Detecting Heavy Metal Pollution in an Organized Industrial Zone: Soil–Plant Accumulation Patterns in a Medicinal Plant (Calamintha nepeta subsp. glandulosa) and Associated Health and Environmental Risk Implications

Dilovasi district of Kocaeli is one of the largest industrial regions, and due to its high production capacity and industrial waste, the soil heavy metal levels in this region are exceptionally high. Consequently, this study focuses on essential elements (B, Ca, Cr, Cu, Fe, K, Mg, Mn, Na, Ni, Zn) and non-essential elements that are considered toxic to humans (Al, Cd, Pb), covering a total of thirteen elements. Accordingly, this study aims to highlight the degree of pollution in a Turkish Organized Industrial Zone located in the Dilovasi district of Kocaeli by quantifying the concentrations of the aforementioned elements in <i>Calamintha nepeta</i> subsp. <i>glandulosa</i> plants and soil samples, and by assessing their potential implications for human health. Significant accumulation of heavy metals in both soils and plant parts suggests that metal contamination, especially that of Fe (up to 1009.2 mg kg^-1), is a matter of great concern in the Dilovasi district. The results revealed that the concentrations (mg kg^-1) of Cr (23.0 ± 0.1), Fe (1292.5 ± 5.6), Pb (36.9 ± 0.1), Zn (151.2 ± 0.8), and Cd (3.6 ± 0.1) were considerably higher. However, the concentrations of Cu, Mn, and Ni were found to be within the permissible limits in accordance with the American Herbal Products Association and the World Health Organization referenced guideline values. Furthermore, heavy metal concentrations in <i>C. nepeta</i> subsp. <i>glandulosa</i> were generally higher in areas characterized by elevated soil metal levels, indicating a clear correspondence between soil contamination and plant metal content. Based on these findings, <i>C. nepeta</i> subsp. <i>glandulosa</i>, a plant with culinary and medicinal value, can be considered a useful bioindicator for assessing local heavy metal contamination.