Impact of cement industries on potentially toxic elements’ contamination and other characteristics of topsoil: A case study

ABSTRACT Due to the elevated levels of potentially toxic elements (PTEs) in the environment, we measured the PTE concentration in topsoils at a distance of 500, 1000, and 2000 m from 3 cement production factories (1 = DG Cement, 2 = Bestway Cement, Kallar Kahar, and 3 = Bestway Cement, Chakwal) toward east, west, north, and south direction. Soil samples were collected and analyzed for cadmium (Cd), chromium (Cr), copper (Cu), iron (Fe), lead (Pb), manganese (Mn), nickel (Ni), zinc (Zn), and cobalt (Co) concentrations. It was recorded that the maximum PTE concentrations were found at 500 m distance and in north direction in 93% of the samples. The maximum Cd, Cr, Fe, Mn, Ni, Zn and Co concentrations were found around Bestway Cement, Chakwal at 4.13, 27.82, 6552.20, 93.47, 99.54, 46.83, and 72.62 mg kg−1, respectively. Similar results were found for the other two industries at same distance and direction. It was also revealed that contamination factor and geo-accumulation index were exceeding in the 84% and 81% of the total samples collected. The findings of the study indicate that there could be toxicity in soil and food crop in vicinity of the area, which should be studied. GRAPHICAL ABSTRACT


Introduction
Environmental pollution is a direct result of humankind's desire to improve life on Earth through exploration.Urbanization, industrial activities, and modern agricultural practices all contribute to this problem by producing byproducts that have negative health effects on people [1].One of the main reasons why humans pollute the environment is because they are always striving for more development.Human activities and natural processes have resulted in environmental deterioration, which has made metal pollution of bodies such as rivers, soil, air, and water a concern and issue in many industrialized countries around the world [2].
The cement industry plays a vital role in the economic development of many countries, including Pakistan.However, the rapid growth of this sector has raised concerns about its potential environmental impacts, particularly regarding potentially toxic element (PTE) contamination and other characteristics of topsoil [3].The PTEs are known to pose serious threats to human health and ecosystem integrity, making their presence in the environment a matter of great concern [4].Pakistan's cement industry has witnessed substantial expansion over the years, fueled by urbanization, infrastructure development, and population growth.With more than 30 cement plants operating across the country, it has become a significant contributor to Pakistan's GDP [5].However, this growth has come at a cost, as the cement manufacturing process involves the use of raw materials and fuels that can contain trace amounts of PTEs.Along with its contribution to the country's GDP, cement industry is also a big contributor of the air pollution via dust and PTEs deposition to soil.The dust primarily contaminated the soils within a 5,000-m radius of the cement plant [6,7].Cement is made mainly from carbonate-rich compounds such as chalk, limestone, sand, and oxides of calcium, aluminum, silicon and iron (Fe) [8,9].Cement can be broken down into subcategories [10] based on the production method and raw materials used.The wind can carry the dust produced during cement manufacturing for either short or long distances [11], which depends on the size of the dust particles produced.In addition, numerous cement plants are the sources of PTEs such as cadmium (Cd), chromium (Cr), copper (Cu), lead (Pb), manganese (Mn), nickel (Ni), zinc (Zn), cobalt (Co), and Fe that are discharged into the surrounding environment [12,13].Elements such as Cd, Cr, Pb and Ni are the elements most detrimental to the surroundings that are released into the air because of cement production [7,14].Soil pollution is a growing problem worldwide because many industries pollute the environment.Mainly, agricultural lands degrade, and several soil properties change during industrial waste generation, the discovery of natural deposits, the production of construction materials, and their use in the national economy [15].When it comes to building, cement is by far the most popular raw material used.Cement consumption has often advanced in tandem with national economies over time [1,16].The rapid growth of industries geared toward meeting the demand for housing and necessities results from the exponential rise in the global population.The primary building material, cement, saw its production speed up.The cement industry is a crucial focus for the infrastructure development of many developing countries today [17,18].Approximately 1 ton of cement is produced annually for every person on Earth [19].
Previous studies have reported the harmful impacts of the cement industries on the surrounding area's soil, plants, and aquatic bodies.
However, no study has comprehensively covered the surrounding area of the industry with respect to distance and directions, which could give more explanation about the extent of soil toxicity in the study areas.So, the study was conducted with the aims to: a) assess the PTEs in soil and their impact on the physio-chemical characteristics of soil near cement plants, and b) the concentrations of PTEs in soils with respect to direction and distance to the industry.

