Given recent reports suggesting that certain contaminants may be present in sewage effluents at levels, which may exert a deleterious impact on fish, it seems pertinent to extend ecological hazard evaluation for such substances to aquatic invertebrates. For this reason, we sought to determine whether 17beta-estradiol (E2), benzo(a)pyrene (BaP), 4-nonylphenol (NP), di(ethyl-hexyl)-phthalate (DEHP), and atrazine (A), individually or in binary mixture, can inhibit the survival, development, or reproductive output of the estuarine copepod Eurytemora affinis. In the first experiment nauplii were exposed to graded concentrations of individual contaminants to determine the 96-h LC50, 10-day no observed effect concentration (NOEC) and 10-day lowest observed effect concentration of each compound. In the second experiment newly released (<24-h-old) nauplii were exposed either to an individual contaminant at the NOEC or to binary mixtures, where each compound was used at half NOEC. The effects were monitored daily for development and sex ratio. After 10 days of exposure, adult males and females were paired and exposures continued to investigate effects on reproductive output (maximum 28 day total exposure). Based on these life cycle parameters the lowest 10-day NOECs were 6+/-4 microg L(-1) for E2, 7+/-3 microg L(-1) for NP, 12+/-3 microg L(-1) for BaP, 25+/-3 microg L(-1) for A, and 109+/-29 microg L(-1) for DEHP. BaP, NP, and DEHP inhibited naupliar development, but in binary mixture with E2 these compounds did not inhibit larval development. The results suggest that endocrine disruption could occur in copepods following exposure to estrogenic compounds, especially if they are exposed starting from embryonic development.