Mobile Soil Fraction and Crop-Tissue Concentrations of Cd, Pb, Cu, and Zn in Agricultural Fields of an Industrial Region of East Kazakhstan: A Descriptive Field Survey

Data relating the plant-available soil fraction of potentially toxic elements (PTEs) to their concentrations in crops are scarce for agricultural land in the industrial regions of Central Asia. This descriptive field survey compares Cd, Pb, Cu, and Zn extracted from the arable horizon with ammonium acetate buffer (pH 4.8) with their concentrations in the roots, stems, leaves, and harvested organs of crops grown on four fields in East Kazakhstan, with a fifth field as a comparison location. Each field carried a different crop and was represented by composite samples, so no between-field difference is attributed to a source. Extractable concentrations were below national hygienic limits for Cd, Pb, Zn, Ni, Cr, and Co, whereas Cu exceeded its limit at three fields by factors of 1.1–1.6. In contrast, Cu, Zn, Pb, and Cd exceeded crop- and organ-specific reference ranges in 29, 27, 27, and 24 of 29 tissue samples, respectively, and tissue Cd increased from summer to autumn in all four paired fields (1.6–2.7-fold). Harmonized Landsat and Sentinel-2 vegetation indices followed crop phenology. The results provide a regional baseline and specify the replicated design required for confirmatory sampling.