These members judge that more evidence is needed that bone fractures occur at an appreciable frequency in human populations exposed to fluoride at 4 mg/L before drawing a conclusion that the MCLG is likely to be not protective.
EPA established an SMCL of 2 mg/L on the basis of cosmetically “objectionable” enamel fluorosis, defined as discoloration and/or pitting of teeth. The SMCL was selected to prevent objectionable enamel fluorosis in a significant portion of the population. EPA reviewed data on the prevalence of moderate and severe enamel fluorosis and found that, at a fluoride concentration of 2 mg/L in drinking water, the prevalence of moderate fluorosis ranged from 4% to 15% and that severe cases were observed at concentrations above 2.5 mg/L. Because of the anticaries properties of fluoride, EPA judged 2 mg/L to be an adequate upper-boundary guideline to limit the occurrence of objectionable enamel fluorosis and provide some anticaries benefit. The SMCL is not a recommendation to add fluoride to drinking water. The SMCL is a guideline for naturally occurring fluoride to be used by the states for reducing the occurrence and severity of enamel fluorosis, a condition considered by EPA to be a cosmetic condition. If fluoride in a community water system exceeds the SMCL but not the regulatory MCL, a notice about the potential risk of enamel fluorosis must be sent to all customers served by the system. The committee evaluated the SMCL only in terms of its protection against adverse cosmetic and health effects, including enamel fluorosis, skeletal fluorosis, and bone fracture. Prevention of caries was not evaluated.
The committee considers moderate enamel fluorosis to be a cosmetic effect, because the available data are inadequate for categorizing the moderate form as adverse to health on the basis of structural or psychological effects. There are no studies since 1993 to assess the prevalence of enamel fluorosis at 2 mg/L, but previous reports have shown a distinct increase (approximately 15%) in moderate enamel fluorosis around 2 mg/L. Thus, the SMCL will not completely prevent the occurrence of moderate enamel fluorosis. As noted above, SMCL was intended to reduce the severity and occurrence of the condition to 15% or less of the exposed population. The available data indicates that less than 15% of children would experience moderate enamel fluorosis of aesthetic concern (discoloration of the front teeth). However, the degree to which moderate enamel fluorosis might go