**Effects of Natural Zeolites on Bioavailability and Leachability of Heavy Metals in the Composting Process of Biodegradable Wastes**

Jiwan Singh, Ajay S. Kalamdhad and Byeong-Kyu Lee

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/63679

#### **Abstract**

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9517(84)90235‐5

184 Zeolites - Useful Minerals

860X(97)00186‐5

10.1021/ie0712434

10.1016/0254‐0584(87)90048‐4

The bioavailability and leachability of heavy metals play an important role in the toxicity of heavy metals in the final compost followed by land application. This chapter examines the effects of natural zeolite on bioavailability of heavy metals (Zn, Cu, Mn, Fe, Ni, Pb, Cd, and Cr) in the form of water soluble and diethylenetriaminepentaace‐ tic acid (DTPA) extractable. The toxicity characteristic leaching procedure (TCLP) test was performed to examine the leachability of heavy metals. Water solubility, DTPA extractability, leachability, and most bioavailable fractions were reduced during agitated pile composting (APC) and rotary drum composting (RDC) of water hyacinth with zeolite addition. The addition of the natural zeolite (clinoptilolite) during the composting process led to an increase in Na, Ca, and K concentrations and signifi‐ cantly reduced the water solubility and DTPA and TCLP extractability of heavy metals. The addition of an appropriate amount of natural zeolite during the composting process enhanced the organic matter degradation, thereby increasing the conversion into the most stabilized organic matter and reducing the bioavailability and leachabil‐ ity of heavy metals.

**Keywords:** Heavy metals, bioavailability, speciation, natural zeolite, composting, water hyacinth, sewage sludge

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

#### **1. Introduction**

Wastewater treatment plants are increasing worldwide due to urbanization and subsequent increases in sewage sludge production. The management of large quantities of sewage sludge generated from water treatment is a critical problem. Therefore, to overcome the undesirable impacts of the disposal of organic wastes such as water hyacinth and sewage sludge on the environment, it is essential to reduce the volume of these wastes and successfully reuse them as a source of organic matter and nutrients.

Composting is highly an economical method for the handling and final disposal of biode‐ gradable wastes because it is helpful for material recycling and disposal [1, 2]. Water hyacinth (*Eichhornia crassipes*) is a commonly used plant for phytoremediation and constructed wetlands due to its high growth rate and great accumulation of inorganic and organic pollutants [1]. Therefore, the composts prepared from water hyacinth and sewage sludge may contain higher concentrations of heavy metals [3, 4]. The presence of nonbiodegradable and toxic heavy metals in the compost normally prevents its reuse in land applications. If compost with a high concentration of heavy metals is applied to soil, the accumulation of heavy metals in the plants and subsequently the food chain poses a risk to animal and human health [4, 5].

The total concentration of heavy metals measured from compost samples digested with strong acids can indicate the possibility of metal pollution, but cannot specify information related to the bioavailability of heavy metals [5, 6]. The bioavailability of any element specifies the fraction of the element's total content that is easily soluble in an aqueous system, and hence is freely available to plants and soil microorganisms. Water-soluble metals are biologically more dynamic and consequently have a significantly higher risk of contaminating the environment [4, 7]. The diethylenetriaminepentaacetic acid (DTPA)-extractable fraction of metals is a supplemental approach to determine the bioavailable fractions of heavy metals in the compost and soil applied with compost [8]. The toxicity characteristic leaching procedure (TCLP) is applied to evaluate the leaching potential of toxic heavy metals present in waste materials and compost. Heavy metals can be leached from compost and soil amended with compost, and hence pollute groundwater and surface water [9]. The leachability of a metal can be distin‐ guished as the ratio of the quantity of the heavy metal leached from the TCLP test to its total concentration. The TCLP test is commonly used to assess the leachability of heavy metals in compost and whether the compost is hazardous or not [10].

Zeolites are natural hydrated aluminosilicate minerals with a three-dimensional framework structure tetrahedrally coordinated to SiO4 and AlO4 [1, 11, 12]. The aluminum ion occupies the center of the tetrahedron of four oxygen atoms. However, the isomorphous replacement of Si4+ by Al3+ produces a negative charge in the lattice. The Na+ , K+ , and Ca2+ are exchangeable for balancing the net negative charge and are commonly exchanged with particular cations (cations of Pb, Th, Cd, Zn, Mn, and NH4) in aqueous solutions [1, 13]. Natural zeolite has been applied broadly for decreasing the mobility and bioavailability of heavy metals in water hyacinth and sewage sludge composting because of its sorption and exchangeable properties for heavy metals [13, 14]. It can uptake heavy metals that are present in the composting mass in easily available fractions, and exchange with Na and K [15].

#### **2. Composting process**

**1. Introduction**

186 Zeolites - Useful Minerals

as a source of organic matter and nutrients.

Wastewater treatment plants are increasing worldwide due to urbanization and subsequent increases in sewage sludge production. The management of large quantities of sewage sludge generated from water treatment is a critical problem. Therefore, to overcome the undesirable impacts of the disposal of organic wastes such as water hyacinth and sewage sludge on the environment, it is essential to reduce the volume of these wastes and successfully reuse them

Composting is highly an economical method for the handling and final disposal of biode‐ gradable wastes because it is helpful for material recycling and disposal [1, 2]. Water hyacinth (*Eichhornia crassipes*) is a commonly used plant for phytoremediation and constructed wetlands due to its high growth rate and great accumulation of inorganic and organic pollutants [1]. Therefore, the composts prepared from water hyacinth and sewage sludge may contain higher concentrations of heavy metals [3, 4]. The presence of nonbiodegradable and toxic heavy metals in the compost normally prevents its reuse in land applications. If compost with a high concentration of heavy metals is applied to soil, the accumulation of heavy metals in the plants

The total concentration of heavy metals measured from compost samples digested with strong acids can indicate the possibility of metal pollution, but cannot specify information related to the bioavailability of heavy metals [5, 6]. The bioavailability of any element specifies the fraction of the element's total content that is easily soluble in an aqueous system, and hence is freely available to plants and soil microorganisms. Water-soluble metals are biologically more dynamic and consequently have a significantly higher risk of contaminating the environment [4, 7]. The diethylenetriaminepentaacetic acid (DTPA)-extractable fraction of metals is a supplemental approach to determine the bioavailable fractions of heavy metals in the compost and soil applied with compost [8]. The toxicity characteristic leaching procedure (TCLP) is applied to evaluate the leaching potential of toxic heavy metals present in waste materials and compost. Heavy metals can be leached from compost and soil amended with compost, and hence pollute groundwater and surface water [9]. The leachability of a metal can be distin‐ guished as the ratio of the quantity of the heavy metal leached from the TCLP test to its total concentration. The TCLP test is commonly used to assess the leachability of heavy metals in

Zeolites are natural hydrated aluminosilicate minerals with a three-dimensional framework structure tetrahedrally coordinated to SiO4 and AlO4 [1, 11, 12]. The aluminum ion occupies the center of the tetrahedron of four oxygen atoms. However, the isomorphous replacement

for balancing the net negative charge and are commonly exchanged with particular cations (cations of Pb, Th, Cd, Zn, Mn, and NH4) in aqueous solutions [1, 13]. Natural zeolite has been applied broadly for decreasing the mobility and bioavailability of heavy metals in water hyacinth and sewage sludge composting because of its sorption and exchangeable properties for heavy metals [13, 14]. It can uptake heavy metals that are present in the composting mass

, K+

, and Ca2+ are exchangeable

and subsequently the food chain poses a risk to animal and human health [4, 5].

compost and whether the compost is hazardous or not [10].

of Si4+ by Al3+ produces a negative charge in the lattice. The Na+

in easily available fractions, and exchange with Na and K [15].

Composting may be defined as a biological breakdown and stabilization of organic substrates, under conditions, which allowed progress of thermophilic temperatures due to heat produced during the degradation of waste biologically. The final product is stable and free from pathogens, and can therefore be applied for land application [16]. **Figure 1** shows the outline of composting process.

