Study of fluoride in soil and plants in posht-e-kooh-e-dashtestan, Bushehr Province

High concentrations of fluorine ion in the Dashtestan area of the Bushehr province, has given rise to the prevalence of dental fluorosis among the local population. The high concentration of this ion in plants provides one possible mechanism for it to enter the body. This, along with the absorption of fluoride from water, can lead to a higher probability of acute fluorosis for the local population. The main objective of this research is to study the fluoride concentration in soil, and its probable bioaccumulation in plants.
Material and methods: Dasthestan's Posht-e-kooh is part of the Dashtestan's district, situated to the east and souteast of the Burazjan district in the Bushehr province. In order to measure the concentration of fluorine in the soil, thirty-four in-situ soil samples were collected from the date orchards and wheat farms. To find the correlation between soil pH and fluoride concentration, soil pH was also measured. In addition, 14 wheat samples and 10 date samples were collected and analyzed for fluoride. Separate samples were taken from the root, stem, and leaf. The F- concentrations in plant and soil samples were determined using the alkaline fusion method with a fluoride ion-selective electrode (Metrohm Swiss model 781 ion meter).
Results: The average fluoride concentration found in dates is 10.0 mg/kg; whereas wheat roots and shoots contain on average 30.0 and 19.0 mg of fluoride per kg, respectively. In the present study, we have found relatively high F- concentrations in dates and wheat, which are staple foods for the population of Bushehr. The average F- content in dates of 10 mg/kg is much higher than the mean value of 2.9 mg/kg reported for Southern Algeria. The uptake of the fluorine ion by plants is controlled by many factors, such as soil type, pH and the clay content of the soil due to direct contact between soil and water. There is no available report regarding the soil of the Algerian region mentioned above. The F- content of wheat is also high, and approximately 10 mg/kg higher in the roots compared to the shoots. The soil in the study area has a pH of 8.03, which means that F- can be absorbed by the plants. F- can be absorbed (transported) from the soil into the stem through fine hair rootlets, and some can reach the leaves. Acidity is the most important factor in the geochemistry of fluoride-bearing soil. An average soil pH of 8.03, shows high alkalinity. High pH value promotes the exchange of OH- anion in the groundwater and F- in some of the minerals present in the soil, which facilitates the leaching of fluoride from the soil into the plant. X-ray diffraction analysis has confirmed the presence of fluoride-bearing minerals in the study area.
Conclusion: Considering the importance of fluoride for the health of teeth and bones, the high concentration of fluoride in dates resulting in a high intake of fluoride by the people living in posht-e-kooh of Dashtestan is cause for great concern. The high concentration of fluoride in the soil and local plants, implies a high probability of fluorine entering the food cycle. Identifying sources of water with high concentrations of fluoride, is an important step in tackling the health problems facing the local population.