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The Distribution and Accumulation Status of Heavy Metals (Pb, Cd, Cu and Zn) in Soils from the Rice Fields of Mada in Kedah, Malaysia

Nasser Alrawiq, J. Khairiah, M. T. Latif and B. S. Ismail

This study was conducted to determine the accumulation and distribution status of heavy metals (Pb, Cd, Cu, and Zn) in the soil fractions of the Muda Agricultural Development Authority (MADA) paddy fields situated in Jitra, in the state of Kedah, Malaysia. The study includes two areas that used different irrigation systems, namely non-recycled (N-RCL) and recycled (RCL) water. Five soil samples were collected from each area. The heavy metals in the soil were extracted using the sequential extraction method. The heavy metals were extracted from the four different fractions in the soil using different reagents. For the extraction from the first fraction, namely the easily leachable and ion exchange fraction (ELFE), ammonium acetate (NH4CH3COO) was used. For the second fraction, the acid reduction fraction (AR), hydroxylamine chloride (NH2OH.HCl) was used, whereas for the third fraction, the organic oxidation fraction (OO), a combination of hydrogen peroxide (H2O2) and CH3COONH4 was used. For the last fraction, the resistant fraction (RR), concentrated nitric acid (HNO3) and perchloric acid (HClO4) were used. The results showed that the heavy metals in the paddy soil fractions were mainly concentrated in the RR fraction. The exceptions were Pb, which was at the highest level in the OO fraction viz. 3.635 and 2.65 mg/kg in RCL and N-RCL irrigation water system. It was found that Cd was more evenly distributed throughout all the soil fractions. The results showed that the concentration of heavy metals in the studied area was in the following decreasing order: Zn > Pb > Cu > Cd.