NHA was applied to soils at molar ratios of P/(Pb+Cd) such as 2:1, 3:1, 4:1 and 5:1. Non-nHA soil
was used as the control. The nHA was thoroughly mixed with the soil to obtain homogeneity, and was
then equilibrated for 60 d, during which soil moisture was maintained with 16-18% (mass percent), and
the soils were thoroughly mixed at weekly intervals. Digestion of soil sample was performed using HCl,
HNO3, HF and HClO4 hot block digestion procedure [21]. Concentrations of Pb and Cd in the digested
solution were measured using ICP-MS (PE, ELAN DRC-e).