**3.1 Presence of fluoride in drinking water and risk for human health**

Fluoride, the 13th most abundant element in the earth's crust, is essential to human life [66]. Elemental fluorine almost never occurs in nature, but fluoride is widely distributed in the Earth's crust, mainly as the mineral's fluorspar, cryolite, apatite, mica, hornblende, and fluorite [67, 68]. **Table 1** shows certain physical and chemical properties of fluoride.

Fluoride participates in the formation of bones and teeth and contributes to their solidification. It enters the body in the form of fluorides through drinking water, food, air, drugs, and cosmetics. It is known to have beneficial and harmful effects on humans [69]. Indeed, its deficiency has long been linked to the incidence of dental caries [70], while prolonged excessive intake has been associated with fluorosis [71]. Large populations throughout parts of the developing world suffer the effects of chronic endemic fluorosis [70].

The most important source of fluoride intake in the human body is drinking water [72]. According to WHO [73], the guideline value for fluoride in drinkingwater is 1.5 mg/L, based on increasing risk of dental fluorosis at higher


#### **Table 1.** *Physical and chemical properties of fluoride.*

concentrations and that progressively higher levels lead to increasing risks of skeletal fluorosis. This value is higher than that recommended for artificial fluoridation of water supplies for prevention of dental caries, which is usually 0.5–1.0 mg/L. WHO [74] recommends that, in setting a standard, Member States should consider drinking-water consumption and the intake of fluoride from other sources. Nevertheless, a content of 1 mg/l of fluoride ions is approximately the desirable concentration in the water supplied to the population to ensure optimal dental health [75]. However, several factors, including temperature, can influence this optimum value, which varies from one climatic region to another. It is therefore important to determine this optimal dose for each region depending on whether it is in a temperate zone or in a tropical zone [76]. Dean [77] has shown that the optimum concentration of fluorine as a function of the ambient temperature is 1.0–1.2 mg/l.

The optimal dose of fluoride in drinking water is defined as the amount of fluoride which decreases the prevalence of dental caries with the absence of significant fluorosis [78–80]. Fluorosis is the demineralization of tooth enamel by excessive fluoride ingestion during the years of tooth calcification [81]. This phenomenon, observed in children, can range from mild fluorosis to a severe manifestation Indeed, Dean [78] observed that 10% of children consuming water containing 1.0 mg/l of fluoride could develop benign fluorosis. It is reported in the literature that children living in the southwestern United States develop severe fluorosis, much more so than those living in the midwestern, while both groups are exposed to the supply systems. Water containing the same concentration of fluorine [82]. Other studies have suggested that the extremely high temperature of the southwest is a major factor contributing to the increase in demand for drinking water and the increase in severe and endemic dental fluorosis [80, 81, 82].

In Haiti, studies carried out on the water resources of the Center-Sud hydrographic region of Haiti (**Figure 2**), revealed fluorine concentrations between 0 and

**Figure 2.** *Map of the "Centre-Sud" hydrographic region of Haiti.*

*Chemical Pollution of Drinking Water in Haiti: An Important Threat to Public Health DOI: http://dx.doi.org/10.5772/intechopen.97766*

2 mg/l [28, 83]. The various localities of this region are exposed to an average daily temperature ranging from 17 to 36° C.

These observations lead on the one hand to questioning the problems of dental caries and fluorosis from which the populations of the areas studied may suffer and, on the other hand, to determine the optimal dose of fluoride in water intended for human consumption. of the Center-South hydrographic region of the Republic of Haiti. Fluoride's exposure is a major public health problem particularly for children. Indeed, intake of high-water fluoride concentration during child's growth and development stages has been associated with mental and physical problems [84–86].

#### **3.2 Water hardness and human health**

Hardness is the traditional measure of the capacity of water to react with soap and describes the ability of water to bind soap to form lather, which is a chemical reaction detrimental to the washing process [87]. Water hardness results from the contact of groundwater with rock formations. It is the sum of the concentrations of dissolved polyvalent metal ions which Ca2+ and Mg2+ are predominant. The sources of the metallic ions are typically sedimentary rocks, and the most common are limestone (CaCO3) and dolomite (CaMg(CO3)2) [66].

Ca and Mg are present as simple ions Ca2+ and Mg2+ with the Ca levels varying from tens to hundreds of mg/L and the Mg concentrations varying from units of tens of mg/L [88]. Magnesium is significantly less abundant than calcium in rocks and in most natural waters. In addition, magnesium concentrations are much lower in the water than calcium. They are generally less than 50 mg/L, although values higher or equal to 100 mg/L are stored particularly in cold climates [87]. The physical and chemical properties of Ca2+ and Mg2+ are presented in **Table 2**.

Hardness (in mg equivalent CaCO3/L) can be determined by substituting the concentration of calcium and magnesium, expressed in mg/L, in the following equation [89]:

$$\text{Total hardness} = 2.497 \left( \text{Ca}^{2+}, \text{mg/L} \right) + 4.118 \left( \text{Mg}^{2+}, \text{mg/L} \right) \tag{3}$$


Each concentration is multiplied by the ratio of the formula weight of CaCO3 to the atomic weight of the ion; hence, the factors 2.497 and 4.118 are included in the hardness relation [89].

