Accumulation of cadmium in the grain of Oryza sativa varieties in the Philippines

Cadmium contamination of paddy soil is a widespread problem in rice-growing areas. For this study, soil containing 1.60 mg/kg of cadmium, the maximum allowable concentration, was used. The cadmium resistance levels (extra vigour) of seventeen rice varieties were tested using a seedling vigour test, fourteen days after seeding. The cadmium-resistant varieties were then transplanted into severely cadmium-contaminated soil under controlled conditions. The accumulation of cadmium in the grain and the biological accumulation coefficient of the cadmium-resistant rice varieties were also determined in both unpolished and polished grains, using the maximum allowable level of cadmium in rice grains (0.15 mg/kg). The soil used in the study contained 10.23 mg/kg of cadmium and was categorised as severely contaminated. Seven rice varieties were identified as cadmium-resistant even in this soil. However, three varieties were found to have low cadmium accumulation in unpolished grains (0.1 mg/kg), a low biological accumulation coefficient value (0.01), zero cadmium content (0.00 mg/kg) and no biological accumulation coefficient value (0.00) in their polished grains. Therefore, it is recommended that cadmium-resistant rice varieties which accumulate low levels of cadmium in their grains (i.e. cadmium-excluder rice) be planted in severely cadmium-contaminated paddy soil. Keywords: bioaccumulation, cadmium excluder, grain, heavy metals, phytostabilisation