The influence of fertilizers on the behavior of fluoride fractions in the alkaline soil

https://doi.org/10.1016/j.jfluchem.2021.109883Get rights and content

Highlights

  • Availability and toxicity of fluoride to plants and animal depends on its existing form.

  • Fertilizers accelerate fluoride release into the soil solution.

  • Di-ammonium phosphate and manure enhance water soluble fluoride through direct input.

  • Urea accelerates fluoride release through altering soil's pH and elemental composition.

Abstract

It has been established that fluoride bioavailability in the soil is defined by the form which it exists rather than the amount of total fluoride. In the soil, fluoride exist in different fractions such as water soluble (Ws-F), Exchangeable (Ex-F), bound to iron/manganese (Fe/Mn-F), organic matter bound (Or-F), and the residual (Res-F). All of these fractions are bioavailable however to different extents in an order Ws-F>Ex-F>Fe/Mn-F>Or-F>Res-F. Agricultural practices such as fertilizer application alters the behavior of these fractions which further affects fluoride bioavailability in the soil. This study investigated the influence of the three commonly used fertilizers (Di-ammonium Phosphate (DAP), Urea, and cow-manure) on the bioavailability of soil fluoride in an alkaline soil. The soil was mixed with either one of the fertilizers then incubated for a period of five months. All three fertilizers increased the amount of Ws-F by 7.8 ± 0.6, 4.1 ± 0.2, 9.6 ± 1.1 mg/kg and Fe/Mn-F by 2.24 ± 0.3, 0.44 ± 0.2, and 2.1 ± 0.2 mg/kg, for DAP, Urea, and manure amendments, respectively, but had no impact on the amount of Or-F. All three fertilizers were observed to enhance the bioavailability of fluoride in the soil by increasing the amount of Ws-F. The fertilizers could have increased the bioavailability of fluoride in the soil directly or indirectly through alteration of pH and the soil elemental composition. The three fertilizers might not be suitable for use in fluoride contaminated alkaline soils as they accelerate fluoride release and hence bioavailability in the soil.

Introduction

Fluoride is beneficial at low concentrations in preventing dental caries and in the development of stronger bones [1] . However, exposure to higher doses leads to a condition called fluorosis which includes dental caries and brittle bones [2]. Water has long been the known main route of fluoride exposure, but food is identified as another noteworthy exposure path [1]. Studies have investigated fluoride uptake and accumulation by crops from the soil [2], [3], [4]. These studies have determined that factors such as type of plant species, soil properties as well as quantity and form with which fluoride exist in the soil influence the amount taken up and accumulated by the plant. The amount of fluoride accumulated by plant finds its way through the food chain thereby prominently affect the top members of the food chain which include human beings [5].

It has been established that mobility, toxicity and bioavailability of fluoride in the soil is defined by the form with which it exists rather than the amount of total fluoride (TF) [2]. Soil fluoride fractions such as water soluble (Ws-F), Exchangeable (Ex-F), bound to iron/manganese (Fe/Mn-F), bound to organic matter (Or-F) and residual (Res-F) fluoride have been successfully extracted [6, 7]. These forms are considered bioavailable such that they can easily be taken up and accumulated by the soil living forms. Although bioavailable, the extent of their bioavailability decreases in an order Ws-F>Ex-F>Fe/Mn-F>Or-F>Res-F. Therefore, the soil containing high concentrations of Ws-F and Ex-F has high fluoride toxicity compared to the remaining fractions whereas Res-F is considered less bioavailable [5, 8, 9]. These fluoride fractions though, are interchangeable from one another subject to changing soil properties like pH, soil organic matter (SOM), and elemental composition, in so doing, it modifies the fluoride bioavailability behavior of the soil [8].

Fertilizers have been used for centuries to maintain and increase food production worldwide as they enable farmers to supply the exact nutrients essential to specific soil requirements. Studies have focused on the impact of fertilizers on crop productivity, organic matter, and other soil properties [10, 11] but little attention has been directed towards its influence on the behavior of detrimental ions such as fluoride that exist in the soil. Like other plant nutrients, fluoride uptake by roots and transfer through the plant begins with dissolution into the soil solution, dislocation by soil salts, or by coming into contact with root exudates. The three processes depend on the surface area of the solid phase of the soil and the soil's bonding strength [12]. Regular inputs of fertilizers into the agricultural soils can alter the above-mentioned soil properties which could either accelerate the release of weakly bound fluoride species or increase the bonding strength of the soil which then reduces its release into the soil solution. Therefore, it is of importance to understand the influence of fertilizers on the bioavailability of fluoride in the soil which is the aim of this work. This study investigated the influence of three commonly used fertilizers (Di-ammonium phosphate (DAP), Urea, and cow-manure) on the behavior of five fluoride fractions (Ws-F, Ex-F, Fe/Mn-F, Or-F and the Res-F). It aims to understand as to whether fertilizer application increases or decreases the bioavailability of fluoride in the soil.

