Exploration and impacts of vehicular-borne potentially toxic elements (VB-PTEs) on Calotropis procera (Aiton) W.T.Aiton: A bioindicator approach

Abstract

• C. procera at high-traffic sites showed higher PTEs, with washing affecting concentrations. • BCF >1 revealed significant uptake of Pb, Cd, Cr, Mn, and Cu. • High traffic density areas showed reduced leaf area, thickness, and stomatal size. • PCA revealed significant correlations between PTEs and morphological traits. • Antioxidant potential and ascorbic acid levels increased in high-density sites. • C. procera is an effective bioindicator of vehicular pollution with high roadside PTE tolerance . This study investigates potentially toxic elements (PTEs) concentrations in both washed and unwashed leaves of Calotropis procera and in the soil near its roots along roadsides with varying vehicular traffic densities. Additionally, it explores the plant's physiological, biochemical, and morpho-anatomical responses to PTEs exposure. Samples of unwashed and washed leaves from roadside areas with very high, high, medium, and low traffic densities, as well as control sites located 100–500 m away from roads, were analyzed for PTEs concentrations, physicochemical properties and morpho-anatomical characteristics. A paired sample t-test revealed significant differences ( p < 0.05) in PTEs concentrations, except for Mn, with higher levels in unwashed leaves compared to washed ones. The highest PTEs concentrations were observed in areas with very high traffic density (VHD), followed by high-density (HD), moderate (MD), and low-density (LD) areas. The study also explored the role of soil as a sink for these contaminants, revealing a strong positive correlation between vehicular density and PTEs level in soil. The bioaccumulation factor (BCF) indicated significant uptake of Pb, Cd, Cr, Mn, and Cu, with lower values for other elements. The study also assessed physiological and biochemical parameters, including chlorophyll content, ascorbic acid, antioxidant potential, and membrane stability index, all of which showed significant variations across sites with different traffic densities. Morphological and anatomical variations, such as reductions in leaf area, leaf thickness, and stomatal dimensions, were observed in polluted areas. Principal Component Analysis (PCA) highlighted the correlations between PTEs, morphological traits, and vehicular density, with notable negative effects at high traffic sites. In conclusion, C. procera is an effective phyto-accumulator and bioindicator of PTEs pollution, with high ecological adaptability, making it suitable for phytoremediation and pollution monitoring. This study highlights the impact of vehicular pollution on plant health and stresses the importance of monitoring these factors for environmental management.