Chronic exposure by ingestion of environmentally relevant doses of 226Ra leads to transient growth perturbations in fathead minnow (Pimephales promelas, Rafinesque, 1820)

Purpose : To assess the impact of environmentally relevant levels of ingested Ra-226 on a common freshwater fish species. Methods : Fathead minnow (Pimephales promelas, Rafinesque) were obtained at the first feeding stage and established on a commercial fish food diet containing Ra-226 in the activity range 10 mBq/g(-1), -10,000 mBq/g(-1). They remained on this diet for 24 months and were sampled invasively at 1,6,18 and 24 months to assess growth, biochemical indices and accumulated dose and non-invasively also at 12 and 15 months to assess growth. Results : Fish fed 10 and 100 mBq/g(-1) diet showed a small transitory deregulation of growth at 6 and 12 months. Fish fed higher activities showed less significant or insignificant effects. There was a trend at 18 months which was stronger at 24 months for the population distribution to change in all of the Ra-226 fed groups so that smaller fish were smaller and bigger fish were bigger than the controls. There were also significant differences in the ratios of protein: DNA at 24 months which were seen as a trend but were not significant at earlier time points. Conclusions : Fish fed a radium diet for 2 years show a small and transitory growth dysregulation at 6 and 12 months. The effects predominate at the lower activities suggesting hormetic or homeostatic adjustments. There was no effect on growth of exposure to the high activities Ra-226. This suggests that radium does not have a serious impact on the ecology of the system and the level of radium that would be transferred to humans is very low. The results may be important in the assessment of long-term environmental impacts of Ra-226 exposure.