**Figure 1.** Outline of composting process.

#### **2.1. Factors affecting the composting process**

The carbon to nitrogen ratio (C/N ratio) can be a crucial factor in the composting process. To determine the optimal C/N ratio is important for optimizing the composting [17]. C/N ratios between 30 and 50 are favorable for the aerobic composting process. At lower C/N ratio, ammonia can be lost and biological activity is also affected, whereas at higher C/N ratio nitrogen may be a limiting nutrient [18]. The particle size of composting materials should be minimized to ensure efficient aeration and easy decomposition by the bacteria, fungi, and actinomycetes. Therefore, waste materials should be shredded into small pieces between 25 and 75 mm prior to composting [18]. Moisture content is another significant factor affecting the composting process, as moisture greatly disturbs the physical and chemical properties of waste biomass in sequence of the degradation of organic wastes [19]. The moisture content should be in the range between 50 and 60% in the composting process. The optimum moisture content is generally considered approximately 55% [18]. Aeration is an important factor for both microbial growth and gas emission in the composting process [20]. The aeration rate strongly affects microbial activity, substrate degradation rate, and temperature variation in the composting processes of organic wastes [21]). Rasapoor et al. [21] reported that low and medium aeration rates increased the concentration of total nitrogen (TN), which drastically decreased the C/N ratio and lengthened the thermophilic phase. The artificial air supply is generally sustained at 1–2 m3 /day/kg of volatile solids. A temperature increase is an indicator of microbial activities in the process of composting, and thus temperature change can be measured as a suitable parameter to regulate the status of composting processes [22, 23]. Temperature can affect the nature of microorganisms and the rate of decomposition of organic wastes [23]. Lin [24] reported that when the temperature was about 65°C, total coliforms dropped. López-Real and Foster [25] reported that the application of 55°C for only 3–4 days completely eliminated all pathogens. Stentiford [26] stated that the composting temperature must be maintained between 55 and 65°C for the inactivation of total pathogens. The pH is another important parameter for the composting process. The pH can be affected during the composting process due to the production of short-chain organic acids from the feedstock since the early phase of the composting process [27]. The short-chain organic acids and ammonia are maintained in a pH range of 4.9–8.3 [28]. Lower pH decreased microbial activity, thus hindering the growth of composting reaction [27]. However, high pH (>8.5) caused nitrogen loss in the form of ammonia [18].


#### **3. Heavy metals in the composting process**

**Table 1.** Heavy metals concentration (mg/kg) in the final compost of different wastes.

The availability of metals in the final compost is the one of the major sources of soil pollution. Heavy metal pollution in the soil is mainly caused by Cu, Ni, Cd, Zn, Cr, and Pb [29, 30]. Some heavy metals (Fe, Zn, Ca, and Mg) have been reported as having a bioimportance to human being and plants. However, some others (As, Cd, Pb, and methylated forms of Hg) have been reported to have no known bioimportance in human biochemistry and physiology, and their consumption even at very low levels can be toxic to living organisms [31]. **Table 1** illustrates the total concentration of metals (Zn, Cu, Mn, Fe, Ni, Pb, Cd, and Cr) in the final compost of different wastes. The total metal contents are increased in the final compost due to the reduction of organic matter and release of CO2 during the mineralization process [4]. The total metal concentration found after strong acid digestion of final compost is useful as an overall pollution indicator but provides no useful information about the bioavailable fractions and chemical speciation of metals [5, 6].

### **4. Heavy metals bioavailability**

strongly affects microbial activity, substrate degradation rate, and temperature variation in the composting processes of organic wastes [21]). Rasapoor et al. [21] reported that low and medium aeration rates increased the concentration of total nitrogen (TN), which drastically decreased the C/N ratio and lengthened the thermophilic phase. The artificial air supply is

of microbial activities in the process of composting, and thus temperature change can be measured as a suitable parameter to regulate the status of composting processes [22, 23]. Temperature can affect the nature of microorganisms and the rate of decomposition of organic wastes [23]. Lin [24] reported that when the temperature was about 65°C, total coliforms dropped. López-Real and Foster [25] reported that the application of 55°C for only 3–4 days completely eliminated all pathogens. Stentiford [26] stated that the composting temperature must be maintained between 55 and 65°C for the inactivation of total pathogens. The pH is another important parameter for the composting process. The pH can be affected during the composting process due to the production of short-chain organic acids from the feedstock since the early phase of the composting process [27]. The short-chain organic acids and ammonia are maintained in a pH range of 4.9–8.3 [28]. Lower pH decreased microbial activity, thus hindering the growth of composting reaction [27]. However, high pH (>8.5) caused nitrogen

**Sewage sludge Municipal solid waste Water hyacinth**

The availability of metals in the final compost is the one of the major sources of soil pollution. Heavy metal pollution in the soil is mainly caused by Cu, Ni, Cd, Zn, Cr, and Pb [29, 30]. Some heavy metals (Fe, Zn, Ca, and Mg) have been reported as having a bioimportance to human being and plants. However, some others (As, Cd, Pb, and methylated forms of Hg) have been reported to have no known bioimportance in human biochemistry and physiology, and their consumption even at very low levels can be toxic to living organisms [31]. **Table 1** illustrates

Zn 233 278 ± 22 297.8 ± 3.0 Cu 62 410 ± 26 103.3 ± 0.8 Mn 59.9 – 1105.0 ± 27.5 Fe 3768 – 13300 ± 30 Ni 23 44 ± 7 235.8 ± 1.8 Pb 101 325 ± 24 1537.0 ± 12.5 Cd 0 3.3 ± 0.4 83.8 ± 1.3 Cr 44.03 52 ± 9.2 279.0 ± 1.3

**Table 1.** Heavy metals concentration (mg/kg) in the final compost of different wastes.

/day/kg of volatile solids. A temperature increase is an indicator

generally sustained at 1–2 m3

188 Zeolites - Useful Minerals

loss in the form of ammonia [18].

**Heavy metals (mg/kg)**

**3. Heavy metals in the composting process**

The bioavailability of heavy metals depends on different extractable fractions rather than on the total metal concentration. Therefore, the bioavailability of heavy metals provides more important evidence of metal toxicity [32]. Even if the heavy metals concentration in sewage sludge or compost is far below the regulation limit, the long-term land application of compost with background heavy metals concentration can increase the content and accumulation of the heavy metals in the soil [10].

Heavy metals in compost and soil amended with compost are commonly separated into two fractions: (i) inert fraction expected as the nontoxic fraction and (ii) the labile fraction, which is supposed to be possibly toxic [33]. To determine the availability of heavy metals, only the labile fraction has been considered bioavailable. The bioavailable fraction can diverge from one metal to another and from one receptor to another. The bioavailability of heavy metals for plants and microorganisms in soil/compost depends on the composition of the different components of soil/compost, such as carbonates, (oxy) metal hydroxides, organic matter, and silica [4, 33].

The heavy metal bioavailability has been considered one of the most critical problematic parameters for the agricultural application of compost [34]. The mobilization of pollutants depends on three factors: their mobility, concentration, and solubility in the compost/soil [33]. The solubility depends on the chemical composition of the leachate in equilibrium with the material; this chemical composition is influenced by the variation of pH that moves the redox equilibrium to predominant forms [33]. Heavy metals are generally present in their hydroxide forms with low solubility at a higher pH. However, at low pH, metals are available in their cationic forms, which are highly soluble and available for plant uptake. There are two types of complex in metal complexation reactions with soil particles: soluble and insoluble. At pH 9, the solubility of Cu is increased due to the formation of soluble complexes [4].

### **5. Effects of natural zeolite on the bioavailability of heavy metals during the composting process**

#### **5.1. Experimental analysis**

The details of waste materials are as follows: control (water hyacinth 90 kg + sawdust 15 kg + cattle manure 45 kg), zeolite 5% (control + zeolite 7.5 kg), zeolite 10% (control + zeolite 15 kg), and zeolite 15% (control + zeolite 22.5 kg) during the agitated pile composting (APC) and rotary drum composting (RDC) of water hyacinth [12, 13]. Water-soluble heavy metals were deter‐ mined after extraction of 2.5 g of sample with 50 ml of distilled water (sample:solution ratio = 1:20) at room temperature for 2 h in a shaker agitated at 100 rpm [4]. DTPA-extractable metals were attained by mechanically shaking 4 g of ground sample (screened through a 0.22-mm sieve) with 40 ml of 0.005 M DTPA, 0.01 M CaCl2, and 0.1 M (triethanolamine) buffered to pH 7.3 at 100 rpm [4]. The standard TCLP method according to the US EPA Method 1311 [35] was applied to the solid samples in order to determine the potential leachability of the heavy metals. A 5 g sample of compost (size less than 9.5 mm) with 100 ml of acetic acid at pH 4.93 ± 0.05 (pH was adjusted by 1 N NaOH) (sample: solution ratio =1:20) was taken in 125 ml reagent bottle and kept at room temperature for 18 h in a shaker at 30 ± 2 rpm. An atomic absorption spectrometer (AAS) (Varian Spectra 55B) was used to analyze Zn, Cu, Mn, Fe, Ni, Pb, Cd, and Cr concentrations in different extracted solutions.

