Tissue distributions of fluoride and its toxicity in the gills of a freshwater teleost, Cyprinus carpio

Fish take up fluoride directly from water and are susceptible to fluoride contamination of their environment. In this study, we examined the tissue distributions of fluoride and its toxicity in the gills of the common carp (Cyprinus carpio) chronically exposed to fluoride. Carp were exposed to a range of aqueous fluoride (35-124 mg/L) and sampled at 30, 60 and 90 days. The accumulation of fluoride in the tissues increased with the level and duration of exposure. Steady state was not achieved under the experimental conditions. The gills accumulated the highest levels of fluoride followed by the liver > brain > kidney > muscle > intestine. A dose-dependent inhibition was observed for the enzyme activities of Na+-K+-ATPase and Ca2+-ATPase in the gills after the fish were exposed for 90 days. Also, accumulation of fluoride was associated with the inhibition of superoxide dismutase (SOD) activities and a dose-dependent stimulation of malondialdehyde (MDA) levels in the gill tissues, suggesting that fluoride promoted oxidative stress in the fish. Microscopic examinations revealed injuries to gill tissues and chloride cells, with the severity of injury increasing with exposure concentration. These results suggest that chronic exposure to elevated concentrations of fluoride may induce toxicity in the common carp.

► There is a strong linearity between exposure concentrations and accumulation of fluoride. ► The gills had the highest levels of fluoride among all the tissues after 30, 60 and 90 days of exposure. ► A dose-dependent inhibition was observed for the enzyme activities of Na+-K+-ATPase and Ca2+-ATPase in the gills after the fish were exposed for 90 days. ► Fluoride caused oxidative stress in the fish. ► Damages of fluoride to the gill tissues increased with exposure concentration.