Spatial distribution, enrichment and potential sources of seldom monitored trace elements in soils of Yellow River Delta, China

Rapid development of industry and agriculture over the past decades have caused serious environmental impacts on the local environment. However, the spatial distribution, sources and risk assessment of seldom monitored trace elements (SMTEs) in the surface soils of Yellow River Delta (YRD) have rarely been reported. In this study, thirty surface soil samples in YRD were collected, analyzed to determine concentrations of 17 SMTEs, and evaluated based on enrichment factor (EF), geo-accumulation index (Igeo), contamination factor (CF) and pollution load index (PLI). Spatial distribution results indicated that relatively high contents of SMTEs in YRD mainly occurred in the western part and oil field pumping units, which was very likely related to petroleum exploitation and refining industries. In line with spatial distributions, the assessment results using EF, Igeo, CF and PLI observed potential contamination for sampling site f4, f5, f8, f13, f14, f18, f23, f30, f32, f36, f37 and f38, and reported obvious enrichment of Cs, Sn, Th, Tl and U for the surface soils of YRD. According to the multivariate statistical analysis results, 17 kinds of SMTEs could be divided into three clusters and the origins of SMTEs may differ for different clusters. Our results indicated that PC1 scores could be regarded as an "anthropogenic impact factor" and an important proxy to represent possible contamination from SMTEs in YRD. This study provides important information for the contamination status of SMTEs in the surface soils of YRD.