ORIGINAL ABSTRACT

Using glyphosate agrochemical components, we investigated their acute toxicity to juvenile Japanese medaka (Oryzias latipes) as well as their toxic impact at gene expression level on the liver tissues of adult medaka using DNA microarray. In our acute toxicity test, juvenile medaka were exposed for 96 hr to each of the following glyphosate agrochemical components: 10~160 mg/l of glyphosate, 1.25~20 mg/l of fatty acid alkanolamide surfactant (DA), and 12~416 mg/l of a fully formulated glyphosate herbicide. As a result, LC(50) values of glyphosate, DA, and the glyphosate herbicide were > 160 mg/l, 8.5 mg/l, and 76.8 mg/l, respectively. On the other hand, adult male medaka fish were exposed to each of the glyphosate agrochemical components for 48 hr at the following concentrations: 16 mg/l of glyphosate, 0.5 mg/l of DA, and 16 mg/l-glyphosate/0.5 mg/l-DA mixture. Interestingly, DNA microarray analysis revealed that there were no significant gene expression changes in the medaka liver after exposure to glyphosate. Nevertheless, 78 and 138 genes were significantly induced by DA and the glyphosate/DA mixture, respectively. Furthermore, we identified five common genes that were affected by DA and glyphosate/DA mixture. These results suggested that glyphosate itself possessed very low toxicity as previously reported by some researchers at least to the small laboratory fish, and the major toxicity of the glyphosate agrochemical resided mainly in DA and perhaps in unintentionally generated byproduct(s) of glyphosate-DA mixture.