Investigation of Lithium Application and Effect of Organic Matter on Soil Health

Abstract

The extensive use of lithium (Li) ion-based batteries has increased the contamination of soil and water systems due to widespread dispersal of Li products in the environment. In the current study, the influence of Li application on soil fertility and leachate was observed. Three soil samples were collected and five treatments of Li (0, 50, 100, 150 and 200 mg/L) were applied. After three months of Li treatment, leachate was collected and soil samples were subjected to physical and chemical analyses. The results showed that the mean values of soil pH were increased slightly after Li application while electrical conductivity (EC) ranged from 1.2 to 5.1 µS/cm, indicating that soil was slightly saline in nature. The sodium was observed to be greater than the recommended values (0.3–0.7 mg/kg) in Li-amended soil while calcium and magnesium values decreased in soils compared to untreated soil. Mean values of phosphorus and potassium were greater before Li application and reduced considerably after Li application. Leachate analysis showed that all the parameters differed significantly except those of zinc and iron. The EC of leachate samples ranged from 2286–7188 µS/cm, which shows strong salinity. The sodium adsorption ratio (SAR) ranged from 1–11, which indicates that it falls into the marginal soil category. Lithium concentration in leachate samples ranged from 0–95 mg/L, which was significantly higher than the acceptable value for lithium (2.5 mg/L) in leachate. A soil sample (3) with an additional 10% organic matter showed that after Li application, the loss of nutrients in leachate was less as compared to the other two samples, demonstrating that organic matter improved soil conditions and suppressed the negative effects of Li on soil. Our results could raise concerns about risks in situations where food and fodder crops are associated with Li-contaminated waste disposal.

1. Introduction

Pollutants mobility is greatly influenced by physical and chemical characteristics of soil, especially those pollutants which are easily water soluble, attached with minerals and organic components present on the surface of soil, or precipitated chemically to solid compounds [1]. The soil physical properties (texture, bulk density, porosity, permeability and color) play a significant role in the promotion of conditions for the interaction between pollutants and soil particles/water and their migration through the soil, until they reach other environmental compartments [2]. For example, due to the presence of pollutants in soil, pore spaces could be clogged, resulting in decreased aeration in soil and water infiltration capacity, and increased bulk density. Introduction of oil-based pollutants which are denser as compared to water might decrease and prohibit soil permeability.

Distribution of lithium (Li) is not abundant but commonly found in nature. It is the lightest monovalent cation among the alkali metals. It is categorized as the 25th most abundant metal element on the earth’s crust. Lithium concentration in soil ranges from <1–200 mg kg⁻¹ and saline and arid soils contain relatively higher concentration [3,4,5]. Lithium presence is detected in primary and sedimentary mountains, marbles, granites and calcareous rocks. It has been present even in larger water bodies such as the Mediterranean Sea, the Southern Sea, the Chinese Sea, the Indian Sea, the Atlantic Ocean, the Red Sea and the Antarctic Ocean [6]. The majority of Li occurs in soil as a component of minerals including spodumene having low solubility in an aqueous environment and dilute acids. Weathering of minerals, rocks and downstream flow of water bodies enhances its level in crop-irrigated agricultural soils. Drinking water and edible crops are the major pathways of Li entry into the food chain [7]; both these sources rely on Li dynamics in soils. Generally, Li concentration in topsoil is less compared to that in underlying soil layers [3]. clay has been reported to show relatively higher concentrations of Li with respect to its organic fraction [8].

The demand for Li-ion batteries as a major power source in portable electronic devices and vehicles is increasing rapidly [9]. As a consequence of increasing global demand, Li production has increased three times since 2000 and current production has reached >600,000 tons [10]. In addition to Li-ion batteries, it is also used in pharmaceuticals, glass, ceramics, coolants for nuclear reactors and some arms manufacturing industries (Kszos and Stewart, 2003). Moreover, Li₂CO₃ is also used as a medicine for bipolar disorder and mood stabilizer. Hence, both natural and man-made sources are contributing to higher concentration of Li in soil and other components of the environment [11]. Although traces of Li are needed for better functioning of animals and humans, higher levels can cause acute and chronic toxic diseases [12]. It is recommended that the daily intake of Li should not exceed 1 mg/day for a 70 kg human adult [13]. The general concentration of Li in humans is about 7 mg while in blood serum it may range from 10 to 15 mg/L. A higher concentration of Li can be extremely poisonous for human beings and mainly affects the central nervous system [4].

