Toxicity of fluoride to Paratapes textilis (Gmelin, 1791) clam: alterations in shell colour, growth, accumulation, digestive gland and feet (Histology) and its potential risk to human health

The toxicity of fluoride to one of the economic clam species in Egypt; Paratapes textilis (Gmelin, 1791) was monitored in the present investigation. After one month of exposure of the bivalve to a fluoride ascending concentration of 2.5, 5, 10, 20 and 40 ppm, many biological aspects were affected. For the first time, fluorosis or whitening of clamshells was clearly observed in all tested fluoride concentrations. Moreover, growth of Paratapes textilis as represented by total length, width and total wet weight showed significant delay compared to the control specimens. A negative decreased percentage change especially in width was recorded for treated samples with fluoride compared to the control ones. Accumulation of fluoride in species organs showed different patterns. In the digestive gland and shell, as the concentration of fluoride increased there was a significant gradual increase in fluoride accumulation. Conversely, in feet, there was an increased accumulation of fluoride up to 5 ppm followed by a gradual decrease. Histology sections showed impairment of the digestive gland tubules structure, pyknosis, vacuolization, hypertrophy, and hyperplasia, especially at low fluoride concentrations. Feet musculature also showed torn and disintegrated muscle fibers in addition to pyknotic nuclei. Partial recovery was observed in sections of clams’ digestive glands and feet subjected to high fluoride concentrations, especially at 40 ppm, which could be attributed to the self-defense mechanism activated by the clam. Amongst the fluoride-treated samples, 2.5 and 5 ppm showed high fluoride bioaccumulation. Assessment of human health risks of fluoride resulting from fluoride-treated Paratapes textilis consumption indicated a potential risk.