#### **Table 2.**

*Physical and chemical properties of Ca2+ and Mg2+.*

Hardness is most expressed as milligrams of calcium carbonate equivalent per liter [90]. Water containing calcium carbonate at concentrations below 60 mg/l is generally considered as soft; 60–120 mg/l, moderately hard; 120–180 mg/l, hard; and more than 180 mg/l, extremely hard [91]. Although hardness is caused by cations, it may also be discussed in terms of carbonate (temporary) and non-carbonate (permanent) hardness [90].

Calcium and magnesium are essential for the human body [90]. They contribute to the formation and solidification of bones and teeth and play a role in the decrease of neuromuscular excitability, myocardial system, heart, and muscle contractility, intracellular information, transmission, and blood contractility [87, 88, 92]. They also play a major role in the metabolism of almost all cells of the body and interacts with many nutrients [93]. However, inadequate, or excess intake of either nutrient can result in adverse health consequences [90].

According to WHO [90] "*Inadequate intakes of calcium have been associated with increased risks of osteoporosis, nephrolithiasis (kidney stones), colorectal cancer, hypertension and stroke, coronary artery disease, insulin resistance and obesity. Most of these disorders have treatments, but not cures. Owing to a lack of compelling evidence for the role of calcium as a contributory element in relation to these diseases, estimates of calcium requirement have been made based on bone health outcomes, with the goal of optimizing bone mineral density.*

*To a great extent, individuals are protected from excess intakes of calcium by a tightly regulated intestinal absorption and elimination mechanism through the action of 1,25 dihydroxyvitamin D, the hormonally active form of vitamin D. When calcium is absorbed more than need, the excess is excreted by the kidney in healthy people who do not have renal impairment*" [90].

Magnesium is the fourth most abundant cation in the body and the second most abundant cation in intracellular fluid [90]. In the cardiovascular system, magnesium is the candidate element. It plays an important role as a cofactor and activator of more than 300 enzymatic reactions including glycolysis, ATP metabolism, transport of elements such as Na, K and Ca through membranes, synthesis of proteins and nucleic acids, neuromuscular excitability and muscle contraction [94]. That can have hand in various mechanism where the main is the calcium antagonist effect which can be direct or indirect [95].

Low magnesium levels are associated with endothelial dysfunction, increased vascular reactions, elevated circulating levels of C-reactive protein (a proinflammatory marker that is a risk factor for coronary heart disease) and decreased insulin sensitivity. Low magnesium status has been implicated in hypertension, coronary heart disease, type 2 diabetes mellitus and metabolic syndrome. Magnesium deficiency has been implicated in the pathogenesis of hypertension, with some epidemiological and experimental studies demonstrating a negative correlation between blood pressure and serum magnesium levels. However, data from clinical studies have been less convincing [90].

Indeed, water hardness has become an important public excess health issue [96]. Kobayaski [97] showed a relationship between water hardness and the incidence of vascular diseases. The scientific literature reported the existence of a relationship between cardiovascular disease mortality and water hardness [98–100]. Miyake and Iki [101] observed a lack of association between water hardness and coronary heart diseases mortality in Japan. Nonetheless, many studies covering many countries suggest such a correlation and geochemically it is worthy of serious study [88]. Based on available information in the literature on the association of water hardness and the incidence of cardiovascular diseases (CVD), Eisenberg [102] considered that Mg seems to be the basic element. Indeed, extremely hard natural water with CaCO3 concentration higher than 200 mg/l with a magnesium concentration

*Chemical Pollution of Drinking Water in Haiti: An Important Threat to Public Health DOI: http://dx.doi.org/10.5772/intechopen.97766*

lower than 7 mg/l may affect various organs including the cardiovascular physiology [87].

In Haiti, studies on the spring waters used to supply a part of the population of the Metropolitan Area of Port-au-Prince (MAPP), the most important urban area of the country, showed a total hardness greater than 200 mg/l, with magnesium concentration less than 7 mg/l [29]. In addition, magnesium concentrations ranging from 5.58 to 6.9 mg/l have been measured in groundwater in the metropolitan area of Port-au-Prince [103]. Drinking water low in Mg significantly increases the likelihood of cardiovascular mortality [104]. Catling et al., [105] found significant evidence of an inverse association between magnesium levels in drinking water and cardiovascular mortality following a meta-analysis of case control studies. In Haiti, cardiovascular disease (CVD) is now the leading cause of adult mortality in Haiti [106, 107].

#### **3.3 Groundwater pollution by heavy metals and human health**

Metals are natural constituents of the Earth's crust. The distribution and fate of metals in the environment is governed by their properties and the influence of environmental factors [108]. In environmental compartments, heavy metals constitute an ecological and human health concern since heavy metals are not degraded biologically like certain organic pollutants [109]. Metals exert biological effects that can be beneficial or harmful. Many metals such as Fe, Cu, Co, Mn, Zn, and Cr are essential for humans, and deficiency states with clinical abnormalities have been identified [27, 108, 110]. Other metals such as Hg, Pb, Cd, and As are not known to be essential for any animals [110]. Essential elements can also cause toxic effects at high doses.

In Haiti, heavy metals (lead, chromium, and nickel) have been measured in groundwater [27]. The physical and chemical properties of these heavy metals are presented in **Table 3**.
