Mobility and bioavailability of selected trace elements in Mediterranean red soil amended with phosphate fertilizers: Experimental study

Trace element (TE) distribution and mobility were monitored in a typical profile of Mediterranean red soil massively amended with phosphate fertilizers (PFs), over a period of 15 months. Samples of soil (across a depth of 55 cm) and entire plants (roots and shoots), collected at different points in time, in addition to PF samples, were analyzed for TEs (Cu, Cd, Zn, and Pb) concentrations, sequentially extracted, and examined under a Scanning Electron Microscopy (SEM) coupled with an Energy Dispersive X-ray Spectrometer (EDX). Results showed peaks in TE mean concentrations (Cu: 43.13, Cd: 0.52, Zn: 116.36, and Pb: 14.92 mg kg− 1) in the soil profile 4 months following PF application, but they did not reach harmful levels. Sequential extractions revealed that the studied TEs were transferred from residual to exchangeable fractions in the amended soil profile (except for Cd), which may consequently lead to their transfer to the saturated zone. The order of TE mobility was: Zn > Cd > Cu > Pb. Amended-soil plants, Cichorium intybus L, accumulated higher TE concentrations (Cu: 9.67, Cd: 0.37, Zn: 13.81, and Pb: 2.58 mg kg− 1) than the reference plants, but they remained within normal reported levels for plants (Cu: 3–20, Cd: 0.5–1.0, Zn: 15–150, and Pb: 2–5 mg kg− 1). Soil–plant transfer factor was notably affected by PF application, with highest acquired values being for Cd. Evidence of fluorine presence was detected by SEM in the amended soil, which should be a matter of concern in PF application.