The Nemerow comprehensive pollution index (NCPI) was calculated to evaluate the contamination status of trace elements in the soils1,33 (Eq. 1). Where Ci is the pollution value of the trace element in the sampling site i. Si is the local background value of the target soil trace elements. The background values of the eight trace elements in Xinjiang are: As (11.20), Cd (0.12), Cr (39.6), Hg (0.02), Pb (13.5), Cu (35.8), Zn (76.8), Ni (26.4) (mg kg−1)34. The classification grades obtained using NCPI are shown in supporting information Table S433.
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