The Nalgonda technique was developed in India in year 1975 by the National Environmental Engineering Research Institute (NEERI), Nagpur, India and named after the village where it was pioneered. It is an aluminum-sulfate-based technique where coagulation–flocculation and sedimentation are applied. A simple model of a treatment system that was developed for use in African countries for domestic use is described below (Fawel et al. 2006).

Two 20-L-capacity plastic buckets are taken and fitted with taps 5 cm above the bottom of the buckets in order to enable trapping of the sludge below the draw-off point. The upper bucket tap is fitted with a tea sieve on which a piece of cotton cloth is placed allowing the water to flow directly into the second clean water bucket. In the first bucket, about 18 L of raw water are filled, and aluminum sulfate and lime are added simultaneously and dissolved/suspended by stirring with a wooden paddle. Stirring is done fast for the first minute and then slowly for next 5 min. Water pH is checked in between; preferably it should remain between 6.2 and 7.6. Aluminum sulfate makes the water acidic and lime is added to adjust the pH towards neutral. The amount of aluminum sulfate and lime required thus depends upon the quality of the untreated water. Usually lime is added at 5 % of the aluminum sulfate added for the treatment. The flocs formed are left to settle for about one hour. The treated water is then run from the tap through the cloth into the treated water bucket from where it is stored for daily drinking and cooking. It is desirable to remove the treated water within a couple of hours after initiating the flocculation process.

Advantages

Limitations/Disadvantages

In this process water is passed through a filter packed with activated alumina. Activated alumina (Al₂O₃) is made from aluminum hydroxide by dehydroxylation in a way that produces a highly porous material that can adsorb fluoride, arsenic, and selenium from water. For household purposes, activated alumina may be filled in ordinary water filtering candles and used for fluoride removal (Srimurali and Karthikeyan 2008). The activated alumina (filter material) requires regeneration after 3–4 months’ use.

Limitations/Disadvantages

KRASS technology applies a direct flow-through type column for defluoridation that can be easily recharged after its exhaustion (Agarwal et al. 1999). The fluoride from water can be removed for an influent pH range of 4.3–9.0 and influent fluoride concentration up to 24 mg/L. Residues of aluminum in treated water are minimal in this process. The exhausted media bed is claimed to be rechargeable up to 35 cycles (Singh and Yadava 2003).

Gastric absorption of fluoride is significantly modulated by dietary factors including the presence of certain divalent or trivalent cations (Rao 1984; Cerklewski and Ridlington 1987). Supplementation of chemical compounds containing these cations can reduce fluoride absorption, hence delay progression of the disease or help alleviate clinical symptoms.

Different aluminum salts (viz. hydroxide, chloride, and sulphate) have been tried with varying degrees of success. Aluminum ions form an insoluble complex with fluoride and reduce absorption of fluoride from the gastrointestinal tract (Spencer et al. 1985). Feed containing 3 % aluminum sulphate and chloride in equal ratio reduced fluoride absorption by 15 % (Grunder 1972). In another study, a 33–45 % decrease in fluoride absorption and lower serum, urine, bone, and teeth fluoride concentrations were observed in sheep after administration of aluminum sulphate (Kessabi et al. 1988). Aluminum chloride has also been reported effective in alleviation of experimental fluorosis in calves and sheep (Said et al. 1977; Mehra 1981). Dietary supplementation of small doses of aluminum hydroxide with 15 mg of fluoride as sodium fluoride greatly reduced the plasma fluoride levels (Spencer et al. 1981). Severity of clinical signs in sheep experimentally intoxicated with fluoride decreased when aluminum hydroxide was administered simultaneously (Zhai et al. 1987).

Calcium compounds are also effective in reducing the toxic effects and fluoride burden in animals. Lower retention of fluoride in the femur of rats was observed when calcium chloride was added to the diet along with sodium fluoride (Weddle and Muhler 1954). Calcium carbonate supplementation in rats is helpful in maintaining a serum fluoride concentration at a less toxic level (Ekambaram and Paul 2002). Addition of 200 g calcium carbonate/day in the diet can reduce the severity of clinical symptoms in lactating animals given a high dose of fluoride (Suttie et al. 1957). As with aluminum, it also reduces the intestinal absorption of fluoride (Harrison et al. 1984). Lower dietary calcium intake is considered a predisposing factor for fluorosis in humans (Mithal et al. 1993; Moudgil et al. 1996).

