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Can Smoke from Coal-Fired Brick Kilns in India Cause Fluorosis in Domestic Animals? if yes, Then Livestock Owners Need to be Made Aware

Shanti Lal Choubisa1, 2*
1Department of Advanced Science and Technology, National Institute of Medical Science and Research, NIMS University Rajasthan, Jaipur 303121, Rajasthan, India.
2Former Department of Zoology, Government Meera Girls College, Udaipur 303002, Rajasthan, India.

Article Info

Received Date: 29 January 2025, Accepted Date: 10 February 2025, Published Date: 13 February 2025

*Corresponding author: Shanti Lal Choubisa, Department of Advanced Science and Technology, National Institute of Medical Science and Research, NIMS University Rajasthan, Jaipur 303121, Rajasthan, India.

Citation: Shanti Lal Choubisa. (2025). Can Smoke from Coal-Fired Brick Kilns in India Cause Fluorosis in Domestic Animals? if yes, Then Livestock Owners Need to be Made Aware. Biomedical and Clinical Research Journal, 1(2); DOI: http;/02.2025/BCRJ/006.

Copyright: © 2025 Shanti Lal Choubisa. This is an open-access article distributed under the terms of the Creative Commons Attribution 4. 0 international License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Abstract

There are more than 140,000 legal and illegal coal-based brick kilns operating in India in rural, urban, agricultural, pasture, and forest areas. These kilns require about 35 million tons of fossil coal every year to run them. During the burning of these coals, a number of fluoride-containing toxic gases such as HF, SiF4, and CF4 are released into the atmosphere along with smoke. These gases not only contaminate the air, soil, and water but also contaminate the surrounding forest vegetation, agricultural and horticultural crops, and animal pastures on which domestic animals such as bovines, sheep, goats, horses, camels, etc. depend. When these animals are repeatedly exposed to kiln fluoride pollution (smoke) or fluoride contaminated food and water for a long time, their health is badly affected and they develop a disease called fluorosis. This disease causes gradual deformation of the teeth and bones of the animals and these pathological changes are called dental fluorosis and skeletal fluorosis, respectively. Workers of coal-based brick kilns and people living around them also often suffer from this disease. In India, there have been some research studies on endemic fluorosis in domestic animals exposed to fluoride emissions or pollution from brick kilns, which show that the smoke from these coal-based brick kilns is not safe for the health of domestic animals

and causes fluorosis disease in them. But most of the livestock owners are unaware of the limping and other health hazards to their pets. However, by taking some preventive measures, these animals can be saved from this kilns industrial fluoride poisoning. This review focuses on fluoride pollution from coal-fired brick kilns and its toxic effects or fluorosis in domestic animals. It also seeks to draw the attention of the veterinary and pollution control departments of the country to this health problem in domestic animals. The author suggests that there is a need for special research work on this health problem caused by smoke from coal-based brick kilns in domestic animals in the country as these animals are basic sources of income for villagers.

Keywords: brick kilns; chronic exposure; coal; domestic animals; fluoride pollution; fluorosis; health; smoke; india

Introduction

Fluorine (F-) is the 9th element in the periodic table and belongs to the non-metals. In fact, it is the most electronegative and highly reactive diatomic yellow-green pungent and irritating gas. Hence it is never found in free form as an element in nature. Fluoride or fluoride compounds are the results or products of chemical combination of fluorine with other elements including some rare gas elements. Fluoride with varying amounts is found in various environments such as water, soil, and air. In general, inorganic forms of fluoride are relatively more toxic than its organic forms [1, 2]. Both humans and animals can be exposed to fluoride through water, air, and food. In India, fluoridated drinking groundwater is the most common source of fluoride exposure to domestic animals, followed by industrial fluoride pollution, and fluoride-contaminated food [1-6].

In India, especially in rural areas or villages, most of the villagers are unaware of the toxic effects of air fluoride pollution caused by coal burning in brick kilns (Figure 1) operating near their area. During coal burning, various types of fluoride containing toxic gases are released into the environment along with smoke. This kiln generated air fluoride pollution (airborne fluoride) is a potential source of fluoride exposure to both villagers and their economically important domestic animals such as cattle (Bos taurus), water buffalo (Bubalus bubalis), sheep (Ovis aries), goat (Capra hircus), horse (Equus caballus), donkey (E. asinus), and dromedary camel (Camelus dromedarius). It is well known that long term exposure of animals to fluoride through any source causes a serious disease called fluorosis [ 1-6]. In India, fluorosis in humans [7-15] and various species of domestic animals [16-28] due to drinking fluoridated water has been widely studied. But studies on fluorosis in animals due to excessive exposure to kiln fluoride emissions or pollution are still limited in the country [29,30]. However, these studies clearly indicate that exposure to kiln fluoride emissions is unsafe for animal health and causes severe fluorosis disease in these animals.

