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Article

Metal Enrichment in Settleable Particulate Matter Associated with Air Pollution in the Andean City of Ecuador

by
David del Pozo
1,*,
Bryan Valle
1,
Daniel Maza
1 and
Ángel Benítez
2,*
1
Departamento de Química, Universidad Técnica Particular de Loja (UTPL), San Cayetano s/n, Loja 1101608, Ecuador
2
Biodiversidad de Ecosistemas Tropicales-BIETROP, Herbario HUTPL, Departamento de Ciencias Biológicas y Agropecuarias, Universidad Técnica Particular de Loja, San Cayetano s/n, Loja 1101608, Ecuador
*
Authors to whom correspondence should be addressed.
Environments 2025, 12(9), 304; https://doi.org/10.3390/environments12090304
Submission received: 23 July 2025 / Revised: 26 August 2025 / Accepted: 28 August 2025 / Published: 30 August 2025
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Abstract

Air pollution is one of the major environmental challenges worldwide. Settleable particulate matter (SPM), related to this environmental problem, contains metals capable of producing negative effects on human health (e.g., cardiovascular and respiratory illness). For this study, continuous monitoring was carried in the urban city of Loja (Ecuador), where 10 points were distributed based on different land uses. Samples were collected on a monthly basis using a passive method, by means of samplers built based on the 502 Method. The gravimetric method was then used in the laboratory to determine the concentration of SPM. The inductively coupled plasma–optical emission spectroscopy (ICP-OES) technique was used to identify the presence of metals as such as Copper (Cu), Lead (Pb), Cobalt (Co), Cadmium (Cd), Chromium (Cr), Silver (Ag), Arsenic (As), and Mercury (Hg) in SPM. The results obtained showed that SPM and As differed significantly between land uses, but most metals showed significant differences in relation to temporal changes. Although 90% of the sampling points show SPM concentrations within the limits established by environmental regulations, some of the points exceed the World Health Organization (WHO) limit of 0.5 mg/cm2. Finally, the temporal changes in more metals were clearly observed, probably because of increased combustion processes (vehicular traffic), with a higher percentage of metals clearly observed during the April and August months. Furthermore, the highest levels of vegetation burning in Loja province, including the surroundings of the city of Loja, occurred in August. This analysis provides essential data to guide environmental monitoring and air quality management strategies, aiming to reduce health risks from long-term exposure to metal-enriched particulate matter.

1. Introduction

Atmospheric pollution is one of the major environmental challenges worldwide, with significant impacts on human health and ecosystems [1,2,3]. Among the most concerning pollutants is particulate matter (PM), which includes fine particulate matter (PM2.5), coarse particulate matter (PM10), and SPM (PM > 10), with metals considered some of the most toxic and challenging elements, as they have a tendency to bioaccumulate [4].
These particles originate from various anthropogenic sources, such as industrial activities, vehicular emissions, and biomass burning [5,6,7]. Within this classification, SPM is particularly relevant due to its ability to deposit on surfaces and accumulate in the environment, potentially leading to long-term effects on air quality and human exposure [8]. SPM, composed of larger particles that tend to settle by gravity, can act as a vector for environmental contamination by incorporating metals from industrial, mining, and urban sources; for example, several metals (Pb, Cd, Ni, and Cr) have been identified in SPM samples collected from various urban and industrial environments, posing significant environmental and public health concerns [9]. On the other hand, a study conducted in a mining and smelting area in southwestern China reported elevated concentrations of Cd, Cr, Cu, Pb, and Zn in settleable particles, with levels exceeding the limits established by the WHO [10].
Beyond its effects on human health, metal contamination in SPM can alter soil and water quality, affecting biodiversity and agricultural productivity [1]. Additionally, studies have demonstrated that inadequate management of electronic waste generates metal emissions that deposit in SPM, increasing exposure in urban and residential areas [11]. The distribution of these metals varies depending on geographic factors and human activities, underscoring the need for continuous monitoring to better understand their dynamics and impacts.
In Ecuador several studies evaluated the effects of air pollution by metals used bioindicators, for example, vascular plants [12,13,14,15,16], bryophytes [17] and lichens [15]. Following this pattern, previous studies that evaluated settleable particulate matter have been realized in Chimborazo Province of the city of Cajabamba [18], Azuay Province of the city of Cuenca [19], and Pichincha province of Quito city [3]. However, to our knowledge, this is the first study to evaluate SMP (PM > 10) and the metals that characterized this contaminant.
In the city of Loja, located in southern Ecuador, vehicular traffic has been identified as one of the main factors of air pollution [16,20] due to the number of cars that contribute to air pollution. Thus, several studies have documented that traffic is one of the main sources in terms of particulate matter [21] and metals such as Cu, Fe, Ba, Sb, Cd, Pb, Zn, Cr, and Ni [12]. For instance, Cr is primarily found in coarse particles, whereas other elements such as Cd, Cu, Pb, and Zn may be present in finer fractions, increasing the likelihood of resuspension and subsequent inhalation in urban environments with high vehicular and industrial activity [22]. At present, there is a limited amount of information on this topic in Ecuador. In this context, the present study aims to assess the concentration of settleable particulate matter in the urban area of Loja and analyze the presence of metals in these particles. This analysis will provide relevant information for the development of environmental monitoring strategies and air pollution control measures, contributing to the reduction in risks associated with prolonged exposure to these contaminants.

