In situ remediation of metals-contaminated soils by using chemical amendments to these sites has been given recently increasing attention. Although the resulting metal compounds are stable under favorable environmental conditions, there is some concern about the dissolution of these compounds in the soil due to variation in some soil properties. A batch and pot experiment was conducted to investigate the behavior of the immobilized metals compounds Cd, Zn, and Pb, due to some changes brought about by variation in soil pH, redox conditions of the soil environment, following the cleaning up of the soil by the in situ remediation technique. Surface soil samples (calciorthids) from three metals-contaminated sites (Atitalaquia I, Atitalaquia II and Tezantepec) previously treated with raw (PR-1), acidulated phosphate rock at 25% (PR-25) and 50% (PR-50) solely or combined with composted biosolids) were equilibrated with 0.5 M MgCl2 or 0.5 M NH2 OH – HCl solution at four pH levels. Soil extracts following centrifugation were saved for final pH determination and metals analysis. Results show that in most soil treatments, amount of metals extracted by both conventional and reducing solutions were significantly influenced by solution pH and metal species. In most PR treatments of SI soil, release of metals from immobilized compounds was less effective at solution pH 6.0, however with the inclusion of biosolids in the treatment effect of solution pH 5 was more apparent in the immobilization of metal compounds.

Variations in the effect of soil treatment on metal immobilization as reflected through the calculated E values of plant metal uptake, the percentage of total amount of immobilized metal, are also discussed.