Boron supplementation reduces the severity of osteofluorosis (Elsair et al. 1980). In a study on water buffalo calves (Bubalus bubalis) exposed to 60 ppm elemental fluoride (as sodium fluoride) on dry matter basis in concentrate ration for 3 months, supplementation of borax (140 ppm elemental boron on dry matter basis) in concentrate ration helped minimize fluoride-induced changes in the hemogram and urinary biochemical profile (Bharti et al. 2007). Likewise, magnesium and selenium compounds are also reported to alleviate animal fluorosis (Han et al. 2006; Khandare et al. 2011).

Practical use of these chemical compounds for a long period is, however, not advisable due to their deleterious side effects. Feeding of aluminum sulphate (1 %) depressed the milk yield of cows (Burns and Allcortt 1964). The addition of aluminum salts can reduce the palatability of the feed (Boddie 1960; Burns and Allcortt 1964). Moreover, aluminum has been found to enhance the toxic effects of fluoride in in vitro studies (Van-der-voet et al. 1999). Fluoride induces release of IL-6 and IL-8, which are mediators of inflammation. Addition of Al³⁺ ions can enhance fluoride-induced IL-6 and IL-8 synthesis in human epithelial lung cells (Refsnes et al. 1999). Long-term boron and selenium supplementation for prophylactic and therapeutic purposes also has limitations including low efficacy, high cost, and undesirable health effects.

In humans, the toxic effects of fluoride are minimal when the diet is rich in different nutrients, particularly protein, calcium, antioxidant minerals, and vitamins such as A, D, E, and C. Clinical symptoms of fluorosis subside after a decrease in fluoride intake and consumption of a diet rich in essential nutrients and antioxidants (Susheela and Bhatnagar 2002). Vitamins A, C, and D are claimed to mitigate the symptoms of fluorosis in humans and retard the development of fluoride toxicosis with vitamin C possessing the greatest effect (Suttie and Phillips 1959). Therapeutic and preventive efficacy of vitamin C has been demonstrated in several experimental studies (Chinoy et al. 1993; Chinoy and Memon 2001). Choubisa and his coworkers opined that high levels of calcium and vitamin C present naturally in plants, grasses, and forage consumed by sheep, goats, and camels are responsible for the lower prevalence of dental and bony lesions in these animal species in comparison to cattle and water buffaloes reared in the same hydrofluorotic areas of Rajasthan, India (Choubisa 2010, 2013; Choubisa et al. 2011). However, this hypothesis does not appear plausible as after oral intake, vitamin C is almost completely destroyed by rumen microorganisms and is not utilized in ruminants (Ranjan et al. 2012). Hence, vitamin C may have some role in fluorosis prevention in simple-stomach animals and humans, but further study is required to elucidate its role in ruminants. Contrary to this, some laboratory animal studies even indicated that blood fluoride concentration (Chan et al. 1992) and fluoride accumulation in bone and soft tissues (Muhler 1958) increase after vitamin C administration during high fluoride intake. In a study in fluorotic human patients, daily oral supplementation of 2 g vitamin C failed to have any effect on urinary fluoride excretion (Krishnamachari and Laxmaiah 1975).

Copper supplementation has been reported to reduce bone fluoride accumulation in rabbits exposed to high dietary fluoride intake (Khandare et al. 2005). In a study, vitamin E and methionine supplementation had a hepatoprotective effect in rats intoxicated with sodium fluoride (Stawiarska-Pieta et al. 2011).

Herbal medicines and plant products can be helpful in the management of various ailments in animals including wounds, fever, anorexia, diarrhea, and snake bite, among others. Due to their low cost, easy availability, and less/no potential toxicity or side effects even at high doses, the quest for effective herbal medicine appears as the rational solution to fluorosis in humans and animals. Several plant products have been tested by various workers from time to time with encouraging results. However, the requirement of large doses and oral administration for a long time seems to limit their practical utility. Details about important plant products found effective in animal fluorosis are summarized in Table 7.2.