Estrogenic effects, reproductive impairment and developmental toxicity in ovoviparous swordtail fish (Xiphophorus helleri) exposed to perfluorooctane sulfonate (PFOS)

Abstract

Due to the wide distribution and persistence of perfluorooctane sulfonate (PFOS), an increasing number of studies are focusing on the toxicological effects of PFOS exposure in mammalian and fish model species. The results of these studies (on estrogenic activity, development and reproduction, etc.), however, are largely inconsistent owing to differences in exposure conditions (exposure time, concentrations, species and test methods, etc.). Oviparous fish species such as zebrafish and common carp are commonly used in PFOS exposure experiments, but no information is available on ovoviparous fish species. Thus, this study adopted as its model the swordtail (Xiphophorus helleri), a small, hardy and easily raised ovoviparous fish species. Males with a xiphoid caudal fin were employed to investigate vitellogenin (VTG) mRNA expression under exposure to a range of PFOS concentrations (0, 0.1, 0.5 and 2.5mg/l PFOS) for three weeks, with one-week recovery in clean water. Females were used to investigate the reproductive toxicity of PFOS exposure, and were exposed to the same concentrations as the males for up to six weeks. Finally, juveniles (20-30 days old) were exposed to 0 and 0.1mg/l PFOS for 90 days to check for developmental impairment. VTG mRNA expression was significantly inhibited at one and two weeks, with up-regulation at three weeks, in all of the exposure groups, but was stimulated only in the 2.5mg/l group at four weeks. The hepatosomatic index (HSI) was elevated in the 2.5mg/l male group at three weeks and in the juvenile group. The gonadal somatic index (GSI) was elevated in the 0.5mg/l female group and in the female juveniles. The 14-day survival rates for offspring differed significantly among the groups. Harmful effects were observed on the growth of the juveniles, but not on the sex ratio or the secondary sex characteristics of the young males. Histopathological changes in the liver were detected in both the male and female groups with the highest exposure. The overall results indicate that differences in model species may influence test results. Juveniles possess excellent qualities for sublethal chemical assessments employing the HSI and GSI under long-term exposure conditions.