Biochar Enhanced Chemical and Biological Properties of Contaminated Soils with Lead

Soil pollution has become a global problem due to the significant increase in the concentration of heavy elements. Lead is one of the most dangerous heavy elements cause damages to soil microorganisms and soil chemical properties. In this study the effect of adding of biochar (EFBB and WSB) with different addition rates (0%, 1% and 3%) in two soil textures (sandy loam, clay loam) contaminated with lead (500 ppm) were studies to approve the role of biochars on some soil chemical properties of soils and microorganisms activity. The results showed the amount of released CO2 has increased up to (127.6 and 123.2 mg CO2 100 g-1 soil) with addition rate (3%) of WSB and EFBB compared to control treatments (45.4 mg CO2 100 g-1 soil). This result indicated that the microorganism’s activity was enhanced with incubation periods in contaminated soils. It was noted that biochars improved soil chemical properties such as OM, OC, CEC, cations of positive elements such as Ca2+, Mg2+, and K+ and improved electrical conductivity EC. A larger surface area and the negative charges content as well as micro pores are made biochars more effective to adsorbed heavy metals, which allows reducing toxicity of lead in contaminated soil and making its environment more suitable for microorganism’s life with enhancing some soil chemical properties. Therefore, it is recommended to add biochar to contaminated soils and it could be an alternative to other treatments due to its low-cost.


Introduction
Recently, Soil and water pollution has become a global problem due to the significant increase in the concentration of heavy elements and different compounds from the permissible level [1].Waste emissions from industries, mining operations, organic waste applications, wastewater irrigation, and improper pesticide and chemical management in agricultural production systems have all been linked to soil contamination [2].Heavy metals are resistant to breakdown in soil for lengthy periods of time, becoming increasingly poisonous to living organisms over time [3,4].These metals are capable of soluble in a soil solution and absorbed by plant roots [5,6].There are many soils factors effect on mobility and solubility of heavy metals in soil such as soil pH, CaCO 3 , soil texture, clay and organic matter contain [7].The particle size distribution reflects on the soil texture.Soil clay contains are most vital on surface adsorption for heavy metals in soils.The clay soil adsorbs higher amount of metals compared to sandy soil [7].Reduction the bioavailability and mobility of heavy metal is one of the 1259 (2023) 012024 IOP Publishing doi:10.1088/1755-1315/1259/1/012024 2 techniques of remediation contaminated soils with heavy metals [8].It can be achieved by treating soils with amendment such as lime, organic matter and so on.One of the recent trends is the use of biochar in this, which is widely used in soil amendment to improve the physical and chemical properties and biological activities of agricultural soils [9].Biochar, derived from renewable resources like plant and animal matter, is an inexpensive and environmentally friendly sorbent [10].Biochar can immobilize heavy metals in the soil and the environment thanks to its adsorbent properties, and it can also boost soil productivity [11].Porous structure, active functional groups, expanded specific surface area, cation exchange capacity (CEC), and a high organic carbon content are just some of the physicochemical features that provide biochar the ability to mitigate organic and inorganic chemicals.Porous structure, active functional groups, expanded specific surface area, cation exchange capacity (CEC), and a high organic carbon content are just some of the physicochemical features that provide biochar the ability to mitigate organic and inorganic chemicals [12,13].The application of empty fruit bunch biochar (EFBB) significantly decreased heavy metal leaching [14].The bioavailability of Pb and Cd was found to be much lower in acidic soil after treatment with EFBB.This reduction was related to biochar's surface area and functional groups, two physicochemical characteristics.The physicochemical properties of calcareous soil is diver from acidic soil such as pH, content CaCO 3 .Moreover, different feedstock and condition used for preparing biochar result biochar with different characteristics and behavior.Therefore, in this study was conducted to determine the effect of two-type biochar (empty fruit bunch biochar -EFBB and wheat biochar -WSB), at different rates (0%, 1% and 3%) on the chemical and biological properties of different calcareous soils in texture (clay loam and sandy loam) contaminated with lead.

Chemicals and Reagents
The solutions were made with distilled water, and all of the chemical reagents were of analytical quality.Lead (II) nitrate of analytical grade, with a purity of 99.99%, was used.The chemicals utilized were of the highest quality, and included barium chloride (98.0%purity), sodium hydroxide (99.00%), hydrochloric acid (37.0%), and phenolphthalein (99.00%).

