A meta-analysis of influencing factors on soil pollution around copper smelting sites

Non-ferrous smelting activities have caused serious heavy metal(loid) pollution in soil which seriously threatens human health globally. A number of studies have been conducted to assess the characteristics and risks of soil heavy metal(loid) pollution around copper (Cu) smelting sites. However, the current research mainly focuses on soil pollution around a single smelter, and the global impact of Cu smelting on soil and its quantitative relationship with related factors need to be further studied. Meta-analysis can integrate a large amount of data and quantitatively analyze the relationship between multiple factors. To investigate the extent to which Cu smelting sites have contributed to heavy metal(loid) pollution in soils, a meta-analysis was conducted on 189 research publications from 1993 to 2023. Furthermore, a single meta regression was used to analyze the relationship between the soil heavy metal(loid)s (HMs) and influencing factors on a global scale. The results of meta-regression analysis showed that compared with the soil background value, Cu smelting significantly increased the concentration of HMs in soil (315%), with the concentration increase for each heavy metal(loid) being: Cu (1012%) > Cd (622%) > As (315%) > Pb (277%) > Zn (188%) > Cr (96%) > Ni (95%) > Mn (45%). Among these, Cu, Cd, and As were the major pollutants in soils around Cu smelting sites. Land use type was a key factor affecting HMs concentrations in surrounding soils, and the influence of non-agricultural land (381%) was greater than that of agricultural land (203%). In addition, the influence of Cu smelting on HMs were negatively correlated with distance (Q_M=9.86) and positively correlated with latitude (Q_M=10.7). There was no significant correlation between heavy metal(loid) pollution and soil chemical properties, average annual rainfall and temperature, longitude, or other factors. Our work may be meaningful to the risk control and remediation for Cu smelting sites.