The estrogenic effect of butylparaben was investigated in a rainbow trout Oncorhynchus mykiss test system. Butylparaben was administered orally to sexually immature rainbow trout every second day for up to 10 days in doses between 4 and 74 mg kg(-1) 2 d(-1) and in the water at 35 and 201 microgram l(-1) for 12 days. Plasma vitellogenin was measured before and during the exposures and the concentrations of butylparaben in liver and muscle were determined at the end of experiments. Increases in average plasma vitellogenin levels were seen at oral exposure to 9 mg butylparaben kg(-1) 2 d(-1). The ED50 values for increase in vitellogenin synthesis were 46, 29 and 10.5 mg butylparaben kg(-1) 2 d(-1), respectively, at day 3, 6 and 12. Exposure to 201 microgram butylparaben l(-1) increased vitellogenin synthesis, but exposure to 35 microgram l(-1) did not. Butylparaben showed little tendency to bioaccumulation in rainbow trout; less than 1 per thousand of the total amount of butylparaben administered orally at 51 mg kg(-1) 2 d(-1) over the 12 days experimental period was retained in liver at the end of the experiment. After 12 days exposure to 35 and 201 microgram butylparaben l(-1), plasma concentrations were 9 and 183 microgram l(-1), respectively, and for the fish exposed to 201 microgram l(-1) there was a positive correlation between concentrations of vitellogenin and butylparaben in the plasma. On the assumption that butylparaben removed from the water phase during water exposure were taken up into the fish, butylparaben uptake rates in the fish exposed to 35 and 201 microgram butylparaben l(-1) were 13 and 78 mg kg(-1) day(-1), respectively.

The ability of 17α-ethinylestradiol (EE2) to elevate vitellogenin levels were investigated in male flounder Platichthys flesus and vitellogenin concentrations in flounders from the Danish coastal environment were determined. Male flounders were exposed to 17α-ethinylestradiol (EE2) via food or water. Average vitellogenin concentrations in the control fish ranged between 25 and 100 ng mL−1. Exposure to 5.1, 8.1 and 16.8 ng EE2 L−1 in water and 500 and 5000 ng EE2 kg−1 body weight (bw) every second day in the food increased the plasma vitellogenin concentration in a concentration and time dependent manner, whereas exposure to 2.7 ng EE2 L−1 in water for 21 d and 5 and 50 ng EE2 kg−1 bw for 12 days in the food did not. EE2 could be detected in liver and testes (but not in muscle) after exposure to 8.1 and 16.8 ng EE2 L−1 in the water and 5000 ng EE2 kg−1 bw in the food; the highest concentration was 6 ng g−1 wet weight in liver. The majority of the male flounders collected from nine coastal Danish sites from 1999 to 2004 had vitellogenin concentrations below 100 ng mL−1, and only at two sites moderate estrogenic inputs were indicated.