#### **5.2. Total concentration of heavy metals**

The total content of heavy metals attained after strong acid digestion is an indicator of compost contamination but cannot provide useful information on the bioavailability of heavy metals in the compost and compost-amended soil [36]. The total concentration of heavy metals was determined during the APC and RDC of water hyacinth with natural zeolite. The total concentration of metals was increased during the APC and RDC process of water hyacinth with natural zeolite (**Table 2**) due to the reduction of organic matter and release of CO2 during the mineralization processes [12, 13]. In the APC process, the total concentration of Zn, Cu, Mn, Pb, and Cd was increased highest in control as compared to the zeolite treatments; however, the total concentration of Fe, Cr, and Ni was increased highest in 5, 10, and 15% zeolite treatments, respectively [12]. In the RDC process, the total concentration of Cr, Cd, Zn, Mn, Fe, and Pb was increased highest in 5% zeolite treatment. The total concentration of Ni and Cu was increased highest in 10% zeolite treatment and control, respectively [13]. The total concentration of Zn and Ni was increased with increasing amount of natural zeolite addition in the APC process; however, the concentration of these metals was reduced with an increasing amount of natural zeolite in the RDC process of water hyacinth. In the RDC process, the percentage increase of metals was reduced with an increasing amount of natural zeolite due to the reduction in efficiency of the composting process. A higher addition of natural zeolite in the RDC process could hold the high amount of moisture that reduced the microbial activity [13]. Zorpas et al. [37] reported that the heavy metals contents were greatly decreased by approximately 100, 17, 31.7, 35.1, 24.0, 60.0, 56.7, and 47.9% for Cd, Cr, Cu, Fe, Mn, Ni, Pb, and Zn, respectively, in the process of composting of sewage sludge with zeolite. Zorpas et al. [38] concluded that the addition of 25% (w/w) zeolite in compost is adequate to eliminate around 12–60% of the heavy metals during sewage sludge composting. Sprynskyy et al. [14] reported that the addition of 9.09% clinoptilolite to the sludge reduced the total concentration of metals to around 11–51%. The increases in the concentration of heavy metals in the composting process were mainly because of the losses of mass [37].


Note: NZ-natural zeolite; control: water hyacinth (90 kg), sawdust (15 kg), cattle manure (45 kg); zeolite 5% (control + zeolite 7.5 kg); zeolite 10% (control + zeolite 15 kg), and zeolite 15% (control + zeolite 22.5 kg).

**Table 2.** Effects of natural zeolite on concentration of total heavy metals during the water hyacinth composting.

#### **5.3. Water solubility of heavy metals**

and zeolite 15% (control + zeolite 22.5 kg) during the agitated pile composting (APC) and rotary drum composting (RDC) of water hyacinth [12, 13]. Water-soluble heavy metals were deter‐ mined after extraction of 2.5 g of sample with 50 ml of distilled water (sample:solution ratio = 1:20) at room temperature for 2 h in a shaker agitated at 100 rpm [4]. DTPA-extractable metals were attained by mechanically shaking 4 g of ground sample (screened through a 0.22-mm sieve) with 40 ml of 0.005 M DTPA, 0.01 M CaCl2, and 0.1 M (triethanolamine) buffered to pH 7.3 at 100 rpm [4]. The standard TCLP method according to the US EPA Method 1311 [35] was applied to the solid samples in order to determine the potential leachability of the heavy metals. A 5 g sample of compost (size less than 9.5 mm) with 100 ml of acetic acid at pH 4.93 ± 0.05 (pH was adjusted by 1 N NaOH) (sample: solution ratio =1:20) was taken in 125 ml reagent bottle and kept at room temperature for 18 h in a shaker at 30 ± 2 rpm. An atomic absorption spectrometer (AAS) (Varian Spectra 55B) was used to analyze Zn, Cu, Mn, Fe, Ni, Pb, Cd, and

The total content of heavy metals attained after strong acid digestion is an indicator of compost contamination but cannot provide useful information on the bioavailability of heavy metals in the compost and compost-amended soil [36]. The total concentration of heavy metals was determined during the APC and RDC of water hyacinth with natural zeolite. The total concentration of metals was increased during the APC and RDC process of water hyacinth with natural zeolite (**Table 2**) due to the reduction of organic matter and release of CO2 during the mineralization processes [12, 13]. In the APC process, the total concentration of Zn, Cu, Mn, Pb, and Cd was increased highest in control as compared to the zeolite treatments; however, the total concentration of Fe, Cr, and Ni was increased highest in 5, 10, and 15% zeolite treatments, respectively [12]. In the RDC process, the total concentration of Cr, Cd, Zn, Mn, Fe, and Pb was increased highest in 5% zeolite treatment. The total concentration of Ni and Cu was increased highest in 10% zeolite treatment and control, respectively [13]. The total concentration of Zn and Ni was increased with increasing amount of natural zeolite addition in the APC process; however, the concentration of these metals was reduced with an increasing amount of natural zeolite in the RDC process of water hyacinth. In the RDC process, the percentage increase of metals was reduced with an increasing amount of natural zeolite due to the reduction in efficiency of the composting process. A higher addition of natural zeolite in the RDC process could hold the high amount of moisture that reduced the microbial activity [13]. Zorpas et al. [37] reported that the heavy metals contents were greatly decreased by approximately 100, 17, 31.7, 35.1, 24.0, 60.0, 56.7, and 47.9% for Cd, Cr, Cu, Fe, Mn, Ni, Pb, and Zn, respectively, in the process of composting of sewage sludge with zeolite. Zorpas et al. [38] concluded that the addition of 25% (w/w) zeolite in compost is adequate to eliminate around 12–60% of the heavy metals during sewage sludge composting. Sprynskyy et al. [14] reported that the addition of 9.09% clinoptilolite to the sludge reduced the total concentration of metals to around 11–51%. The increases in the concentration of heavy metals in the composting

Cr concentrations in different extracted solutions.

process were mainly because of the losses of mass [37].

**5.2. Total concentration of heavy metals**

190 Zeolites - Useful Minerals

The water-soluble fraction of heavy metals in the compost was lower than their total concentration, which is the most toxic fraction in the final compost [39]. **Table 3** shows the changes in the water solubility of the heavy metals during the APC and RDC processes. The water solubility of the metals (percentage of total metal) was decreased by approximately 80.0% for Zn, 76.7% for Cu, 83.1% for Mn, and 100% for Cr in the APC process [40]. However, during the RDC process of water hyacinth, the water-soluble fraction of the heavy metals was decreased (percentage of total metal) by approximately 71.3% for Zn, 79.1% for Cu, 78.3% for Mn, 76.8% for Fe, and 89.4% for Cr. The highest reduction of water-soluble Zn, Cu, Mn, and


Note: ND-not detected; control: water hyacinth (90 kg), sawdust (15 kg), cattle manure (45 kg); zeolite 5% (control + zeolite 7.5 kg); zeolite 10% (control + zeolite 15 kg), and zeolite 15% (control + zeolite 22.5 kg).

**Table 3.** Effects of natural zeolite on water solubility of heavy metals during water hyacinth composting.

Cr was observed in 5% zeolite treatment, whereas a higher reduction of Fe was observed in 10% zeolite treatment [41]. The water-soluble fractions of Ni, Pb, and Cd were not found in the APC and RDC processes. The addition of zeolite significantly reduced the water-soluble Cu, Mn, Fe, and Cr contents during the composting water hyacinth composting process. In the APC process of water hyacinth with natural zeolite, the highest reduction in water-soluble concentration of Zn was found in control. However, the highest reduction in water-soluble fraction of Zn, Cu, Mn, Fe, and Cr was observed in 10% zeolite treatment [40]. In the RDC process, the highest reduction in water-soluble fraction of Zn, Cu, Mn, and Cr was observed in 5% zeolite treatment; however, the highest reduction in Fe was observed in 10% zeolite treatment. The poor reduction in water solubility of metals was observed in 15% zeolite treatment likely due to the higher addition of zeolite, which could hinder the composting process by absorbing water content leading to the clumping of compost biomass [41]. Watersoluble fractions of Ni, Pb and Cd were not found in all zeolite treatments during the APC and RDC processes of water hyacinth [40, 41]. The highest reduction in water solubility of metals was achieved in 10% zeolite treatment during the APC process; whereas in the RDC process of water hyacinth the highest reduction was observed in 5% zeolite treatment. Stylianou et al. [42] reported that during the sewage sludge composting process, decomposed organic matter plays an important role in releasing water-soluble heavy metals, which increases the availability of their exchangeable forms that can uptake by natural zeolite through ion exchange process.

