The Association of Heavy Metals with Iron Oxides in the Aggregates of Naturally Enriched Soil.

Soils in three horizons from a naturally heavy metals enriched region were distributed into six size aggregates (> 2, 2-1, 1-0.6, 0.6-0.25, 0.25-0.053, < 0.053 mm) to determine the relationships of heavy metals (Cd, Cu, Mn and Pb) and iron oxides. The results showed that the percentage of microaggregates (size < 0.25 mm) was in the order: topsoil (A) > subsoil (B) > parent material (C), and contamination with Cd and Pb were primarily restricted to topsoil. Generally, heavy metal preferred to attach to the fine particles. Moreover, the content of Fe positively correlated with the contents of Cu, Mn and Pb in aggregates from topsoil. For aggregates from subsoil, the contents of free iron oxides and crystalized iron oxides positively correlated with the contents of Mn and Pb. For aggregates from parent material horizon, the contents of Cd, Mn, Cu and Pb, total iron and crystalized iron oxides were significantly correlated, respectively.