The perchlorate anion (ClO4-) is known to inhibit thyroid function in mammals. While a great deal of information exists regarding the impact of perchlorate on mammals, data on the impact on aquatic organisms is sparse. In some locations in the United States, perchlorate has been found at part per million concentrations in surface water inhabited by fish.
The objective of this project was to determine the toxicological impact of perchlorate on fish at environmentally relevant levels.
Adult male and female common goldfish (Carassius auratus) were exposed in a laboratory flow-through exposure system for 30 days to four concentrations of perchlorate ranging from 14 ppb to 31 ppm, along with controls. Exposure was continued to 60 days for an additional set of controls and 31 ppm treatment groups. Gonadosomatic index (GSI), gonad histology, and plasma sex steroids (17β-estradiol, testosterone, and 11-ketotestosterone) were examined to assess reproductive function. Thyroid activity was assessed by use of a nonparametric rank-order assessment method developed for fish during this study.
Significant increases in head kidney thyroid activity occurred at 1200 ppb and 31 ppm in females and at 31 ppm in males. Pharyngeal thyroid activity increased in both male and female goldfish exposed to 31 ppm perchlorate. Exposure to perchlorate concentrations up to 31 ppm for 30 or 60 days had no effect on GSI. Some statistically significant effects on plasma sex steroid concentrations were observed for both sexes, but the differences were small and concentrations remained within normal ranges previously reported for goldfish in this reproductive state.
This project provided data on the impact of perchlorate to aquatic ecosystems. The controlled laboratory studies helped to determine the concentration of perchlorate necessary to produce adverse effects on fish.