Many concerns raised recently regarded the environmental safety of alkylphenol polyethoxylate surfactants (APEOs).They are widely used in detergents, paints, herbicides and many other formulated products. It has been estimated that 60% of APEOs ends up in the aquatic environment; they are biodegraded and transformed into alkylphenols, such as nonylphenol and octylphenol that are hydrophobic and tend to accumulate in sediments. In this study we tested representatives of the most environmentally important groups of alkylphenolic compounds through a recombinant yeast bioassay using <i>Saccaromices cerevisiae</i> strain RMY326. The Yeast Estrogen Screen test (YES-test) is based on the DNA sequence of human estrogen receptor α (hER α) and the reporter gene <i>lac-Z</i> expressing the <i>Escherichia coli</i> enzyme β-galactosidase. Furthermore, we assessed the embryotoxicity of these compounds on the crustacean <i>Daphnia magna</i>through the well-known ability of alkylphenols to interfere with the metabolic elimination of testosterone. Daphnids (<24h old) were exposed to test compounds for different weeks and examined daily for released offspring. Offspring were counted, removed and examined microscopically to identify any developmental abnormalities. The results of YES-test showed the ability of the alkylphenols to stimulate the synthesis of β-galactosidase in the yeast. 4-<i>tert</i>-octylphenol and 4-nonylphenol were the most potent (100 times less than 17β-estradiol used as control) with full dose-response curve. These data indicate that the use of recombinant yeast cells is an interesting complement to study the effects of xenobiotics on the response of vertebrate hormone receptors to the studies with test animals or vertebrate cell cultures. Furthermore, the most of APEOs investigated were also found to be embryotoxic. <i>D. magna</i> showed the first effects after three weeks of exposure even if the high concentrations (in the order of mcg/L), at which abnormalities occurred, indicate that environmental concentrations pose no imminent risk.
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