Fluoride is very much essential for healthy growth of teeth and bones if it present between 0.6-1.5 ppm in drinking water, but if the level is higher than 1.5 ppm  causes dental and skeletal fluorosis, decalcification ,     and nervous disorder occurs but less than 0.6 ppm, bones and teeth will be fragile [1,2].Fluorosis  is crippling  disease which equally widespread in under developing and developed countries of the word [3].At present ,different experimental data having uncertainty as to whether fluoride has carcinogenic properties for humans ,and  also it is more toxic than lead   and less than arsenic (As) [4].  The lethal dose for adults is 0.2-0.35 gm. of Fluoride ion- per k.gm body weight. Fluoride is widely used in various branches of industry and some fluoride compounds are formed as by-products in certain processes. Excessive amounts of fluoride in the form of different compounds can enter the human body by means of polluted air, water and the food chain [5]. Fluorides are released into the environment naturally through the weathering of minerals, industrial products and phosphate fertilizer [6]. In recent years, much interest has centered around the physiological effect of fluorides and rapid, reliable, and sensitive methods for quantitative determination of the fluoride ion have become increasingly important. The methods for the determination of fluoride full into three principle groups: classical (titrimetric and gravimetric), potentiometric and spectrophotometric.

The spectrophotometric methods are most widely used for the determination of fluoride ion, but they are not so good in low level fluoride samples [1,4,5,7,8]. Therefore, the use of spectrophotometry is still met investigated. Spectrophotometric methods can be classified into two categories; Direct methods based on mixed ligand complex formation [6,9 -12], indirect methods based on substitution of colored complexes with F- [2,13-18]. Several other methods have been reported for the determination of fluoride, such as titrimetric [19-21], and gravimetric [22,23. Environmental pollution arising from the distribution of elements by natural or anthropogenic processes distort geochemical systems. The natural geochemical compositions of rocks and soils that make up the environment where we live may become direct risks to human health and may be the underlying cause of element deficiency and toxicity. These kinds of problems facing human life require urgent attention. Fluoride is a mineral that occurs naturally in almost all foods and water supplies. The fluoride ion comes from the element fluorine. It exists only in combination with other elements as a fluoride compound such as fluorite (CaF2), Cryolite (Na3AlF6), Topaz, Tourmalines and micas. Groundwater may have greater opportunity to contain appreciable amounts of fluoride depending on geological conditions. The aim of this research was to conduct and verify, at a regional scale, the influence of geoenvironmental contamination on the health of population. It was observed that fluoride may reach the hazardous concentration in some of groundwater wells of the study area as a result of geochemical processes. Their concentration increase produces adverse health effects, through ingestion of contaminated groundwater, on the expose population [24].

Fluorosis

Ingestion of excess fluoride, most commonly in drinking-water, can cause fluorosis which affects the teeth and bones. Technically, dental fluorosis is a developmental defect of enamel that can occur when a higher than optimal amount of fluoride is ingested at the same time as the stage of tooth development when enamel is being formed. The severity of the fluorosis is directly related to the age of the child at exposure, the type of exposure, the level of exposure, and the duration of exposure. It is important to note that fluorosis can only occur during the period when teeth are developing. Once teeth have formed, fluorosis can no longer occur. The mildest form of dental fluorosis may appear in about 10 percent of those exposed to optimally fluoridated water. Most mild to moderate fluorosis occurs not from the ingestion of properly fluoridated water, but from the unnecessary and inappropriate prescribing of fluoride supplement tablets, drops for children in fluoridated areas and the inappropriate ingestion of large amounts of fluoride-containing toothpaste by young children not properly supervised during tooth brushing. The presence of dental fluorosis at any aesthetic level is not related to any other adverse conditions in humans, nor is there any evidence to show that dental fluorosis is a precursor to any disease or dysfunction. Mild to moderate dental fluorosis is no more a pathological condition than is having freckles. There has never been a single valid, peer-reviewed laboratory, clinical or epidemiological study that showed that drinking water with fluoride at optimal levels caused cancer, heart disease, or any of the other multitude of diseases proclaimed by very small groups of antifluoridationists to be caused by fluoridation. Because fluoride is so effective, those fortunate enough to be provided with fluoridated water can count on an up to 40- to 50-percent reduction in the number of dental cavities they would have experienced without fluoridation. Fluoridation is an extremely cost-effective public health measure because the technology is so simple and the fluoride so inexpensive. Mottled enamel or dental fluorosis has been claimed to be an indication of the "toxic effects of fluoridation" by those opposed to fluoridation. Fluoridation is a form of nutritional supplementation that is not unlike the addition of vitamins to milk, breads and fruit drinks; iodine to table salt; and both vitamins and minerals to breakfast cereals, grains and pastas. The protection of fluoridation reaches community members in their homes, at work and at school -- simply by drinking the water. The only requirements for the implementation of fluoridation are the presence of a treatable centralized water supply and approval by appropriate decision makers.