2. Materials and Methods

2.1. Study Area

The study area corresponds to the urban area of the city of Loja (Figure 1), located in the southern part of Ecuador at an altitude of 2065 m above sea level (a.s.l.) and an urban area of 57.3 km2 [23].
Ten monitoring points were established for five different land uses (Figure 2), taking into consideration vehicular mobility flows, the busiest avenues, and the activities carried out in the city. The points were distributed as follows: (i) Commercial (CM): considering areas with a predominance of activities related to the exchange of goods and services, such as neighborhood, sectoral, zonal, and city commercial services; (ii) Social Services Equipment (EQ1): considering goods and services related to health, education, culture, recreation, and sports; (iii) Public Services Equipment (EQ2): including services related to the administration and management of the city such as public administration services, funeral services, infrastructure, and transportation facilities; (iv) Industrial (IND): corresponding to settlements intended for the elaboration, transformation, treatment, and manipulation of inputs for the production of goods or material products; and (v) Residential (R1): areas whose main destination is permanent human housing.

2.2. Design and Sampling

SPM collectors (Figure 2) were constructed following Method 502 (Methods of Air Sampling and Analysis, 3rd Edition, Intersociety Committee, 1988, New York, USA) [24,25], in accordance with the Annex 4 of Ministerial Agreement 097-A, which establishes measurement methods for air quality criteria pollutants. The collector structure was built using a 12 mm iron rod, reaching a height of 1.20 m. The main body consisted of a 6″ PVC tube with a height three times its diameter. A fine electro-welded mesh ring was installed at the top to prevent interference from feathers, stones, and leaves. At the base, a 6″ funnel was connected to a 1-gallon collection container, selected for its low surface roughness and reduced likelihood of particle accumulation, ensuring optimal distilled water flow during sample collection.
For installation at monitoring sites, the collectors were placed at heights ranging from 2.4 m to 15 m above ground level in open spaces without nearby obstructions. Samples were collected continuously for 30 days during the period from April to August 2023, following Annex 4 and Method 502. At the end each month, the collectors were rinsed with distilled water to remove any adhered particles before transferring them to the laboratory for analysis. The laboratory phase applied the gravimetric method by measuring weight gain in 47 mm quartz filters (insoluble particles) and porcelain capsules (soluble particles). Filters and capsules were dried in an oven at 105 °C for 45 min and stabilized in a desiccator for 20 min before recording the initial weight.
Collected samples were stirred to ensure homogenization, and adhered residues were scraped off using a stainless steel spatula. The mixture was then sieved through a 1 mm stainless steel mesh to remove impurities. Vacuum filtration was performed, separating the retained particles in microfiber filters and extracting 25 mL of filtrate for porcelain capsules. The filters were dried at 105 °C for 2 h, while the capsules remained until complete evaporation of the liquid. Finally, both samples were stabilized in a desiccator, and their final weight was recorded.
Microfiber filters were used to determine metal content in SPM. After five months of sampling, 50 samples were obtained and calcined in a muffle furnace at 450 °C for 3 h to remove organic matter. Subsequently, microwave-assisted acid digestion (EPA 3052) was performed for siliceous and organic matrices using 9 mL of HNO3 and 1 mL of HF. The digested liquid was then filtered and diluted to 25 mL with distilled water in Falcon tubes for analysis via inductively coupled plasma–optical emission spectroscopy (ICP-OES). Standards of 0.01, 0.1, and 1 ppm were used for the calibration curve [26,27]. The heavy metals analyzed were selected based on urban, industrial, and vehicular activities, focusing on Copper (Cu), Lead (Pb), Cobalt (Co), Cadmium (Cd), Chromium (Cr), Silver (Ag), Arsenic (As), and Mercury (Hg) [28,29].