Lithium causes renal toxicological disorders such as tubular damage and sclerotic glomeruli [14]. Long-term Li accumulation in various parts of humans also produces digestive and neurological disorders.

Contamination of soil with Li is likely to increase because of its broader occurrence in the environment, particularly with the disposal of Li-ion batteries [15]. Compared to other cations in soil, Li is more mobile and may leach into receiving waters, being taken up by plants, or cause biological damage [16]. The presence of Li in soil may lead to its entry into plants as Li exists abundantly in leafy vegetables, which are a major source of Li in the human diet.

The intake of Li-contaminated water and edible crops are the major sources of Li entry into the food chain and both these sources rely on the Li concentration in soil [7]. At high levels in the soil, Li is toxic to all plants but uptake and sensitivity to Li are species-dependent. In general, more Li is taken up by plants from acidic soils than alkaline soils. When Li and other elements are added in the soil, it has been observed that Li becomes more mobile as compared to other elements [17]. It quickly leaches through soil and interacts with plant roots and microorganisms present in soil. Matrices of silicate or its interlayers are associated with Li and only available to soil when minerals break down as a result of weathering. Thus, there is a dire need to study the effect of Li on soil health, which ultimately influences plants’ growth and Li exposure to humans. To our knowledge, limited/no data exists in which the effect of Li on soil health has been analyzed specifically in Pakistan.

Thus, the current study aimed to investigate the effect of Li application (0–200 mg/L) on physical and chemical parameters including texture, pH, EC, organic matter, sodium absorption ration (SAR), and major cations and anions of three soil samples—two natural soil samples and one with organic matter addition. Finally, the impact of Li application on leachate collected from soil samples was also investigated.

2. Materials and Methods

2.1. Description of Study Area and Collection of Soil Samples

The study was conducted in two districts (Lahore, Sheikhupura) of Punjab, Pakistan (Figure 1). Lahore district is the provincial capital as well as the largest city (district) of the Punjab province, Pakistan, which is bounded by 73.22°–74.45° E, 31.20°–31.60° N, with ~4000 km area (Figure 1). The population of Lahore was more than 6.5 million in 2007 [18]. Overall, Lahore ranks second among the urban centers of Pakistan. It is situated on an alluvial plain of the left bank of the River Ravi. Here the clay loam increases as the distance from the riverbed increases [19]. Many considerable modifications in lithologies have been reported, while the major minerals found in Lahore soil are muscovite, chlorite, biotite and quartz along with small proportions of other heavy minerals [18].

Sheikhupura is located about 36 Km from Lahore. Sheikhupura lies 73°59′3.49′′ E and 31°42′51.16′′ N with a total population of about 3,321,029. The studied location is an important component of Rechna Doab and formed from sub-recent sediments which were induced by a spill channel forming from the Chenab River. Clay materials exist in a few old basins and channel levees. The soil material is likely of the age of Late Pleistocene, made from a mixture of metamorphic and calcareous sediments of the Lower Himalayas [20].

Two soil samples were collected from two different sites. Sample 1 was collected from the botanical garden of Government College University, Lahore district, Punjab (Pakistan). Sample 2 was collected from Kala Shah Kaku campus, Government College University, Lahore, located in Sheikhupura district, Punjab (Pakistan). The soil of the botanical garden lacks any kind of pollutants and was intact in its natural form. The garden has a collection of both indigenous and exotic plants from various parts of the world, mainly sub-Himalayan areas. Sample 3 was formed by taking soil from the botanical garden and adding 10% organic matter. Representative soil samples were collected from the top 30 cm soil layers for the experiment. Soil sampling was carried out with the help of an auger. All the samples were collected in zipper bags and labeled properly.

2.2. Preparation and Analysis of Soil Samples

Samples were brought to the research lab for further analysis. All physical and chemical analyses were carried out on soil samples before lithium (Li) application. Plastic cylinders with 15 cm inner diameter and 35 cm height were used to contain 30 cm -long soil columns. A porous plate was fixed at the bottom end of each column. Soil samples were analyzed before and after Li application.

