Long-term orchard practice affects the ecological and human health risk of soil heavy metals in a calcareous environment

The contamination of agroecosystems with heavy metals, caused by the long-term agricultural practices (e.g., the application of extensive agrochemical), has become a high-priority issue for soil-food-human health. Our study aimed to estimate the effect of the agricultural activities on contamination severity and health risk potential of heavy metals in the soil-urban apple orchards versus control soils across various soil types and apple cultivars. This research assessed pollution index (PI), pollution load index (PLI), ecological risk (ER), bio-concentration factor (BCF), hazard quotient (HQ), and overall hazard index (HI). The results revealed a significant increase in the concentration of all metals of the orchard soils, ranging 30-51%, 19-24%, 70-137%, 25-33%, and 16-23% for Zn, Cu, Cd, Pb, and Ni, respectively, versus those in the control soils. Compared to the control soils, PI, PLI, and ER reflected a significant increase in the orchard soils ranging 13-67%, 18-45%, and 18-33%, respectively, which has downgraded their scoring class by one grade. Cd and Pb were not detected in the samples collected from the apple cultivars 'Golden Delicious' (GD) and 'Red Delicious' (RD), indicating no toxic levels of Cd and Pb. Compared to the GD, the concentration of Zn, Cu, and Ni was comparatively higher in RD, implying varying heavy metal accumulation potentials in two different apple cultivars. The mean HQ and HI were in the low category (0.1 <= HQ and HI < 1) in both GD and RD cultivars, meaning that GD and RD are safe for local residents to be consumed and do not pose a significant potential risk to the health of consumers. However, HQ and HI were significantly higher in the RD cultivar than in the GD cultivar in most apple samples.