Occurrence and health risks of heavy metals in plastic-shed soils and vegetables across China

Heavy metal (HM) contamination of plastic-shed vegetable production (PSVP) areas is a great concern in China because of severe soil quality deterioration and the risk of HM accumulation in vegetables. However, the national pollution status and corresponding health risks of HM pollution in Chinese PSVP soils and vegetables are unknown. In this study, a comprehensive investigation of eight HMs (As, Cd, Cr, Cu, Hg, Ni, Pb and, Zn) pollutants and the associated risks in Chinese PSVP systems were conducted based on a database compiled from previous research. The results indicated that the mean concentrations of all eight HMs in plastic-shed soils (PS) were greater than those in adjacent open-field agricultural soils (OS), especially Cd, which exceeded its maximum limited value and had the highest average geo-accumulation index of 1.21. Longer period of PSVP cultivation can lead to soil acidification and higher accumulation of HM in PS. Obvious accumulation of HM has also occurred in vegetables grown in PSVP areas, especially in leafy vegetables. Health risk assessment revealed that enough attention should be paid to the cancer risk posed by ingesting the leafy vegetables grown in PS. Furthermore, Cd was identified as the top priority metal for risk management, followed by Cr, Pb, and Ni. Impact factors analysis indicated that high inputs of fertilizers and fungicides, lagged regulations and standards, inefficacious monitoring and management, and weak environmental awareness are the dominant factors leading to HM accumulation in PSVP systems. In the future PSVP processes, an integrated monitoring, evaluation, and management system should be established to promote a healthy and sustainable development.