Apart from the brick kiln industries in the country, several coal burning and industrial activities, such as power generation stations and manufacture of steel, iron, aluminium, zinc, phosphorus, chemical fertilizers, cement, hydrofluoric acid etc. are also potential sources of fluoride pollution [1,3]. This industrially emitted fluoride not only contaminates the surrounding environment including soil, air and fresh water bodies but also contaminates vegetation, agricultural and horticultural crops, animal pastures and several other biological communities on which domestic animals survive [31]. When domestic animals are excessively exposed to these fluoride contaminated sources, they develop a variety of toxic effects in their teeth (dental fluorosis), bones (skeletal fluorosis), and soft organs (non-skeletal fluorosis) [3, 32-39]. If humans [40-43] and wild animals [44-51] come in contact with industrial fluoride pollution they will also develop fluorosis disease. In this mini review, the focus is on fluoride pollution from coal-fired brick kilns and its toxic effects or fluorosis in domestic animals. The author has also tried to draw the attention of the veterinary and pollution control departments of the country towards this burning health problem in domestic animals due to kiln-generated fluoride pollution. The author suggests that there is a need for special research work on this kiln fluoride pollution-based health problem in various species of domestic animals in the country as these animals are basic and important economic sources of villagers or livestock owners.

Coal-fired brick kilns

According to an estimate, there are about 140,000 registered brick kilns (Figure 1) operating in India not only in rural and urban areas but also in agricultural and forest areas [52]. But in many places in the country, thousands of brick kilns are unregistered and illegal, operating even near human settlements. This shows that the kiln industry is not being properly regulated in the country. In the country, most of these kilns are coal-based and about 35 million tonnes (MT) of coal are consumed every year as fuel for the production of heat energy [53]. In fact, in India, brick kilns are the second largest industrial consumers of coal after the steel industry. These coal-based kilns are one of the potential sources of industrial fluoride exposure to both humans and animals. Actually, these natural or fossil coals are rich in fluorine/fluorides. Its concentration range in most coals is 20–500 μg g−1, with an average value of about 150 μg g−1 [54, 55]. The fluoride content in Indian coals generally ranges between 10−20 g/ton [56, 57]. During the combustion of coal in brick kilns, a large amount of toxic compounds of fluorine such as HF, SiF4, and CF4 are also released or emitted into the atmosphere along with other toxic gases and solid waste products [54, 55] in the form of smoke.

Figure 1. Old or traditional (a) and modern or fixed chimney bulls trench (b) coal-fired brick kilns in India.

Kiln industrial fluorosis 

It is well known that excessive fluoride exposure through ingestion and/or inhalation to any fluoride containing sources such as drinking water, air, and foods for prolonged period then it became toxic to body and cause a fluorosis disease in both man and animals. Fluorosis developed in animals from coal- based brick kiln industries is also known as “kiln industrial fluorosis”.  Though, fluoride has biological significance, both beneficial and harmful to humans and animals. In fact, it is essential for about four vital physiological functions: calcification or mineralization of teeth and bones, maintenance of fertility, hematopoiesis, and enzyme activation and is, therefore, considered one of the 14 essential elements [58]. But the necessity of fluoride in biological functions is still controversial or doubtful, probably because the amount required is so low that deficiency cannot be produced even under the most careful laboratory conditions using trace element sterile isolators [59].

Chronic kiln fluoride pollution or kiln fluoridated smoke also has the potential to cause fluorosis which has been reported in both wild and domestic animals. In India, kiln industrial fluorosis has also been reported in domestic animals [29, 30]. These studies clearly indicate that fluoride pollution or fluoridated smoke from kiln is also one of the potential sources of causing fluorosis in domestic animals in the country. Fluorosis is primarily characterized by pathological or clinical changes in teeth and bones and other health hazards in animals. In general, exposure to any fluoride source in humans and animals causes fluorosis, it basically manifests in three forms depending on the organs involved or affected, namely dental fluorosis (dental mottling), skeletal fluorosis (bone deformities), and non-skeletal fluorosis (changes in soft organs) [60, 61]. But it is not necessary that these three forms are present in the same fluorosed animals. However, out of these flouroses, skeletal fluorosis is more dangerous and highly painful.

Dental fluorosis, which is the earliest visible clinical sign of chronic fluoride intoxication in animals, is sensitive, indexive, irreversible, and widespread in fluoride endemic areas. Clinically, it is marked by diffuse hypocalcifications that usually appear as bilateral, striated and horizontal opaque light to dark brown pigment streaks on the tooth surface (Figure 2) [60, 61].  Dental fluorosis may also appear as light to dark brown spots, patches, and fine dots or granules on tooth enamel. The most negative or worst aspect of dental fluorosis is that it reduces the life span or longevity of  animals. In fact, the severe form of dental fluorosis causes serious problems in grazing and chewing foo]d, which can lead to starvation and weakness in animals and cause death [1, 62]. Severe dental fluorosis causes premature death of animals and causes huge economic losses to livestock owners [23,39].