Location and Description of Study Area

The study area is situated in the north eastern part of Mosul city and located approximately between latitude 36? 23? 48? – 36? 26? 00? and longitude 43? 02? 15? – 43? 07? 20?. It covers an area of about 90 km2 with its elevation varying from 250 - 220 m above sea level Figure (1). The climate is considered to be semi-arid and the annual precipitation being approximately between (320-400) mm. 90% of the total rainfall occurs from Oct.- April. The area is characterized by well-developed dendritic type of drainage system. Tributaries are considered to be non-perennial, as it carries water during rainy season and rainfall of high intensity and long duration. Coarse textured patterns noticed in the plains indicating high rainfall infiltration. The regional slope of the studied area is towards the south where the Tigris River. The most important activity of the area is agriculture, and the chief crops are wheat, barley and vegetable.

Figure1: Well Location of the Study Area.

Laboratory Analysis

In order to study the groundwater content of fluoride. Groundwater samples of the study area were conducted and analyzed in the Environmental Laboratories (WSP) of Nottingham University, using Ion chromatography [25] as shown in Table (1). An ion chromatograph, model Dionex-2020 was used for the analysis of the fluoride (F-). The Dionex-2020 ion chromatograph is a dual-channel, high performance chromatographic system featuring two precision analytical pumps, a dual-channel advanced chromatography module with optional column heater, and two conductivity detectors.

Table1: Fluoride Concentration and Chemical Characteristics of Groundwater Samples of the Study Area.

Geology of The Study Area

Fluoride in groundwater is mostly of geological origin. Waters with high levels of fluoride content are mostly found at the foot of high mountains and in areas where the sea has made geological deposits. Groundwater may have greater opportunity to contact appreciable amounts of fluoride depending on geological conditions of the study area.

The geological succession of the study area ranging from Middle-Upper Eocene to Quaternary see Figure (2):

Figure 2: Geology of the study area.

Al Fatha Formation of Middle Miocene

This formation is cropped out along the foothill of Bashiqa anticline composed of gypsum, anhydrite, marl, clay, green marl and lime stone [26,27].

Injana Formation of Upper Miocene

This formation crops out in several places of the study area, composed of sand stone, marl, lime stone and thick beds of red to brown sand stone [26].

Quaternary Sediments

The Quaternary sediments are mostly covering the total area under study. This sediment includes residual soil (sandy and loamy soil) and flood plain deposits which consist of sand, silt and clay, and slope deposits which consist of rock fragments, sand and silt which is slightly cemented. The thickness varies greatly from less than 2 m. to over 5 m.

Fluoride is a normal constituent of natural water and its high concentration in drinking water supplies produce dental fluorosis, which increase with increasing fluoride ion. The optimum F- ranges from 0.7 to 1.5 mg/l and the WHO maximum permissible level for F- is 1.5 mg/l. Both excess and lack of F- represent a dental problem. The maximum F- concentration in groundwater samples of the study area is 2.4 mg/l which is higher than the permissible level of the standard guide line of WHO for drinking water (0.1 - 1 mg/l). Concentrations in drinking-water of about 1 mg0. l–1 are associated with a lower incidence of dental caries, particularly in children, whereas excess intake of fluoride can result in dental fluorosis, [33,34]. Researcher and dentist are recommended people to use fluoride –rich tooth paste. Observed of fluoride concentration in groundwater of the study area shows a link with soil type and soil composition.

In this work, a method was developed for the determination of fluoride ion in different ground water samples. The method does not need heating or solvent extraction step. The method relies on the use of simple techniques and can be used for routine determination and quality control of fluoride ion. Fluoride naturally occurring in water can be above, at, or below recommended levels. Fluoride concentrations above drinking water have been detected in some of groundwater samples of the study area. Groundwater of the study area varies considerably from one place to another due to natural geological conditions. Concentration of fluoride in some groundwater samples are within the permissible level of the WHO recommended level, whereas other samples are higher than these limits.

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