Is Industrial Fluoride Pollution Harmful to Agricultural Crops? Farmers Need to Know

Industrialization is more important for running and strengthening the economic system of any country. But there are many industries that also emit fluoride along with other toxic gases, causing fluoride pollution. Due to this, not only air, soil, and water but also herbage, vegetation and agricultural crops get contaminated with fluoride. Among these industries, coal-burning power stations and brick kilns and the manufacture or production plants of steel, iron, aluminum, zinc, phosphorus, chemical fertilizers, glass, plastics, cement, oil refineries, etc. are the most common sources of fluoride pollution. Fluoride is released from these sources into the surrounding environment in both gaseous and particulate or dust forms. Studies have revealed that chronic exposure to this industrial fluoride is unsafe or harmful to agricultural crops and produces a variety of toxic effects. In fact, industrial fluoride enters crop plants mainly through the stomata of the leaves. However, it can also enter through the root in fluoride-contaminated soil. The bioaccumulation of fluoride in plants disturbs their morphological, physiological, and biochemical parameters. The persistence of fluoride bioaccumulation in crop plants adversely affects their photosynthesis, respiration, mineral nutrition, fertilization, germination, growth and development, bio-chemical processes, and agricultural productivity. The most common visible pathognomonic symptoms of industrial fluoride poisoning in crop plants have been found to be stunted growth (dwarfism), chlorosis, necrosis, abscission of leaves, flowers, and fruits, and decreased seed production. Once plants develop necrotic spots on their leaves, the damage cannot be reversed by any treatment. But most of the farmers are not aware of these side effects on crops or the economic loss caused by industrial fluoride emissions. The current communication focuses on whether industrial fluoride pollution is harmful for the health of agricultural crops. Simultaneously, research gaps are also highlighted for further research work on industrial fluoride toxicity in diverse agricultural crops.

Keywords:Abscission; Chlorosis; Crops; Dwarfism; Industrial fluoride pollution; Necrosis; Photosynthesis; Phytotoxicosis; Productivity; Respiration; Toxic effects

Fluoride is found naturally in almost every ecosystem or environment with varying concentrations [1,2]. However, its presence in water and air is more important for the health of humans and domestic animals. It is clear from several research studies that repeated exposure to fluoride from any medium or source over a long period of time is unsafe and extremely harmful not only to humans [3-7] and domestic animals [8-13] but also to various agricultural crops [14-22]. However, chronic fluoride poisoning (fluorosis) in humans [23-32] and various species of domestic animals [33-55] through drinking fluoridated water has been more widely studied worldwide. In various agricultural crops, chronic fluoride poisoning or toxicity due to chronic exposure of fluoride through industrial fluoride pollution and fluoridated water has also been studied by many workers [14-22]. The current communication focuses on whether industrial fluoride pollution is unsafe or harmful for the health of agricultural crops. Along with this, research gaps have also been highlighted for further research work on the industrial fluoride-induced toxic effects on diverse species of agricultural crops.

It is a well-known fact that industrialization is more important than ever run and strengthen the economic system of any country. That is why every country pays special attention to industrialization. But it is also true that, due to industrialization in one way or another, our ecosystem or environment is also suffering a lot of damage. Due to this, not only the health of humans and animals but also agricultural production is deeply affected. The main reason for this is the air and water pollution caused by them. But most people do not know that there are many factories or industries running around us that emit fluoride along with other toxic gases in the environment, causing fluoride pollution. Due to this, not only air, soil, and water but also herbage, vegetation, and agricultural feed and crops get contaminated with fluoride. Among these industries, coal-burning power stations and brick kilns and the manufacture or production of steel, iron, aluminum, zinc, phosphorus, chemical fertilizers, glass, plastics, cement, oil refineries, and hydrofluoric acid plants or unites are common sources of industrial fluoride pollution [1] (Figure 1). However, coal-fired brick kilns are the commonest and main source of industrial fluoride pollution in rural areas [11,12] and these are mostly established on or near agricultural land or fields (Figure 2). These industrial sources or activities release fluoride into the surrounding environment in both gaseous and particulate or dust forms. However, the spread of fluoride pollution is more dependent on wind direction and its velocity.

Figure 1:Potential sources of industrial fluoride pollution. Atomic power stations (Fig a) and cement plants operating in or near various agriculture crops (Figs b-d).

Figure 2:Fluoride pollution from coal-burning brick-kilns operating in or near various agricultural crops.

