Xanthium strumarium L. an Alien Invasive Species in Khyber Pakhtunkhwa (Pakistan): A Tool for Biomonitoring and Environmental Risk Assessment of Heavy Metal Pollutants

In this study, X. strumarium L., an alien invasive species, was used for the first time as a biomonitor of selected heavy metals (Pb, Cd, Zn, and Cu) in Khyber Pakhtunkhwa, Pakistan. The soil and plant samples were collected from 15 locations categorized as roads, urban, and rural sites based on origin and intensity of the heavy metals for comparison. All the metal concentrations were quantified from the acid-digested samples using atomic absorption spectrophotometer (AAS) to achieve accurate and reliable results. As expected, we found a decreasing trend in heavy metal concentrations in soils and plants from roads to rural control sites (ordered as road > urban > rural). Pearson's correlation analysis was carried out to explore the origin of heavy metals contaminants. We found road traffic vehicles and smelter emissions to be the key drivers, followed by anthropogenic sources such as industrial and domestic wastewater and crush plants. Considering the environmental toxicity of HMs, Cd concentration was above the permissible limit proposed by World Health Organization (WHO), allowing us to forewarn the residents about its potential health risks. This work exposed that X. strumarium appears as a suitable bioindicator based on its strong metal accumulation capacity. Likewise, we concluded that other invasive species could also be utilized for biomonitoring to improve our understanding of the environment's quality more profitably in the region.