Factors Affecting the Levels of Pb and Cd Heavy Metals in Contaminated Farmland Soils

The toxicity and bioavailability of heavy metals depends upon characteristics of the surrounding soil matrix.To assess the risk of heavy metals in soil, it is necessary to understand the relationships between the heavy metals and other soil chemicals.Lead (Pb) and cadmium (Cd) in soils affected by gold mining in China were studied.The influences of organic matter, cosmids and pH on the bioavailability of Pb and Cd were determined.Soil organic matter and pH were the main factors influencing bioavailability of Pb and Cd.The total amount of Pb or Cd was positively associated with soil organic matter content but the levels of water-soluble and ion-exchangeable Pb and Cd decreased when organic matter increased.Soil cosmids did not significantly affect the bioavailability of Pb and Cd.Activity and bioavailability of heavy metals increased with low soil pH, while the content of Cd in the carbonated and ferric-manganese oxidation states increased.For farmland soil contaminated by Pb and Cd, the use of organic fertilizers and soil maintenance at neutral to alkaline pH can help reduce heavy metal risks in agricultural products.