Appraisal of Heavy Metals Accumulation, Physiological Response, and Human Health Risks of Five Crop Species Grown at Various Distances from Traffic Highway

Road surfaces and vehicular traffic contribute to heavy metals (HM) contamination of soil and plants, which poses various health risks to humans by entering the food chain. It is imperative to evaluate the status of contamination with HM and associated health risks in soils and plants, especially food crops. In this regard, five crop species, i.e., strawberry (Fragaria ananassa), wheat (Triticum aestivum), tomato (Lycopersicon esculentum), sugar cane (Saccharum officinarum), and tobacco (Nicotiana tabacum), were evaluated at 0–10, 10–50, and 50–100 m distance from the highway near the urban area (Takht Bhai) of Mardan, Khyber Pakhtunkhwa, Pakistan. Lead (Pb) and cadmium (Cd) accumulation, phenolics, carotenoids, chlorophyll, and proline contents in plant parts were assessed. Pb and Cd in plants decreased with an increase in distance. Pb was above the critical limit in all plants except wheat, Cd exceeded the permissible level of the World Health Organization in all plants except wheat and tomato. Pb and Cd were higher in strawberries. Tomato and strawberry fruits, tobacco leaves, and sugarcane stems showed higher Pb contents at a 0–10 m distance. Phenolic contents in leaves were higher than in roots. The target hazard quotient (THQ) in edible parts of most crops has been greater than one, which presents a threat to human health upon consumption. To the best of our knowledge, this study presents the first holistic approach to assess metal contamination in the selected area, its accumulation in field-grown edible crops, and associated health risk.