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.
Highlights
Because of the rapid economic growth, social linkage and spread activities, transportation is the pillar of accessibility systems
The percentage reduction of chlorophyll ‘b’ content in the leaves of the studied tree species is in this order: Ficus Platyphylla 63.23%, Polyalthia longifolia 46.51%, Terminalia catappa 39.13% and Mangifera indica, 35.85% (Table 2)
A reduction in total chlorophyll content in the samples from polluted sites was observed with Polyalthia longifolia having 47.42% reduction, Mangifera indica, a decrease of 35.85%, Terminalia catappa having 33.88% reduction, Ficus Platyphylla 21.05%
Summary
Because of the rapid economic growth, social linkage and spread activities, transportation is the pillar of accessibility systems. It is a decisive factor of economic growth and social interactions in most countries. Motor vehicles emit significant amounts of CO, SOx, NOx, VOCs, HC, NOx, Cu, Cd, Co, Cr and Pb, responsible for 60–70% of urban air pollution [15, 18, 49]. Most of these pollutants found in the cities can be removed from
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