻¹ ). Average score per taxon (ASPT) for benthic animals and Index of Biotic Integrity (IBI) for fish were applied as indices of aquatic habitat conditions. The results of toxicity test were compared using ASPT and IBI. The different levels of toxicity were detected in the seawater of Japan. At the Husino River area, toxicity cannot be detected. In rivers, high toxicity appeared at urban districts without sewerage. By Spearman coefficient, the relationship between toxicity and high biochemical oxygen demand (BOD) were obtained. BOD household wastewater contains hydrophobic toxic matters; otherwise, seawater in industrial area does not show clear relationship between toxicity and chemical oxygen demand. Gas chromatography to mass spectrometry simultaneous analysis database may give an answer for the source of toxicity, but further test is required. Ratio of clear stream benthic animal sharply decreased over 0.25 of LT ₅₀ ⁻¹ or 0.5 of ET ₅₀ ⁻¹ . Tolerant fish becomes dominant over 0.3 of LT ₅₀ ⁻¹ or 0.5–1.0 of ET ₅₀ ⁻¹ . By Pearson product–moment correlation coefficient, correlation coefficient between toxicity and ASPT was obtained at −0.773 (ET ₅₀ ⁻¹ ) and −0.742 (LT ₅₀ ⁻¹ ) at 1 % level of significance with a high negative correlation. Toxicity (LT ₅₀ ⁻¹ ) has strong correlation with the ratio of tolerant species. By Pearson product–moment correlation coefficient, correlation coefficient between toxicity and IBI obtained were −0.155 (ET ₅₀ ⁻¹ ) and −0.190 (LT ₅₀ ⁻¹ ) at 1 % level of significance and has a low or no correlation between toxicity and IBI. Even with low toxic environmental waters, toxicity test using 100-fold concentrated and medaka early fly could detect acute toxicity. The detected toxicity seemed to limit the inhabiting aquatic species in the water body.