Medaka (Oryzias latipes) Embryo Toxicity of Treated Leachate from Waste-Landfill Sites

It is of growing social concern that water quality and aquatic environment are threatened with pollution by leachate from waste-landfill sites. This study investigates medaka-embryo toxicity of treated leachates that are released into aquatic environments as effluent. Leachate exposure does not inhibit induction of hatching enzymes in medaka embryo. Leachate-exposed embryos showed delayed hatching compared to non-exposed embryos. Furthermore, exposure of larvae engendered malformations such as scoliosis and lordosis. Those malformations were observed mostly subsequent to exposure of leachate that was diluted to 60%, which implies a range of 250-300 mOsm/L. This osmotic pressure is similar to that of blood of teleost fish, including medaka fish. This osmotic pressure effect on enhancement of malformation toxicity was also observed in exposure of carbaryl (an insecticide) at a constant carbaryl concentration (4 mg/L) and different osmotic pressures (10-400 mOsm/L) . Malformation by carbaryl exposure was observed mostly at 250-300 mOsm/L. It decreased markedly at 400 mOsm/L. These results suggest that osmotic pressure is a factor in enhancing leachate toxicity. The release of the treated leachates into aquatic environments should be seen as a new environmental risk to aquatic organism/ecosystems.