#### **5.4. DTPA extractability**

Cr was observed in 5% zeolite treatment, whereas a higher reduction of Fe was observed in 10% zeolite treatment [41]. The water-soluble fractions of Ni, Pb, and Cd were not found in the APC and RDC processes. The addition of zeolite significantly reduced the water-soluble Cu, Mn, Fe, and Cr contents during the composting water hyacinth composting process. In the APC process of water hyacinth with natural zeolite, the highest reduction in water-soluble concentration of Zn was found in control. However, the highest reduction in water-soluble fraction of Zn, Cu, Mn, Fe, and Cr was observed in 10% zeolite treatment [40]. In the RDC process, the highest reduction in water-soluble fraction of Zn, Cu, Mn, and Cr was observed in 5% zeolite treatment; however, the highest reduction in Fe was observed in 10% zeolite treatment. The poor reduction in water solubility of metals was observed in 15% zeolite treatment likely due to the higher addition of zeolite, which could hinder the composting process by absorbing water content leading to the clumping of compost biomass [41]. Watersoluble fractions of Ni, Pb and Cd were not found in all zeolite treatments during the APC and RDC processes of water hyacinth [40, 41]. The highest reduction in water solubility of metals was achieved in 10% zeolite treatment during the APC process; whereas in the RDC process

**methods Control Zeolite 5% Zeolite 10% Zeolite 15% Control Zeolite 5% Zeolite 10% Zeolite 15%** 

30 1.25 0.87 0.46 0.59 0.92 0.55 0.49 0.97

20 1.264 0.991 0.725 0.9125 1.09 0.49 0.435 1.691

30 12.68 3.65 1.11 1.29 75.08 9.92 3.65 6.59

20 3.36 0.98 0.965 1.25 20.28 10.715 10.8 37.57

30 0.54 ND ND 0.38 ND ND ND ND

20 0.4 0.235 0.3325 0.64 ND ND ND ND

Note: ND-not detected; control: water hyacinth (90 kg), sawdust (15 kg), cattle manure (45 kg); zeolite 5% (control +

Zn (mg/kg) Cu (mg/kg)

Mn (mg/kg) Fe (mg/kg)

APC 0 3.38 3.59 1.49 1.42 1.12 1.73 1.77 1.60

RDC 0 2.28 2.542 1.57 1.368 2.28 1.703 1.825 2.512

APC 0 8.50 10.89 3.80 2.90 16.14 15.28 9.11 8.89

RDC 0 9.99 3.29 3.34 1.965 19.32 21.55 31.09 47.79

Cr (mg/kg) Ni, Pb and Cd (mg/kg) APC 0 2.07 0.43 0.62 0.73 ND ND ND ND

RDC 0 1.69 1.605 1.725 0.76 ND ND ND ND

**Table 3.** Effects of natural zeolite on water solubility of heavy metals during water hyacinth composting.

zeolite 7.5 kg); zeolite 10% (control + zeolite 15 kg), and zeolite 15% (control + zeolite 22.5 kg).

**Composting Days Water-soluble metals concentration**

192 Zeolites - Useful Minerals

It has been considered that DTPA is a chelating agent and generally used for the analysis of metals availability for plants in the soil amended with heavy-metal-contaminated compost or sewage sludge at regular or even higher concentration [43]. In the case of added zeolite, the amount of DTPA-extractable Pb, Cu, and Zn significantly decreased in the composting because of the higher ion exchange capacity [10]. The DTPA extraction efficiency of the metals was decreased by about 56.6% for Zn, 85.4% for Cu, 81.7% for Mn, 78.5% for Ni, and 75.5% for Cr in the APC of water hyacinth with natural zeolite [40]. However, the DTPA extraction efficiency of metals was decreased by about 58.6% for Zn, 81.1% for Cu, 48% for Mn, 52.1% for Fe, 93.2% for Ni, and 77% for Cr during the RDC process of water hyacinth with natural zeolite [41]. A decrease in DTPA-extractable heavy metals were more found in the RDC process than in the APC process (**Figure 2**). DTPA-extractable concentrations of Pb and Cd were not observed during the APC and RDC processes of water hyacinth with zeolite. In the APC process of water hyacinth, the highest reduction in DTPA extractability of Cu and Mn was observed in control; however, Zn, Cu, Ni, Fe, and Cr were reduced in 5 and 10% zeolite treatments in comparison to the control [40]. The DTPA extraction of Zn, Mn, and Fe was increased in control during the RDC process. However, in the zeolite-added compost, the DTPA extractability of Zn, Cu, Mn, Fe, and Cr was reduced significantly. The reduction in DTPA-extractable heavy metal can be attributed as ion-exchange process where metal cations are mainly exchanged with Na, K, and Ca. DTPA-extractable fraction of Pb and Cd were not found in all zeolite treatments during the APC and RDC processes of water hyacinth [40, 41]. A higher reduction in DTPA extraction of Ni was observed in 10% zeolite treatment followed by 5 and 15% zeolite treatments, and control in the APC process of water hyacinth [40]. A decrease in DTPA-extractable metals in the final compost of water hyacinth with zeolite addition can be attributed to the ligneous bulking agent (sawdust) promoting both the formation and complexation ability of humic acid, resulting reduction in bioavailability of heavy metals [41]. The reduction of DTPA extractability of Zn, Cu, Ni, and Cr was also observed by Chiang et al. [10] during the sewage sludge composting with natural zeolite. In the control test, the concentrations of all tested DTPA metals were higher than those in the zeolite treatments. In matured compost product from the control test, the DTPA solution extracted about 65.0, 18.7, 63.2, and 39.5% of the total Zn, Ni, Cu, and Pb, respectively [10]. DTPA-extractable heavy metal reduction is attributed to the mechanism of ion-exchange processes where metal cations are mainly exchanged with Na, K, and Ca during the compost‐ ing process [11, 15]. Furthermore, the reduction in DTPA-extractable metals at the end of the composting process due to the transformation of organic matter leads to the formation of metal-humus complexes, which make the metals insoluble and thus less easily extractable [44]. Xiong et al. [45] concluded that ligneous bulking agents, especially wood sawdust, promote both the formation and complexation ability of humic acid, which can reduce the bioavaila‐ bility of heavy metals, thus reducing the pollution risk of heavy metals in the agricultural application of compost.

**Figure 2.** Changes of DTPA-extractable concentration of heavy metals during the agitated pile (a–f) and rotary drum (g–l) composting of water hyacinth (NZ-natural zeolite).


#### **5.5. Leachability of heavy metals**

Xiong et al. [45] concluded that ligneous bulking agents, especially wood sawdust, promote both the formation and complexation ability of humic acid, which can reduce the bioavaila‐ bility of heavy metals, thus reducing the pollution risk of heavy metals in the agricultural

**Figure 2.** Changes of DTPA-extractable concentration of heavy metals during the agitated pile (a–f) and rotary drum

(g–l) composting of water hyacinth (NZ-natural zeolite).

application of compost.

194 Zeolites - Useful Minerals

**Table 4.** Threshold limits for leachable heavy metals (mg/kg).

The TCLP test is intended to define the mobility of organic and inorganic constituents that are available in liquid and solid wastes [35]. TCLP is used to evaluate the suitability of compost for land application or whether it should be considered a hazardous waste. The procedure is planned to check the leaching possibility of metals in the compost material for agricultural application. The controlling limits for the leached fraction of toxic heavy met‐ als are based on avoiding groundwater pollution through metals, which can create a risk to human health and environment [30]. According to the US EPA [35], the threshold limit for heavy metals contamination in compost is given in **Table 4**. The TCLP-extractable heavy metal concentrations (mg/kg) were in the range of 0.82–3.0, 1.2–3.7, and 12.7–17.9 for Cd, Cr, and Pb, respectively, in the mature compost, confirming that water hyacinth compost was not hazardous to the soil application.

The TCLP-extractable heavy metals were in compliance with the EPA regulatory thresholds limit. **Table 5** shows the variation of leachable heavy metals (Zn, Cu, Mn, Fe, Ni, Pb, Cd, and Cr) during the APC and RDC processes of water hyacinth with natural zeolite. In the APC process of water hyacinth, the TCLP concentration of metals were reduced approximately 61.4% of the total Zn, 72.0% of Cu, 51.4% of Mn, 73.9% of Fe, 64.6% of Ni, 53.3% of Pb, 82.8% of Cd, and 59.7% of Cr in zeolite treatments [40]. In the RDC process of water hyacinth, the leachability of heavy metals was reduced (percentage of total metal) approximately 67.4% for Zn, 52.7% for Mn, 67.0% for Fe, 67.9% for Ni, 71.0% for Cd, and 72.6% for Cr in zeolite treatments. However, the highest reduction in leachability of Cu (73.2%) and Pb (72.4%) was found in the control during the RDC process of water hyacinth [41]. A higher reduction in leachability of metals was observed in zeolite treatments when compared to control in both APC and RDC of water hyacinth [40, 41]. In the RDC process, the highest reduction in leachability of Zn, Mn, Fe, and Ni was observed in 5% zeolite treatment, whereas the reduction of Cd and Cr was observed in 10% zeolite treatment. In the water hyacinth composting with natural zeolite, the pH of the initial feed mixture was enhanced in comparison to control, which reduced the leachability of heavy metals [40, 41, 46]. Furthermore, the reduction in the leachable concentration of heavy metals might be due to humic substances formed at the end of composting process, which had a capacity to form a complex with metals [1, 47]. The reduction in the leachability of Cu and Pb was not significant in any of the zeolite treatments in comparison to control. Increasing the amount of zeolite addition did not reduce the leachability of metals. The reduction in the leachability of heavy metals was much less in 3% zeolite treatment in comparison to control and 1 and 2% zeolite treatments during the RDC process.


Note: Control: water hyacinth (90 kg), sawdust (15 kg), cattle manure (45 kg); zeolite 5% (control + zeolite 7.5 kg); zeolite 10% (control + zeolite 15 kg), and zeolite 15% (control + zeolite 22.5 kg).