Materials and methods
The research was done on the Eastern side of the motorway in Kallar Kahar, District Chakwal, close to three cement industries (DG Cement Chakwal, Bestway cement Chakwal, Bestway cement Kallar Kahar).We chose three distinct locations 500, 1000, and 2000 m apart from each of these cement factories in the eastern, western, northern, and southern compass directions.The goal was to determine the soil damage caused by cement industry dust.From each industry, 12 samples from top soils (0-15 cm) were taken.There were three replicates for each site's sample.

Study area
The study area is Kallar Kahar, Chakwal District, Punjab, Pakistan (32°47 N, 72°42 E) (Figure 1).In this region, limestone, sandstone, and shale make up the bulk of the district Chakwal's soil.Calcareous and structurally fragile are its basic characteristics.Materials like boulders, stones, gravels, etc. can be found over the district's vast, degraded, unleveled terrain.Soil types range from sandy loam to loam.In addition, the soil structure varies significantly across the two regions of the Murree district.The soil in the higher areas comprises reddish or purple sandstones, while the soil in the lower regions comprises greyish sandstones.

Sampling locations
The field was visually subdivided into uniform sections, and the litter on its surface was removed.The soil sample was collected with an auger designed to plough to a depth of 6 inches.After that, 2 kg of sample was collected from each sampling point from all four directions and 500, 100, and 2000 m away from each industry (DG Cement Chakwal, Bestway cement Chakwal, Bestway cement Kallar Kahar) and direction, and the degree of soil contamination with cement dust was studied in the laboratory.

Analytical analysis
The obtained samples were crushed in an electric grinder.For the digestion of samples, a representative 1 g (dry weight using physical balance, which have no zero error) sample was digested with repeated additions of nitric acid (HNO 3 ) and hydrogen peroxide (H 2 O 2 ).The resulting digestate was reduced in volume while heating and then diluted to a final volume of 100 mL deionized water.This digestate was filtered using Whatman filter paper No. 44 and residues were rinsed.The residue was returned to the dilution flask, refluxed with additional HCL, and then filtered again.Then samples were run at ICP-OES (Agilent Technologies, 720-ES, U.S.A.) for the determination of Cd, Pb, Fe, Cu, Mn, Ni, Zn, and Co [20].A pre-calibrated pH meter (Lovi Bond, SD-300, Amesbury, UK) and EC meter (Metrohm 914, Herisau, Switzerland) were used for sample's pH and electrical conductivity, respectively.The soil total nitrogen was analyzed by Kjeldahl apparatus (Fisher Scientific, Buchi K-350, UK) [21], while phosphorus concentration in soil samples was analyzed through spectrophotometer (Lovibond, Spectro direct, Salisbury, UK) [22].

Quality assurance and control procedures
All chemicals and solvents used were of analytical reagent grade procured from Merck (Darmstadt, Germany).All the data were collected in three replicates, and the reported results were the average of three replicated treatments along with the standard deviations.Sample blank and a standard reference material (SRM) were also prepared and analyzed for data validation.

Risk assessment indices
The risk assessment of the PTEs based on the data collected were calculated and presented as geoaccumulation index (Igeo) [23] and contamination factor (CF) [24].

Statistical analysis
The analytical data of various heavy metal concentrations in soil were analyzed using a three-way ANOVA (p < 0.05).The data were presented using R software (version 4.2.0)employing ggplot2 packages, and Origin 2022b (Origin Corp., U.S.A.).

Soil properties
The and phosphorus with varying distances and directions is also shown in Figure 2.

