The concentration and distribution of selected heavy metals (Pb, Cd, Cu and Zn) in soils collected from the rice fields of MADA in Kedah, Malaysia

The present study was carried out to determine the concentration and distribution status of some heavy metals (Pb, Cd, Cu and Zn) in the paddy field soil fractions of MADA in the state of Kedah, Malaysia. Five replicate samples were randomly collected from five paddy fields in the MADA area of Jitra. The heavy metals in the soil were extracted using sequential extraction method that was presented by Badri and Aston [1], which consisted of four different fractions using different reagents. The first fraction of extraction is the easily leachable and freely exchangeable fraction (ELFE), which uses ammonium acetate (NH4CH3COO). The second fraction is acid reduction fraction (AR), which uses hydroxylamine chloride (NH2OH_HCl), while the third fraction of extraction called the organic oxidation fraction (OO) was carried out using the combination of hydrogen peroxide (H2O2), and ammonium acetate (NH4CH3COO). The last fraction called the resistant fraction uses concentrated nitrate acid (HNO3) and perchlorate acid (HClO4). Generally, all the paddy soils in this study contained low levels of Pb, Cd, Cu and Zn concentration compared to the other paddy soils. The result showed that the concentration of heavy metals in the studied area was in the following decreasing order i.e.: Pb < Zn < Cu < Cd. The results also showed that the concentration of heavy metals in the paddy soil fractions were mainly concentrated in the RR fraction except for Pb, which was at the highest level in the OO fraction, whilst Cd was more evenly distributed throughout the whole soil fraction. In general, Pb was the highest metal concentration found in the OO fraction followed by Zn in the RR fraction of the soil fractions.