Fish-based biomonitoring to determine toxic characteristics of complex chemical mixtures: documentation of bioremediation at a pesticide disposal site

Medaka ( Oryzias latipes ) embryo and larval short-term bioassays were used to rapidly demonstrate changes in toxicity of aqueous soil extracts at a pesticide disposal site before and after bioremediation. By chemical analysis, concentrations of most pesticides (particularly endosulfans) decreased after the 63-day bioremediation. In static larval assays of extracts before bioremediation, concentrations from 2.2 to 2.9% produced 50% larval mortality after 72 h exposure, whereas extract concentrations of 18 to 34% were required after remediation. Extract concentrations required to inhibit normal embryo development increased from 10% before bioremediation to 20% afterwards. Aqueous extracts from untreated soil were nonmutagenic (Ames bioassay) and, nine months after a 72-h exposure, were associated with no histopath-ologic alterations. Advantages inherent with medaka embryo and larval bioassay indicate that fish-based biomonitoring might significantly improve efforts to characterize hazardous waste sites.