Soil Sampling and Spiking Process
Two calcareous soils with different texture (Clay loam and Sandy loam) were sampled from the different fields at Diyala State.Clay loam and Sandy loam soil samples were taken at a location at 33°51.14.326N / 44°38.58.482E and 33°51.51.210N / 44°39.03.299E, respectively, according to a global positioning system.Using an auger and a shovel, we dug up soil samples from a depth of 0 to 30 centimeters.The samples were taken to the drying room in the College of Agriculture at the University of Diyala, where they were air-dried before being pulverized with a mortar and pestle and sieved through a 2 mm mesh.Pb (500 mg kg -1 ) was added to the soils in discrete doses.Pb (NO 3 ) 2 was used as the chemical component for the soil spiking.Lead compounds were dissolved in pure water to the appropriate quantity, and then added to the soils after thorough mixing.After that, we kept the soils at 70 percent field capacity and at room temperature (25±2 degrees Celsius) for 30 days in an incubator.Following incubation, the soil was sieved through a 2 mm stainless steel sieve to create consistent samples.The samples were later used after being kept at room temperature.

Physicochemical Analysis of Soil
The approach described in [15] was used to analyze soils for texture and particle size distribution.We took soil samples in triplicate and used a Crison pH meter and a HANNA instrument EC meter to evaluate the pH and electrical conductivity, respectively.The Walkley-Black method was described in [16] used to determine the soil organic matter content in the soils.The CEC of the soils samples were determined using ammonium acetate (NH 4 OAc) 1M buffered at pH 8.2 and sodium acetate1M buffered at pH 7. The extracted sodium was determined by Flame Photometer to calculate the CEC in the soils [17].1259 (2023) 012024 IOP Publishing doi:10.1088/1755-1315/1259/1/0120243 Some soluble ions content of the soils' samples was determined according to [18].For potassium were determined by Flame photometer in extracted solution (soil: water ratio 1:5) Na 2 EDTA.For calcium and magnesium was determined by titration the extraction solution of 1:1 soil: water with 0.01 N Na-EDTA using Murexide inductor.The carbonate mineral was determined by calsimeter using concentrated HCl [19].Table 1 shows the some physiochemical properties of the soils.
Table 1.Some Chemical and physical properties of soils.

Preparation and Characterisation of Biochar
Biochar was produced using a variety of feedstock from a number of different countries.Bangi Lama, Selangor, Malaysia is where we bought the Malaysian biochar empty fruit bunch biochar (EFBB).This biochar was made using a gradual pyrolysis technique at a low temperature (300 °C) in a horizontal rotating kiln.The Iraqi biochar wheat straw biochar (WSB) was prepared under low temperature (300 °C) using an electric furnace (Nabenthem-Germany) for 2 h with heating rate 10 ºC min -1 under oxygen limited conditions.The biochar's were brought to the laboratory, where they were passed through a metal sieve (< 50 µm) as recommended by [15].Before being analyzed, both the EFBB and WSB biochar samples were stored at room temperature.Using the Brunauer-Emmett-Teller method, we determined the surface areas of the EFBB and WSB through N2 adsorption at 77 K.The multipoint BET technique was used to determine the total surface area.Using a pH meter (Crison), we were able to calculate the EFBB and WSB pH values in accordance with [20].The EC measurements of the EFBB and WSB were determined by Soaking the sample in distill water at a biochar/water ratio of 1:5 (w/v) and agitated for 24 h using EC meter (HANNA instrument).
The CEC of the EFBB and WSB were measured according to [21]

Incubation Study
A factorial laboratory experiment was conducted a randomized complete block design (RCBD) to study the effect of different types and rates of biochar on chemical and biological properties of different contaminated soils with lead in texture (sandy loam and clay loam).The release of CO 2 from the treatments was determined during the incubation periods as indicator about enhancing the biological properties of contaminated soil.The two types of biochar's (EFBB and WSB) were added individually with the rate (0, 1% and 3%) to 100 g of two soil texture (sandy loam or clay loam) contaminated with lead in airtight containers.Each treatment was replicated thrice.The experiment included 30-unit treatments were incubated for 90 days at room temperature (28±2°C) and the soil moisture was maintained at 60% field capacity.The amount of released CO 2 that measured during the incubation periods using 20 mL of NaOH was trapped in a small open tube and placed inside airtight containers.After each incubation period, drops of barium chloride solution were added to small cans containing 20 mL of NaOH, and titrations were done using HCl in the presence of phenolphthalein indicator to clarify the endpoint.The CO 2 reacted with NaOH and produced turbid sodium carbonate, which is deposited by adding drops of barium chloride solution.Soil-release CO 2 mg was measured according to the following equation: where: B is the volume of acid consumed (mL) in control treatment, V is the volume of acid consumed (mL) in treatment, N is the normality of HCl and E is the equivalent weight of CO 2 , which is equal to 22. 2. The CO2 released was measured each week of incubation periods (90) days.
After the end of the incubation period, the pH, EC, OM, C, Ca, Na, K and CEC of each experimental unit were determined as described previously.

