Pollution Level and Sources of Heavy Metals in Indoor Dust from College of Science, University of Anbar Campus, Iraq

This research aims to evaluate the level of heavy metal pollution [Cadmium (Cd), Cobalt (Co), Chromium (Cr), Copper (Cu), Lead (Pb) and Zinc (Zn)] in indoor dust samples taken from the College of Science at the University of Anbar in Iraq and their likely sources. Atomic absorption spectrophotometer was used to evaluate the dust samples that were taken from 39 locations (classrooms, offices, and laboratories). Zn > Pb > Cr > Co > Cu > Cd was the order in which the heavy metal concentrations were found. The findings showed that all metal concentrations at various times exceeded background values. Using the geo-accumulation index (Igeo) and contamination (CF), the pollution level was calculated. The values of Igeo and CF indicate that the indoor dust in the College of Science is heavily polluted with Pb and Cd and is unpolluted to moderate polluted with the other metals. Pb, Cd, and Zn may be released from anthropogenic sources, while Co, Cr, and Cu may come from a combination of sources, according to the coefficient of variation (CV) comparison of the heavy metal concentrations with background values, Pearson’s correlation, cluster analysis (CA), and principle component analysis (PCA).


Introduction
Heavy metals (HMs) are more common in larger amounts in a variety of environmental systems due to their stability and Inability to degrade [1].Organic pollutants and hazardous HMs have been spread into the air, dust, soil, and water because of the fast process of urbanization and industrialization [2][3].Dust is defined as a solid substance or particulate that settles as a fine powder (less than 100 mm) on the surface of an object or the ground [4].Due to its components and properties, dust serves as a key connection in the air, soil, and water ecosystems and serves as a monitor of environmental quality [3,5].The dust pollution level of indoor environments (homes, buildings, classrooms, campuses, offices … etc.) is 2-5 times higher than in outdoor environments [6].Over 90% of a person's lifetime is exposed to indoor dust and its pollutants [7].In educational institutions, studies concerning heavy metal concentrations, pollution levels, and source identification has mostly focused on kindergartens and primary schools.[7,[8][9][10][11].There are very few studies on HMs pollution in universities campuses [12][13][14][15].Campus dust heavy metals (HMs) pollution is a major issue, with possible effects on college students not insignificant [15].This study's primary goals were to: (1) ascertain the amounts of Cr, Cd, Co, Cu and Pb in indoor dust from College of Science campus, University of Anbar, Iraq; (2) to assess these metals' levels of pollution; (3) characterize the sources of these heavy metals using multivariate statistics.This is, to our knowledge, the first research in Iraq to evaluate the HMs in campus dust.

Sample collection and analysis
Thirty nine samples of indoor dust were gathered from the College of Science/ University of Anbar, Iraq.The indoor dust was sampled from laboratories, classrooms, and offices.A plastic brush and pan were used to collect the dust samples from floors, desks, and window sills between October and November 2021.To generate a composite sample, three to five individual samples were extracted and carefully mixed.In a polypropylene container, the generated composite samples were stored until digestion and analysis.A microwave-assisted acid digestion procedure was used to digest the materials1 gram from each sample of dust was put into a beaker along with 20 ml of acids mixture of HCl: HNO3 a ratio of 3:1 to digest the sample into the microwave.The digestion process was continued until dryness of the solution, then left to cool down, mixed with a small amount of distilled water, filtered then completed with distilled water to 50 ml.The samples were stored in particular containers ready for detecting and measuring the heavy metal content using FAAS (Flam Atomic Absorption Spectrometry) instrument (Phoenix -986, USA).

Pollution Level Assessment Methods
Two indices, the geo-accumulation index (Igeo) and contamination factor (CF) were utilized to estimate the level of pollution in dust samples of the research area.

