Assessment of Heavy Metals in Soils and Tuber Crops on Ex-Mining Land of Southern Perak, Malaysia

Large areas of ex-mining lands in Southern Perak, Malaysia, are used for the cultivation of vegetables, fruits and tuber crops due to the shortage of land for agricultural productions. These areas have been cultivated for more than 20 years. Recent studies have reported that ex-mining land used for the cultivation of tuber crops and some fruits were found to be contaminated by heavy metals. Heavy metals concentrations may be high due to the use of high amounts of organic fertilizers (chicken dung) and agrochemicals (fertilizers, pesticides). There is a growing concern and awareness amongst consumers that long term addition of fertilizers may accumulate heavy metals in soil and taken up by tuber crops grown in the ex-mining lands. Heavy metals are known to cause detrimental health effects to human. Thus, a study concerning heavy metals contamination on tuber crops cultivated on ex-mining lands had been conducted. iii Four major cultivation areas were selected for this study namely; Kg. Baharu Bikam, Tapah Road, Pekan Pasir and Kg. Baru Cold Stream. The farms in these areas were found to be the largest tuber crops production in southern Perak. In the cultivated areas, sampling sites were chosen where the tuber crops were ready for harvest. Each sampling site, 3 soil samples and tuber crops were sampled. The three soil samples from each point were combined to form a composite sample. The soils were collected by using a stainless steel auger. An hundred eighty soil samples were collected from the cultivated soils which is 60 soil samples for each 3 depths (0-20 cm, 20-40 cm and 40-60 cm). While only 60 soil samples were collected on topsoil (0-20 cm) from the uncultivated exmining lands. The uncultivated soils were collected for the determination of heavy metals and used as background values (control). An overall total of 240 soil samples were taken from the cultivated and uncultivated soils. The crops selected were tuber crops such as tapioca, yam bean, sweet potatoes and Chinese radish. For each sampling site, geographic coordinates were recorded using global positioning system (GPS). The soils were air-dried, crushed, sieved to pass 2 mm sieve and analysed for the texture, mineralogy, pH, total organic carbon (OC), cation exchangeable capacity (CEC), total heavy metals content (Pb, Ni, Zn, Cd and Cu) and available heavy metals extracted with three different extractants i.e. 0.1 N HCI, EDTA and DTPA. While heavy metals in tuber crops were extracted using dry-ashing method. The heavy metals (Pb, Ni, Zn, Cd and Cu) were determined by Atomic Absorption Spectrophotometer (AAS). From this study, it was found that, the uncultivated soils in the study areas can be categorized according to their texture i.e sand, sandy clay loam and sandy loam. Sand texture consists of 89.5 to 91.5% sand and very low clay content (7- 10%). Sandy clay loam texture consists of 15.5 to 1 8.4 % sand and very high in clay content which is 41.8 to 42 %. Sandy loam consists of 12 to 19.5 % clay, 70 to 75.5% of sand and 15.5 to 18 % of silt. The pH of topsoils in the cultivated ex-mining soils of southern Perak had a mean value of 6.08. The mean cation exchange capacity of the cultivated exmining soils was 0.77 cmo1,kg-' soil. The soils have a mean organic carbon content of 0.66 %. On the other hand, soils in the uncultivated lands have pH, CEC, OC, with the values of 4.56, 0.35 cmolJcg-' and 0.31 %, respectively. Generally, there is a significant increase at p5 0.05 of pH, OC and CEC in the cultivated soils. Mean concentration of Zn in the cultivated soil was the highest followed by Pb, Cu, Ni and Cd, with values of 15.84 mgkg-', 10.43 rngkg-', 4.20 mgkg-', 3.07 me', and 0.84 mgkg-', respectively. In the uncultivated soil, a similar trend in heavy metal concentrations was observed for Zn, Pb, Cu, Ni and Cd with mean values of 8.09 mgkg-', 5.78 mgkg-', 1 .I9 mgkg-', 1 .OO rngkg-' and 0.69 mgkg-', respectively. T-test analysis showed that metal concentrations in cultivated soils are significantly higher at p10.05 level than in uncultivated soil except for Cd. However, both levels are still below the critical heavy metal concentrations limits in agricultural soils of Peninsular Malaysia and the concentration ranges (using the 95th percentile), except for Cd. Total Pb and Cd concentration in soil were significantly positive correlated with available Pb using 0.1N HCl extractant (r = 0.41*, n= 60) available Cd using DTPA (r= 0.23*, n=60). On the other hand, total Ni in soil was significantly negative correlated with available Ni using DTPA (I=-0.38, n=60). Regardless of the extraction methods used (O.1N HCl, EDTA or DTPA), no significant correlation was found between total Cu and Zn in soil and available Cu and Zn. Correlation analysis between heavy metals in tuber crops with available heavy metals indicates that, there was no relationship between total heavy metals in the tuber crops and available heavy metals in soil using different extraction methods except for Zn and Cu, which have a negative correlation using 0.1 N HCI (r = -0.25*, n= 60) and DTPA (I-=-0.22*, n=60), respectively. Amongst all of the crops studied, Chinese radish, tapioca and sweet potato contains the highest concentration of 15.33 mgkg-' Zn, 0.85 mgkg-' Pb and 0.12 mgkg-I Cd, respectively. On the other hand, yam bean showed that the lowest concentration of Zn, Cd, Cu and Ni with values of 2.41 mgkg-', 0.07 mgkg-', 0.63 mgkg-' and 0.56 mgkg-I, respectively. Lead is significant higher at pi0.05 in yam bean than in sweet potato and Chinese radish. There is no significant difference in the concentrations of Cd in all tuber crops studied. Copper show significant higher in tapioca than in sweet potato followed by Chinese radish and yam bean. Zinc concentration is significantly higher in Chinese radish than in tapioca, sweet potato and yam bean, while Ni is significantly higher in Chinese radish than in yam bean. Results from this study show an increased concentration of heavy metals in Chinese radish followed by tapioca, sweet potato and yam bean, but the heavy metals levels of all the tuber crops studied were still below the Maximum Permissible Concentration (MPC) as stated in the Malaysia Food Act (1983) and Food Regulation (1 985). Spatial distribution map is usefkl to detect the spatial area, which are low, optimum or high in heavy metal concentration. Tapah Road areas have the highest concentration of heavy metals in all elements studied with Zn value of 17.41 mgkg-', followed by Pb, Cu, Ni and Cd. On the other hand, Kg. Baharu Bikam has the lowest concentration for all elements. Statistical analyses indicate that there is no significant difference at p10.05 of heavy metals content in soil among those areas. vii

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