Abstract

Background: When stones are crushed, the finer dust gets airborne and escapes as fugitive emissions, constituting dust pollution problems in the vicinity with severe adverse effects on the ambient air quality and human health. Methodology: In this study, active sampling method was deployed to sample and obtain the ambient concentrations of CO, SO₂, H₂S and PM (of sizes 2.5 and 10 microns) in the fugitive emissions from selected manual stone crushing sites in North Central Nigeria. The trapped particles sampled were analysed for particulate-associated heavy metals such as Cd, Co, Cr, Cu, Pb, Mn, Ni, Fe, and Zn by Atomic Absorption Spectrometry (AAS). Principal Findings: The observed mean concentration of CO, SO₂ and H₂S sampled were 0.12 mg/m³, 0.06 mg/m³ and 0.004 mg/m³, respectively. The mean concentration of PM_2.5 was observed to be 26.5 µg/m³ (ranged from 8 µg/m³ to 70 µg/m³) which is about 76.7 % higher than the World Health Organization (WHO) air quality guidelines (15 µg/m³ for 24- mean for PM_2.5). The Mean concentration of PM₁₀ was observed to be 54.36 µg/m³ (ranged from 17 µg/m³ to 143 µg/m³) which is about 20.8 % higher than the World Health Organization (WHO) air quality guidelines (45 µg/m³ for 24-mean for PM₁₀). AAS analysis revealed that metal- bearing particulates have significant levels of the selected heavy metals except copper that was below detection limit: Cr, Mn, Fe, Pb, Zn, Ni, Cd and Co were respectively, 48.0 mg/m³, 82.0 mg/m³, 140.0 mg/m³, 202.0 mg/m³, 34.0 mg/m³, 1403.0 mg/m³, 21.0 mg/m³, 60.0 mg/m³. Conclusion: All the metals (Pb, Ni and Cd), classified by IARC as carcinogenic in humans (group 1) greatly exceeded on average the annual EU’s limits (500, 20, 6 and 5 ng/ m³ respectively).

1. Introduction

According to several researchers, airborne contaminants can lead to respiratory and cardiovascular conditions like bronchitis, cardiac arrhythmia, lung inflammation, lung fibrosis, deep vein thrombosis, and lung cancer ^{1, 2, 3, 4, 5, 6}. It has also been noted that these detrimental health effects are caused by particulate matter (PM) and other pollutants like CO and SO₂. Stone crushing is a rising source of particulate matter emissions in Nigeria, which come in a variety of sizes and chemical compositions. Due to a lack of resources and technical know-how for mechanized stone crushing, manual stone crushing industries are becoming more prevalent and common sights along several highways leading to major Nigerian cities. Stone crushing has become the main source of income for low income earners in Nigeria.

Despite being extremely time-consuming and frequently dangerous, the technique has gained popularity among many individuals, particularly young people and women, as a favorable pastime in light of the current severe economic crisis and lack of attractive job prospects to address the country's massive unemployment problem. The large health effects from exposure to fugitive emissions from quarry activities are caused by the fact that the persons involved in these activities are frequently in clusters and dispersed inside the microenvironments of rock formations. The lack of information now available regarding the deterioration of air quality caused by these units' operations, accompanying occupational exposures, and potential health effects is a significant downside to this industry in Nigeria.

Notably, size reduction occurs during crushing operations; larger stones and fragmented pieces become too crushed, which leads to the generation of stone dust ⁷. The finer dust becomes airborne and escapes as fugitive emissions, creating dust pollution issues nearby that have a serious negative impact on the quality of the surrounding air and human health. These have an effect on the microenvironments' air quality and may cause respiratory illnesses, poor sight, and a decrease in the growth of vegetation. According to ⁸, stone crushing operations are a significant source of dust generation in the areas close to the facilities and in the communities in those areas. Oxides of sulphur, Oxides of nitrogen, and particulate matter (PM_2.5 and PM₁₀) are some factors that are considered for the investigation of ambient air quality within the microenvironments of manually operated stone crushing businesses ⁹.

