Assessment of iron-based and calcium-phosphate nanomaterials for immobilisation of potentially toxic elements in soils from a shooting range berm

Abstract

Shooting range facilities in military areas have been indicated as a hotspot of land degradation with high contents of Potentially Toxic Elements (PTEs). Currently, based on the new nanomaterials with specific characteristics, nanoremediation technologies are used to immobilise and to reduce the availability of PTEs in field and laboratory conditions. In this study, the effects of nano-hydroxyapatite and/or hematite on PTEs immobilisation (As, Cd, Cu, Pb, Sb and Zn) in military shooting range soils were assessed through the measure of available and leachable forms with three single-extractions: calcium chloride (0.01M CaCl2), low molecular weight organic acids (10 mM LMWOAs) and toxicity characteristic leaching procedure (TCLP). A sequential chemical extraction was used to determine the distribution of the PTEs in the different geochemical phases of the soils before and after the nanomaterial treatments. Results showed that the availability of PTEs decreased, especially for Pb (40–95%) and Zn (50–99%) after nanomaterial treatments. When both nanomaterial (hydroxyapatite + hematite) were combined, the immobilisation rate improved. However, when each nanomaterial was added individually to the soils, some elements, such as, Cu or Sb, showed a slight increment of their mobilisation. The sequential chemical extraction showed that the highest percentage of PTEs were mainly in the residual fraction before and after adding nanomaterials, being even higher in soils after the nanomaterial treatments. Likewise, the mobile fractions decreased after the treatment with nanomaterials. Our findings suggest that nanoremediation techniques improve the soil conditions, but they should be used carefully to avoid mobilisation of non-target PTEs or unexpected potentially impacts for soil biota.