Cadmium contamination in paddy soil and rice grain in Mae Tao Creek, Thailand

In late 2003 Land Development Department (LDD) became seriously concerned with the cadmium contamination problem in Huay Mae Tao (Mae Tao creek), Mae Sot District, Tak Province. It gave a negative impact not only to human health but also to socio-economy of people living in that area. Therefore, LDD took responsibility to study and prevent cadmium contamination in the food chain. Samples of paddy soil and rice grain were collected from 532 fields from November-December 2004. The results showed that Cd concentrations were between 0.1-284 mg kg-1 in soil and between <0.01-5.96 mg kg-1 in rice grain, with 68.61% of rice grain not safe according to CCFAC standard and the JECFA Provisional Tolerable Weekly Intake (PTWI) for Cd per kg Body Weight (BW) per week. This PTWI value is established on the basis of preventing negative impacts on human health via dietary Cd. For air-dry soil, the amount of Cd in soil cannot be used to predict the uptake of Cd to rice grain. The results of the study also show that soil pH was not an important factor that determined the uptake of Cd to the rice grain because the pH of the limestone-derived soil is already high. Therefore it is not necessary to raise soil pH with lime in this area. For the benefit and safety of the consumer from Cd contaminated edible plants. Estimated mean WI values for residents in Huay Mae Tao from rice intake were associated with estimated WI values >7 g Cd kg-1 BW. Except for Khang Phiban village, this poses to a significant risk to public health. It is recommended that land use pattern in all areas that receive irrigation from Huay Mae Tao should establish soil and water conservation system for growing alternative crops. At present land use pattern has been changed to grow non edible crops. It is necessary to study the exact contaminated area and find the best way to remediate area for sustainable land use. However it is necessary to have soil and water conservation to prevent soil erosion and Cd dispersion, the study of Cd contamination and dispersion in soil and plant is also necessary. Knowledge from the research is useful for long-term soil management and sustainable land use.