Section snippets

Soil Sampling and fertilizer treatments

The soil used in this experiment was collected from a farm in an area known to contain high fluoride in water and soil. The area is located at the slopes of Mount Meru, Arusha, Tanzania with coordinates 3°10’35” S 36°51’35” E. The farming practices involve maize and beans cultivation during the rainy season and horticultural production (Tomato, kale, cabbage, and onions) under irrigation during the dry season. The soil has regularly been supplied with DAP, Urea, and manure fertilizers for more

Soil characterization

The average values of soil properties are presented in table 2. The soil properties observed are in concordance with those obtained by Rizzu et al., (2020) who used the same agricultural soil to investigate fluoride uptake by maize and bean plants [5]. The soil is characterized as sandy loam with a total fluoride (TF) concentration of 422 ± 52.9 mg/kg containing Ws-F of one order of magnitude less than TF and therefore very likely to cause toxicity to fluoride-sensitive plants and animals. The

Conclusion

This study investigated the influence of the three fertilizers on the bioavailability of fluoride fractions in the alkaline soil. the three fertilizers used for this study contained different concentrations of the bioavailable fluoride the highest being di-ammonium phosphate (DAP) followed by manure. All three types of fertilizers increased the amount of water soluble fluoride (Ws-F) as well as the amount of iron/manganese bound fluoride (Fe/Mn-F) but had no observable impact on organic matter

Declaration of competing interest

The authors declare that there are no conflicts of interest whatsoever in publishing this article

Acknowledgment

This work was funded by the Partnership for Applied Skills in Sciences, Engineering and Technology-Regional Scholarship Innovation Fund (PASET-RSIF) and the East and West Africa farming system-BELT (EWA-BELT) Horizon 2020 project No. 862848.

References (31)

  • H. Gao et al.

    Influences of charcoal and bamboo charcoal amendment on soil-fluoride fractions and bioaccumulation of fluoride in tea plants

    Environ. Geochem. Health

    (2012)
  • W. Chen

    Effect of nitrogen fertilizer on fluorine species and soil pH in fluorine-contaminate soil

  • A. Arnesen

    Availability of fluoride to plants grown in contaminated soils

    Plant Soil

    (1997)
  • R.J. Haynes et al.

    Influence of lime, fertilizer and manure applications on soil organic matter content and soil physical conditions: a review

    Nutr. Cycl. Agroecosyst.

    (1998)
  • N.K. Mahal et al.

    Nitrogen fertilizer suppresses mineralization of soil organic matter in maize agroecosystems

    Front. Ecol. Evol.

    (2019)
  • Cited by (13)

    • Hydroxyapatite-activated seaweed biochar for enhanced remediation of fluoride contaminated soil at various pH ranges

      2023, Environmental Advances
      Citation Excerpt :

      The impact of initial fluoride concentration on HSB defluoridation capacity was studied by spiking the soil with 25, 50, 75, and 100 mg/L fluorides in form of NaF and incubating for 1 month before the experiment. The selected properties of the soil used for this study are presented in Table 1 and the soil analysis was conducted as per our previous study (Moirana et al., 2021). In each of the batch experiments, 5 g of the soil sample was mixed with the selected adsorbent dose, moistened, and incubated for 12 h before the test experiment begins.

    • Fluoride accumulation characteristics in a northern China apple orchard that has had long-term phosphate fertilization

      2023, Science of the Total Environment
      Citation Excerpt :

      Li et al. (2017) demonstrated that under natural soil conditions, F was slightly mobile, therefore the WF content in normal soil is low and that mobility was influenced significantly by soil OM and pH (Shu et al., 2003; Geretharan et al., 2018; Yu et al., 2020; Loganathan et al., 2008). Moirana et al. (2021) reported that because it changes pH and the soil elemental composition, fertilizers can directly or indirectly increase the soil's WF content. In this study, the experimental apple orchard soil was alkaline (pH > 8), and that higher pH may be another reason why fluoride migrated so deep.

    • Role of rice cultivation on fluorine distribution behavior in soda saline-alkali land

      2022, Science of the Total Environment
      Citation Excerpt :

      The presence of an electrical charge attracts ions, such as exchangeable cations, to gain stability. Consequently, exchangeable cations are held by negatively charged clay minerals in soil (Moirana et al., 2021). Therefore, the number of exchangeable cations and Ex-F was limited by negatively charged clay particles (Rizzu et al., 2020).

    • Effects of soil fluoride pollution on wheat growth and biomass production, leaf injury index, powdery mildew infestation and trace metal uptake

      2022, Environmental Pollution
      Citation Excerpt :

      Soil F makes complexes with several elements such as Al, Fe and calcium (Ca), oxides which regulate F bioavailability to plants (Kupiec et al., 2019). Sequential extractions of soil F indicates that soil F fractions associated with water and soil organic matter dominate soil solution followed by Ca and metal oxides; however, water and calcium chloride (CaCl2) soluble F fractions are more bioavailable to plants and correlated strongly with the F uptake by plants (Yi et al., 2017a,b; Moirana et al., 2021). Therefore, soils having higher concentrations of water soluble and exchangeable F induce high F toxicity to plants (Arnesen, 1997).

    View all citing articles on Scopus
    View full text