The Uptake and Concentration of Fluoride by the Blue Crab, Callinectes sapidus

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Abstract
Fluoride uptake was studied in the blue crab,Callinectes sapidus Rathbun, in reference to a potential source of pollution in the Pamlico River estuary, North Carolina. Special attention was given to fluoride accumulation in crab tissues and to the effect of fluoride on crab growth. At 20 ppm fluoride in the water, the growth increment of crabs decreased 4.5% per molt. The cumulative effect over a 20-molt life cycle of a typical blue crab would be a 52% reduction in final average size. Under these conditions, maximum adult crab carapace width would decrease from 204 mm to 98 mm. Fluoride concentrations higher than 20 ppm had an even greater inhibitory effect on growth. Fluoride uptake rates were studied in exoskeleton, gill, hepatopancreas, and muscle tissues. Concentration of this ion in crabs from natural, unpolluted water (0.5–1.5 ppm F−) averaged 298 ppm in the exoskeleton, 253 ppm in the gills, 22 ppm in the hepatopancreas, and 10 ppm in the muscles on a dry weight basis. Crabs were maintained, and tissue analyses were made, for up to 90 days at 20 and 100 ppm, 22 days at 200 ppm, and 70 days at 400 ppm fluoride. The tissues accumulated significant amounts of fluoride at all experimental water fluoride levels. Additional tests were conducted on 30-day uptake rates at 0.5, 2, 8, 32, and 128 ppm fluoride. Significant accumulation occurred in all tissues at 8, 32, and 128 ppm fluoride in the water, while at 2 ppm the tissue fluoride content remained basically unchanged. The samples from the 0.5 ppm fluoride environment, at the end of the 30-day experiment, contained less fluoride than the control crabs. Rates of fluoride release from tissues were also determined for up to 20 days in fluoride-free water following the initial 30 days in fluoridated water. All tissues released fluoride readily, and most returned to near-normal tissue levels in the 20-day period. Of the tissues studied, the muscles are the most important to man since this is the portion of the crab most often consumed. The uptake data at 20 ppm fluoride in the water showed that the accumulation of fluoride in muscle tissue was approximately 50 ppm after a 90-day exposure period. Since this represents fluoride concentration on a dry weight basis, and crab muscle loses about 75% of its weight when dried, these fluoride levels must be reduced by 75% to obtain wet weight data. Calculations based on 12.5 ppm on a wet weight basis show that approximately 5.7 mg of fluoride per pound of crab meat can be expected if the crabs are subjected to 20 ppm fluoride in the water for as long as 90 days. Fluoride concentrations higher than 20 ppm in the water resulted in a much greater accumulation of this ion in the dried muscle samples (up to 600 ppm in water containing 400 ppm F−). This shows that crab muscle tissue can accumulate enough fluoride to present a potential public health problem.

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