The results show an increasing trend for Cd (p < 0.05; 0.0081 mg kg1 year1), a decreasing
trend for Cu (p < 0.05; -0.80 mg kg1 year1), and no significant trend for Pb (p ¼ 0.155), Zn (p ¼ 0.746),and Ni (p ¼ 0.305). The increasing rate of Cd from the meta-analysis is consistent with the rate (0.0013 mg kg1 year1) derived from the mass balance calculation for Cd, where atmospheric deposition originated from intensive coal combustion is considered as the main source of Cd in the topsoil. The decreasing trend of Cu is likely due to largely reduced application of copper-based agrochemicals.Environmental regulation and soil remediation are needed to protect food safety and ecosystem from heavy metal pollution, especially Cd.