**Table 5.** Effects of natural zeolite on leaching concentration of heavy metals during agitated pile and rotary drum composting of water hyacinth.

#### **6. Conclusions**

natural zeolite, the pH of the initial feed mixture was enhanced in comparison to control, which reduced the leachability of heavy metals [40, 41, 46]. Furthermore, the reduction in the leachable concentration of heavy metals might be due to humic substances formed at the end of composting process, which had a capacity to form a complex with metals [1, 47]. The reduction in the leachability of Cu and Pb was not significant in any of the zeolite treatments in comparison to control. Increasing the amount of zeolite addition did not reduce the leachability of metals. The reduction in the leachability of heavy metals was much less in 3% zeolite treatment in comparison to control and 1 and 2% zeolite treatments during the RDC

**Composting methods Days Leaching concentration of heavy metals**

**Control Zeolite**

**(5%)**

APC 0 30.39 57.53 42.53 37.22 3.47 7.60 12.0 8.0

RDC 0 42.22 50.08 38.15 24.77 6.60 13.18 7.31 6.13

APC 0 155.10 283.40 259.50 254.0 141.50 53.45 31.02 27.87

RDC 0 205.10 184.10 180.40 140.20 121.70 48.30 27.10 32.80

APC 0 10.90 17.60 13.42 9.93 36.50 38.50 37.0 36.79

RDC 0 8.60 7.69 5.50 5.33 53.20 26.05 22.05 21.40

APC 0 1.50 1.98 1.26 1.35 4.62 6.90 5.70 4.30

RDC 0 1.86 1.75 2.95 4.55 6.10 2.53 4.30 2.55

Note: Control: water hyacinth (90 kg), sawdust (15 kg), cattle manure (45 kg); zeolite 5% (control + zeolite 7.5 kg);

**Table 5.** Effects of natural zeolite on leaching concentration of heavy metals during agitated pile and rotary drum

zeolite 10% (control + zeolite 15 kg), and zeolite 15% (control + zeolite 22.5 kg).

composting of water hyacinth.

**Zeolite (10%)**

Zn (mg/kg) Cu (mg/kg)

Mn (mg/kg) Fe (mg/kg)

Ni (mg/kg) Pb (mg/kg)

Cd (mg/kg) Cr (mg/kg)

**Zeolite (15%)**

30 28.62 23.855 18.86 25.99 3.50 2.88 4.38 3.58

20 21.27 22.20 21.28 20.99 2.30 7.40 3.60 4.45

30 233.80 247.90 216.90 210.55 136.70 26.32 16.44 14.99

20 175.50 119.60 130.0 133.90 63.30 27.40 23.40 24.0

30 9.50 7.56 7.60 6.84 32.0 280.0 27.0 29.0

20 3.60 2.80 2.10 3.29 17.0 12.87 12.65 17.80

30 1.20 0.49 0.43 0.66 3.82 4.38 4.08 2.78

20 1.02 0.82 1.22 3.01 3.65 1.18 1.41 1.65

**Control Zeolite**

**(5%)**

**Zeolite (10%)**

**Zeolite (15%)**

process.

196 Zeolites - Useful Minerals

The addition of natural zeolite (clinoptilolite) during the composting process led to significantly reduce the water solubility, and DTPA and TCLP extractability of heavy metals. The TCLP test proved that the concentrations of all selected heavy metals in control and the concentrations of the heavy metals released from the zeolite-treated compost were below the threshold limits. The highest reduction in the bioavailability and leachability of the heavy metals was observed in zeolite treatments 5 and 10% during the APC and RDC processes of water hyacinth. The addition of natural zeolite at suitable concentration successfully reduced the bioavailable and leachable fraction of heavy metals during the composting process of sewage sludge and water hyacinth. Natural zeolite takes up a significant amount of heavy metals during the composting of organic wastes. Addition of the natural zeolite during the composting process led to the increased Na, Ca, and K concentrations and effectively reduced water solubility and DTPA and TCLP extractability of heavy metals. The optimum percentage of zeolite addition in composting mass could fasten degradation of organic biomass; therefore, it decreased the bioavailability and leachability of the heavy metals during the composting process.

#### **Acknowledgements**

This work was supported by a National Research Foundation of Korea (NRF) grant funded by the Ministry of Science, ICT, and Future Planning (2013R1A2A2A03013138).

### **Author details**

Jiwan Singh1 , Ajay S. Kalamdhad2 and Byeong-Kyu Lee3\*

\*Address all correspondence to: bklee@ulsan.ac.kr

1 Department of Environmental Science, Babasaheb Bhimrao Ambedkar University, Lucknow, India

2 Department of Civil Engineering, Indian Institute of Technology Guwahati, Guwahati, In‐ dia

3 Department of Civil and Environmental Engineering, University of Ulsan, Ulsan, Republic of Korea

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### **The Influence of Zeolites on Quality Indicators of Soil-Plant Connection and Food Safety**

Aleksandra Badora

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/64590

#### **Abstract**

Applying zeolites to natural environment is important from the point of view of monitoring the toxic metals' mobilization (Al(III), Mn(II), Cd(II), and Pb(II)) as well as microelements (Fe, Mn, Zn, and Cu). These elements influenced food chain and their deficiency as well as excess and determined plant quality and health of humans and animals. Furthermore, zeolites, while having particular physical, physicochemical, and chemical properties, interact with physical, physicochemical, chemical, and biological features of the soil and may lead to alterations in their properties. This exchange is dependent on many factors, i.e. pH, concentration of metal ions in solution. When natural zeolites are applied, one should bear in mind that they are ecological material and do not show any harmful action neither to humans nor to animals. Studies in this chapter will show the influence of described and tested zeolites on the properties and quality indicators of the first food chain link: soil-plant as well as on the quality of food. It would allow to understand, predict, and control the behavior of these elements in natural environment as well as evaluate their potential toxicity and bioavailability.

**Keywords:** heavy metals, zeolites, some soil properties, some element ratios in plants, food security

#### **1. Introduction**

The primary effect of the negative impact of acidic reaction consists in adverse changes in physical, chemical, and biological properties of soils, as well as poor growth and develop‐ ment of plants (lower yields). Secondary effect is the mobilization of aluminum and heavy metal ions in amounts proportional to the acidity of the soil. In acidic soils with pH below 4.2, aluminosilicates are decomposed, whereas the concentration of Al3+ and Mn2+ ions that occupy

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

space of Mg2+ and Ca2+ in the sorption complex and contribute to increased leaching of alka‐ line cations is increased. These changes are a major cause of poor growth and development of crops [1–4]. At first, high concentration of aluminum ions has a destructive effect on the root system, which makes nutrient uptake difficult and results in Mg and P deficiency symptoms in plants and their poorer growth. Aluminum ions also limit the growth of shoots leading to the decay of vertices and the necrosis of leaves. Aluminum also forms the ion ratios in cereals, including enhancement of K:(Ca + Mg) ratio and affects the higher content of Mn and Fe in the above-groundpartsofplants.Finally,toxic aluminumreduces thequantityandqualityof cereal crops [2, 3, 5]. Considering the influence of environmental conditions on the quality of wheat grain, the health aspect of raw material cannot be overlooked, especially the content of heavy metals, including cadmium, even small amounts of which are harmful to the health of hu‐ mans and animals and which is characterized by very high mobility within the environment. Cereals are the main source of cadmium for humans.

There is quite broad differentiation in the quantity of cadmium uptaken from the soil. More cadmium is absorbed by durum rather than common wheat kernels [6, 7]. Diverse cadmium levels are also found in grains depending on the cultivar [8–11]. The presence of heavy metals, such as Pb and Cd, in the soil, significantly affects the quality of grain yield, since exceeding the permissible content of these elements in the intervening purchase of cereals (>0.2 mg/kg) disqualifies the grain for further processing and consumption, which may lead to substantial economic losses. It is therefore necessary to monitor the heavy metals content in soils [12, 13].

Applying new sorbents, such as zeolites, in natural environment is important from the point of view of monitoring the toxic metals mobilization (Al, Mn, Cd, and Pb) as well as microele‐ ments (Fe, Mn, Zn, and Cu) or macroelements (Mg, Ca, and K). These elements influenced food chain and their deficiency as well as excess and determined plant quality and health of human and animals [4, 5, 14]. Furthermore, new substances, while having particular physical, physicochemical, and chemical properties, interact with physical, physicochemical, chemical, and biological features of the soil, its phases (solid, liquid, and gaseous), as well as its compo‐ nents (mineral-organic complex, soil solution) and may lead to alterations in their properties [14–18]. This exchange is dependent on many factors, i.e. pH, concentration of metal ions in solution, and their speciation. The transport of inns in the environment begins in the liquid phase. This pathway is not only the manner in which ions translocate but also has significant importance for metal accumulation in plants and the food chain [10, 11, 19–21]. Therefore, the knowledge of the properties and behavior of new substances in particular elements of a natural environment does not only have cognitive, but also social aspects.

