A review on heavy metals contamination of crops and agriculture soils of peninsular Malaysia

The concentrations of heavy metals in soil are closely related to the biological and geochemical cycles that are influenced by anthropogenic activities. In Peninsular Malaysia, studies on heavy metals contamination in the common agricultural soil and crops mainly focused on the uptake by plants in relation to its concentration in the soils and the speciation of heavy metal in soils are still lacking. To monitor heavy metals in soil, the 95th percentile of the 241 samples of agricultural soils in Peninsular Malaysia has been taken as the critical baseline level. The critical concentration of Cd, Cr, Cu, Ni, Pb and Zn in soil are 0.30, 60.9 47.3, 41.3, 65.8 and 92.0 mg kg-1, respectively. The concentration of heavy metals for most Malaysian agriculture soil and crops, especially vegetables, fall within the typical range for unpolluted soil and the maximum permitted concentration for agriculture food. The maximum permitted concentration of heavy metal for Malaysian food for As, Pb, Cu, Sn, Zn, Hg, Cd and Sb are 1, 2, 30, 40, 40, 0.05, 1 and 1 mg kg-1, respectively. Elevated concentration of heavy metals especially Cu and Zn found in some Malaysian soil and vegetables are mainly associated with the large input of organic fertilizer particularly from animal manure. The buildup of Cd concentration in some soils may be linked to the continuous use of fertilizer sources that contain traces of Cd. Soil chemical characteristic of the soil such as pH, organic matter and type of parent material influenced the availability of heavy metals in soil.