It was concluded that source of cadmium contamination was soil containing high level of cadmium, which evidences were not sufficient to confirm that whether cadmium was from natural zinc mineralized area or contamination by zinc mining activities, flooded or eroded into natural and man-made water supplies which was, then, irrigated into rice paddy fields. Cadmium was eventually transferred from soil into rice, the only plant known to absorb cadmium completely.
Results showed that cadmium levels in 154 soil samples ranged from 3.4 – 284 mg Cd/kg soil which was 1.13 – 94 times European Economic Community (EEC) Maximum Permissible(MP) soil cadmium concentration of 3.0 mg Cd/kg soil and 1,800 times the Thai standard of 0.15 mgCd/kg soil.
Moreover, rice samples from 90 fields were found to be contaminated with cadmium ranging from 0.1 to 4.4 mg/kg rice while the mean background Thai rice Cd concentrations as reported by Pongsakul and Attajarusit (1999) was 0.043 ± 0.019 mg/kg rice.
With this amount of cadmium presented in rice and based on Thai daily rice consumption,it was estimated that local residents would have been exposed to cadmium 14 – 30 times higher than the Joint FAO/WHO Expert Committee on Food Additives (JECFA) Provisional Tolerable Weekly Intake (PTWI) of 7 μg Cd / kg body weight (BW) per week.