## 1 Introduction  
Heavy metal (HM) pollution has spread across the biosphere, making it a serious worldwide concern because of its risk to humans and animals [1, 2]. Various anthropogenic activities are mostly related to urban--rural gradients and industrialization, such as mining, application of fertilizers, smelting and industrial manufacturing processes, which can lead to the release of the HMs into the environment [3, 4, 5]. HMs are a serious matter of concern as these elements are non-biodegradable and persist in the soil for a much longer time than in other parts of the environment [6, 7]. High concentrations of toxic metals, includingZn, Cu, and Cd are mostly due to human activities [8; 9]. Metal contamination in the environment would affect the diversity, microbial properties, and functional diversity of soils [10; 11]. Moreover, increased concentration of metal in the soils can be transferred and deposited into plants and likewise to human beings, producing numerous serious health disorders [6; 12].  
Numerous tools for remediation of contaminated soils have been undertaken, such as chemical/physical treatment and excavation of contaminated material. However, significant efforts have been made lately to identify cost-effective solutions for remediation of HMs-contaminated soil [13; 14; 15]. Recently, these cost-effective approaches, such as phytoremediation, have become a subject of public and scientific interest to alleviate HM pollutants from the soil, water, and air [16; 17; 18]. Phytoremediation is the use of plants to remove contamination from the soil, sediments, and water [19]. Metal hyperaccumulator plant species have been reported, but they are slow-growing, less abundant, and produce little biomass [20; 21]. Phytoremediation treatments may be more successful if native plant species can overcome these hurdles. Native plants are frequently efficient in growth, reproduction, and survival when faced with challenging circumstances [22; 23]. Therefore, the search for native plants with phytoremediation potential is important and continues [24; 25].  
A few natural, well-adapted plants have been utilized extensively for HM phytoremediation applications, including lemongrass (vetiver), Siam weed, wild grasses, Crotalaria, Avena, and Sesbania species [26; 27; 28]. _C. procera_, a traditional medicinal plant that may accumulate considerable amounts of HMs [29; 30], is a dominating species in Khyber Pakhtunkhwa, and has been evaluated for its phytoremediation potential in this study. Furthermore, _C. procera_ was chosen as a HMs pollution biomonitor for a variety of reasons: it may be found on the roadside, in urban and rural regions; it has a wide geographical range and ecological distribution; and sampling, identification, and cultivation are simple and inexpensive [29; 31].  
The World Health Organization (WHO) and the United States Environmental Protection Agency (USEPA) have recognized strict criteria for maximum acceptable limits for accumulation of HMs in soil. Toxicant levels in urban soils have been closely monitored and extensively recorded in developed nations, such as North America and Europe [32; 33], Still, HM pollution and remediation data are critically deficient in underdeveloped countries. The lack of funds for other treatments makes phytoremediation especially well-suited to these developing nations, where labour, knowledge, and cost-cutting measures are crucial [31]. This study was carried out to fill the gap by presenting a thorough picture of HM contamination in the semi-arid region of Khyber Pakhtunkhwa, as well as identifying prospective candidate species for effective, practical phytoremediation. The present study aims to investigate the toxic levels of Zn, Pb, Cu, and Cd using _C. procera_ L. as a bioindicator; and to evaluate the extent of metal accumulation potential of _C. procera_ in Khyber Pakhtunkhwa, Pakistan.