Question

The disease caused by excess fluoride in water is:
A. paralysis
B. lung cancer
C. skeletal fluorosis
D. dental caries

Answer 1

Hint: Fluorine is a highly reactive and electronegative element. Once it enters the body dissolved in water as ${F^ - }$(fluoride) ion, it will be attracted by positively charged ions like calcium \[(C{a^{2 + }})\].

Complete step by step answer:
We know that fluoride ions after entering the body through the blood vessels in the mouth or through the gastrointestinal tract reach the various organs and tissues in the body. Being a negative ion, fluoride is attracted by ions like \[C{a^{2 + }}\].
Bones and teeth have the highest amount of calcium and attract the maximum amount of fluoride ions forming calcium fluorapatite crystals \[\left[ {C{a_5}{{(P{O_4})}_3}F} \right]\]. Thus, amount of calcium in bones decreases leading to weakened bones. This leads to skeletal fluorosis.
Skeletal fluorosis causes severe pain, rigidity or stiffness in major joints of the body like neck, backbone, shoulder, hip, and knee joints. The bone structure changes and ligaments calcify resulting in impairment of muscles and ligaments. The bones become more susceptible to fractures.
The cause for fluorosis is excessive intake of fluorides from sources such as food, water, air and excessive use of toothpaste.
The most significant source of all is drinking water. If concentration of fluoride ions in water is more than $1.5$ mg/litre, it causes moderate level chronic exposure to fluoride ions. Exposure over a period of time results in fluorosis.
Therefore, the disease caused by excess fluoride in water is skeletal fluorosis.

Hence, the correct answer is C.

Note:
In its advanced stages, skeletal fluorosis can be extremely painful. Apart from its effects on bones, skeletal fluorosis shows side effects as well like rupture of stomach lining and nausea. High fluoride dose can also damage parathyroid glands which regulate calcium concentration in the body.