Among zeolites, clinoptilolite is the most common and the best studied one, not only due to its largest abundance in nature and lowest prices, but also the widest scope of its physico‐ chemical properties [22]. This zeolite is characterized by the following features: large sorp‐ tion and ion-exchange capacity, ion-exchange selectivity, properties of molecular sieve, catalytic activity, structural thermal stability at temperatures of up to 700–750°C. The chemical composition of zeolites determines their behavior under particular conditions. In an alkaline environment, these minerals are decomposed—their fibrous crystals collapse—mordenite converts into analcites. In an acidic environment, a zeolite can be completely deprived of cations, which in consequence produces a hydrated amorphous silica skeleton that retains its initial shape of crystal. Natural clinoptilolite is characterized by Si/AI ratio >4 as well as higher contents of Na+ and K+ cations in relation to Ca2+, Ba2+, and Sr2+. When natural zeolites are applied, one should bear in mind that they are ecological material and do not show any harmful action neither to humans nor to animals. Therefore, zeolites found quite wide spectrum of application as additives to feed and fertilizers [23], as well as soil conditioning agents [24–26]. Ion-exchange ability and sorption capacity of natural zeolites can be used at gradual and uniform release of nutrients into the soil, which prevents against their quick elution [27]. Applying zeolites to the production of mineral fertilizers allows a gradual and controlled introduction of such necessary nutrients as potassium ammonium or phosphates into the soil. Moreover, fertilizers containing some addition of zeolites modified with Cu(II) ions can be applied to copper-deficient soils. Thus, it is possible to reduce the soil irrigation, because water is well retained within zeolite's structure, as well as to decrease soil acidity [2– 4, 8, 28] and to reduce the temperature oscillations. These sorbents can also be effectively used as pesticide and herbicide carriers [29].

The group of goals, which the author of this chapter proposed to describe are based on own research and literature and focus on the influence of zeolites on the following quality indica‐ tors: changes in the physicochemical properties of certain soils (pH, sorption capacity, bases saturation degree, and amounts of Cd and Pb in soils), certain food quality factors connected to toxic substances and elements (ratios of Fe:Mn and K:Ca + Mg) as factors in plants (wheat and rape).

#### **2. Methodology**

space of Mg2+ and Ca2+ in the sorption complex and contribute to increased leaching of alka‐ line cations is increased. These changes are a major cause of poor growth and development of crops [1–4]. At first, high concentration of aluminum ions has a destructive effect on the root system, which makes nutrient uptake difficult and results in Mg and P deficiency symptoms in plants and their poorer growth. Aluminum ions also limit the growth of shoots leading to the decay of vertices and the necrosis of leaves. Aluminum also forms the ion ratios in cereals, including enhancement of K:(Ca + Mg) ratio and affects the higher content of Mn and Fe in the above-groundpartsofplants.Finally,toxic aluminumreduces thequantityandqualityof cereal crops [2, 3, 5]. Considering the influence of environmental conditions on the quality of wheat grain, the health aspect of raw material cannot be overlooked, especially the content of heavy metals, including cadmium, even small amounts of which are harmful to the health of hu‐ mans and animals and which is characterized by very high mobility within the environment.

There is quite broad differentiation in the quantity of cadmium uptaken from the soil. More cadmium is absorbed by durum rather than common wheat kernels [6, 7]. Diverse cadmium levels are also found in grains depending on the cultivar [8–11]. The presence of heavy metals, such as Pb and Cd, in the soil, significantly affects the quality of grain yield, since exceeding the permissible content of these elements in the intervening purchase of cereals (>0.2 mg/kg) disqualifies the grain for further processing and consumption, which may lead to substantial economic losses. It is therefore necessary to monitor the heavy metals content in soils [12, 13].

Applying new sorbents, such as zeolites, in natural environment is important from the point of view of monitoring the toxic metals mobilization (Al, Mn, Cd, and Pb) as well as microele‐ ments (Fe, Mn, Zn, and Cu) or macroelements (Mg, Ca, and K). These elements influenced food chain and their deficiency as well as excess and determined plant quality and health of human and animals [4, 5, 14]. Furthermore, new substances, while having particular physical, physicochemical, and chemical properties, interact with physical, physicochemical, chemical, and biological features of the soil, its phases (solid, liquid, and gaseous), as well as its compo‐ nents (mineral-organic complex, soil solution) and may lead to alterations in their properties [14–18]. This exchange is dependent on many factors, i.e. pH, concentration of metal ions in solution, and their speciation. The transport of inns in the environment begins in the liquid phase. This pathway is not only the manner in which ions translocate but also has significant importance for metal accumulation in plants and the food chain [10, 11, 19–21]. Therefore, the knowledge of the properties and behavior of new substances in particular elements of a natural

Among zeolites, clinoptilolite is the most common and the best studied one, not only due to its largest abundance in nature and lowest prices, but also the widest scope of its physico‐ chemical properties [22]. This zeolite is characterized by the following features: large sorp‐ tion and ion-exchange capacity, ion-exchange selectivity, properties of molecular sieve, catalytic activity, structural thermal stability at temperatures of up to 700–750°C. The chemical composition of zeolites determines their behavior under particular conditions. In an alkaline environment, these minerals are decomposed—their fibrous crystals collapse—mordenite converts into analcites. In an acidic environment, a zeolite can be completely deprived of

Cereals are the main source of cadmium for humans.

204 Zeolites - Useful Minerals

environment does not only have cognitive, but also social aspects.

The experimental unit during incubation studies consisted of a pot containing 0.5 kg of airdried soil weight of natural origin, from the acidity soil class considered as acidic soils (pH range 4.5–5.5). The soil moisture content will be maintained at the level of 60% of the field water capacity, optimum for a proper growth and development of test plants. Common wheat (*Triticum aestivum* L.) of Opatka cv. was the test plant used for the soil incubation experiments. Twelve seeds will be sown in each pot. After emergence (KD = 11, according to Zadoks), the number of plants will be reduced to six. Plants will be harvested at full ripeness. Rape biomass was harvested at the shooting stage (KD = 20), according to Zadoks—grade proposed by the European Association for Plant Breeding. Variants of Pb experiment were composed by introducing lead salts (in the form of Pb(NO3)2) in the amount of 100 mg Pb/kg soil, immobi‐ lizing agents such as zeolites—clinoptilolite (Fluka) at the following rates: zeolite-1—300 mg/ kg soil, zeolite-2—600 mg/kg soil. Variants of Cd-experiment were composed by introducing cadmium salts (in the form of CdCl2) in the amount of 5 mg Cd/kg soil, immobilizing agents such as zeolites—clinoptilolite (Fluka) at the following rates: zeolite-3—15 mg/kg soil, zeolite-4 —30 mg/kg soil. Both plants were growing in both Pb and Cd experiments.

The soil material was subjected to the following analyses: pH in 1 mol KCl /dm3 at soil-solution ratio equal to 1:2.5, hydrolytic acidity—Hh, contents of exchangeable metal forms (Cd, Pb) in soils was determined in 1 M HCl at soil-solution ratio equal to 1:10. The extraction was supported by intensive mixing using rotational mixer for 1 h. Measurements will be made by means of atomic absorption spectrometry using the Hitachi Z-8200 device with Zeeman's polarization. The content of exchangeable ions (K, Na, Ca, and Mg) was also determined by means of extraction in 1 M CH3COONH4 and AAS determination (as above).

The plants' material was collected after harvesting. After drying at 70°C, plant samples were digested in concentrated H2SO4 with the addition of 30% H2O2 to accelerate the process. In achieved mineralized solutions, determinations of Fe and Mn ions were made. In addition, the following items were calculated: the sum of exchangeable alkali (S = Na+ + K+ + Ca2+ + Mg 2+), sorption capacity (*T* = Hh + *S*) expressed in mmol (+)/kg of soil as well as the alkali saturation degree (*V* = *S*/*T* × 100%), molar ratios of Fe:Mn and K:(Ca + Mg) for investigated plants as food quality factors, the achieved numerical data were processed statistically applying variance analysis with Tukey confidence semi-intervals at the significance level of 0.05.

#### **3. Zeolites and some soil condition**

Zeolites exerted their strongest influence on the pH values increase in the soil contaminated with lead compounds, namely at higher doses (**Figures 1** and **2**). During the second experi‐ mental year (under rapeseed), soil pH values decreased and the soil reaction became acidic instead of slightly acidic with oscillations around 4.5–5.5 (**Figures 1** and **2**). Many authors observed different impact of zeolites on the change in pH values [1–3, 7, 29] and on the decrease in mobility of various heavy metals in soils. The reactions could be also dependent on cadmium and lead chemistry, which is connected with the strength of alkalization of both elements [7, 10, 17, 18].

**Figure 1.** The pH values of soils with Pb and zeolites—own results—(blue color – under wheat, red color – under rape‐ seed).