Statistical Analysis
Before performing statistical analysis, we made sure that the experimental data were consistent and that the variances were normally distributed.An analysis of variance (ANOVA) was then performed on the data in SAS (version 9.4).Tukey's test was used to examine whether or not there were statistically significant differences between the means of the treatments, and the significance threshold was set at 95% ( α= 0.05).

Soil and Biochar Properties
3.1.1.Organic Matter OM and Organic Carbon OC Table (3) shows the amount of soil organic matter in the experimental treatments.According to the results, there was a clear difference among the rate and type of biochars levels and different soil texture in organic matter of soil after incubationperiods.In the control treatment of sandy loam soil, it reached the lowest value about (1.45 gk g -1 ), while in WSB3% treatment with same texture soil it reached around 16.32 g kg -1 .In clay loam soil texture, the lowest value about 8.72 g kg -1 at control treatment.While, the highest value was nearby 30.977 g kg -1 at the clay loam texture with treatment WSB3%.Sandy soil treatment have lower organic matter content than clay loam soils, due to the low organic matter content of sandy soils and the increase in the rate of oxidation [23].An increase in the organic matter was observed when sandy loam soils to which biochar has been added, as it was about (16.327 g kg -1 ) at the WSB1% treatment, which is a significant increase compared to the sample control treatment (1.453 g kg -1 ).The increase in the organic material in the sandy loam soil will be according to the rates of biochar addition in descending order as follows: The results also showed that there is a difference between the control treatment of clay loam soil (8.723 g kg -1 ) and the treatment WSB3% (30.977 g kg -1 ).Therefore, the increase in organic material in the clay loam soils are descending as follows: From Table (3), we notice an increase in the percentage of organic carbon (OC) in the treatments to which biochar was added compared to the control treatment, as it reached (0.947%) for the sandy loam WSB3% compared to control (0.084%) for the sandy loam.The control treatment clay loam soil was about (0.505%), while the increase in organic carbon in the WSB 3% treatment was around (1.796%).
The observed increase in OC, OM could be due to the content of biochar from carbon Table (2) that may occur when adding biochar to the soil [24][25][26], indicated that the addition of biochar led to an increase in organic matter and organic carbon, and that increase varies from one soil to another.

CaCO 3 Carbonate Minerals
Table (3) shows the content of carbonate minerals in the study treatments, as the values ranged between 10.8 g kg -1 to 7.6 g kg -1 in the control sandy loam and WSB1% sandy loam, respectively.The carbonate minerals amount was reduced by 3.2 g kg -1 .As for the clay loam soil, it was 34.7 g kg -1 in the control treatment and it reached 24.2 g kg -1 in the clay loam WSB3%, which reduced carbonate minerals by 10.5 g kg -1 .In general, most soils in arid and semi-arid regions such as Iraq are characterized by high content of the carbonate minerals, Calcite (CaCO 3 ) is the main component of these minerals [27].The biochar reduced carbonate minerals in the both texture soils.This is necessary to reduce the alkalinity of the calcareous soil, which makes the nutrients more accessible to the plant [30].

Soil Reaction (pH) and Electrical Conductivity (EC)
From Table (3) the pH ranged between 7.6 -7.3 in the two texture soils of the study treatments.The soil pH was reduced between 0.3 to 0.2 with the treatment WSB3% and WSB3% in the clay loam and sandy loam, respectively.This is similar to what was found by previous study adding biochar to the soil can increases the pH [31].Also, it notes that the value of EC in the clay loam WSB3% treatment and sandy loam WSB3% treatment were 3.96 and 3.09 dSm -1 , respectively, which is an increase compared to the control treatments for both soils clay loam and sandy loam, which amounted 1.55 and 0.67 Ds m -1 , respectively.This is similar to what was indicated by [25,32,33], showed that the addition of biochar led to a gradual increase in soil pH and electrical conductivity (EC).Addition of biochar can also modify the electrical conductivity (EC), [34].

