Assessing Seasonal Concentrations of Airborne Potentially Toxic Elements in Tropical Mountain Areas in Thailand Using the Transplanted Lichen Parmotrema Tinctorum (Despr. ex Nyl.) Hale

By inergency On Mar 19, 2023

Assessing Seasonal Concentrations of Airborne Potentially Toxic Elements in Tropical Mountain Areas in Thailand Using the Transplanted Lichen Parmotrema Tinctorum (Despr. ex Nyl.) Hale

3.2. Contamination Levels of Each Element in the Studied Sites

The contamination level of each PTE at each site was estimated using a CF value, which was based on the average concentration of each PTE found in the transplanted lichen P. tinctorum at the cleanest site of each park (KYC, DI1). At the KYNP, a total of 120 CFs from all PTEs at all monitoring sites (KY1–KY8) recorded during the rainy season were classified as showing no (14%), light (22%), medium (25%), and heavy (39%) contamination, while those recorded during the dry season were classified as showing no (6%), light (20%), medium (22%), and heavy (52%) contamination (Table 3). The PTE showing the highest contamination as indicated by the average CFs from all sites (excluding KYC) and seasons was Pb (6.19), followed by Cd (5.21), Co (5.15), Cr (4.96), Ni (4.58), Mo (4.07), As (3.79), Sb (3.54), V (3.46), Al (3.42), Cu (2.37), Fe (2.29), Mn (2.09), Ti (1.87), and Zn (1.08). All elements, except Zn, showed heavy contamination (CF > 3) at some sites, especially at the park entrances (KY7, KY8). At the DINP, the CFs from all monitoring sites recorded during the rainy season were categorized as showing no (24%), light (30%), medium (17%), and heavy (29%) contamination, while those recorded during the dry season were grouped as no (16%), light (27%), medium (26%), and heavy (31%) contamination. The PTE showing the highest contamination as indicated by the average CFs from all sites (excluding DIC) and seasons was Mo (4.58), followed by Pb (3.56), Ni (3.50), Cr (3.26), Cd (2.76), Sb (2.59), Al (2.49), Co (2.39), V (2.30), As (2.10), Mn (2.06), Ti (1.98), Fe (1.93), Cu (1.48), and Zn (1.37). All elements, except Cu, Fe, and Zn, showed heavy contamination at some sites, especially at sites close to the communities and park office (DI6, DI7). The range of the CF of each PTE from all monitoring sites in each park were illustrated in Table 4.

The PTEs in the air of the studied parks can originate from several sources. Tourism contribute PTEs through traffic vehicles and tourist activities such as cigarette smoking and camping [1,3,5,10,42]. Local anthropogenic sources include fossil fuel combustion by automobiles, agricultural activity, and open burning, while natural sources include rock and soil weathering, forest fire, wind-blown dust, and the decomposition of dead materials [6,13]. Irrespective of emission sources, these elements can be toxic to human health and organisms in ecosystems. Previous studies reported that the concentrations of some PTEs, including Co, Cu, Fe, Mn, Ni, Pb, and Zn, in the lichens Ramalina celastri and Usnea amblyoclada were correlated with pharyngitis, tonsilitis, asthma, laryngitis, and allergic rhinitis in children under six years old [43]. In addition, the concentration of Co in the lichen Canoparmelia texana was linked with cardiovascular diseases in adults [44]. The effects of each PTE on human health and plants were partly summarized in Table 5.

3.3. Air Pollution Level at Each Monitoring Site

The level of air pollution based on the 15 investigated PTEs at each site, season, and park was revealed by the PLI. This index is frequently used to estimate air pollution loads at the studied sites in previous studies [27,38,39,40,41,78]. At the KYNP, the PLIs at all sites during the dry season were higher than those during the rainy season (Figure 6a), which indicated higher pollution loads during the dry season. During the dry season, the lowest PLI (1.05) was observed at the control site (KYC) and was classified as no pollution, while the PLIs at eight monitoring sites ranged from 1.55 to 5.73 (mean of 3.58) and were classified as medium to very high pollution. During the rainy season, the PLI was also lowest at the control site (0.95) and was grouped as no pollution, whereas the PLIs at the other sites ranged from 1.25 to 4.34 (mean of 2.73) and were categorized as light to very high pollution (Table 3). The slightly higher PLI at the KYC during the dry season compared to the rainy season probably came from natural origins such as rock and soil weathering, wind-blown dust, and the decomposition of dead materials. In addition, rainfall and air humidity were also the main factors that determined the concentrations of air pollutants. Rainfall can remove pollutants from the air, and air humidity can reduce the resuspension of soil dust and the diffusion of air pollutants. The different gaps in the PLIs between the rainy and dry seasons at the monitoring sites (Figure 6c) probably originated from natural origins, road traffic, and tourist activities. The numbers of visitors and vehicles during the dry season were approximately 2.7 and 2.1 times higher at the KYNP and DINP (Table 2), respectively, than those during the rainy season. Automobiles release elemental pollutants into the air via fossil fuel combustion, brake abrasives, clutch systems, tire wear, engines and components, road damage, and the resuspension of soil dust [22,79,80]. In addition, tourist activities such as cigarette smoking and camping might contribute some pollutants to the air [10]. Excluding the KYC, the lowest PLI was observed at the summit site (KY1), and it then increased at the lower elevation sites and was highest at the park entrances (KY7, KY8). These two sites were located closer to communities, urban areas, and roads, and had higher number of automobiles. The average PLIs of all sites in both seasons in descending order were as follows: KY8 > KY7 > KY4 > KY6 > KY5 > KY3 > KY2 > KY1 > KYC. The PLIs of four sites, KY4, KY6, KY7, and KY8, were estimated as having very high pollution during both seasons, while KY3 and KY5 showed very high pollution during the dry season. The category of no pollution was not found from all eight monitoring sites, and the light pollution category was only observed at the summit site, KY1, and during the rainy season.