Geo-accumulation index (Igeo)
In order to assess the concentration of HM pollution in sediment and soil, [16] developed the geoaccumulation index (Igeo).The following algorithm is used to calculate Igeo: IOP Publishing doi:10.1088/1755-1315/1300/1/0120193 Where HM geochemical resource levels are expressed by Bn and Cn is the metal amount that was actually calculated.A factor of 1.5 is inserted to account for differences in the resource levels caused by geological activity.Muller graded Igeo in seven different ways [17 ].

Contamination Factor (CF)
The amount of metal pollution of dust is evaluated by the contamination factor (CF), which is computed as follows: Where Cm sample indicates the amounts of a particular element in the dust and Cm indicates the background value of the element.The contamination factor (CF) is divided into four classes: contamination (< 1) considered minimal, contamination (1 ≤ CF < 3) considered moderate, contamination (3 ≤ CF < 6) considered significant, and (CF > 6) considered extremely high [18 ].

Identification of Heavy Metals Sources
The coefficient of variance (CV) was used to compare heavy metal levels with metal background levels, and multivariate statistical methods such as correlation matrix, cluster analysis (CA) and principal component analysis (PCA) were used to determine the sources of heavy metals in indoor dust from the Faculty of Science.

Statistical Multivariate Methods
Enrichment factor analysis cannot detect sources in complicated source setups due to its poor ability to distinguish between different sources [19].The ability to discriminate between various sources is improved by multivariate statistical technique like principal component analysis (PCA), cluster analysis (CA), and correlation analysis.

Correlation Matrix Analysis(CMA)
Analytical statistical techniques such as correlation matrix analysis are used to assess potential linearity.The degree to which correlation can be applied successfully depends on the kind of parameter and the kinds of current variables under study [20].The correlation analysis is sometimes referred to as an effective factor analysis because it illustrates the relationships between several parameters, such as the sources of chemical elements and affecting factors [21].Heavy metal chemical-environmental linkages that may indicate relationships between their origins can be investigated using correlation analysis [19].

Cluster Analysis (CA)
CA is a process used in advance of data analysis to help solve the challenge of sorting the data.This technique seeks to group or nodulate data.High internal homogeneity and high exterior heterogeneity are both present in each cluster [22].Hierarchical cluster analysis, the most widely used cluster analysis method, which separates the data into discrete clusters before connecting each cluster one at a time until there is only one remaining cluster [23].

Principle Components Analysis (PCA)
PCA is a method of evaluating observations that are represented as a data matrix and characterized by several relevant parameters that are usually correlated with each other [24].The basic components are analyzed using a series of previously derived variables called factors, eigenvectors, and loadings to find important data.Each unit receives a score consistent with the PC's prediction for it.
3rd Due to the absence of guidelines for the amounts of HMs in the dust, the means levels of the HMs in the indoor dust of the study site were compared with their guidelines in the soil, Table 1.The comparison's findings demonstrated that all heavy metals' mean concentrations in indoor dust were higher than recommended levels.This result reflects that the dust in the College of Science is contaminated with Cd, Cr, Co, Cu, Pb and Zn.To our knowledge, there are no studies available on the level of HMs in universities and colleges in Iraq, so the amounts of HMs recorded in indoor dust at the College of Science / University of Anbar were compared with studies carried out in universities around the world, Table 2.The findings of the comparison showed that the amounts of some metals in the indoor dust of the College of Science at Anbar University were greater than what was documented in the dust of other universities.The others results were lower Cd, Cr, Co, Cu, Pb, and Zn metal mean level in classrooms, laboratories and offices dust as summarized in Table 2 [13], [25], [26], [27], [15].Mean concentrations in the dust of laboratories of the departments of biology, chemistry and physics are illustrated in Figure 3, while the mean amounts of those HMs in the classes of the departments of biology and chemistry are shown in Figure 4. Figure 2 demonstrates that the concentration of cadmium is higher in laboratory dust than in classroom dust, which is higher than the dust in offices.The mean level of Co, Cr and Cu take the following descending order: offices > Labs > classroom, while the mean concentration order of Cu order is as follows: offices > classroom > labs.The descending ranking of the mean concentration of Zn is as follows: chemistry > biology > physics.The laboratories differ in the nature of the use of chemicals.The laboratories of chemistry and biology departments use more chemicals in terms of quantity and quality.Therefore, it is predicted that heavy metal amounts in the dust of laboratories of Chemistry and Biology departments will be higher than in the laboratories of the physics department.The remarkable result of the present study is that the amounts of Cd, Cr and Pb were higher in the dust of the laboratories of the Department of Physics than in the laboratories of the Departments of Chemistry and Biology [27] found that mean amounts of Pb in physics laboratories was higher than that in Chemistry and Biology laboratories in UITM, Malaysia.
The results of ANOVA between the amounts of HMs in offices and laboratories dust revealed substantial differences at (p≤ 0.05) between the amounts of Cr, Cu and Zn.This result suggests different sources of releasing these metals in offices and laboratories dust.The ANOVA exhibited insignificant differences at (p≤ 0.05) between the amounts of Cd, Co ,and Pb in offices and laboratories dust indicating that these metals are released from common origins.The ANOVA of concentration of Cd in laboratories showed significant differences at (p≤ 0.05) suggesting different sources of Cd, while exhibiting insignificant differences for other metals indicating a common sources.The ANOVA results revealed negligible variations in the concentrations of HMs in classrooms dust suggesting common origin for these metals.