A number of manually operated stone crushing clusters, many of which are found at the base of rock formations, are particularly prevalent in north central Nigeria. A typical cluster can consist of fifteen workers, including women and children, who spend an average of 10 hours each day at the crusher sites. North central Nigeria has a distinctive terrain with enormous rock formations, which contributes to the huge scale of manual stone crushing quarries even though all geographic regions of the nation are home to a variety of rock formations. The microenvironments of the stone crushing sites predispose the workers to a number of occupational hazards, including silicosis, which is brought on by prolonged exposure to particles rich in free silica ⁸. This is brought on by the workers' regular exposure to high concentrations of dust brought on by the crushing operations at these sites. According to ¹⁰, severe respiratory injuries can result in lung functioning abnormalities that are reversible in some situations but may result in irreparable damage in others, including lung cancer. ¹¹ found that humans' respiratory systems are capable of filtering out big particles. Some tiny particles can still get through, though. 3 million premature deaths worldwide occurred in 2016, according to the World Health Organization (WHO) ⁶. Despite the lack of evidence between long-term exposure to coarse particles and mortality, according to ^{5, 12} found that exposure to coarse particles has pro-inflammatory and cytotoxic consequences. Studies by [12-18] ¹² and others estimated the impact of PM on human health as well as the associated impact from the chemical composition. These metal-bearing particles may contain As, Cd, Co, Cr (VI), and Ni, which have all been linked to a higher risk of cancer. According to ¹⁹, the majority of metals are hazardous and may have serious negative consequences on health, including various cancers. This is due to the finding made by ²⁰ that dust particles differ in size and have a significant surface area, which makes them a great vehicle for the transportation and deposition of heavy metals in the environment.

Fine particulate matter (PM_2.5, particles with aerodynamic diameters 2.5 µm) has a larger surface area per unit mass than coarse particulate matter, which makes it easier for PM_2.5 to accumulate heavy metals. PM_2.5 is also more dangerous than coarser PM due to its longer residence time in the atmosphere and deeper penetration into the lungs ⁶. Many sources that emit heavy metals into the air have been studied and documented in literature, but little research has been done on the heavy metal emissions from manually crushed stone in Nigeria. Due to the physical processes that create atmospheric particles and the atmospheric processes that regulate the fate and evolution of particle size distributions, the size of atmospheric particles can be related to their sources in the atmosphere. Physical processes, such as the resuspension of soil and road dust, sea spray, agricultural tilling, vehicular abrasion (i.e., tyre and brake wear), and fugitive dust emission from industrial sources, are the main causes of coarse PM (particles with aerodynamic diameters between 2.5 µm and 10 µm) production (IARC, 2015). The sizes of particles span over around five orders of magnitude, from groupings of molecules at the nanoscale (for example) to grains of dust at the scale of tens of micrometers. While it is possible to measure the distribution of particle sizes, most measures only record the mass of particles falling within a given size range. For instance, PM_2.5 refers to PM with aerodynamic diameters of less than 2.5 µm. Other typical size categories include total suspended particles (TSP), ultrafine PM (PM < 0.1 μm)., and PM10 (PM < 10 μm).

According to the ²¹, coarse PM is defined as the fraction having sizes between 2.5 and 10 micrometers. These size classes correspond to size ranges utilized in health research and are pertinent to PM dynamics in the environment and uptake in the human body. According to ²², the presence of heavy metals in urban dust and soils is a significant sign of environmental contamination. Due to the activity of stone crushing in Nigeria, research to determine their levels in the atmosphere is therefore crucial. There aren't many thorough researches on the environmental effects of Nigeria's emissions of metal-bearing particles, particularly those from manual stone crushing.

This research seeks to determine the effects of fugitive emissions from a few chosen groups of manually operated stone crushing locations in north central Nigeria and their heavy metal constituents.

