Abstract
The estrogenicity of oβ, mβ, and pβdichlorobenzene (DCB) was evaluated with a yeast estrogen screen (YES) and zebrafish (Danio rerio) vitellogenin (VTG) assays. With the YES, pβDCB and mβDCB were found to be estrogenic in a concentrationβresponsive manner. The relative potency measured with the YES (relative to 17Ξ²βestradiol) was 2.2 Γ 10^β7^ for pβDCB and 1.04 Γ 10^β8^ for mβDCB. Following acute toxicity tests with the zebrafish, plasma VTG production was measured to examine the in vivo estrogenic activity of the three compounds after a 14βd exposure. Adult zebrafish were exposed to different concentrations of oβ, mβ and pβDCB, ranging from 0.1 to 32 mg/L; ethynylestradiol ([EE2]; 5 ng/L, 10 ng/L, 50 ng/L, and 100 ng/L) was used as a positive control. After exposure, blood samples were taken and protein electrophoresis was performed to determine the relative VTG content. Gonadosomatic indices (GSI) and condition factors (CF) were also calculated. Elevated VTG levels and decreased female GSIs were found in fish exposed to β₯5 ng EE2/L and in fish exposed to β₯10 mg pβDCB/L. Low GSIs coincided with high levels of VTG in the blood of female zebrafish. This relation was not only found in fish exposed to EE2 but also in controls and fish exposed to DCB. Therefore, a direct or indirect effect of VTG on the GSI is suggested rather than a direct toxic effect of the tested compounds on the gonads.