Pollution Levels Assessment
Two indices including geo-accumulation index (Igeo) and contamination factor (CF) were employed to assess the level of pollution of indoor dust with HMs.Results of the calculation of Igeo and CF are listed in Table 3.

Geo-accumulation Index (Igeo)
The Igeo values for Cd and Pb in indoor dust are 2.11 and 2.29, respectively.According to Muller's classification [16], the indoor dust is categorized as moderately to strongly contaminated with Cd and Pb.The Igeo values of Co and Zn in indoor dust are 0.57 and 0.51, respectively.Both values point out that the indoor dust in the research area is categorized as unpolluted to moderately polluted.This result may be reflected in the common origin of Co and Zn in indoor dust.The Igeo values of Cr and Cu in indoor dust are -0.31 and -0.04, respectively.According to Muller's classification, the indoor dust of the research area is classified as unpolluted with Cr and Cu.

Contamination Factor (CF)
The CF values of HMs in indoor dusts of the study area are listed in Table 3. Cd and Pb in indoor dust from the College of Science have CF values of 7.50 and 7.37, respectively.According to Hakanson's classification, the indoor dust has a very high pollution with Cd and Pb.The CF values of Co, Cr, and Zn in indoor dust of the study area indicate that indoor dust has moderate contamination with Co, Cr, Cu and Zn.The higher level of Cd and Pb pollution in the indoor dust of the research area is linked to the traffic emissions due to the proximity of the College of Science to the entrance of University of Anbar and the parking lot.

Correlation Matrix Analysis(CMA)
Result of the Pearson correlation analysis for the metals in the indoor dust from College of Science/University of Anbar is listed in Table 4.The results revealed that there are considerable positive good associations at the p ≤ 0.05 between Co -Cr (r = 0.54) and Co -Zn (r = 0.41).The powerful positive associations between the Co -Cr and Co -Zn reflect the common source or origin for these metal pairs.Table 4. CM between HMs in the indoor dusts.Marked correlations are significant at p < .05.

Cluster Analysis(CA)
Ward's method was utilized to do the hierarchical cluster analysis (HCA) on the consistent data set.Figure 5

