Natural radionuclides in agricultural plants from northern Thailand

Thailand is predominantly an agricultural country. The Northern Region occupies the second largest cultivated land area in the country. To establish baseline data for future environmental monitoring, seventy-nine plant samples including vegetables, fruits and tobaccos and their relevant soils were collected from the major plantation zones of Northern Thailand. Activity concentrations of natural radionuclides in the samples were determined using gamma-ray spectrometry technique. The median activity concentrations of ²²⁶Ra and ²²⁸Ra in the soil samples were higher than worldwide value, while as those of ⁴⁰K were comparable with worldwide value. There was a large variation and non-uniform distribution in the soil samples. The activity concentrations of ²²⁶Ra, ²²⁸Ra and ⁴⁰K in the plant samples varied widely within plants and between species and were very low compared to their relevant soils. A decreasing trend of their activity concentration has been observed in the order leaf > stem > rhizome/root (as found in galangal); and leaf > stalk/stem (as found in lemongrass). (authors)