Effect of dietary 1,3,6,8-tetrachlorodibenzo-p-dioxin on the Japanese freshwater fish Oryzias latipes (Medaka) and aquatic snail Indoplanorbis exustus (Indohiramakigai)

Abstract

During the Japanese spring, many tons of herbicide are used to control weeds in rice paddies. Some of these herbicides are contaminated with 1,3,6,8-tetrachlorodibenzo-p-dioxin (1368-TCDD) and have given rise to residue levels of up to 40 ppb in some Japanese aquatic species. Japanese Medaka ( Oryzias latipes) and Indohiramakigai ( Indoplanorbis exustus) snails were chosen to represent aquatic species that might be exposed to elevated levels of agriculture derived 1368-TCDD. The Medaka were challenged with food contaminated with 40 ppb - 400 ppm 1368-TCDD, and the Indohiramakigai allowed to feed on the resulting detritus. Grab samples of both fish and snails were analysed for 1368-TCDD by GC-HRMS-SIM. Results show that the Medaka absorbed only 0.05 – 0.1 % of the dioxin content of their food and that the absorbed 1368-TCDD was almost totally depurated within 56 days. The Medaka appeared to suffer no harmful effects, even at the highest doses. Indohiramakigai snails were very much more efficient at absorbing 1368-TCDD from their detrital food source. Their populations were reduced dramatically, even at the lowest dioxin dose.