2.3. Data Analysis

Boxplots were used to visualize the variation in SPMm and metals across land use types and months. The effects of land use and month on the metals present in SPM were modeled using non-parametric Kruskal–Wallis tests because the Shapiro–Wilk test revealed that all heavy metals do not follow a normal distribution (p value < 0.05). Principal Component Analysis (PCA) was applied to visualize whether land use and month influenced the presence of different metals in SPM. To test for significantly different metal concentrations and detect the effects of land use and month, we performed a two-factor permutational multivariate analysis of variance (PERMANOVA) using the Bray–Curtis distance measure and 9999 Monte Carlo permutations. All analyses were calculated utilizing the statistical software R 3.2.2 [30].

3. Results and Discussion

SPM and As differed significantly among land uses; however, the other metals present in sedimentable aerosols (Table 1) showed no clear significant difference (Figure 3).
The metals detected in SPM based on land use (CM, EQ1, EQ2, IND, and R1), shows that only the mass of settleable particulate matter (SPMm) and arsenic (As) exhibited statistically significant differences (Kruskal–Wallis test, p < 0.05). This finding aligns with previous research highlighting As as one of the most critical metals in atmospheric pollution within urban and industrial environments [31]. Regarding As, elevated concentrations in service-equipment (EQ1) zones corroborate studies that associate its release with smelting processes, pesticide application, and the erosion of As-rich soils [32,33], underscoring its marked toxicity and persistence in the environment [34]. Following this pattern, in 44 urban cities in China, Duan and Tan [35] showed that arsenic is a serious air pollution problem. The high variability of SPM can be attributed to anthropogenic factors, including industrial activity, vehicular traffic, and limited vegetative cover in certain areas [36,37]. Conversely, the absence of significant differences for Pb, Co, Cd, Cr, Cu, Ag, and Hg suggests that their concentrations may be influenced by a wide range of common sources (e.g., road dust, vehicular emissions, tire abrasion, and fuel combustion) or by atmospheric dispersion that masks the specific signature of each land use [38,39,40,41]. This pattern of spatial homogeneity is further supported by the principal component analysis, which, according to the reported results, does not yield a clear separation among the different land use categories (Figure 4).
Most metals differed significantly across months; however, SPM, Cr, and Hg metals showed no clear difference (Figure 5).
Comparing the metals across months (April, August, July, June, and May), significant differences in Pb, Co, Cd, Cu, Ag, and As were observed (Kruskal–Wallis, p < 0.05), whereas SPM, Cr, and Hg showed no notable monthly variations. Lead (Pb) exhibited particularly high values in July (up to 33.15 ppm at “Barrio Las Pitas”), aligning with its primary sources in vehicular traffic, leaks of fuels, and lubricants [42,43]. Cobalt (Co) peaked in July as well (21.034 ppm at “UNL”), attributable to both industrial and urban activities, as well as natural combustion processes [44]. Cadmium (Cd) reached a maximum level in April (96.081 ppm at “ILE”), consistent with the literature that links it to industrial operations, cigarette smoke, and fertilizer usage [36]. Furthermore, copper (Cu) exhibited its highest concentration in April (63.85 ppm at “ILE”), in agreement with findings that identify tire abrasion, diesel exhaust, and mechanical workshops as key emission sources [41].