Potentially toxic element concentrations in soil
According to the study, the cement industry's emissions included PTEs such as Cd, Pb, Fe, Cu, Mn, Ni, Zn, and Co and spread through wind, precipitation, and anthropogenic means.Top fertile layer of soil is deteriorated due to PTEs loaded emissions which are deposited to it even longer distances i.e. up to 2000 m.In this investigation, it was found that PTEs pollution in north direction of the industries was the most polluted part at a distance of 500 m for each industry.The maximum Cd, Cr, Fe, Pb, Mn, Ni, Zn, and Cu were found at 500 m and the concentrations were 3.87, 23.45, 6554.90, 90.78, 97.95, 42.76, 69.07, and 24.90 mg kg −1 , while Cu was found maximum at 29.45 mg kg −1 at 1000 m distance in same direction (Figure 3, Table 2).Figures 3 and 4 also show the concentrations of Cd, Pb, Fe, Cu, Mn, Ni, Zn, and Co in the soils at 500 m, 1000 m, and 2000 m from the DG Cement (Chakwal), Bestway cement (Chakwal), and Bestway cement (Kallar Kahar).It was evident from all tree sites that the greatest concentration of PTEs occurred at 500 m northward.The concentration of PTEs dropped as the distance from the source (cement mill) increased; this was attributed to wind speed and particle weight of PTEs.Moreover, the different concentrations of different PTEs in the soil at 500, 1000, and 2000 m are given in Table 2. Iron (Fe) concentration in all three cities was exceptionally high (2000-6000 mg/kg).

Pearson's correlation and hierarchical clustering analysis
Pearson's correlation coefficients with clustering analysis were used to quantify and show the relationships between the various studied parameters of soil (e.g.EC, pH, N, and P) and soil metals (e.g.Cd, Cr, Pb, Cu, Fe, Mn, Ni, Zn, Cu) (Figure 5) with higher magnitude correlation indicating greater levels of significance for the inter-relationship.Soil P and K had a strong positive relationship with Fe emissions from DG cement (R 2 = −0.72),Cd with Fe in Bestway Kallar Kahar (R 2 = 0.44), Cu in Bestway Kallar Kahar (R 2 = 0.81), Ni (R 2 = 0.73), and Pb in Bestway cement Chakwal (R 2 = 0.52).Overall, all the studied parameters were found more interactive in 500 m distance from the industries (Figure 6).

Risk assessment indices
After further exploring the current status and profile of PTEs in the vicinity of cement industries, it was noted that the distance and direction to the all three industries were interlinked to each other, and risk indices were decreased with the increase in distance.To further explore the pollution status of PTEs in study area, the PTE concentrations were evaluated with respect to Geo accumulation Index (Igeo, Table 3) and contamination factor (CF) in study area (Table 4).Results indicated that maximum Igeo and CF were noted for Fe in all three industries at 500 m distance in north direction followed by Pb and Cr.The contamination factor range is <1-≥6.The range below 1 is considered low contaminated, 1 ≤CF < 3 is moderately contaminated, 3 ≤ CF < 6 is considerably contaminated, while CF ≥ 6 mean highly contaminated.The values of the Igeo 0 ≤ indicate no pollution, and the values 0 ≤ Igeo ≤ 1 show non-