Higher levels of the total sorption capacity were recorded in variants with the addition of zeolites in the presence of both heavy metals (**Tables 1** and **2**). It was found that, in comparison with the first year of experiments, the *T* value increased in the second year by over 8 mmol (+)/ kg. The base saturation degree (*V*) was within the range of optimum limits and for Polish soils did not exceed 90%. The parameters of *V* were significantly differentiated between the tested plant species in both experimental years. The value of *V* indicators was found to be higher by about 10% in the first year of experiments as compared with the second year (**Tables 1** and **2**). A higher increase was also recorded for the variant with a double dose of zeolites (0 + Cd + zeolites-4) (**Table 2**).

soils was determined in 1 M HCl at soil-solution ratio equal to 1:10. The extraction was supported by intensive mixing using rotational mixer for 1 h. Measurements will be made by means of atomic absorption spectrometry using the Hitachi Z-8200 device with Zeeman's polarization. The content of exchangeable ions (K, Na, Ca, and Mg) was also determined by

The plants' material was collected after harvesting. After drying at 70°C, plant samples were digested in concentrated H2SO4 with the addition of 30% H2O2 to accelerate the process. In achieved mineralized solutions, determinations of Fe and Mn ions were made. In addition, the

sorption capacity (*T* = Hh + *S*) expressed in mmol (+)/kg of soil as well as the alkali saturation degree (*V* = *S*/*T* × 100%), molar ratios of Fe:Mn and K:(Ca + Mg) for investigated plants as food quality factors, the achieved numerical data were processed statistically applying variance

Zeolites exerted their strongest influence on the pH values increase in the soil contaminated with lead compounds, namely at higher doses (**Figures 1** and **2**). During the second experi‐ mental year (under rapeseed), soil pH values decreased and the soil reaction became acidic instead of slightly acidic with oscillations around 4.5–5.5 (**Figures 1** and **2**). Many authors observed different impact of zeolites on the change in pH values [1–3, 7, 29] and on the decrease in mobility of various heavy metals in soils. The reactions could be also dependent on cadmium and lead chemistry, which is connected with the strength of alkalization of both elements [7,

**Figure 1.** The pH values of soils with Pb and zeolites—own results—(blue color – under wheat, red color – under rape‐

+ K+

+ Ca2+ + Mg 2+),

means of extraction in 1 M CH3COONH4 and AAS determination (as above).

following items were calculated: the sum of exchangeable alkali (S = Na+

**3. Zeolites and some soil condition**

10, 17, 18].

206 Zeolites - Useful Minerals

seed).

analysis with Tukey confidence semi-intervals at the significance level of 0.05.

**Figure 2.** The pH values of soils with Cd and zeolites—own results—(blue color – under wheat, red color – under rape‐ seed).


**Table 1.** Total sorption capacity (*T*) and bases saturation degree (*V*) of investigated soils with Pb (own results).


**Table 2.** Total sorption capacity (*T*) and bases saturation degree (*V*) of investigated soils with Cd (own results).

Here, the presented results of the experiments revealed that the soil pH is largely determined by the presence of zeolites and also changes in toxic element contents in soil. Characteristics of the soil sorption complex indicate that applying immobilizing agents had an impact on the improvement of its properties through an increase in total sorption capacity (*T*) and bases saturation degree (*V*), both in variants with no heavy metals and lead-contaminated ones, which may be contributed to soil pH increase and, in consequence, a lower share of acidic cations. It was mainly zeolites at their double doses that affected the increase in total soil sorption capacity, which was also probably the consequence of pH changes. Those results could even be confirmed by other authors [22, 29]. Numerous authors [2, 7, 14, 16, 17] have reported that minerals in the soil contain permanent charges, while sorption capacity increases along with soil pH value, mainly due to the dissociation of H+ and Al3+ ions originating from these permanent charges on mineral fragments of the sorption complex. To improve the physicochemical properties of soil is one of the basic conditions that sorbents used for the detoxication of soils contaminated with heavy metals should meet [21].


**Table 3.** The content of Pb and Cd in the investigated plants grown on soils with Pb and zeolites (own results).

The results revealed that applying sorbents contributed to a decrease in mobile lead ion concentrations in soil. In the soil under wheat, lead ion detoxication was observed after introducing a lower zeolite dose, whereas higher rates of the zeolite appeared to be the most efficient Pb2+ immobilizing agent in the soil under rapeseed. On the other hand, numerous authors [10, 17, 21] have reported the lower affinity of cadmium, as compared to lead ions, toward zeolites; here, presented results did not reveal that cadmium can be equally sufficiently bound by those minerals (**Table 3**).

**No. Variants (A)**

208 Zeolites - Useful Minerals

**T mmol (+)/kg V (%)**

**(B)**

**Table 2.** Total sorption capacity (*T*) and bases saturation degree (*V*) of investigated soils with Cd (own results).

Here, the presented results of the experiments revealed that the soil pH is largely determined by the presence of zeolites and also changes in toxic element contents in soil. Characteristics of the soil sorption complex indicate that applying immobilizing agents had an impact on the improvement of its properties through an increase in total sorption capacity (*T*) and bases saturation degree (*V*), both in variants with no heavy metals and lead-contaminated ones, which may be contributed to soil pH increase and, in consequence, a lower share of acidic cations. It was mainly zeolites at their double doses that affected the increase in total soil sorption capacity, which was also probably the consequence of pH changes. Those results could even be confirmed by other authors [22, 29]. Numerous authors [2, 7, 14, 16, 17] have reported that minerals in the soil contain permanent charges, while sorption capacity increases

these permanent charges on mineral fragments of the sorption complex. To improve the physicochemical properties of soil is one of the basic conditions that sorbents used for the

**Wheat grain Rapeseed biomass Wheat grain Rapeseed biomass**

 0 57.03 71.12 80.72 70.99 0 + zeolites-3 57.98 75.21 80.79 69.35 0 + zeolites-4 59.29 76.61 80.81 72.33 0 + Cd 70.50 78.37 81.12 69.55 0 + Cd + zeolites-3 69.03 79.98 82.64 69.00 0 + Cd + zeolites-4 73.19 82.55 83.57 71.13

**Under rapeseed**

**Under wheat**

**Under rapeseed**

**(B)**

and Al3+ ions originating from

**(B)**

**Under wheat**

LSD0.05 A 9.01 6.72

along with soil pH value, mainly due to the dissociation of H+

detoxication of soils contaminated with heavy metals should meet [21].

 0 + Pb 0.80 1.78 0 + Cd 2.98 32.85 0 + Pb + zeolites-1 0.85 3.40 0 + Cd + zeolites-3 2.82 23.70 0 + Pb + zeolites-2 0.70 3.00 0 + Cd + zeolites-4 2.74 27.83 LSD 0.05 0.16 3.71 LSD 0.05 2.80 14.23

**Table 3.** The content of Pb and Cd in the investigated plants grown on soils with Pb and zeolites (own results).

The results revealed that applying sorbents contributed to a decrease in mobile lead ion concentrations in soil. In the soil under wheat, lead ion detoxication was observed after

**No. Variants Pb Variants Cd**

B 4.91 1.29

**(B)**

It is necessary to emphasize that the reduction in cadmium concentration in both plants was observed (**Table 3**), although the pH in soil was almost at the same level in all variants with this element and zeolites—at around 6 under wheat and around 5 under rape (**Figures 1** and **2**). Such a clear effect was not observed in the Pb reduction. Many authors [4, 9, 28] have shown that zeolites can decrease cadmium toxicity more than other heavy metals. Other authors [5, 30] noted that rape and wheat showed different reactions to different heavy metal toxicity levels.

The increase in the cation sorption capacity is strongly associated with the decrease in toxic metals mobility within the soil environment. Increase in the total sorption capacity index results from the introduction of a material containing functional groups. These materials are clay minerals. Clay minerals having a larger number of pH-dependent sites (e.g. montmoril‐ lonite) are more important for heavy metals sorption, as opposed to those producing more pHindependent sites, e.g. kaolinite. Metal—solid phase in the soil bindings formed due to nonspecific sorption manifests a weaker character of bonds with the presence of water molecule between the metal and the adsorbent. Numerous studies revealed the immobilizing effect of zeolites, both natural and artificial, on toxic elements. Synthetic zeolites of the 13X and 4A types were found to reduce the availability of Pb by 70%, Cu by 57%, Ni by 53.5%, Zn by 67.5%, and Cd by 61%, as well as Pb content in tissues of certain plant species [21]. It was also reported that the addition of a natural zeolite, clinoptilolite, had positive effects on the increase in cation-exchangeable capacity (CEC) of the soil [2, 3, 21–23].

