Effects of binary mixtures of six xenobiotics on hormone concentrations and morphometric endpoints of northern bobwhite quail ( Colinus virginianus)

Abstract

This study investigated the effects of six endocrine disrupters in five different doses (0.1, 0.3, 1, 3, 10 mg/kg or μg/kg) in ethanol administered by oral gavage to bobwhite quail eggs. Six eggs each were in each dose group of coumestrol, ethynyl estradiol, indole-3-carbinol, o, p′-DDE, p, p′-DDE, or TCDD. Eggs were also dosed in two sets. One set was ethynyl estradiol (0, 0.03, 0.1, 0.3, 1.0, 3.0, 10.0 μg/kg) and TCDD (0, 0.003, 0.01, 0.03, 0.1, 0.3 μg/kg). This set was dosed below the air cell with corn oil as vehicle. Also, northern bobwhite quail eggs were injected in ovo with nine binary mixtures of six xenobiotics prior to incubation (coumestrol (0.3 mg/kg), ethynyl estradiol (3.0 μg/kg), indole-3-carbinol (3.0 mg/kg), o, p′-DDE (1.0 mg/kg), p, p′-DDE (1.0 mg/kg), TCDD (0.1 μg/kg)). The mixtures injected were p, p′-DDE+indole-3-carbinol, coumestrol+indole-3-carbinol, TCDD+indole-3-carbinol, p, p′-DDE+ o, p′-DDE, p, p′-DDE+ethynyl estradiol, coumestrol+ethynyl estradiol, coumestrol+TCDD, o, p′-DDE+ethynyl estradiol, TCDD+ethynyl estradiol. Eggs were dosed once prior to initiating incubation. Quail were allowed to hatch and were sacrificed at 21 days of age. Blood, measurements, and tissues were collected. Survival was significantly affected by increasing concentrations of TCDD in ethanol as revealed by trend analysis. Survival was also affected significantly by o, p′-DDE in ethanol but not by trend. Survival results of mixtures indicate significant differences among mixture, mixture components, and controls for coumestrol+TCDD, ethynyl estradiol+TCDD, and indole-3-carbinol+TCDD. Some trends from doses of single compounds that are supported by results in the literature were observed for hatchling weight of ethynyl estradiol dosed females, weight gain of indole-3-carbinol dosed males, weight gain and liver somatic index of o, p′-DDE dosed males, spleen somatic index of TCDD dosed males, and weight gain, gonad somatic index and egg gland somatic index of TCDD dosed females. In conclusion, the dose–response treatments appeared to have effects beyond effects on survival of in ovo dosed quail. For mixtures, plasma estradiol concentrations were significantly different among coumestrol+ethynyl estradiol, ethynyl estradiol, coumestrol, and vehicle treatments. Liver somatic index among the same treatments was also significantly different. Kidney somatic index among ethynyl estradiol+ p, p′-DDE, ethynyl estradiol, p, p′-DDE, and vehicle treatments was significantly different. Plasma estradiol and plasma testosterone ratios were very different among o, p′-DDE+ p, p′-DDE, o, p′-DDE, p, p′-DDE, and vehicle treatments. Coumestrol and ethynyl estradiol appear antagonistic for plasma estradiol concentrations and liver somatic index when both chemicals are present together. Ethynyl estradiol and p, p′-DDE appear to act additively on kidney somatic index when combined together. Mixtures of compounds used in this study indicate effects very different from either or both mixture components, indicating the lack of predictability of chemicals when combined in mixtures.