Effects of road traffic on photosynthetic pigments and heavy metal accumulation in tree species of Kumasi Metropolis, Ghana

Abstract

This study was undertaken to examine changes in the content of pigments and accumulation of metals from vehicular pollution in selected species of roadside trees under vehicular pollution. A major arterial road with heavy vehicle emissions in the Kumasi Metropolis was designated as the polluted site, while Kwame Nkrumah University of Science and Technology Campus was designated as the control site. Four tree species (Terminalia catappa, Mangifera indica, Ficus platyphylla and Polyalthia longifolia) selected for the study were well distributed and abundant in the polluted and control sites. Photosynthetic pigments and levels of heavy metals (Pb, Cu, Cd and zinc) were assessed in their leaves. Chlorophyll and carotenoid contents were determined by absorption spectrometry, while the metal accumulation index (MAI) was used to determine the total metal accumulation capacity of the tree species. We observed a reduction in photosynthetic pigments in the leaf samples from the polluted site. Ficus platyphylla had the maximum reduction in total chlorophyll (49.34%), whereas Terminalia catappa recorded the lowest reduction (33.88%). Similarly, the largest decrease (31.58%) of carotenoid content was found in Terminalia catappa trees and the lowest in Polyalthia longifolia (16.67%). The Polyalthia longifolia, Ficus platyphylla and Terminalia catappa leaf samples collected at the polluted site recorded a higher ratio of chlorophyll a/b. Heavy metal (Cu, Pb, Zn and Cd) accumulation in leaf samples was higher in the polluted site than in the control, as expected. The highest metal MAI value was recorded in Mangifera indica (5.35) followed by Polyalthia longifolia with 4.30. The findings from this study specifically demonstrate that air contamination induced by vehicles decreases the level of photosynthetic pigments in trees subjected to roadside emissions. It is clear that both chlorophyll a/b and chlorophyll/carotenoid ratios will act as very useful stress-level markers. Elevated heavy metal levels in the tree species along arterial roadsides indicate that they serve as heavy metals sink. The change in MAI resulting from different pollution burden is an indication that the removal capabilities of the tree species differ from each other. We therefore suggest M. indica and P. longifolia as potential species to be used in air pollution reduction plans in the city.

Variation in Pb and Zn concentrations in different species of trees and shrubs and their organs depending on traffic density

“…It has been determined that Zn concentration in Nerium oleander leaves in different seasons varies between 33-47 million ppb in the control environment, while it varies between 55-75 million ppb in areas with traffic (Santos et al 2019). Similarly, it has been reported in different studies that Zn concentration increases with traffic density (Uka et al 2021). Compared with similar studies, our results show that Pb and Zn concentrations are relatively lower than in polluted areas in other regions but higher than in clean places.…”

“…For instance, the Pb concentration is higher in the samples collected from polluted areas than in the control samples. Pb concentrations were 1,780, 1,750, and 1,280 ppb in the control samples of Terminalia catappa, Mangifera indica, and Polyalthia longfolia species, respectively, while in the samples taken from the polluted areas they reached 3,210, 3,410, 4,680 ppb, respectively (Uka et al 2021). While the background values of Pb content in Platanus orientalis, Robinia pseudoacacia and Ulmus minor leaves amounted 2,700 ppb, it was determined that Pb content increased to 15,700 ppb in areas with heavy traffic and up to 18,800 ppb at Gisha bridge (Abbasi et al 2017).…”

“…In some studies, Pb concentrations were reported to be 11,934.00 ppb in unwashed leaves of Buxus sempervirens (Mossi 2018), 17,900.00 ppb in leaves of Aesculus hippocastanum (Turkyilmaz et al 2020), and 5,077.00 ppb in unwashed branches of Ligustrum vulgare (Sevik et al 2020c). It was pointed out that Pb concentration in plants increased significantly with the traffic density (Uka et al 2021). For instance, the Pb concentration is higher in the samples collected from polluted areas than in the control samples.…”

The Effects Morpho-Anatomical Characters Leaves Tectona grandis and Gmelina arborea as Carbon Dioxide Absorption in Unhas Urban Forest

“…In each leaves plant containing chlorophyll a (C55H72O5N4Mg), dark green and light green leaves containing chlorophyll b (C55H70O6N4Mg), chlorophyll plays an important role in photosynthesis [41], [42], [43]. Leaves exposed to air pollution, such as dust, can be absorbed into the leave stomata, then go to mesophyll tissue, dust that accumulates on mesophyll tissue causes damage to cells that contain chlorophyll, thus affecting photosynthesis [44], [45], [46], [47].…”

Heavy metal absorption in the leaves of evergreen trees (Saraca asoca and Syzygium cumini) in Kanchipuram town, Tamil Nadu, India

“…Plants are greatly used for bio monitoring to trace out the deposition or accumulation of toxic heavy metals and considered as the key element in the environment to minimize the level of pollution IOP Publishing doi:10.1088/1755-1315/1100/1/012018 2 thereby acting as bio indicators of atmospheric pollution. Several parts of the plants were utilized for indicating the background air pollution out of which tree leaves took the significant role as bio monitors for the heavy metals [22,23].…”