Purpose

In situ remediation techniques are currently limited for agricultural soil contaminated by heavy metal(loid)s, particularly for alkaline soil. In this study, we applied the amendments (Chinese loess, attapulgites, and composted sludge) to a contaminated alkaline agricultural soil to compare their effectiveness in immobilizing heavy metal(loid)s.

Materials and methods

Soil was collected from the uppermost 20 cm of a heavily contaminated cornfield in Baiyin, China. The amendments were added to the soil at the ratios of 1%, 5%, 10%, and 15%. Controls without amendment were also included. The effectiveness of amendments was evaluated using single extractions and Tessier sequential extraction procedure. The extractants in the single-step extraction were H₂O, calcium chloride (CaCl₂), diethylenetriaminepentaacetic acid (DTPA), and hydrochloric acid (HCl). Seed germination was performed with the soil after immobilization for 180 days.

Results

Chinese loess effectively reduced the toxicity of heavy metal(loid)s and improve seed germination rates compared with attapulgites (ATPs) and composted sludge. Composted sludge effectively transformed heavy metal(loid)s, particularly Cu, from the carbonate fraction into the organic matter or the residual fraction. The concentrations of heavy metal(loid)s extracted with DTPA were positively correlated with the summation of the exchangeable and carbonate fractions (P < 0.05). A high seed germination rate could be obtained when the four amendments were added at the ratios between 5 and 10%.

Conclusions

Chinese loess was effective and safe to immobilize heavy metal(loid)s in contaminated alkaline agricultural soil. DTPA performed the best in predicting the availabilities of As, Cd, Pb, Cu, and Zn in the soil.