Bioaccumulation and risk assessment of potential toxic elements in the soil-vegetable system as influenced by historical wastewater irrigation

To investigate the pollution status and probable health risk of potential toxic elements (PTEs) in soil and vegetables in historical wastewater irrigation region, eight types of vegetables (n = 73) and corresponding soils were collected to determine the contents of Pb, Cd, Cu, Zn, Ni and Cr, and their potential health risk to local vegetable consumers. The results showed that the mean contents of Pb, Cd, Cu, Zn, Ni and Cr in these soils were 39.72, 1.06, 38.47, 255.00, 27.45 and 61.83 mg/kg, respectively, with Cd exceeding the national standard of China (0.6 mg/kg, GB 15618–2018). Nemerow integrated pollution indices revealed that more than 50% of these soils were slightly or moderately polluted. The activity ratios of Pb, Cd, Cu and Zn ranged from 0.18 to 0.26, which was much higher than that of Ni and Cr. The average PTEs in vegetables were all within the limitation of China or FAO/WHO (except for Pb). However, the PTEs accumulation capacity in different vegetables varied greatly, with the bioaccumulation factor of cilantro (0.023, 0.232, 0.031, 0.063, 0.009 and 0.007 for Pb, Cd, Cu, Zn, Ni and Cr) and white radish (0.004, 0.058, 0.008, 0.021, 0.003 and 0.002 for Pb, Cd, Cu, Zn, Ni and Cr) being the highest and lowest, respectively. Health risk assessment revealed that local residents suffered both non-carcinogenic and carcinogenic risk, with the hazard index (HI) ranging from 0.73 to 2.45 and 2.02–6.53, and the target carcinogenic risk (TCR) ranging from 2.22 × 10−3 to 5.92 × 10−3 and 6.67 × 10−3 to 1.70 × 10−2 for adults and children, respectively. Pb and Cd contributed more than 62.37% of the HI, and Cd contributed more than 79.42% of the TCR. These results indicate that historical wastewater irrigation has a long-term impact on local food safety and potentially adverse consequences for human health.