Pesticide and Surfactant Mixtures Alter Sexual Differentiation in Japanese Medaka (Oryzias latipes)

Effects-directed analyses of water extracts from the San Francisco Bay Delta of California using estrogenic activity indicated that the pesticides, bifenthrin, and diuron, as well as alkylphenol surfactants, were observed in active fractions. To determine whether the estrogenic activity of the mixture had any impacts on sexual development, Japanese medaka (Oryzias latipes) embryos were exposed to an ambient concentration of the compounds, individually and as mixtures, using components of the US Environmental Protection Agency (USEPA), Endocrine Disruptor Screening Program, and Organisation for Economic Co-operation and Development (OECD) assay. In medaka exposed to diuron, or surfactants alone, the percentages of phenotypic females were 88.9 +/- 19.2% and 66.4 +/- 3.8%, respectively. When diuron was combined with surfactants, 93.3 +/- 5.8% of the animals were female. To evaluate whether phenotypic females were changed from genetically male animals, the expression of the male-specific gene (DMY) was measured in animals following treatment. Treatments with ambient concentrations of surfactants and diuron had animals with higher percentages (78 +/- 19%) of phenotypic females that were derived from genotypic males. Our results demonstrated that mixtures of pesticides and surfactants may alter sexual development after embryonic exposure in fish.