Principle Components Analysis (PCA)
By combining varimax rotation with Kaiser Normalization, PCA was utilized to identify the origins of heavy metals in indoor dust from College of Science, University of Anbar.The PCA results show three eigenvalues with numbers higher than one, corresponding to a total of 69.14% of the variance, Table 5.
Table 5. Factor loadings (varimax rotation) of HMs in outdoor and indoor dusts from College of Science, marked loadings are >0.70.
The factor (1) has a substantial positive loading (PL) on Cd and accounts for 30.66% of the overall variation.The factor (2) shows notable positive loadings on Co and Zn and explains 20.53% of the overall variance.The factor (3) exhibits 17.95% of the overall difference and has substantial PLs on Cr and Pb.Positive loading (PL) levels were categorized by [28] as high PL (0.75-1.0), mild PL (0.5-0.75), and low PL (0.3-0.5).The heavy metals may be influenced by the same source, based on high PL value [22].A modest loading value suggests that the heavy metals may be impacted by a variety of sources [33].
According to the coefficient of variation (CV) values, the HMs in indoor dust from College of Science may be split into two categories Cd, Cu, Zn, and Pb which have VCs greater than o.25 and Cr and Co have VCs less than 0.25.It is claimed that as heavy metal content increases, anthropogenic influence on heavy metal also increases [31].Based on VCs of Cd, Cu, Zn, and Pb, it is expected that anthropogenic sources have an impact on these metals to be quite high, while Cr and Co are affected to lesser extent by human activities.
The amounts of Cd and Pb are over six times greater than background amounts of HMs in the indoor dust of the College of Science, indicating clear anthropogenic sources, while the amounts of Co and Zn are only slightly greater than background levels, showing the impact of anthropogenic sources.The close of the Cr and Cu amounts to the background amounts suggests a natural source.Results of correlation matrix analysis of HMs in indoor dust from College of Science (Table 3) showed that there are a notable positive correlations at the p ≤ 0.05 between Co -Cr (r = 0.54) and Co -Zn (r = 0.41) indicating common source or same origin.
The CA analysis result is partially consistent with the PCA analysis result and includes much information about heavy metal sources.Based on the CA analysis results, Zn displays a large distance from the other heavy metals suggesting that Zn has positive sources with other metals.The PCA result shows that Zn has positive loading strong with Co in Factor (2).The PCA result exhibits that Cd has positive strong loading, while the CA result shows that Cd was classified in one subcluster.This result implies that Cd has different sources from other metals.Cr and Pb display strong positive loadings (Factor 3) which serves as a sign of the same sources.Pb and Cr were categorized in the same subcluster based on their high degree of similarity suggesting the same source.Cu and Co were classified in the same subcluster but they did not combine in one factor.
Results of VCs, comparison of Cd with its background value, CA and PCA suggest that the Cd mainly comes from the anthropogenic sources.According to researches by Shen et.al. 2018 andŁapiński et.al. 2020 [32-33], higher Cd concentrations in the dust were related to tire wear and lubricating oil and automobile emissions.One of the sources of Cd is engine wear and emissions from diesel fuel [34 ].Due to the lack of efficient ventilation systems in the buildings of the College of Science and its proximity to the university entrance and the parking lot, the high amounts of Cd in indoor dust of College of Science can be attribute to traffic emissions, and there may be a contribution to the use of chemicals in its laboratories.
The significant positive correlation between Co and Zn suggest a common source.Both metals have concentrations that are more than twice as large as their background amount.The PCA result shows that Zn has a positive loading strong with Co in Factor (2).These findings suggest that the high amounts of Zn and Co come mainly from anthropogenic sources.The VC of Co is low (0.19) indicating a natural source.Geogenic factors include the weathering of crustal materials and air inputs can be responsible for the concentration of Co [35].The smelting and mining industry [36 ],as well as the wear of moving automotive parts [37], are the origins of the high amount of Zn in dust.The Co and Zn concentrations could be related to mining and industrial operations [38].Co is thought to come from the nonferrous or ferrous industries [39 ].The Co may have been released into the air and then redeposited on the surface from various manufacturers or plants [40 ].
The close value between the amounts of Cu in indoor dust and its concentration in the background suggests natural sources (soils).The low value of the coefficient of variation for Cu indicates a weak effect of anthropogenic sources on the content of both in indoor dust of the research area.The emissions from automobile oils [41 ] engine wear and tear [37 ], and traffic emissions [42 ] were identified as sources of copper in both indoor and outdoor dust.Cu is also produced in the ambient environment by the burning of lubricating oil in diesel engines and by exhaust emissions [42].
While the concentration of Cu and the amount in the background are relatively near, suggesting a natural source (soils), the amount of Pb was greater than its amount in the background, suggesting an anthropogenic source.Pb and Cr were grouped together in the same sub-cluster of the CA dendrogram and showed positive strong loadings in factor (3) of PCA.This findings can be described by the fact that human activity raises the amount of chromium in the dust.The Industrial activities contribute to raises the amount of chromium in dust [43].Previous research claimed that the main source of lead (Pb) in indoor dust came from automobile emissions [44], [42].The use of paints that contain Pb may be a human source of Pb in indoor dust [13].Because of the proximity of the College of Science buildings to the entrance of vehicles that enter the campus, to the parking lot, and because of the ventilation systems being open, road dust resulting from traffic emissions contributes to the high ampunt of lead in the indoor dust in the College of Science.
Based on the above, we find that the main contributor to the indoor dust pollution of the College of Science with measured heavy metals is the outdoor dust.The buildings with open ventilation systems (e.g.College of Science buildings) affect the movement of outdoor dust pollutants into indoor dust [45].There is a relationship between dust and climate variables that enters the indoor environments, which leads to an increase in the chemical composition of building dust [46].The nature of the open ventilation system in the laboratories of the College of Science, in addition to the laboratory activities, may affect the amounts of HMs in the indoor dust.