Yes, industrial fluoride has the potential to harm a variety of agricultural crops. This has been proven by several studies conducted on a variety of agricultural crops [14-22]. In fact, industrial fluoride contaminates not only crop plants but also agriculture soil and freshwater ecosystems. Therefore, fluoride can enter plants through two main routes. First, air-borne deposition of gaseous fluoride due to industrial fluoride pollution occurs through stomatal diffusion. Through leaf stomata, fluoride penetrates the cell wall and migrates to the margins and tips of leaves, which are the sites of greatest volatilization [56]. The second route is through a passive diffusion process in the roots of plants in fluoride contaminated soil and fresh water. Fluoride is subsequently transported through the xylem via-apoplastic and simplistic pathways in a directional distal movement to the shoot [57]. In fact, fluoride moves into the transpiration stream from the roots and/ or through the stomata, where it eventually accumulates in the leaf margins. Generally, fluoride accumulation follows the order of soil > root > shoot > grain. The bio-availability of fluoride to plants is mainly influenced by the presence of metal ions such as calcium (Ca), aluminum (L), and phosphorus (P), the pH of the solution, and the type of soil [58].

Repeated or chronic industrial fluoride exposure for long period of time and its persistence bioaccumulation produces diverse adverse toxic effects in both seasonal and off-season agricultural crops, vegetables, and trees [14,17,20]. In fact, bioaccumulation of fluoride in different parts of plants disturbs or causes adverse changes in various physico-biochemical or metabolic processes and ultimately triggers the development of various side effects or ill effects. Ultimately, these effects reduce the annual productivity or yield and harvest index of the agricultural crop.

The most common and earliest visible morphological changes induced by fluoride in crop plants are stunted growth (dwarfism syndrome), necrotic lesions or necrosis, chlorosis, abscission of leaves, flowers, and fruits, leaf damage, tip burning, and curling of leaves that spread inward (Figures 3 & 4) [14,20]. Once plants develop necrotic spots on their leaves, the damage cannot be reversed by any treatment. In fact, fluoride has the ability to inhibit or alter the physiology of photosynthesis and other biological processes such as seed germination, respiration, CO2 assimilation, protein and nucleotide synthesis, carbohydrate metabolism, hormonal imbalance, various enzyme activities, gene expression patterns, inhibition of developmental and reproductive capabilities, etc. These parameters have been well studied scientifically by several researchers on a variety of agricultural crops [59-65]. Ultimately, these fluoride-induced morpho-physiological changes affect the rate of agricultural productivity or yield due to which the farmers suffer huge economic losses. Scientific evaluation has not yet been done on such economic losses, which is also very important. This type of evaluation is very important and helps in the determination of economic policy. However, which agricultural crop is more susceptible, sensitive, or less tolerant to industrial fluoride is not yet clear. Therefore, there is still a need for more comparative studies on the sensitivity of different species of agricultural crops to fluoride.

Figure 3:Rice plants (Oryza sativa) showing leaf necrosis with burnt margin due to chronic fluoride exposure through industrial fluoride pollution [14].

Figure 4:Stunted growth in rice plants (Oryza sativa) due to chronic fluoride exposure through industrial fluoride pollution [14].

The magnitudes of these pathological changes in crop plants are generally dependent on the industrial fluoride concentration, the frequency and duration of exposure, and the density of its bioaccumulation. However, more studies are needed on the diverse factors that influence the severity of the toxic effects of industrial fluoride in plants as studied in humans and animals [66-73]. The findings of such studies are more useful in amelioration fluoride toxicity in agricultural crops. Moreover, there is also a great need for studies and guidelines for the correct diagnosis of fluoride induced toxicity in crop plants as in humans and domestic animals [74-77]. However, accurate detection of fluoride toxicity in crops can be easily done by fluoride estimation in their feed [78].

“A major danger from industrial fluoride poisoning in crops is the possibility of fluorosis in animals and humans by eating fodder and grain from these crops, respectively. In fact, there are more chances for the presence of fluoride in their fodder and grains [79- 81]. Interestingly, most people are unaware of this. So it is very important and necessary to prevent or control industrial fluoride pollution in rural or agricultural areas. This can be made possible by adopting effective scientific techniques, thereby reducing fluoride emissions. In addition, there is a need for regulators of fluoride emissions, as well as stricter laws and their effective implementation. Otherwise, the owners and management of these fluoride-emitting industries will not pay attention to the fluoride pollution and will also be careless towards it”.

In or around the agricultural lands, several industries, such as coal-burning power stations and brick kilns and the manufacture or production plants of steel, iron, aluminum, zinc, phosphorus, chemical fertilizers, glass, plastics, cement, oil refineries, and hydrofluoric acid are sources of fluoride pollution. Fluoride from these sources is released into the surrounding environment, contaminating various ecosystems and agriculture soil and crops. The continuous bio-accumulation of industrial fluoride in agricultural crop plants is not safe and harmful and causes many mild to severe pathological changes (stunted growth, necrosis, chlorosis, abscission of leaves, flowers, and fruits, leaf damage, tip burning, curling of leaves, and various physiological processes) in them and ultimately reduces their productivity. Fluoride-induced necrosis is irreversible damage in crop plants. Furthermore, there is also a great need for correct guidelines for the correct diagnosis of fluoride-induced toxicity in plants. Prolonged consumption of fodder and grains of fluoride affected crop plants, which are also harmful for domestic animals and humans, respectively. Therefore, it is very important to stop or reduce industrial fluoride pollution, which is possible by making strict laws and implementing them effectively.

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