Evaluating the sources and enrichment of rare earth and trace elements in sediment of Little Zab River, Sardasht, Northwest Iran

The geochemistry of rare earth and trace elements in sediments provides insights into their origin and the potential effects of human activity on the river ecosystem. This study examined the concentration, bioavailability, and sources of heavy metals and rare earth elements in sediments of the Little Zab River in West Azerbaijan province (Iran), using a combination of analytical techniques (total concentration and selective extractions) and data analysis (enrichment factors, rare earth anomalies, advanced statistical analysis). Average concentrations of As, Cr, Cu, Fe, Ni, Pb, and Zn were 9.11, 163.71, 37.47, 36,684.3, 99.41, 8.94, and 85.76 mg/kg, respectively, with nearly half existing in the residual phase, therefore non-bioavailable. The Positive Matrix Factorization (PMF) model identified four factors reflecting semi-natural, urban, agricultural, and industrial origins, beside a shared urban-agricultural source for heavy metals. Cr and Ni showed higher concentrations than guideline values in most sampling stations (even in the upstream sample). Total REE concentrations ranged from 88.6 to 173.5 mg/kg, averaging 127.6 mg/kg, with a positive Eu anomaly. Correlation analysis and comparisons to European shale and continental crust standards suggested a terrestrial origin for the REEs. These findings indicate that urban and agricultural activities around the Little Zab River have not significantly disrupted its natural ecosystem. However, it is shared between different countries and is prone to transboundary pollution.