2. Materials and Methods

The Federal Capital Territory (FCT) of Nigeria and six states in the nation's central region were included in the study. The seven states that make up North Central Nigeria are geographically located in the central belt area of the nation, starting in the west and extending to the confluence of the Rivers Niger and Benue. Benue, Plateau, Nasarawa, Niger, Kogi, and Kwara are the north central states and are situated at an altitude of 115 meters above sea level, as indicated in Figure 1. 80'000'' N and 800'0'' E DMS are its coordinates (in Degree Minutes Seconds). Its Joint Operation Graphics reference is NC32-14, and its UTM position is LP88. Due to its distance from the equator, its climate, the tropical savanna climate, has a clearly defined rainy season with a single peak known as the summer maximum. With an average annual rainfall of roughly 1,500 mm and a peak rainfall in September, the temperatures range from above 18.54°C to 36.9°C. In total, fourteen sites were chosen at random from these thematic regions shown in Figure 1.

The Basement Complex and the Younger Granites make up around 50% of Nigeria's entire 935,000km2 landmass, while the Cretaceous to Recent Sediments (Tertiary & Quaternary), which are in the six (6) primary sedimentary basins of the nation, make up the majority of the other 50%.

• Pre-Cambrian-Lower Palaeozoic rocks of the crystalline Basement complex make up around 50% of Nigeria's total surface area and can be split into three primary geological age regions.

• The Basement Complex in the North-Central region of Nigeria has less than 10% of the Jurassic Younger Granite and the Quaternary Volcanism.

• Sediments from the Cretaceous to Recent Epochs make up around 40%. deposits were made in Nigeria's Middle Benue Trough, Niger Basin, northeastern Chad Basin, and northwesterly Sokoto Basin.

These geological age provinces are distributed differently across the North Central States. Parts of Kwara, Nasarawa, Niger, Benue, Kogi, Plateau State, and the Federal Capital Territory (FCT) include the basement complex rocks. At least four main orogenic cycles of deformation, metamorphism, and remobilization are thought to have had an impact on them: the Liberian (2,700 Ma), Eburnean (2,000 Ma), Kibaran (1,100 Ma), and Pan-African cycles (600 Ma).

Intense deformation, isoclinal folding, regional metamorphism, and significant migmatization were common characteristics of the first three cycles.

Younger Granite Complexes are made up of a number of unique intrusions that are frequently arranged in a concentric fashion. The complexes' rock types, according to ²³, include rhyolites, granites, syenites, and basic rocks. These are typically found in Nasarawa and sections of the Plateau. Rhyolites come in two varieties on the Jos Plateau, the early and late rhyolites. Although they vary in mineralogy and texture, granites are a constant throughout the region. They are predominately granites made composed of riebeckite granite, biotite granites, and the hornblende granite and porphyries group.

Numerous colored minerals, including fayalite, hedenbergitic pyroxene, hornblende, arfvedsonite, and biotite, are found in the hornblende granites and porphyries group. The term "granite porphyry" is used to describe these facies of the hornblende granites, which may take the form of massive plutons with a granite texture within ring dykes ²³. Early ring dykes on the Jos plateau are usually composed of coarse hornblende-biotite-granite or granite porphyry, which is also common as plutons. The most prevalent and common rock types on the Plateau are biotite-granites. They contain a wide range of accessory minerals, including zircon, fluorite and iron oxides, thorite, monazite, and xenotime ²⁴ and they produce some of the largest individual intrusions ²³.

Certain regions of Niger, Kogi, Benue, Nassarawa, Plateau, and the FCT have the Cretaceous to recent sediments (Tertiary & Quaternary) that make up the troughs.

Using the CW HAT 200 Particulate Sampler, an active sampling tool, the ambient levels of particles with aerodynamic diameters of 2.5 µm and 10 µm were measured in-situ in the quarries. Additionally, using a multi-gas active sampler known as the Altair Multi-gas detector, various gaseous contaminants including CO, SO₂, and H₂S were sampled. For the collection and analysis of particles in the PM_2.5 size range, there is no ready-made approach. Since manual stone crushers frequently sit down to complete their responsibilities, these active devices were placed at a distance of only 0.5 to 1.0 meters (50 cm to 50 cm) from the ground levels.

