Distribution characteristics and sources of soil heavy metals in soils in the area of northeastern Huludao City

Land quality geochemical assessment at a scale of 1: 250, 000 was carried out in the Longgang, Lianshan and Nanpiao districts in the northeast Huludao city, which is a typical industrial and mining city in Liaoning Province. Topsoil, deep soil, and samples from vertical profile were collected in the study area. To determine the dynamics of the soil heavy metals distribution patterns, concentrations and species of eight elements in samples of seven different size fractions were used. The results show that the average content of eight soil heavy metals in the topsoil and deep soils of the study area was higher than the background values of them in Liaoning Province, and the high concentrations of Cd, Cu, Pb, Zn, Hg, As in topsoil were delineated along the coast and inland areas of Longgang District. The high-value areas of Ni and Cr were mainly distributed above the Lower Cretaceous and Middle Jurassic volcanic rock strata. The average value of the enrichment coefficient of each heavy metal was Cd> Hg> Pb> Zn> As> Cu> Cr> Ni. Cd and Hg were strongly enriched in large areas in the study area with the average value of the enrichment coefficient 3.41 and Hg 2.93 respectively. Cd in soil is mainly in ion exchange fraction with the highest ecological risk, accounting for 54.38% of the total amount. In the soil profile, Cd, Pb, Hg and Zn show the characteristics of surface aggregation, while Cu, As, Cr and Ni show curves with a steady change. The distribution of heavy metals in soil was spatially consistent with that of parent material. The average value of the single pollution index of each heavy metal is Cd> Zn> Cu> Pb> Cr> Ni> As> Hg, of which Cd pollution level is higher. It is indicated that the distribution of Zn, Cu, Cd, As and Pb in topsoil are mainly affected by human activities such as industry, transportation, life and mining. The distribution of Cr and Ni are mainly parallel with geological background. High concentrations of Hg in soil are primarily caused by coal combustion. © 2021, Editorial Board of China Environmental Science. All right reserved.