Heavy metals in fertilizers and effect of the fertilization on heavy metal accumulation in soils and crops

This paper systematically reviewed the status of heavy metal contents in chemical fertilizers and manures, and effects of the fertilizers application on heavy metal accumulation in soils and crops. The contents of zinc (Zn), copper (Cu), cadmium (Cd) and lead (Pb) in superphosphate are higher than those in nitrogen fertilizers, potash and NPK compound fertilizers. The concentrations of Pb in organic-inorganic compound fertilizers are higher than those of other fertilizers. Generally, the heavy metal contents in organic manures such as livestock manure, compost of sewage sludge are higher than those of the chemical fertilizers. The concentrations of Cu, Zn, arsenic（As） and Cd in pig manure are higher than those of other organic wastes. Chicken manure has high chromium（Cr） concentration, sludge and compost of municipal wastes have high Pb or Hg concentrations. Commercial organic fertilizers have higher Zn, Pb and nickel (Ni) concentrations than those of composts of sludge and municipal wastes, and have higher mercury（Hg） contents than those of animal manures. Most research results show that applications of NPK increase soil Cd and Pb contents, and organic fertilizer increase soil Cu, Zn, Pb and Cd contents compared with the control. The effect of chemical fertilizer applications on heavy metal accumulation in crops is not clear, while most studies show that applications of organic fertilizers could improve Cu, Zn, Cd and Pb concentrations in edible parts of crops, and the affection depends on type/amount of organic fertilizers, soil type, soil pH and crop varieties. Future research should focus on the following aspects: 1) Input/output balance of heavy metals in typical soil-plant systems; 2) Dynamics of heavy metal contents and availabilities in soils affected by long-term application of fertilizers; 3) The maximum bearing years for heavy metals under typical fertilizer application patterns in typical planting system; 4) The maximum permissible concentrations for heavy metals in applied fertilizers under current nutrient management practices.