Figure 2. Bovine calves suffering with moderate to severe dental and skeletal fluorosis due to chronic fluoride exposure through drinking of fluoridated water.

Skeletal fluorosis is of utmost importance as it reduces mobility at a very young age by causing various gradual changes in bones such as periosteal exostosis, osteosclerosis, osteoporosis, and osteophytosis [63-65]. These changes manifest clinically as vague aches and pains in the body and joints of fluorosed animals. Excessive accumulation of fluoride in muscles also reduces movements and the condition leads to lameness which is the worst state of skeletal fluorosis. Once skeletal fluorosis is developed then it will be remained forever in animals, in fact, it is incurable. 

The third form of fluorosis, non-skeletal fluorosis is the initial stage of fluoride poisoning in animals exposed to fluoride. Various health issues such as gastrointestinal discomforts (intermittent diarrhoea or constipation, abdominal pain, flatulence, etc.), urticaria, frequent urination (polyuria), excessive thirst (polydipsia), reproductive function, lethargy, muscle weakness, abortions, stillbirths, etc. are the results of chronic fluoride exposure or intoxication [60, 61]. These are the early symptoms of chronic fluoride poisoning in animals and are generally reversible.

The prevalence and severity of fluorosis are influenced by several determinants or factors other than fluoride concentration and frequency and duration of exposure such as age, sex, habits, nutrition, environmental factors and individual sensitivity, biological response, tolerance and genetics [66-73]. To know the persistence of fluoride contamination in the environment, estimation of fluoride in environmental samples such as feed and fodder is a better option [74]. However, unlike morbidity and mortality, fluoride content in biological samples such as milk, urine, blood serum, teeth, bones, etc. is also a better bio-marker for knowing chronic fluoride toxicity [75, 76].

Prevention of kiln industrial fluorosis

Fluorosis in domestic animals caused by exposure to fluoride-rich smoke emitted from coal-fired brick kilns not only weakens the health of the animals but also has a socio-economic impact on the livestock owners [23,39]. Once animals get this disease, it cannot be cured by any medicine or treatment, i.e. this disease remains in the animal for life. But by being aware and taking some precautions, this disease can be prevented from occurring in domestic animals. For this, animals should be protected from coming in contact with the fluoride pollution of the kiln. This is possible only when domestic animals are neither kept nor allowed to graze near the kilns. Another option is that reared animals should be shifted to such areas where there is no kiln fluoride pollution. The effects of industrial fluorosis can also be prevented by giving nutritious food to animals. Amelioration of fluorosis in animals can be done by minimizing the fluoride absorption or enhance excretion through supplementation of calcium carbonate or gluconate, aluminum salts, magnesium metasilicate, magnesium hydroxide, and boron [1]. However, the treatment becomes ineffective when the animals develop symptoms of fluorosis. Therefore, livestock farmers and villagers should be made aware of this health problem caused by the smoke from coal-based brick kilns in the country.

Conclusion

Thousands of legal and illegal coal-fueled brick kilns are operating in rural and urban areas of India. These are potential sources of fluoride exposure for domestic animals grazing in their vicinity. When coal is burned, these kilns also emit smoke continuously, which contains many fluoride-containing toxic gases. These gases contaminate the surrounding air, pastures, drinking water sources, vegetation, and agricultural crops on which the animals often depend. These domestic animals will develop fluorosis if they are repeatedly exposed to kiln fluoride pollution or kiln smoke over a long period of time. This kiln industrial fluorosis in domestic animals not only makes the animals lame but also worsens the socio-economic condition of the cattle keepers. But the research work on fluorosis in animals due to kiln fluoride pollution has been very limited in the country. Therefore, there is a need to do more such research studies on this subject. Their research results will also help in making national health policies to prevent fluorosis in animals. Most of the livestock keepers are also not aware of kiln industrial fluorosis, therefore, it will prove to be more important to make these people aware about this airborne fluoride poisoning in animals. To prevent fluorosis in animals due to kiln industrial fluoride pollution, the concerned departments like veterinary and pollution control in the country also need to make special efforts.

Funding source
No funding source for this work.

Acknowledgments
The author thanks to Prof. Darshana Choubisa, Department of Prosthodontics and Crown & Bridge, Geetanjali Dental and Research Institute, Udaipur, Rajasthan 313002, India for help.

Conflicts of interest
The author has no conflicts of interest.

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