Additionally, these sources were investigated for the heavy metals were present. The dust was collected using a Respirable Dust Sampler, an air check sampler that operates at a flow rate of 5 to 500 ml/min, on Whatman GF/A (size 25.4 cm × 20.32 cm) filter paper. SKC 224-XR Series Pumps were used with this sampler (Model 224-PCXR8). For three hours at each site, the sampler was positioned on a platform 1.5 m above the ground as shown in Figure 2. Atomic absorption spectrometry (AAS) was used to examine these trapped particle samples for particulate-associated heavy metals such Cd, Co, Cr, Cu, Pb, Mn, Ni, Fe, and Zn. The average sampling time was 3 hours due to the workers' epileptic work patterns, which allowed for breaks for rest, customer service, or complete shutdowns of operations. The sampling that was done during the wet season was similarly limited by the weather. As a result, the sample times for the aforementioned events were capped at fewer than three hours. Figure 2 shows stone crushing activity being carried out manually.

Atomic Absorption Spectrometry (ASS) was used to examine the heavy metal components of the particulate emissions from the groups of manually operated stone crushing operations. This calls for the fusion or digestion of powerful acids to dissolve the heavy metals in solution. Because inorganic acids are inexpensive, easily accessible, and the digested solutions have a low salt content, strong acid digestion is perhaps the most often utilized breakdown method for determining the amounts of heavy metals in air pollution.

In a fume hood, 2-3g of filter membrane was weighed into a 250 ml beaker. The tri-acid combination was then added to the beaker, along with 6ml HNO3, 3ml HCL, and 1ml HCLO4. The sample was heated to a colorless, turbid-free state on a hot plate at 90°C on the fume cup board. With the help of a glass funnel and Whatman filter papers with a pore size of 120mm, the sample was filtered while still warm to allow metals to precipitate into a 50ml volumetric flask. With distilled water from a cleaned bottle, the volume was brought up to the 50ml mark and taken for analysis. UNIFORM PROCEDURE The (AAS) 210VGP Atomic Absorption Spectrophotometer was used for the examination of the chosen heavy metal in accordance with ASTM D1971/D4691.

Using the SPSS software, descriptive statistics of CO, SO₂, H₂S, PM_2.5, and PM₁₀ sampled in-situ the microenvironments of the chosen quarries were conducted. Additionally, the descriptive statistics of the discovered heavy metals (Cd, Mn, Pb, Cr, Zn, Co, Fe, Ni, and Cu) were obtained using SPSS. Additionally, Microsoft Excel was used to collect the bar chats and display the respective levels of the pollutants across the various quarries.

3. Results and Discussion

The manually quarried rocks in FCT, Kwara, and Niger states belong to the Precambrian Basement Complex; Plateau State has a mix of the Precambrian Basement Complex and the Jurassic Younger Granites; and finally, Benue, Kogi, and Nasarawa States have a mix of the Precambrian Basement Complex and the Cretaceous (Tertiary & Quaternary) types.

The rocks being manually extracted from the Precambrian Basement Complex are migmatites, gneiss, granite gneiss, quartzites, agmatite, leucocratic gneiss (belonging to the Migmatite-Gneiss complex), muscovite granite, quartz diorite, coarse-porphyritic granites, medium-grained granites, and microgranite (all belonging to the Older Granite series). Sandstones, Shales, Ferruginized ironstones, and Ferruginized sandstones were the rock types identified to be crushed at the Cretaceous (Tertiary & Quaternary) sites.

At the Jurassic Younger Granites sites found dominantly in Plateau State, the identified mined rock types are basalts (Tertiary-Quarternary volcanic), rhyolites, ignimbrites, welded tuff, biotite granite, biotite hornblende granite, coarse-grained biotite granite, coarse-grained hornblende biotite granite, hornblende granite, medium-grained hornblende granite, medium-grained aegirine granite, pinkish granite, and pyroxene granites.