#### **4. Zeolites and certain elements' ratios in plants as food security factors**

The concept of culture (fertility) of soil means such a condition of the soil which provides growing plants with a sufficient amount of nutrients, water, and air, and is the result of many natural and soil-forming factors dependent on the climate, bedrock, and vegetation. The highest cereal yields can be usually obtained from soils abundant in high cultures (with an optimum content of available forms of plant nutrients such as Mg, K, Ca, P, N, and humus), with regulated relations between water and air and with the pH value close to neutral (pH 5.6–7.2) [13].

The present study revealed the influence of zeolites on the changing of investigated ratios such as Fe:Mn and K:Ca + Mg) (**Figures 3** and **4**). The presence of zeolites influenced positive regulation of Fe:Mn ratios in both investigated plants in the variations with Cd in soil (**Figure 4**). In the variations with Pb in soil (**Figure 3**) optimal values of Fe:Mn ratios were obtained only for wheat grain, not for rape, where lower manganese uptake was observed. Many studies [6, 8, 9, 14] have shown that the varied concentration of heavy metals has substantial influence on other elements' uptake by plants.

**Figure 3.** The influence of zeolites used for soils polluted with Pb on Fe:Mn ratio changing in wheat grain (blue color) and rapeseed biomass (red color)—own results.

The content of microelements in soils and their availability to plants depends on many factors [2–4]. Manganese deficit impairs metabolic functions of plants and reduces the sowing value of seeds. Feeding plants of winter and spring wheat with microelements has positive effects on the features of grain quality such as gluten content and sedimentation rate [4, 13, 31, 32].

**Figure 4.** The influence of zeolites used for soils polluted with Cd on Fe:Mn ratio changing in wheat grain (blue color) and rapeseed biomass (red color)—own results.

In the case of K:(Ca + Mg) ratios, the presence of zeolites for the Pb and Cd immobilization, a stronger positive change was observed for wheat grain than for rape (**Figures 5** and **6**). Many authors [4, 9, 14] have shown that the optimal presence of K and Ca and Mg elements in raw materials is very important for food quality. The presence of undesirable substances in plant material entails a risk to consumer's health. The security of crop production is therefore closely linked to the status of the natural environment. Certain substances used a few dozen years ago have been interacting with the environment and the trophic chain until now, being subject to its continuous bioaccumulation [13, 20, 31]. The Polish production fields are characterized by the lack of so-called "elements of life" (Mg, Se). Magnesium deficiencies in the area of agri‐ cultural production result in deficiencies of these elements in plant material. Using zeolites for Cd and Pb immobilization in soils may also change the presence of K, Mg, and Ca in plants (**Figures 5** and **6**). The elements discussed above become parts of the food chain mainly through soils: solid surface (soil) attracts and retains the ions, atoms or the molecule layer. The sorption abilities of the soil result from the properties of the sorption complex made of soil colloids: clay minerals (smectites, vermiculite, illite, and kaolinite), crystalline and amorphous iron and aluminum oxides, amorphous minerals, humus, and clay-humus complexes [15–17, 19, 26].

Many studies [6, 8, 9, 14] have shown that the varied concentration of heavy metals has

**Figure 3.** The influence of zeolites used for soils polluted with Pb on Fe:Mn ratio changing in wheat grain (blue color)

The content of microelements in soils and their availability to plants depends on many factors [2–4]. Manganese deficit impairs metabolic functions of plants and reduces the sowing value of seeds. Feeding plants of winter and spring wheat with microelements has positive effects on the features of grain quality such as gluten content and sedimentation rate [4, 13, 31, 32].

**Figure 4.** The influence of zeolites used for soils polluted with Cd on Fe:Mn ratio changing in wheat grain (blue color)

substantial influence on other elements' uptake by plants.

210 Zeolites - Useful Minerals

and rapeseed biomass (red color)—own results.

and rapeseed biomass (red color)—own results.

**Figure 5.** The influence of zeolites used for soils polluted with Pb on K:(Ca + Mg) ratio changing in wheat grain (blue color) and rapeseed biomass (red color)—own results.

Food of either plant or animal origin (sometimes also mineral) is consumed in order to provide the body with energy and nutrients. The basic unit of energy understood in this sense is kilocalorie. Such a measurement system makes it possible to estimate the amount of energy needed by the human body to regenerate itself. An insufficient amount of energy and a low intake of calories lead to hunger and subsequently to death. The daily number of calories required by a person depends on age, sex, body weight, type of work performed, and climate. The World Health Organization (WHO) has established that an adult person requires a minimum of 2200 cal/day to survive. The effects of qualitative malnutrition are not easily noticeable. People affected by it may have a normal body weight and still suffer from the effects of qualitative malnutrition. Vitamin and mineral salts deficiency can lead to serious health issues, such as significantly greater susceptibility to infectious diseases, loss of vision, anemia, coma, reduced knowledge acquisition skills, intellectual development disorder, various forms of physical deformities, and finally death. The most common deficiencies involve the following three elements: vitamin A, iron, and iodine [4, 12, 13, 20, 29, 31, 32].

**Figure 6.** The influence of zeolites used for soils polluted with Cd on K:(Ca + Mg) ratio changing in wheat grain (blue color) and rapeseed biomass (red color)—own results.

#### **5. Summary**

It is important to know that half the people suffering from micronutrient deficiency are usually afflicted by cumulative deficiencies of elements, i.e. they are simultaneously lacking several vitamins and minerals in their diet. Qualitative malnutrition is a direct or indirect cause of half of deaths among children under five in the world. As a consequence of deliberate intervention in agro-ecosystems, a man can control their productivity and increase the amount of produced biomass, which can be utilized as food for humans, feed for animals, and raw material for many industry branches. Future of the agriculture should therefore be based on a variety of plants species, from which new, healthier, and less processed goods are made. Such approach promotes not only the safety, but also the nutritional sovereignty of societies.

Zeolites have appeared to be promising binding agents for lead ions mobility and for cadmium at lower doses. Also soil pH values have been changing due to applied sorbents, largely determining the forms of toxic metals in soils. Zeolites improved properties of the soil sorption complex through the increase of total sorption capacity as well as base saturation degree, which met the necessary condition of the lack of toxicity to immobilization of the heavy metals contaminated soils. Zeolites influence also the changing of Fe:Mn and K:(Ca + Mg) ratios in the investigated plants like wheat and rape. These factors can describe the quality of food products made from these plants.

### **Author details**

intake of calories lead to hunger and subsequently to death. The daily number of calories required by a person depends on age, sex, body weight, type of work performed, and climate. The World Health Organization (WHO) has established that an adult person requires a minimum of 2200 cal/day to survive. The effects of qualitative malnutrition are not easily noticeable. People affected by it may have a normal body weight and still suffer from the effects of qualitative malnutrition. Vitamin and mineral salts deficiency can lead to serious health issues, such as significantly greater susceptibility to infectious diseases, loss of vision, anemia, coma, reduced knowledge acquisition skills, intellectual development disorder, various forms of physical deformities, and finally death. The most common deficiencies involve the following

**Figure 6.** The influence of zeolites used for soils polluted with Cd on K:(Ca + Mg) ratio changing in wheat grain (blue

It is important to know that half the people suffering from micronutrient deficiency are usually afflicted by cumulative deficiencies of elements, i.e. they are simultaneously lacking several vitamins and minerals in their diet. Qualitative malnutrition is a direct or indirect cause of half of deaths among children under five in the world. As a consequence of deliberate intervention in agro-ecosystems, a man can control their productivity and increase the amount of produced biomass, which can be utilized as food for humans, feed for animals, and raw material for many industry branches. Future of the agriculture should therefore be based on a variety of

three elements: vitamin A, iron, and iodine [4, 12, 13, 20, 29, 31, 32].

color) and rapeseed biomass (red color)—own results.

**5. Summary**

212 Zeolites - Useful Minerals

#### Aleksandra Badora

Address all correspondence to: aleksandra.badora@up.lublin.pl

Department of Agricultural and Environmental Chemistry, Subdepartment of Quality and Standardization of Plant Materials, University of Life Sciences in Lublin, Lublin, Poland

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[8] Badora A. 2001. Aluminum and manganese mobility in the soil. Polish J. Soil Sci., 34,

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[16] Sposito G., 1989. The chemistry of soils. Oxford University Press, Oxford, England.

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214 Zeolites - Useful Minerals

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656.

432.


### *Edited by Claudia Belviso*

This book collects recent results about research activities on zeolites, from synthesis to application. It is composed of two sections. The first is devoted to articles and brief review articles on the synthesis of zeolite from fly ash and final application of these newly formed minerals to solve environmental problems. The second part of the book provides useful information on different applications both of natural and synthetic zeolites ranging from environmental pollution to industrial and commercial applications. The performance of zeolite molecular sieves, hollow titanium zeolites and luminescent zeolites is interesting considering the new frontiers reached by the research on zeolites.

This book is a useful instrument for researchers, teachers and students who are interested in investigating innovative aspects of the studies on zeolite

Zeolites - Useful Minerals

Zeolites

Useful Minerals

*Edited by Claudia Belviso*

Photo by Lyocsa / iStock