Chemical ReviewsREVIEW climatic conditions. Here, groundwater flow is slow and reaction times between water and rocks are therefore enhanced. Fluoride buildup is less pronounced in the humid tropics because of high rainfall inputs and their diluting effect on groundwater chemical composition. However, in tropical countries like India, the problem of excessive fluoride is more severe, particularly in arid parts of the country. Beside natural sources, fluoride ions can also be found in effluents from semiconductor, metal processing, fertilizers, and glass-manufacturing industries. 3À7 The discharge of such wastewater into the surface water would lead to increased levels of fluorides in surface and groundwater. Global and Indian Scenario1.2.1. International Status. The problem of excessive fluoride in drinking water has engulfed many parts of the world, and today many millions of people rely on groundwater with concentrations above the World Health Organization (WHO) guideline value. 8 There are >20 developed and developing nations in which fluorosis is endemic. 9 High fluoride concentrations in groundwater are also found in the USA, Africa, and Asia. 10,11 The most severe problem associated with high fluoride waters occurs in China, 12 India, 13 Sri Lanka, 14 and Rift Valley countries in Africa. High fluoride ground waters have been studied in detail in Africa, in particular in Kenya and Tanzania. 15À19 High fluoride groundwater is also found in the East Upper Region of Ghana. 20 In the early 1980s, it was estimated that ∼260 million people worldwide (in 30 countries) were drinking water with >1 mg/L of fluoride. 21 1.2.2. Current Status in India. In India, fluoride was first detected in drinking water at Nellore district of Andhra Pradesh in 1937. 9 Since then, considerable work has been done in different parts of India to explore the fluoride-laden water sources and their impacts on human as well on animal health. At present, it has been estimated that fluorosis is prevalent in 17 states of India, indicating that endemic fluorosis is one of the most alarming public health problem of the country, especially in Rajasthan,

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