Unfortunately, vegetables are commonly cultivated with untreated wastewater and consumed by human beings who often ignore their harmful impacts on health. The industrialization and urbanization in developing countries have led to the release of increasing amounts of heavy metals (HM) into the environment. Regular monitoring of metal concentration levels in contaminated soils and edible plants is essential to prevent their excessive build-up in the diet and food chains. This study aimed to determine the concentration and accumulation of selected HM in the soil-plant system from a field located in D.I. Khan, Pakistan. Thereby, determinations of copper (Cu), lead (Pb), cadmium (Cd), chromium (Cr), iron (Fe), nickel (Ni), and cobalt (Co) were assessed in the soil of the field as well as in the roots, stems, leaves, and grains of ridge gourds (RG) and sponge gourds (SG). The gourds were irrigated with untreated wastewater and removed from the soil when completely matured. Their parts were then separated and digested for HM analyses, which were performed by atomic absorption spectrophotometry. Mean HM concentrations of each gourd were compared to each other within the same vegetable or between the vegetables. Intra-analyses depicted a similar quantitative distribution of HM in the RG or SG parts. Independently of the gourds' variety, Fe and Pb were the most concentrated HM, and Pb was particularly concentrated in grains. Mean concentrations of Pb and Co in these vegetables were found to be toxic, since they exceeded the safe limits recommended by the Food and Agriculture Organization/World Health Organization (FAO/WHO). Inter-analyses of HM concentrations performed between RG and SG parts revealed that the mean concentration of Pb was significantly higher in roots of SG compared to that of RG. Nevertheless, mean Cr concentrations were significantly higher in all parts of RG compared to that of SG. The concentrations of Co were insignificantly different between the parts of these two vegetables. Also, the assessment of hyperaccumulation factors demonstrated that these gourds are hyperaccumulators, improper for dietary intake and commercialization, but might be useful for phytoremediation. Taken together, our data shed light on the urgent need for developing sustainable agriculture in Pakistan.
