Assessment of metal pollution caused by automobiles and its effects on physiological and biochemical aspects of roadside plants

Abstract

Emissions of metal pollutants from automotive activities along roadside is currently considerably influencing on human health. Plant leaves prove a sink and good indicators for metal pollutants. Hence, this study examined the level of metallic ions in plants and soil along Faisalabad-Gojra Motorway and Gojra-Jhang Road with diverse traffic densities varying spatio-temporally (2017-2018). The metal contents (Pb, Cd, Cu and Zn) were analyzed in plants, soil and petroleum samples by atomic absorption spectrophotometer. Physiological and biochemical attributes i.e. gas exchange, photosynthetic pigments, organic osmotica, reactive oxygen species and antioxidants of collected leaves samples of (Calotropis procera L., Xanthium strumarium L., Cynodon dactylon L., Parthenium hysterophorus L., Withania somnifera L., and Datura alba L.) were also examined. Metal content in soil and plant samples along roadside significantly varied compared to control (away from road edge). The metal contamination varied among seasons i.e. summer>autumn>spring>winter. The order for pollution of metals was recorded along roadside i.e. Zn>Cu>Pb>Cd. Among roads GJR had higher mean of metals compared to M-4 due to difference in roads condition and traffic density. The concentration of these metals in plants and soil of various sites during different seasons were positively correlated with traffic density. Metal pollutants reduces photosynthetic pigments total soluble proteins, total soluble sugars, rate of transpiration stomatal conductance and rate of photosynthesis. However, a stimulatory response was recorded for total free amino acids, total phenolics content, hydrogen peroxide, peroxidase and superoxide dismutase enzymes, malondialdehyde, sub stomatal CO2 Conc. and water use efficiency. Among wild plants species Calotropis procera plant leaves showed higher concentration metals (Pb, Cd and Cu) while, Withania somnifera plant showed more Zn content, therefore, these wild plants in future used as indicators of metal pollution.