Conclusion
The amounts of HMs in the indoor dust of the College of Science buildings were in the following descending order: Zn > Pb > Cr > Co > Cu > Cd.The mean amounts of HMs in the indoor dust are greater than the amounts in the background by a number of times, ranging from slightly greater than one time for Cu and Cr, more than two times for Co and Zn, to more than six times for Cd and Pb.The Igeo and CF values reveal that the indoor dust in the College of Science is heavily contaminated with Pb and Cd and is not contaminated to the moderate contaminated with the other metals.The main contributor to the indoor dust pollution of the College of Science with heavy metals is the outdoor dust.The laboratory activities may influence the amounts of HMs in the indoor dust.The coefficient of variation (VC), comparison of HMs concentrations with their concentration in the background, Pearson's correlation, (CA), and (PCA) indicate that Pb, Cd , and Zn may be released from anthropogenic sources while Co, Cr , and Cu may be participated by mixed sources (natural and human ).

Figure 1
displays the location of the College of Science within the campus of the University of Anbar.The College of Science includes two buildings, the first comprises the Departments of Chemistry and Biology, and the second building, which is newer than the first building, includes the Departments of Physics, Applied Geology and the Deanship of the College.The College of Science is located at the entrance to the university campus and near the main car park.

Figure 1 .
Figure 1.Location of the research area.The red rectangular is College of Science, University of Anbar, Iraq.

Figure 2 .
Figure 2. The mean level of some HMs in indoor dust of College of Science, University of Anbar.

Figure 3 .
Figure 3.The mean level of some HMs in classrooms dust in College of Science, University of Anbar.

Figure 4 .
Figure 4.The mean concentrations of some HMs in laboratories dust in College of Science, University of Anbar.

8 Figure 5 .
Figure 5. CA dendrogram for HMs in indoor dust from College of Science.

Table 1 .
Scientific Conference of Iraqi Desert Geology (IDGC 2023) Statistical AnalysisThe academic statistics software STATISTICA, version 13.3 for Windows, was used to conduct the following analyses: PCA, CMA, CA, and descriptive statistics.3.Results and Discussion3.1.Concentrations of Heavy MetalsTable1provides the background information and explanatory statistics for the heavy metal concentrations in the indoor dust of the College of Science, University of Anbar, Iraq.Concentration of the HMs in indoor dust from College of Science 4 2.6.

Table 2 .
amounts of element (mg/kg) compared with other reported researches from universities around the world.

Table 3 .
Geo-accumulation index (Igeo) and contamination factor (CF) of HMs in indoor College of Science dust.