A total of thirty-four (34) distinct rock types were produced by all of these. One hundred percent of the rocks being crushed in Kwara state are metamorphic kinds, represented by gneisses and granite gneisses, according to a subsequent analysis of the distribution of the rocks being crushed in the research region. Similarly, migmatite/migmatite gneisses (69.23%), gneiss (7.69%), porphyroblastic granite gneiss, and granite gneisses (23.07%) make up 100% of the rocks being manually crushed in the FCT. In the state of Benue, volcanic rocks, represented by granites, account for 70% of the rocks being manually crushed. Sedimentary rocks, represented by shales and sandstones, account for 20%. In the state of Kogi, sedimentary rocks made up of ironstone and ferruginous sandstone account for 40% of the manually crushed rocks, while 10% are mostly made up of granite. Metamorphic rocks, represented by gneisses (40%) and quartzite (10%), make up 50% of the manually crushed rocks. The igneous rocks that make up 40.66% of the manually crushed rocks in Nasarawa state are granite, pegmatite, and diorite; the metamorphic rocks that make up 41.66% of the manually crushed rocks are granite gneiss, gneiss, and agmatite; and the sedimentary rocks that make up the remaining 16.66% are ferruginized sandstone. In Niger State, igneous rocks, such as granites, account for 91.66% of the manually crushed rocks, while metamorphic rocks, such as mylonitic amphibolites, account for 7.69%. In Plateau State, igneous plutonic rocks, represented by granites, account for 61.90% of the manually crushed rocks, followed by igneous volcanic rocks, represented by rhyolites, welded tuff, and basalts, at 23.81%, and metamorphic rocks, represented by migmatites, at 41.28%.

Manual Crushing is an unmechanized process, hence fugitive emissions are significantly reduced. This is primarily so that only a crusher may work at a given location, however they may be grouped together with ten or more workers. The potential dangers these sources portend may not lie so much in the volume of the pollutants released as in the way the crushers are positioned; in several recorded instances, the crushers are positioned so that they are facing the fugitive emissions while crushing stone as presented in Figure 2. Due to this, the released particles are now easily able to enter their nasal cavities and enter the lungs. Due to the fact that roughly 90% of stone crushers prefer to work without either nasal masks or eye protection glasses, the risks associated with manually operated stone crushing have grown significantly. The average concentrations of gaseous (CO, SO₂, and H₂S) and particulate (PM_2.5 and PM₁₀) pollutants were measured in-situ at the 14 manual stone crushing locations chosen from among those in six north central states and the Federal Capital Territory (FCT), and are shown in Table 1. Figure 3 illustrates the considerable sizes and levels of variation in the observed concentrations of particulates across the selected sites. This supports ²⁵ finding that PM levels fluctuate significantly and depend on the size fraction being considered. The average PM_2.5 concentration was 26.5 µg/m³ (with a range of 8 µg/m³ to 70 µg/m³), which is approximately 76.7% higher than the World Health Organization's (WHO) air quality standards (15 µg/m³ for 24-mean for PM_2.5) ²⁶. The average PM₁₀ concentration was found to be 54.36 µg/m³ (with a range of 17µg/m³ to 143 µg/m³), which is about 20.8% higher than the WHO's air quality recommendations (45 µg/m³ for the 24-mean for PM₁₀). These levels are, however, somewhat below the National Ambient Air Quality Standards (NAAQS) for the United States of America, which are 35 µg/m³ for PM_2.5 and 150 µg/m³ for PM₁₀, respectively. These showed that PM_2.5 was 24.29% below the NAAQS level for the 24-hour mean and that PM₁₀ was 63.76% below the NAAQS level for the 24-hour mean.

The ratio of the mean average values of PM_2.5/PM₁₀ ranged from 0.45 to 0.56 at the 14 locations monitored across the different states in north central Nigeria where manual stone crushing was carried out, with an estimated mean of 0.49. This falls into the expected range provided by ²⁶. The estimated range of the annual average values (PM_2.5/PM₁₀) for the 21 regions examined globally in 2005 is 0.13 to 0.94, according to ²⁷. It suggests that a significant share of PM₁₀ emissions from manual stone crushing operations. When compared to PM₁₀, PM_2.5 (particles with aerodynamic dimensions less than 2.5 µm) has a larger surface area per unit mass, making it easier for PM_2.5 to accumulate heavy metals. Due to its longer residence period in the atmosphere and deeper lung penetration than coarser PM, PM_2.5 is likewise more dangerous ²⁶.