The highest silver (Ag) concentration (1.583 ppm) was recorded in August at “Cantaclaro” (Industrial site), a result associated with mining activities, fuel combustion, and natural erosion of silver-bearing rocks [45]. Meanwhile, arsenic (As) once again presented elevated levels in April (13.723 ppm at “Cantaclaro”), potentially linked to industrial activities and the runoff of sediments during precipitation events [33]. In contrast, SPM, Cr, and Hg remained relatively stable month to month, suggesting that their sources and emission dynamics did not undergo substantial changes during the study period. PCA ordination showed a clear separation between metals present in sedimentable aerosols in the different months; for example, August was influenced by Cd and Ag. For April, the metals present in SPM were Cr, Cu, and As (Figure 6).
This pattern was confirmed by PERMANOVA, which showed that SPM was structured according to the month, and a large component of variation (45% explained variance) was associated with this factor (Table 2).
These outcomes are consistent with complementary studies that also document Pb as the predominant metal across various land uses and over multiple sampling months [46,47]. Although leaded gasoline was phased out in Ecuador in 1998 [48], the persistence of Pb can be explained by the gradual release of historically accumulated deposits in soils and sediments [47]. Moreover, the monthly variability of concentrations aligns with the complexity of atmospheric profiles in Latin America, produced by a convergence of agricultural sources, residual leaded fuels, and the abrasion of construction materials [49]. In this context, several metals (Pb, Cr, Cd, Cu, and Co) can adhere to and be transported alongside SPM, sharing common geochemical interactions [50,51]. The strong relationship between Pb and Cu, for instance, is frequently tied to vehicular emissions and the use of pesticides and fertilizers, practices still observed in nearby agricultural areas and associated with the dispersal of metals in the settleable fraction [52,53,54].
The limitations of our research are related to extending the sampling duration over a full year and recording environmental factors. Therefore, future research should consider incorporating additional variables, particularly meteorological conditions and forest vegetation. Previous studies have reported the influence of temperature and precipitation [55] wind direction and speed [56], seasonality [8], rainfall [57], forest vegetation [58], lichens [59], and bryophytes [60] on SPM and metal concentrations. In addition, future studies could also include other common metals, such as Zinc, Aluminum, and Nickel [56,57,61,62], to complement the findings.

4. Conclusions

The urban area of Loja has SPM across various land uses, containing heavy metals such as lead, cobalt, cadmium, chromium, copper, silver, and arsenic, related to air pollution. Lead is the most prevalent heavy metal in urban zones influenced by constant vehicular traffic and industrial zones, while the most contaminated land use in the urban area of Loja is industrial. Most metals may originate from anthropogenic activities such as high vehicular traffic, the presence of hardware stores and metallurgical industries, poor vehicle maintenance, and wood treatment processes in carpentry. Additionally, several values of settleable particulate matter exceed WHO recommendations, highlighting the need for pollution control and mitigation measures. Most metals showed temporal changes, probably due to increased combustion processes, where a higher percentage representation of metals was clearly observed during the April and August months, which can be explained by the increase in air pollution. Finally, the temporal variation in the metal content in SPM must also be considered in the other months.