The PLIs at all sites in the DINP were also higher during the dry season than during the rainy season (Figure 6b). The numbers of visitors and vehicles were higher during the dry season (Table 2). During the dry season, the lowest PLI was found at the summit site, DI1 (1.16), and was grouped as no pollution. The PLIs at all monitoring sites (including DI1) ranged from 1.16 to 4.43 (mean of 2.59) and were classified as having no to very high pollution. During the rainy season, the PLI was lowest at the DI1 (0.80) as well and was classified as no pollution. Meanwhile, the PLIs at all monitoring site ranged from 0.80 to 3.92 (mean of 2.16) and showed no to very high pollution. Unexpectedly, the PLIs at the original assigned control site (DIC) were the third lowest in both seasons, after DI1 and DI2. Because this site was located inside the forest with dense canopy and approximately 600 m far from the main road, the contamination of the PTEs at this site probably originated from the natural source as mentioned earlier. The average CFs of all PTEs and seasons at the DI1 were close to those at the KYC (the control site at KYNP). Therefore, the baseline of atmospheric contamination caused by the investigated PTEs in this park was considered at the DI1 instead. The higher PLI recorded at the DIC during the dry season than during the rainy season probably came from natural origins, as occurred in the KYNP. The higher different gaps in the PLIs at DI6 and DI7 compared to the other sites indicated more impacts from road traffic and human activities (Figure 6d). These sites were located close to the local communities, local market, and park office, and they had a higher traffic density. The average PLIs of all sites in both seasons in descending order were as follows: DI7 > DI6 > DI3 > DI8 > DI5 > DI4 > DIC > DI2 > DI1. The PLIs of three sites, DI3, DI6 and DI7, were estimated as having very high pollution in both seasons, and DI8 showed very high pollution during the dry season. The category of no pollution was observed at DI1 and DI2, and the light pollution could be found at DIC, DI2 and DI4.

The higher atmospheric contamination caused by the investigated PTEs during the dry season were clearly demonstrated in both mountains. This season obviously had the higher number of visitors and vehicles; thus, this contamination may have come from road traffic and tourist activities. Moreover, locations that had higher traffic vehicles and tourist’s activities also showed higher pollution loads as indicated by the PLIs. This finding can indicate the impact of tourism on atmospheric contamination in natural areas. The monitoring sites were designed to locate the roadside from the park entrances to the summit points; therefore, the obtained data can reveal the atmospheric contamination in the ecosystems and communities along the roads. Forest ecosystems were located alongside the roads, and most of the monitoring sites were located at forest edges; thus, this result can indicate forest edge contamination. Several organisms, such as flowering plants, bryophytes, ferns, lichens, fungi, and animals, were found at these forest edges. Air pollution can destroy them, especially the sensitive groups, such as lichens and bryophytes. In addition, the air quality of the nearby communities was also affected. Overall, the result of this study can be used for planning and managing tourism in parks for the sustainability of natural areas and for protecting human health.

This study was performed during the COVID-19 pandemic in Thailand, which restricted the numbers of visitors and vehicles in parks. At the KYNP, the numbers of visitors and vehicles were approximately 35% and 16% lower during the rainy season and 10% and 6% lower during the dry season, respectively, than those in 2019 before the COVID-19 pandemic in Thailand. Moreover, at the DINP, the numbers of visitors and vehicles were approximately 99.9% and 100% lower during the rainy season and 48% and 37% lower during the dry season, respectively, than those in 2019. The pollution level might be different when tourism is in full swing; thus, reinvestigation is needed to reveal the air pollution situation during the time of normal tourism activity in parks. This study confirms that the air of the mountain areas can be contaminated by PTEs of both natural and anthropogenic origins. Thus, the appropriate planning and management of tourism and human activities in naturally revered areas will promote good health and sustainable ecosystems. There are several pollutants emitted from automobiles, such as NO₂, SO₂, PAHs, VOCs, and other PTEs, and measuring these pollutants will reveal the overall air quality in parks. The extent of air pollutant diffusion and monitoring inside forests should be investigated to estimate forest contamination. Lastly, air quality can change with space and time, and regular measurements are necessary for a sustainable environment in natural areas.