⁸’s evaluation of a group of 50 stone crushing plants in Pammal, a suburb of Chennai, the capital of Tamil Nadu State in India, found that downwind average PM_2.5 and PM₁₀ concentrations ranged from 73 to 388 µg/m³ and 110 to 1200 µg/m³, respectively. For PM_2.5 and PM₁₀, the observed downwind average values ranged from 8 to 70 µg/m³ and 17 to 143 µg/m³, respectively. It is 82.0%-89.0% lower than the levels observed by ⁸ for PM2.5 and 84.5%-88.1% lower than the levels observed by ⁸ for PM₁₀. This is clearly significantly lower than the observed concentrations by ⁸, which were mechanically operated cluster of stone crushing units. observed downwind average values ranged from 8 to 70 µg/m³ and 17 to 143 µg/m³, respectively.

The levels of various gaseous pollutants as CO, SO₂, and H₂S were detected in-situ using the Multi-gas Altair 5X Detector. The gaseous emissions throughout the selected quarry sites differ greatly, as seen in Figure 4. However, the mean measured concentrations of CO, SO₂, and H₂S for the samples are shown in Table 1 as 0.12 mg/m³, 0.06 mg/m³, and 0.004 mg/m³, respectively. Additionally, Table 1 shows that the observed mean SO₂ level across these sites ranged from 0.00 to 0.44 mg/m³ and was 0.06 mg/m³ on average. This is 95.4% lower than the NAAQ Standards yet 33.33% higher than the WHO recommendations. In particular, the mean CO level that was found varied from 0.00 to 0.55 mg/m³, which is 99% below the WHO recommendations. According to Figure 3, CO levels were higher at crushing sites along major highways and at sites where heating by wood fuel occasionally for weakening rocks for later breaking. These sites are ABJ B, NSW C, PLA, and PLC. Generally speaking, low CO concentration levels were sampled (typically below WHO and NAAQ guidelines), with the exception of locations along busy highways with heavy traffic. The levels of SO2 sampled are not significantly high. However, there are signs that prolonged exposure could result in serious occupational risks.

The risk assessment's context plays a significant role in defining the kind of analysis that is most suited in any given circumstance. Due to the requirement to establish the baseline data of emissions from the manual stone crushing activities, site-specific assessments were used in this study. Exposure to metal-containing particles happens almost constantly, in all kinds of microenvironments-even indoors. Table 1 displays the summary information (mean, minimum, and maximum values) for the elemental levels of the selected metals (Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, and Zn) over the course of the study. Table 1 demonstrates that, with the exception of copper, which was below the detection threshold, the metal-bearing particles have significant quantities of the selected metals. The concentrations of Cr, Mn, Fe, Pb, Zn, Ni, Cd, and Co were 48.0 mg/m³, 82.0 mg/m³, 140.0 mg/m³, 202.0 mg/m³, 34.0 mg/m³, 1403.0 mg/m³, 21.0 mg/m³, and 60.0 mg/m³, respectively. As seen in Figure 5, both the compositions of the metal-bearing particles and their absolute quantities vary significantly between the measured sites. Nickel, lead, and iron were the metals with the highest amounts of significant emissions, whereas copper had the lowest levels. The compositions of the metal-bearing particles around quarry sites in Nigeria, much less all the places a person may travel, is rarely, if ever, fully described, which makes it difficult to interpret these exposures.

The order of the selected heavy metal sampled and analysed depict Ni as having the highest level (see Figure 5). Fe and Mn, two of the main elements found in the earth's crust, were noteworthy based on their average concentration. In particular, their total made up around 11% of all the trace elements sampled. The yearly EU limits for Pb, Ni, and Cd (500, 20, 6, and 5 ng/m³, respectively) were all significantly exceeded by all three metals, which the IARC has designated as group 1 carcinogens in humans. It is important to note that Pb concentrations in all of the samples were many orders of magnitude greater than their limit values. ²⁸ established varied concentrations of heavy metals in the following descending order: Mn > Cr > Cu > Pb > Ni > Cd. However, in this work, concentrations of heavy metals from manually operated quarry sites in the following descending order: Ni > Pb > Fe> Mn > Co>Cr > Zn> Cd. This provided a better perspective of the impact of these metals.

