生物応答を用いた排水試験法案の検証と事業場排水の実態調査

Abstract

In view of developing a bioassay for use into effluent management system in Japan, short-term toxicity tests using fish, daphnids, and algae were selected as a battery of bioassays, which evaluate the integrated effect of effluent, and "a draft protocol of bioassays for effluent testing" has been prepared. To examine the robustness, sensitivity and reproducibility of the draft protocol, we conducted an inter-laboratory trial where the same effluent was tested by 9 laboratories in Japan. No observed effect concentrations (NOEC) of the test effluent in all the laboratories were within the median +/-1 dilutions, suggesting that the variability between laboratories was at acceptable level. Furthermore, testing of reference chemicals by 10 testing laboratories showed that the reproducibility of the bioassays was relatively higher than that exhibited in the inter-laboratory validation of similar bioassays conducted by US EPA. However, the percentage of minimum significant difference (PMSD) and control coefficient of variation (CV) in the almost all the Japanese laboratories were at acceptable levels (as appears in the US EPA report), indicating that the intra-laboratory precision and the sensitivity of each test was sufficient. We investigated the value of using IC20 for fish, IC25 for daphnids, and IC5 for algae as an alternative to NOEC. With this approach, toxicity survey of 91 effluent samples conducted from 2008 to 2013 found that 36% of effluents were toxic to at least one of the three test species even after 10-fold dilution. The test species that demonstrated toxic effects were different in each sample; thus, we suggest that effluent toxicity evaluation should be based on more than one species due to different sensitivities.