2.2.1. Preparation of Soil Sample

Soil samples were ground and sieved (10 mm). The prepared soil samples were poured into the cylinder with stirring to prevent layering and to settle the soil to bulk density. Each soil sample’s weight was almost 3 kg when poured into the cylinder. The experiment was carried out on 30 soil columns: 3 soil types (soil series) × 5 lithium concentrations × 2 replications for each treatment.

2.2.2. Preparation of Lithium Treatments

Five different concentrations of Li were prepared and applied to each soil column. Concentrations of Li were 0, 50, 100, 150 and 200 mg/L. For Li treatment, salt was added to the water and the volume of water was raised up to 1000 mL and divided into 3 equal parts for each soil sample. The pH of each Li concentration was also determined before applying to the soil samples and measured as 7.54, 7.6, 7.64, 7.67 and 7.70 for 0, 50, 100, 150 and 200 mg/L of Li, respectively.

2.3. Application of Lithium Treatments on Soil Samples

Five different concentrations of Li were applied to each soil sample; i.e., sample 1, sample 2 and sample 3 and their respective replica samples. After application of Li, soil samples were irrigated on a regular basis to collect leachate at the bottom. Leachate collection was gravity based and carried out on a monthly basis for further analysis and the experiment was carried out for a total of three months.

2.4. Collection and Analysis of Soil and Leachate Samples

After three months, leachate was collected in the separate bottles and analyzed again and soil samples after Li application were also collected to compare with previously done physical and chemical analysis.

The following physical and chemical analyses were carried out in the laboratory.

2.4.1. Soil Texture

Soil texture was measured by a hydrometer. The United States Department of Agriculture [21] soil textural triangle method was used to identify the textural classes.

2.4.2. pH

The pH was determined from soil extracted by using Inno Lab pH [22].

2.4.3. Electrical Conductivity (EC)

The EC (1:1) was determined from soil extracted by using an EC meter (Model: Eco Sense EC300).

2.4.4. Organic Matter

Organic matter was determined by dry ashing method while organic carbon was determined from organic matter by using Equation (1):

organic carbon % = (organic matter %)/1.742

(1)

2.4.5. Sodium Adsorption Ratio (SAR)

SAR was calculated by using Equation (2) [23]:

SAR = Na⁺ ÷√ (Ca²⁺ + Mg²⁺)/2

(2)

2.4.6. Phosphorous (mg/kg)

Phosphorous in soil was determined by Olsen’s method using a spectrophotometer [24].

2.4.7. Nitrogen (%)

Nitrogen in soil was determined by using the Kjeldhal method, which involves three steps; i.e., digestion, distillation and titration (Equation (3)):

N(%) = (A − B) × N × E × R × 100/weight of sample (mg)

(3)

where A = volume of H₂SO₄ titrated for the sample (mL)

• B = digested blank titration volume (mL)
• N = normality of H₂SO₄ solution
• E = atomic weight of N.
• R = ratio between total volume of the digest and the digest volume used for distillation.

2.4.8. Ca²⁺ and Mg²⁺ (mg/kg)

The Ca²⁺ + Mg²⁺ were determined by titration with EDTA (ethylene diamine tetra acetic acid) using buffer solution and indicators used were Eriochrome Black-T and ammonium perporate.

2.4.9. Sodium (Na), Potassium (K)

AFP-100 Flame photometer was used for Na and K estimation in soil by using 1:1 soil water extract.

2.4.10. Chloride (mg/L)

Chloride was determined by the titration of (1:1) soil water extract against AgNO₃ by using indicator K₂CrO₄. At the end point, the solution was brick reddish in color.

2.4.11. Metals

Three metals, Li, zinc (Zn) and Fe (iron), were measured with the help of an atomic absorption spectrophotometer.

2.5. Statistical Analysis

Statistical analysis was carried out by using IBM SPSS statistics 25. Means and standard errors were calculated for all parameters. Map was prepared using Arc GIS (10.2.2). To compare different soil parameters with respect to treatments of three soil samples, one-way ANOVA was applied, and to compare the soil parameters after and before Li application on soil samples, one-way ANOVA was applied. Tukey’s HSD test was applied to data and significance was observed (p < 0.05) [25].

