Combined Toxicity and Bioconcentration of Fluoride and Arsenic in African Catfish Clarias gariepinus (Burchell, 1822)

Laboratory experiments were performed to examine the combined toxic effects of two important aquatic contaminants viz., arsenic and fluoride on African catfish, Clarias gariepinus. Additionally, the bio concentration factors (BCFs) of the two contaminants in tissues and blood of catfish were also determined. The LC50 for sodium fluoride and arsenic trioxide were determined to be 619.3 mg L-1, 30.3 mg L-1, respectively. Erratic swimming movements with hyperactivity, loss of equilibrium, augmented air gulping and decreased food consumption were observed in the experimental groups. In co-exposure groups of arsenic and fluoride, the concentration of fluoride in fish tissues increased with increasing water fluoride concentration in the test aquaria with significant differences (P<0.01) between different groups. Also significant differences (P<0.05) in tissue concentrations of arsenic between groups were observed in response to different concentrations of water arsenic. However, the differences in blood fluoride and arsenic concentrations were not significantly dissimilar (P>0.05) among the exposure groups. Arsenic was observed to exceedingly bioaccumulate and biomagnify in the tissues. Perhaps due to the complex formation of arsenic and fluoride the bio concentration of arsenic in tissues was observed to decrease with increasing water fluoride concentration and vice-versa. The study concludes that fluoride may interfere with the bio-concentration of arsenic.