Spatial Distribution and Source Identification of Trace Metals in Topsoil in Nanyang City, Henan Province, China

Trace metals (TMs) in soil have garnered widespread attention due to their adverse impacts on crop production and human health. In this study, 385 topsoil samples (0–20 cm) and 118 deep soil samples (150–200 cm) were collected from Nanyang City to investigate the spatial distribution, contamination, and source allocation of TMs. Geographic information system analysis, contamination factor (CF), geo-accumulation index (I_geo), and positive matrix factorization (PMF) model were utilized. The results showed that the mean contents of Cu, Hg, Pb, and Zn in the study area's topsoil (25.50, 0.035, 28.51, and 79.46 mg kg⁻¹) exceeded background values. CF and I_geo results indicated that over 60% of soil samples were contaminated by Hg, the main contaminant in soil. By combining correlation and PMF analysis, three sources of TMs were identified for (a) Pb (75.4%), Hg (63.7%), and Zn (55.6%), primarily associated with industrial emissions and atmospheric deposition; (b) Co (57.5%), Cr (50.8%), Cu (59.2%), and Ni (46.4%) mainly originated from natural sources; and (c) As (72.8%) primarily from agricultural activities. The proportions of the three sources were 36.27%, 39.76%, and 23.97%, respectively. Anthropogenic sources contributed the most to soil TMs (60.24%), higher than natural sources, indicating substantial accumulation of TMs in topsoil due to significant anthropogenic activities. This study provided useful information for environmental management planning, decision-making, and contamination assessment.