3. Results and Discussion

3.1. Soil pH

The mean values of soil pH increased after lithium (Li) application when compared to soil before Li application; soil pH ranged from 7.2 to 7.7, which increased and ranged from 7.9 to 8. Figure 2 shows the mean values of pH of three soil samples with five treatments. It can be observed that with the increase in Li concentrations in each sample, pH was also increased and the highest pH value was noted in sample 3. The mean values of untreated soil show that soil samples were slightly alkaline in nature and became more alkaline after Li application. Soil pH expresses soil acidity and alkalinity [26]. According to USDA [21], the standard value of pH of soil ranges from 7.6–8.0, which is considered as medium quality soil for agricultural use, while for good quality soil the pH range should be 7–7.5. In this study the application of Li increased the pH of soil, thus changing the nature of soil from good quality soil to medium quality soil with respect to pH.

3.2. Electrical Conductivity (EC)

The EC values ranged from 1.2 to 5.1 µS/cm for three soil samples, which showed that soil was slightly saline in nature (Figure 3). The EC was slightly saline before Li application and became strongly saline after Li application. It was found that with the increase in Li concentration in each sample, the EC was also increased. Highest EC value was found in sample 2 treatment 4 and lowest value of EC was of sample 3 with no Li application.

3.3. Sodium in Soil Samples

Mean values of sodium (Na) ranged from 8–17 mg/kg (Figure 4). According to USDA (2007), the desired value for sodium ranges from 0.3–0.7 mg/kg while in our study the Na concentration in soil samples before and after Li application was greater than the acceptable value, which is not suitable for soil. Figure 4 shows the mean values of Na ions of three soil samples with five treatments. The increase in Li concentration in soil samples caused an increase in Na ions concentration with the maximum concentration recorded in sample 1 of treatment 4 while minimum in sample 3 with no Li application.

3.4. Chloride in Soil Samples

Figure 5 shows the mean values of chloride (Cl) ions of three soil samples with five treatments. It was determined that with the increase in Li concentration in each sample, Cl ions were also increased. The highest Cl ions value was found in sample 1 treatment 4 and lowest value of chloride (mg/L) was in sample 1 with no Li application. Chloride ranged from 3–63 mg/L, which shows it was suitable both for drinking and irrigation. The standard value of Cl for drinking water is <250 mg/L [27] and for irrigation water it is <100 mg/L [28].

Calcium is an essential part of the cell wall and it also helps in cell division and elongation, and gives cell protection, aiding cell wall development, metabolism and nitrate uptake. Magnesium helps in protein synthesis and energy generation to perform the activities of plants. The values of Ca and Mg ranged from 1–4 mg/kg which shows that before Li application the concentration of Ca and Mg was medium but after Li application it decreased and became low according to the requirement of soil (Figure 6). Figure 7 shows the mean values of SAR of three soil samples with five treatments. It shows that with the increase of Li concentration, SAR was increased except for in sample 2. The highest SAR value was in sample 1 treatment 4 and the lowest value of SAR was in sample 1 with no Li application. SAR ranged from 1–11 mg/kg, which shows that it fell into the marginal category.

Table S1 shows the mean values of all soil samples for pH, EC (µS/cm), OM (%), sodium (mg/kg), chloride (mg/L), calcium and magnesium (mg/kg). The highest mean value was for sample 1 before Li application for EC. Table S3 shows the significance of remaining parameters in which only EC is significantly different, while pH, OM (%), Na (mg/kg), Cl (mg/L), Ca and Mg (mg/kg) are not significantly different (p < 0.05). Table S3 shows the significance of all parameters of three soil samples after Li application on each treatment. All parameters show significant difference (p < 0.05). Organic matter (%) ranged from 0.48–0.98, which indicates that soil was deficient in organic matter. Mean values of organic matter were better in soil samples before Li application and ranged from 0.7–0.9, which indicates that soil conditions were better before Li application and as organic matter increased, compactibility decreased (resistance to deformation and elasticity increased). Variation in compactibility is sensitive to even relatively small changes in the amount of organic matter [29] and after Li application its value decreased (0.4 to 0.6). Moreover, Li application might have inhibited/decreased the microorganism metabolic activity which causes soil organic matter decomposition [30]. Our results are consistent with the findings of Enya et al. [30], who also reported that microorganism metabolic activity was lower in heavy metals (Cr, Zn and Pb)-polluted soils.

