Detection of exposure effects of mixtures of heavy polycyclic aromatic hydrocarbons in zebrafish embryos

Abstract

In this study we evaluated the exposure effects of mixtures of five polycyclic aromatic hydrocarbons (PAHs); namely, benzo[a]anthracene, benzo[a]pyrene, benzo[b]fluoranthene, benzo[k]fluoranthene and chrysene on zebrafish embryos. Supplementation of the exposure media with 0.45\% dimethyl sulfoxide and 50ppm of Tween 20 could guarantee the solubilization and stabilization of the PAHs up to 24h without affecting the embryos development. The exposure effects were tested by detecting the differential expression of a number of genes related to the aryl hydrocarbon receptor gene battery. Effects were detectable already after 6h of exposure. After 24h of exposure, all PAHs, except for benzo[a]anthracene, acted as potent inducers of the gene cyp1a1. Benzo[k]fluoranthene was the major inducer; the effect caused by the mixture at the lower concentration tested (1ngml(-1)) was dominated by its presence. However, in the mixture at the highest concentration tested (10ngml(-1)) it caused less induction and was not dominant. No significant bioaccumulation values were detected on embryos exposed to the PAHs tested in this study; however, the results obtained, indicated that PAHs undergo a very rapid metabolization inside the embryos, and that those biotransformation products yield changes on the expression of genes involved in the aryl hydrocarbon receptor pathway. Future work should focus on identification of the PAH metabolization products and on the effect of these metabolites on toxicity. Copyright (c) 2016 John Wiley \& Sons, Ltd. Our objective was to detect in a realistic and accurate manner the effects of mixtures of heavy polycyclic aromatic hydrocarbons (PAHs) in zebrafish embryos. Assays were performed in the darkness, supplementing the exposure solution with dimethyl sulfoxide and Tween 20. PAHs did not bioaccumulate in zebrafish embryos; however, genes were induced already after 6h of exposure indicating that the exposure effects are due to PAH metabolites formed shortly after uptake. Benzo[k]fluoranthene was responsible for the induction of cyp1a1 in the mixture at low concentration, but not at the high concentration tested.