Discussion
This study analyzed the concentrations of PTEs around all four directions (north, west, south, east) of the three cement factories at 500, 1000, and 2000 m away from the source of pollution i.e. industries.As pollution extent depends upon the local conditions, and wind direction [25].In case of this study, the PTE concentrations were found higher in the north and west directions around all three industries.As wind blows south to north and east to west from the nearby cement factories, and it is the primary source of air pollution in the study area.Soil contamination by cement industry dust alters the soil physical and biological qualities and chemical composition.The soil type, condition, and pollutant load all have a role in determining the extent of the transformation [26].It was noted that the study area's cement plants are a significant contributor to surface soil contamination due to its operations, and cement raw material deposits can be found in the associated system.They affected varying soil depths, depending on the nature and extent of pollution.The physico-chemical attributes differed most noticeably from the top layer.The emissions from cement industries impact soil pH, electrical conductivity (EC), and phosphorus concentrations.The process of cement manufacturing has the potential to emit pollutants into the atmosphere, resulting in the deposition of acid rain on soil surfaces [27].This deposition may subsequently cause a change in soil pH levels, so impeding the development of plants.In this study, the soil pH was recorded variable and ranging from 7.94 to 8.45, indicating the impacts of acid rain as previously reported by [27].The soil EC   ranged from 105 to 288.9 µS cm −1 , which could be due to the presence of particulate matter emitted into the atmosphere might lead to an elevation in soil electrical conductivity (EC) as a result of salt deposition and previously reported by [28].This brisk change in soil EC has the potential to negatively impact both plants and soil structure.Furthermore, it is important to note that the aforementioned emissions have the ability to introduce phosphorus compounds into the soil, which might possibly lead to nutrient imbalances and subsequent environmental concerns [29].
The PTEs are classified as xenobiotics, as they serve no physiological purpose and can even cause significant harm at low doses.The PTEs include Cd, Cr, Fe, Mn, Ni, Zn and Co, and numerous others.Because of their toxicity to both humans and plants at high concentrations, the solubility of metal ions in water is often cited as a serious environmental problem [30].Pakistan's environmental problems stem mainly from the country's recent unbalanced economic development.Due to people moving from the countryside to the cities, Pakistan's main cities are seeing rapid, unplanned growth, making the situation more difficult for local governments to manage.Urban congestion is the primary cause of natural resource depletion, especially in light of the limited resources available to municipal authorities and other utility service providers (air, water, and soil quality) [31][32][33][34][35][36] The higher PTE concentrations due to industrial activities, especially cement industries, have distinct characteristics and behaviors in soil, which contribute to their accumulation and potential environmental impacts [37,38].Nickel is a naturally occurring metal found in soil, rocks, and minerals.It has low mobility in soil due to its tendency to bind strongly with organic matter and clay minerals.The accumulation of Ni in soil can occur through natural weathering processes, volcanic emissions, and atmospheric deposition [39].Additionally, human activities such as industrial activities, mining, and the use of nickelcontaining fertilizers or pesticides can contribute to its accumulation in soil [40].Nickel is relatively immobile in soil, which means it tends to stay in the upper layers rather than leaching into groundwater.However, in high concentrations, nickel can be toxic to plants, microorganisms, and certain animals [41].Lead is a toxic metal that is not naturally abundant in soils but can be introduced through human activities such as industrial processes, mining, lead-based paint, and leaded gasoline.Once deposited in soil, lead can persist for a long time due to its low mobility [42].It tends to bind strongly with soil particles and organic matter.
The accumulation of lead in soil depends on factors such as the intensity and duration of pollution sources, soil properties, and environmental conditions.Lead contamination in soil is a concern because plants, posing risks to human health through the food chain, can take it up.Additionally, lead can leach into groundwater under certain conditions, further contributing to environmental contamination [43].Copper is an essential micronutrient for plants and animals, but excessive amounts can be toxic.It is commonly used in agriculture as a fungicide and in various industrial processes.Copper has moderate mobility in soil, and its accumulation depends on factors such as soil pH, organic matter content, and the presence of clay minerals [44].Acidic soils tend to bind less copper, increasing its mobility and potential for leaching into groundwater.Copper can accumulate in soils over time through repeated applications of copper-containing pesticides or fertilizers.Excessive copper levels in soil can inhibit plant growth and affect soil microorganisms [45].Like lead, copper can also be taken up by plants and transferred through the food chain.Zinc is an essential micronutrient for plants and animals, playing a crucial role in various biological processes.It occurs naturally in soil and can be found in rocks and minerals.Zinc has moderate mobility in soil and can be accumulated over time through natural weathering processes [46].Human activities, including industrial processes, mining, and the use of Zncontaining products such as fertilizers and pesticides, can also contribute to its accumulation in soil.Zinc is less likely to leach into groundwater compared to other PTEs due to its strong adsorption to soil particles.However, excessive zinc levels can be toxic to plants, affecting their growth and development.Like copper and lead, zinc can be taken up by plants and can pose risks to organisms through the food chain [47].
The Cd is a naturally occurring element found in small amounts in rocks, minerals, and soils.A highly toxic metal poses risks to human and environmental health.Cd has a high mobility in soil, meaning it can easily move through the soil profile and leach into groundwater [48].It has a strong affinity for binding to soil particles and organic matter, which influences its behavior and availability to plants and organisms [49].Cadmium is not biodegradable, meaning it persists in the environment for a long time.Cadmium can enter the soil through various sources.Natural processes such as weathering of rocks and minerals contribute to the background levels of cadmium in soil.However, human activities are the primary drivers of cadmium accumulation in soil.Industrial activities, mining, smelting, waste incineration, and the use of cadmium-containing products such as batteries, pigments, and fertilizers can release cadmium into the environment [50].Once Cd is introduced into the soil, it can accumulate over time due to its low degradation and high affinity for soil particles.Cd has a strong tendency to adsorb onto clay minerals and organic matter in the soil, especially under neutral to slightly acidic conditions.This adsorption process reduces its mobility and availability to plants.However, in acidic soils, cadmium can be more soluble and mobile, increasing the risk of leaching into groundwater [51].Plants can take up Cd from the soil through their roots.The extent of Cd uptake depends on factors such as the concentration of Cd in soil, soil pH, organic matter content, and the specific plant species.Some plant species, known as accumulators, have the ability to accumulate higher levels of cadmium in their tissues without showing visible signs of toxicity.These plants can then transfer cadmium through the food chain when consumed by animals [52].From this study, all the studied PTEs were found higher at 500 m distance from the industries followed by 1000, and 2000 m.The higher concentrations of the PTEs were due to a mix of natural processes and anthropogenic activities associated with cement manufacture.The reasons include emissions originating from many production operations, which emit dust and particulate matter containing PTEs into the atmosphere [29,53].Furthermore, PTEs pollution is exacerbated by several factors such as the utilization of raw materials, inadequate waste management practices, leaching from storage of cement and clinker, incidents during transportation, and deposition from the atmosphere, which this study reports and supported by [54][55][56][57][58][59][60].

