The permissible concentration of fluorides in drinking water is

Ans. C 0.5 - 0.8 (Ref. Park's textbook of PSM - 22nd/pg. 467, 597) ENDEMIC FLUOROSIS # The permissible concentration of fluorides in drinking water is 0.5 to 0.8 mg/L. # Where drinking water contains excessive amounts of fluorine (3-5 mg/L), endemic fluorosis has been observed. # Certain parts of the country, e.g., Andhra Pradesh, Punjab, Haryana, Karnataka, Kerala, and TN are known for it. # Dental Fluorosis: Ingested during the years of tooth calcification essentially during the first 7 years of life by "mottling of dental enamel", which has been reported at levels above 1.5 mg/L intake. Mottling is best seen on the incisors of the upper jaw. # Skeletal Fluorosis/ Genu valgum: Lifetime daily intake of 3.0-6.0 mg/L or more. # Prevention: Changing the water source. # Nalgonda technique for defluoridation of water. The presence of following chemicals in excess of prescribed limits may constitute ground for rejection of the water as a source of public water supply: # Inorganic constituents: - Arsenic: recommended maximum limit of the concentration is 0.01 mg/L. - Cadmium 0.003 mg/L maximum limit. - Chromium - Cyanide: maximum limit 0.07 mg/L. - Fluoride should not be more than 1.5 mg/L - Lead - Mercury: 0.001 mg/L minimum upper limit. Bacterial plate count on yeast extract agar after incubation at 22degC for 7 days might serve as the best general-purpose indicator of microbiological quality. - Selenium - Nitrite and Nitrate: When nitrate level in drinking water exceeds 50 mg/L, methemoglobinemia may occur; most susceptible are bottle-fed infants of less than 3 months. Nitrate is a good indicator of past contamination. # Organic constituents - Polynuclear aromatic hydrocarbons - Pesticides