High pH causes blockage in roots, preventing absorption of certain elements which are necessary for plant growth. The pH of leachate ranged from 7.1–7.9, which shows that it was acceptable in terms of irrigation and drinking water standards (acceptable range 6.5–8.5). A high pH value shows alkalinity and it was due to Li salt added to soil samples. Alkalinity has a negative impact on human health. The EC is directly related to the concentration of free ions in water. Ions such as chlorides, sulfides and metals (zinc, iron, etc.) are responsible for conductivity in water [31]. The EC of leachate ranged from 2286–7188 µS/cm, which shows strong salinity (acceptable range 250 µS/cm) (FAO, 2004). Salinity was due to Li, which affects water density, consequently high density has a negative impact on crops as well as human health [31]. Sodium in leachate ranged from 3–27, which means it was within the acceptable range (200 mg/L) [27]. Calcium and Mg are responsible for hardness of water. Both elements are essential for higher crop production but in a limited amount. If they exceed acceptable levels, they not only affect the characteristics of soil but also damage plug pipes and irrigation pipes and machinery used for agricultural purposes and cause coagulation in rotatory parts of machines [32].

3.5. Phosphorus, Nitrogen and Potassium in Soil Samples

Table S2 represents the mean values of phosphorus (P), nitrogen (N) and potassium (K) both before and after Li application. Mean values of P, N and K were greater before Li application and low after Li application. The highest mean value was of K (mg/kg) in sample 1 before Li application (9.0133 ± 0.008) and the lowest mean value was of potassium (mg/kg) in sample II after Li application (0.0270 ± 0.881). Table S2 shows the significance of P, N and K. Phosphorus and K levels were significantly different (p < 0.050), while N levels were not significantly different; i.e., 0.434. Figure 8 shows the mean values of P of three soil samples with five treatments. It was observed that with the increase in Li concentration, P was also increased for sample 1 and there was an irregular trend in sample 2 and 3. Highest P value was in sample 3 treatment 4 and the lowest value of P was in sample 1 with no Li application. Phosphate is an integral nutrient for plant growth, however, a high level of phosphate in irrigation water is not acceptable as it causes deficiencies of other nutrients present in soil. A high range of phosphate should be treated before its applicability [33]; the range of phosphate in agricultural water should be less than 5 mg/L [28] while in leachate it should not exceed 0.2–0.9 mg/L, and in our study it did not exceed the recommended limit.

Figure 9 shows the mean values of K of three soil samples with five treatments. It shows that with the increase in Li concentration, K concentration was also increased except for in sample 2. The highest K value was in sample 2 treatment 4 and the lowest value was in sample 1. Potassium is an important macronutrient for plant growth. Standard value for K is 0–2 mg/L [28] and range for leachate is 141–354 mg/L. Potassium is necessary to start enzymatic activities, helps the crops to absorb water from the roots and stops plants losing water. Potassium has the capacity to increase food production in plants and it plays an important role in fighting pests and severe weather conditions in plants. Potassium ranged from 84–118 mg/L for the three soil samples, which shows the soil did not have sufficient K and was less fertile. However, concentration of K was higher before Li application and decreased when Li was applied to the soil, which suggested that Li decreases soil fertility.

3.6. Metals Concentration in Leachate

Table 1. Mean values of metals present in leachate of three soil samples after lithium application.