Conclusions
This study measured the potentially toxic elements and basic soil quality indicators around cement industries at 500, 1000, and 2000 m distances and all four directions.It was concluded that highest pH (8.58) was observed from Bestway Cement (Kallar Kahar) at a distance of 500 m, while highest EC (288.12 us/cm) was also found at same distance around at both DG Cement (Chakwal), and Bestway cement (Chakwal).The highest nitrogen (167 ppm) and phosphorus (2.52 ppm) values found at 2000 m distance near Bestway, Chakwal and Kallar Kahar, respectively.The potentially toxic element's concentrations such as Cd, Cr, Cu, Fe, Pb, Mn, Ni, Zn, and Co were the contamination and geo-accumulation factors used to indicate the soil contamination/risk indices also indicated high soil contamination due to cement industry emissions deposited on the soil.Moreover, it was suggested either that relocating a cement factory away from a residential area could extend or reduce the harm caused by PTEs globally.In this way, we can reduce soil and water pollution by imposing a positive impact on people's health.

Figure 1 .
Figure 1.Study area and sample collection points.

Figure 3 .
Figure 3.The concentrations of PTEs (mg/kg) in soil samples at 500, 1000, and 2000 meters toward east, west, north, and south of DG Cement (Chakwal).Error bars show standard deviation of three replicates (n=3).

Table 1 .
Physico-chemical properties of soil samples.Values after ± represent standard deviation of three replicates (n = 3).

Table 2 .
The different concentrations of different PTEs in soil.Values after ± present standard deviation of three replicates (n = 3).

Table 3 .
Risk assessment indices contamination factors (CF) of the study area.

Table 4 .
Risk assessment indices geo-accumulation index (Igeo) of the study area.