Cadmium contamination in soils under rice cultivation

In recent years, there has been an increasing concern over cadmium (cd) in the environment because of its highly toxic to human. Cadmium in soils can be removed by edible plants and it represents a direct pathway for it`s incorporation into the human food chain. A study was conducted to evaluate Cd in the rice growing area. The study also investigated the relationship between total Cd in the soil and its uptake by rice (grain). In this study, soil sample (0-15 cm) were collected from the MUDA Irrigation Scheme in Kedah and Perlis. Ten soil series were collected (Kuala Kedah, Kuala Perlis, Tualang, Chengal, Kundor, Guar, Kangkung, Tebengau, Rotan and Sedaka). In the five soil series (Kuala Perlis, Kuala Kedah, Sedaka, Tebengau and Guar), Cd in the soils sampled at 0-5 cm, 5-10 cm, 10-15cm, 15-20cm, 20cm-25 cm, 25-30 cm, 30-35 cm, 35-40 cm and 40-45 cm depth was analysed. The Cd contents in the soils were extracted with HC1 HNO subscript 3 at 3:1 v/v (aqua-regia). The soils were sampled during land preparation, after planting and after harvesting. The Cd (60 samples with 6 replication for 10 series) in rice grain was extracted with 20% HNO subscript 3. All the extracts were analysed for Cd using an atomic absorption spectrophotometer. Our results indicated that Cd in the soils varied with different sampling time except the Rotan and Guar series. The highest concentration of Cd in the soil was found in the Kuala Kedah series. The concentration of total Cd in the soils was 0.747-0.561 lambda g/g. However, these values were below the Maximum Permitted Concentration (MPC) currently found in some developed countries. The results also showed that the Cd content was the highest in the topsoils (0-30 cm). The levels decrease with soil depth. Total Cd in the soils was significantly correlated with the Cd in the grains (r square = 0.75) if data from Kuala Kedah soil was not taken into account. The Cd content in the grains was 0.030-0.024 lambda g/g. These values were below the Australia MPC of 0.05 lambda g/g. The results indicated that the current practices in rice production increase Cd contamination both in soils and rice grains.