Validation of a short-term toxicity bioassay using three marine fish species in embryonic to larval stages

Abstract

The whole effluent toxicity (WET) test with freshwater aquatic organisms has already been validated for freshwater effluent management. Because the effluent is directly discharged into the coastal areas in Japan, there is an urgent need to establish a WET protocol for marine organisms. We have developed a draft protocol for a short-term chronic toxicity bioassay system to assess the effect on embryonic to larval stages of marine and brackish fish species (draft version). This study performed an inter-and intra-laboratory test using three marine fish species, Mummichog (Fundulus heteroclitus), Java medaka (Oryzias javanicus), and Red seabream (Pagrus major). Moreover, the validity and reproducibility of the draft protocol were assessed. The survival and hatchability of three fish and larval growth of F. heteroclitus and O. javanicus were evaluated as endpoints after exposure to two typical toxicants, hexavalent chromium (K₂Cr₂O₇; Cr) and 3,5-dichlorophenol (3,5-DCP). First, a satisfactory validity for the survival and hatchability for the control was obtained. Thereafter, we calculated the coefficient of variation (CV) of EC₂₅, obtained from inter-laboratory trials to examine the reproducibility of the test for respective endpoints. As a result, CV for at least one of the endpoints was within the allowable range (35%) for individual fish species, indicating a robust validity of the WET protocol for marine organisms. Future studies are necessary to clarify the usefulness of the protocol by applying it to effluents discharged into the coastal areas.