Author Contributions

Conceptualization, D.d.P., B.V., and D.M.; methodology, D.d.P., B.V., and D.M.; validation, D.d.P., B.V., and D.M.; formal analysis, D.d.P. and Á.B.; investigation, D.d.P. and Á.B.; data curation, D.d.P. and Á.B.; writing—original draft preparation, D.d.P. and Á.B.; writing—review and editing, D.d.P. and Á.B.; All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the Universidad Técnica Particular de Loja, grant POA-VIN-056.

Data Availability Statement

The original contributions presented in this study are included in the article. Further inquiries can be directed to the corresponding author.

Acknowledgments

We thank the Private Technical University of Loja (UTPL) for funding this Open Access publication.

Conflicts of Interest

The authors declare no conflicts of interest.

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Environments 12 00304 g001
Figure 1. Location of SPM monitoring points in Loja, showing five different land uses.
Figure 1. Location of SPM monitoring points in Loja, showing five different land uses.
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Figure 2. Land use categories for SPM collectors based on Method 502 in the city of Loja.
Figure 2. Land use categories for SPM collectors based on Method 502 in the city of Loja.
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Figure 3. Boxplot of SPMm and metals present in SPM by land uses.
Figure 3. Boxplot of SPMm and metals present in SPM by land uses.
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Figure 4. PCA of SPMm and metals present in SPM by land use.
Figure 4. PCA of SPMm and metals present in SPM by land use.
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Figure 5. Boxplot of SPMm and metals present in SPM by month.
Figure 5. Boxplot of SPMm and metals present in SPM by month.
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Figure 6. PCA of metals present in settleable particulate matter by month.
Figure 6. PCA of metals present in settleable particulate matter by month.
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Table 1. Mean concentration of SPMm and metals across land use categories present in sedimentable aerosols.
Table 1. Mean concentration of SPMm and metals across land use categories present in sedimentable aerosols.
Land UsePointSPMm (mg/cm2)Pb (ppm)Co (ppm)Cd (ppm)Cr (ppm)Cu (ppm)Ag (ppm)As (ppm)
CM10.1516.162.333.548.4512.200.001.95
20.2120.522.894.9312.0610.680.200.00
EQ230.3916.704.931.826.9113.220.092.43
40.4416.022.954.7015.3415.210.220.00
EQ150.2820.614.772.528.1421.890.121.60
60.4115.875.342.0410.7516.460.112.11
IND71.2114.737.983.2436.3823.100.120.00
80.3522.344.0311.6112.5118.700.362.74
R190.4117.102.942.746.219.810.070.00
100.2022.533.272.158.3611.820.050.34
Table 2. Results of two-way PERMANOVA between month and land use according to metals present in sedimentable aerosols.
Table 2. Results of two-way PERMANOVA between month and land use according to metals present in sedimentable aerosols.
FactorDfSSR2F p-Value
Month42.47850.450049.20610.001
Land use40.47590.086421.06420.41
Residual453.02880.54996
Total495.50731
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del Pozo, D.; Valle, B.; Maza, D.; Benítez, Á. Metal Enrichment in Settleable Particulate Matter Associated with Air Pollution in the Andean City of Ecuador. Environments 2025, 12, 304. https://doi.org/10.3390/environments12090304

AMA Style

del Pozo D, Valle B, Maza D, Benítez Á. Metal Enrichment in Settleable Particulate Matter Associated with Air Pollution in the Andean City of Ecuador. Environments. 2025; 12(9):304. https://doi.org/10.3390/environments12090304

Chicago/Turabian Style

del Pozo, David, Bryan Valle, Daniel Maza, and Ángel Benítez. 2025. "Metal Enrichment in Settleable Particulate Matter Associated with Air Pollution in the Andean City of Ecuador" Environments 12, no. 9: 304. https://doi.org/10.3390/environments12090304

APA Style

del Pozo, D., Valle, B., Maza, D., & Benítez, Á. (2025). Metal Enrichment in Settleable Particulate Matter Associated with Air Pollution in the Andean City of Ecuador. Environments, 12(9), 304. https://doi.org/10.3390/environments12090304

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