The effects of toluene on embryos and fry of the Japanese medaka Oryzias latipes with a proposal for rapid determination of maximum acceptable toxicant concentration

Fertilised eggs at various stages of development and newly hatched fry of medaka Oryzias latipes were exposed to a series of concentrations of the water-soluble extract of toluene. Static bioassays were conducted and TL₅₀ calculations made. In addition, the embryos were examined for the presence of developmental anomalies. The mean 96 h TL₅₀ for eggs was 54 mg/litre. The early (<3·5h) and late (>192 h) stages were more sensitive than the average. The newly hatched fry were not as sensitive to toluene as were the embryos.

In addition to acute toxicity effects, concentrations of toluene as low as 41 mg/litre produced teratogenic effects in susceptible embryos. We propose that the observation of these defects in the transparent eggs constitutes a simple and rapid tool for the estimation of Maximum Acceptable Toxicant Concentration (MATC) for fish.