Toxicity of C-10-, C-11-, C-12-, and C-14-polychlorinated alkanes to Japanese medaka (Oryzias latipes) embryos

Japanese medaka (Oryzias latipes) eggs were exposed to aqueous concentratio ns of six polychlorinated n-alkane (PCA) standards (C10H15.5Cl6.5, C10H15.3 Cl6.7, C11H18.4Cl5.6, C12H19.5Cl6.5, C14H24.9Cl5.1, and C14H23.3Cl6.7) of k nown carbon chain length and chlorine content to assess their toxicity. Egg s were also exposed to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) to act as a positive control. Chlorinated paraffins are complex industrial products for which there is a lack of toxicological data on individual congeners. Hi gh aqueous concentrations of C10H15.5Cl6.5 and C10H15.3Cl6.7, (9,600 and 7, 700 ng/ml, respectively) caused 100% mortality in eggs, but no other signif icant mortalities or lesions were observed at lower concentrations or in an y eggs exposed to the other PCAs. Larvae from eggs exposed to high concentr ations of the C-10-, C-11- and C-12-PCAs were extremely lethargic or did no t move, although a heart beat was present. The concentrations in these expo sures and the tissue concentrations of the larvae were at levels that shoul d elicit narcosis. Concentrations of the C-14-PCAs in larvae did not reach narcotic levels, and larvae in these exposures appeared normal with no sign s of narcosis. The TCDD was found to be extremely embryotoxic, consistent w ith past work using Japanese medaka eggs. The ratio of LC50 of TCDD to the LC50 of the PCAs, based on acute toxicity and TCDD results, were all <0.000 1, and most were <0.000001. These results suggest that the acute mechanism of toxicity of lower chlorinated, short (C10-13) and medium (C14-18) carbon chain PCAs is narcosis and that chlorine substitution on the terminal carb ons of PCAs does not significantly increase nor decrease the toxicity of C- 10- and C-14-PCAs. However, additional work is needed to assess a greater r ange of PCAs as well as their sublethal effects and chronic toxicity.