<prompt> The permissible concentration of fluorides in drinking water is1.5 - 2.52-Jan0.5 - 0.80.1 - 0.2  <response>: Ans. C 0.5 - 0.8 Ref. Parks textbook of PSM - 22ndpg. 467, 597 ENDEMIC FLUOROSIS The permissible concentration of fluorides in drinking water is 0.5 to 0.8 mgL. Where drinking water contains excessive amounts of fluorine 3-5 mgL, 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 mgL intake. Mottling is best seen on the incisors of the upper jaw. Skeletal Fluorosis Genu valgum: Lifetime daily intake of 3.0-6.0 mgL 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 mgL. - Cadmium 0.003 mgL maximum limit. - Chromium - Cyanide: maximum limit 0.07 mgL. - Fluoride should not be more than 1.5 mgL - Lead - Mercury: 0.001 mgL 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 mgL, 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 