By comparing these metals' levels to those of Immediate Detrimental to Life and Health (IDLH) values and the Occupational Safety and Health Administration, ²⁹ was able to gain a better understanding of their effects. Figure 6 illustrates that Ni, Pb, Co, and Cd are much higher in this order than the immediate Detrimental to Life and Health (IDLH) values and those of Occupational Safety and Health Administration. To safeguard workers from both acute and chronic exposure scenarios, OSHA defined allowable exposure levels that shouldn't be exceeded during each 8-hour work shift of a 40-hour workweek. According to the metal concentrations observed at the selected crushing locations, manual stone crushers are exposed to unacceptably high quantities of Nickel, Lead, Cobalt, and Cadmium.

The fugitive emissions from stone crushing contain non-volatile metals, which have a significant impact on the health of employees who are frequently exposed to them. Even if metals are not the main contributors to particle mass, small-scale industrial operations like stone crushing can be enormous sources of metals that can be detected in the microenvironments of the quarries and the nearby regions ^{30, 31}. By contrasting the measured values with the occupational/industrial limits established by ²⁹ and shown in Table 1, a better understanding of the degree of occupational hazards caused by extensive exposure to metal-bearing particles by manual stone crushers can be obtained. These metals can be identified by other characteristics, such as water solubility (extended to solubility in biological fluids), particle size distribution, and effects on the environment and human health. The majority of metals released during combustion activities, such as the burning of trash or fossil fuels, occur in tiny particles or the fine fraction, which is frequently represented by particles with a diameter of less than 2.5 µm (PM_2.5). The larger-sized, coarser particles, on the other hand, are the result of mechanical disruption, such as crushing, grinding, the evaporation of sprays, or the suspension of dust from agricultural and building activities.

4. Conclusion

Different gaseous components (CO, SO₂, and H₂S) and particles of sizes 2.5 micron and 10.0 micron (PM_2.5 and PM₁₀) were regularly monitored in order to assess outdoor pollution levels as a result of fugitive emissions from manual stone crushing facilities throughout north central Nigeria. In particular, the mean CO levels that was found varied from 0.00 to 0.55 mg/m³, which is 99% below the WHO recommendations. According to ABJ B, NSW C, PLA, and PLC, CO levels were greater at crushing facilities near major highways where there were instances of heating rocks with fuel wood to make them more brittle for breaking later. With the exception of locations near congested highways with heavy traffic, low CO concentration levels were often sampled (frequently below WHO and NAAQ guidelines). The observed mean level of SO₂ at these sites ranged from 0.00 to 0.44 mg/m³, with a mean value of 0.06 mg/m³. This is 95.4% lower than the NAAQ Standards yet 33.33% higher than the WHO recommendations. This demonstrates that even if the mean level of SO₂ is not appreciably high, there are signs that prolonged exposure could result in serious occupational risks. The heavy metal concentrations in manually operated quarry sites were determined in the following order: Ni >Pb >Fe> Mn > Co>Cr > Zn> Cd. The yearly EU limits for Pb, Ni, and Cd (500, 20, 6, and 5 ng/m³, respectively) were all significantly exceeded by all three metals, which the IARC has designated as group 1 carcinogens in humans. It is important to note that Pb concentrations in all of the samples were many orders of magnitude greater than their limit values. Even at low quantities, exposure to metals in the microenvironments of the selected quarry sites predisposes the workers to a wide range of adverse consequences on human health, including cancer and damage to important organs.

Acknowledgements

The research was supported by TETFund National Research Fund (NRF) Code: TETF/DR&D/CE/NRF/STI/36/VOL.1

Ethical Clearance

Ethical approval was granted by National Health Research Ethics Committee of Nigeria: Approval No. NHREC/01/2007-01/06/2020.

Conflicts of Interest

Authors declare that they have no conflicts of interest.

References