Cation Exchange Capacity CEC and exchangeable Ca, Mg and K
From Table (3), the CEC of the treatments compared to the control soil sample in sandy loam soil for WSB was arranged between 8.17-10.22Cmol + kg -1 for control and sandy loam WEB3% treatments, respectively, by an increase of 2.05 Cmol + kg -1 .While with EFBB, the amount of increase was 1.62 Cmol + kg -1 in EFBB 3% treatment compared to control.Similarly, in clay loam soil, the increase was 2.5 Cmol + kg -1 in the clay loam WSB3% treatment and 0.7 Cmol + kg -1 in the clay loam EFBB 3% treatment.This is consistent with what was found by [25,35], suggest that the increase in CEC may be due to the inherent properties of biochar feedstock with their high surface area, good porosity, content functional groups and its CEC.
In sandy loam soil treatment the exchangeable cations were increased from 149. , and K + , respectively.The ash content of the biochar is responsible for the increased exchangeable cations in the biochar-treated soil.Captured mineral nutrients like Ca, Mg, and K are quickly released from biochar due to its high ash concentration [36] , [37].These results are similar to those of [33] and [38].
In terms of nutrient availability, CEC, amount of organic matter, and some physical characteristics such as soil pores, soil particle size, and surface area.This is similar to what was found by [39] , [40] , showed that alluvial clay soils were more abundant and diverse in microbiota.

The Results of the CO 2 Released from the Samples
The effect of the soil texture was highly significant in amount CO 2 released , as the average amount of CO 2 measured in the clay loam soil was (134.46 mg CO 2 /100gm), while in the sandy loam soil it was (51.04 mg CO 2 /100gm).The effect of biochar treatment was highly significant, as the average released amount of CO 2 from the control soil was 45.4 mg CO 2 /100 g soil.While in the soil treated with WSB 3% gave the highest amount of CO 2 was reached to 127.6 mg CO 2 /100 g soil.The reason for the superiority of the WSB treatment may attributed to the fact that the latter contained a higher surface area (Fig. Where it was found, that the biochar produced from wheat straw was the most effective in improving and stabilizing soil chemically and physically [40].As well to ability of biochars to adsorbed heavy metals such as Pb [40] which decreased the toxicity effect of these heavy metal on microorganisms activity [14,41,42]. For interaction effect of two factors texture of soils and biochar treatment, there was highly significant different among the treatments.The clay loam soil treated with WSB3 % gave the highest amount of CO 2 which reached to (174.5 mg CO 2 /100 g soil) with non-significant differences with EFBB3% treatment with same soil (165.7 mg CO 2 /100 g soil).This is due to the enhanced the activity of microorganism in soils by adding organic materials [43,44].

Conclusions
In conclusion, the experimental results show an improvement in soil chemical properties such as OM, OC, CEC, cations of positive elements such as Ca 2+ , Mg 2+ , and K + and electrical conductivity.In addition, it showed the amount of released CO 2 has increased with addition both types of biochar (WSB and EFBB) compared to control treatments.Therefore, there are due to its low-cost and their properties, biochars could be an alternative treatment when add to the contaminated soils to reduce soil pollution toxicity.

Ethics
In this study, there was no human being or animal used for experimental purposes.

Data Accessibility
We have successfully identified all datasets needed to fully understand this article within the text itself.

Conflicting Interest
There was no financial or personal bias in the development of this study.

Figure 1 .
Figure 1.Show the SEM of EFBB and WSB.

Table 2 .
(2)n et al., (2015)n et al., (2015).One gram each of EFBB and WSB was added to 20 milliliters of 0.5M BaCl2 in Falcon tubes.A 0.45 m filter was used after the mixture was centrifuged at 200 rpm for 2 hours.Atomic adsorption spectrometry was used to determine the concentration of exchangeable bases (Na, Mg, K, Ca, Mn, and Fe) in the filtrate.When determining the CEC, all cations were added together.C, H and N in the EFBB and WSB were measured using a TruSpec CHNS analyser, as shown in the Table(2).Some chemical properties of biochar.

Table 3 .
Chemical properties of soil samples treated with different biochar.

Table 4 .
Amounts of CO 2 released in mg CO 2 /100g of soil.

Amounts of CO 2 released in mg CO 2 /100g of soil Sandy loam Clay loam Effect of Biochars Treatments Texture * Biochar
7Treatments Amounts

of CO 2 released in mg CO 2 /100g of soil Sandy loam Clay loam Effect of Biochars Treatments Texture * Biochar
Different letters are significantly different among treatments, and similar letters are not significantly different.