Metals	Treatments	Means ± S.E
Lithium (mg/L)	S1 To	0.26 a ± 0.03
	S1 T1	11.26 ab ± 2.34
	S1 T2	4.90 a ± 1.15
	S1 T3	7.9 ab ± 0.17
	S1 T4	61.66 c ± 7.688
	S2 To	1.666 a ± 0.176
	S2 T1	8.66 ab ± 0.260
	S2 T2	8.566 ab ± 0.64
	S2 T3	69.86 c ± 9.03
	S2 T4	61.86 c ± 5.25
	S3 To	0.42 a ± 0.17
	S3 T1	4.700 a ± 1.609
	S3 T2	27.43 b ± 5.13
	S3 T3	75.66 cd ± 5.600
	S3 T4	95.93 d ± 1.822
Zinc (mg/L)	S1 To	0.0042 ± 0.0029
	S1 T1	0.0013 ± 0.0008
	S1 T2	0.0058 ± 0.0027
	S1 T3	0.0014 ± 0.0098
	S1 T4	0.0036 ± 0.001
	S2 To	0.100 ± 0.0098
	S2 T1	0.036 ± 0.022
	S2 T2	0.040 ± 0.011
	S2 T3	0.043 ± 0.03
	S2 T4	0.006 ± 0.006
	S3 To	0.046 ± 0.041
	S3 T1	0.036 ± 0.02
	S3 T2	0.020 ± 0.00
	S3 T3	0.0026 ± 0.002
	S3 T4	0.056 ± 0.026
Iron (mg/L)	S1 To	0.1208 ± 0.07
	S1 T1	0.086 ± 0.018
	S1 T2	0.086 ± 0.018
	S1 T3	0.086 ± 0.075
	S1 T4	0.28 ± 0.075
	S2 To	0.24 ± 0.052
	S2 T1	0.113 ± 0.003
	S2 T2	0.25 ± 0.02
	S2 T3	0.2167 ± 0.03
	S2 T4	0.120 ± 0.0057
	S3 To	0.266 ± 0.157
	S3 T1	0.116 ± 0.03
	S3 T2	0.176 ± 0.127
	S3 T3	0.156 ± 0.017
	S3 T4	0.212 ± 0.135

Values with different letters in rows are significantly different at p < 0.05.

shows the mean values of metals present in leachate of three soil samples after Li application. Average highest mean values were for Li, in which the greatest value was in sample 3 with treatment 4. Table S4 shows the significance of metals Li, iron (Fe) and zinc (Zn) present in the leachate of soil samples. Lithium and Zn levels were not significantly different while Fe levels were significantly different (p < 0.050). Lithium in leachate ranged from 0–95 mg/L while the standard value for Li should be less than 2.5 mg/L [28] in irrigation water; however, some studies showed that few crops tolerate concentration of Li up to 5 mg/L. Lithium is toxic for citrus fruits even in relatively smaller amounts and its recommended limit is 0.075 mg/L.

Lithium is the smallest alkali metal with a high density of charge that contributes to its unique characteristics. Lithium’s ionic radius is well suited to the octahedral cavity in clay minerals, leading to Li retention which can cause changes in leachate chemical properties [34]. Amorphous materials like allophane and imogolite present in clay are also responsible for retaining lithium through adsorption [35]. Soil texture and organic matter present in soil are the main factors responsible for governing Li behavior in soil. Organic matter plays a pivotal role in the immobility of Li in soil [36,37,38].

Lithium has a comparatively low toxicity for animals, with a lethal dose of less than 500 mg/kg bodyweight in rats [4]. Goldstein and Mascitelli [39] assumed that increased Li intake would reduce levels of aggression and violence. Humans may be exposed by increasing Li concentrations as it enters the environment through the usage and disposal of products which contains Li. Concentrations of Li in soil range from <1–200 mg/kg [4] and higher concentrations of Li occur in arid and saline soils [3]. The clay fraction of soil contains higher Li concentrations than the organic soil fraction, with the Li present in holes within clay minerals [40]. Sample 3 with additional 10 % organic matter showed that after Li application, loss of nutrients in leachate was less as compared to the other two samples, which indicates that organic matter improves soil conditions and suppresses the effect of Li on soil.

4. Conclusions

Lithium has an overall negative impact on soil, as after Li application loss of important nutrients has been observed. In this study, lithium increased alkalinity and salinity of soil by increasing its pH. Hardness of soil was also observed. Essential nutrients for plant growth such as Na, K and N also decreased in soil after Li application. Results indicated that Li is a mobile element as its value was high in leachate while it also removed nutrients from soil into the leachate and polluted the water by increasing nutrients’ concentration beyond their acceptable values. Our study also concluded that organic matter addition to the soil reduces negative impacts of Li on the soil and minimizes the loss of nutrients.