【Paper】
Medaka（Oryzias latipes）Embryo Toxicity of Treated Leachate from Waste-Landfill Sites
Kohei Sumitani*, Shosaku Kashiwada**, Kae Osaki,* Masato Yamada***, Shino Mohri***
Shigeki Yasumasu****, Ichiro Iuchi**** and Yoshiro Ono*
* Graduate School of Natural Science and Technology, Okayama University
** Nicholas School of the Environment and Earth Sciences,
Duke University, NC, USA
*** National Institute for Environmental Studies
**** Life Sciences Institute, Sophia University
† Correspondence should be addressed to Yoshiro Ono:
Graduate School of Natural Science and Technology, Okayama University
（3-1-1 Tsushima-naka, Okayama, 700-8530 Japan）

Abstract
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（4mg/L）and different osmotic pressures（10-400mOsm/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.

Key words: embryo, leachate, hatching inhibition, hatching enzyme, environmental risk