**2.1 Air**

Even though F is extensively distributed in the environment, only a small portion of overall human fluoride exposure is through the air [4, 5]. This is because the F concentrations in the air are relatively low in non-industrial locations, but they rise steeply among industrial places where phosphate fertilizers are produced or fluoride-containing coal is burnt. As a result, human exposure to fluoride from ambient air has been estimated to be only about 1–4 mg/day [6]. This is insignificant compared with other sources of human fluoride exposure [7, 8]. Nonetheless, F can enter the air from sea spray, and therefore, the immediate atmosphere might be expected more enriched near or within the coastal areas [9]. No data were found on fluoride levels in ambient air or residential soil.

#### **2.2 Water**

F is generally prevalent in many water supplies and drinking water sources around the world because they leach into groundwater from F-containing rocks and soils [10]. Because drinking water is fluoridated artificially in certain regions, this is often the major contributor to daily F consumption by humans in those areas. It is found that children who drink 1 L of water per day may consume up to 1.2 mg of fluoride per day [9]. WHO (World Health Organization)'s maximum permissible limit of F in drinking water is 1.5 mg/L and highest desirable limit is 1.0 mg/L.Estimation of

*Sources of Human Overexposure to Fluoride, Its Toxicities, and Their Amelioration Using… DOI: http://dx.doi.org/10.5772/intechopen.103714*

human lethal F shows a wide variation of values that range from 16 to 64 mg/kg in adults and from 3 to 16 mg/kg in children.

#### **2.3 Toothpaste, mouthwash, and fluoride supplements**

Over 80% of the toothpastes sold around the world are fluoridated, with fluoride concentrations ranging from 1 to 1.5 mg/g [11]. It is believed some fluorides are absorbed straight into the tooth enamel when a person brushes with fluoride toothpaste. Adults are estimated to ingest about 0.02–0.1 g of toothpaste per day; however, children may ingest 0.2–0.8 g per day [12]. Fluoride concentrations in mouthwashes range from 0.23 to 0.97 mg/gram [11]. Adults are likely to use and consume these more frequently than youngsters. On average, an adult person can swallow roughly 1.0 g of mouthwash every day, while a youngster would take about 0.5 g, according to the Office of Environmental Health Hazard Assessment (OEHHA).

#### **2.4 Fluoride exposure from agricultural foodstuffs**

Although raw foods contain some F, the greater portion of F exposure through the diet is as a result of F added to foods when they are cooked or processed with high F water. Nonetheless, among the foods that are highest in F include tea and ocean fish containing bones or bone meal. The consumption of tea in larger quantities can represent a potential F health risk because the tea plant (*Camellia sinensis*) is known to uptake high F levels from the soil and to accumulate them in the leaves, from where

**Figure 1.** *Sources of fluoride and fluoride cycle in the environment.*

it is easily released during the infusion of tea leaves during brewing. For communities with low F levels in foods, contribution in adults ranges from 0.3 to 1 mg/day.
