BIOACCESSIBILITY ASSESSMENT OF 232Th AND 238U FROM LANTHANIDE CONCENTRATE AND WATER LEACH PURIFICATION RESIDUE IN MALAYSIA

The aim of this case study was to estimate the bioaccessibility of Th and U from lanthanide concentrate (LC) and water leach purification (WLP) residue of Lynas Advanced Materials Plant by analysing the solubility of these radionuclides in synthetic gastrointestinal fluids. A DIN in vitro bioaccessibility method was applied to determine the targeted radionuclides from the LC and WLP residue, which were further evaluated through inductively coupled plasma mass spectrometry. Th and U concentrations in the gastrointestinal fluids portrayed the maximum amount of contaminants that were potentially available for intestinal absorption and transfer into the blood. The maximum concentrations of Th in the LC and WLP residue were 0.1410 ± 0.0331 mg kg and 0.1621 ± 0.1190 mg kg, respectively. As for U in the LC and WLP residue during the intestinal phase for high-risk cases, the maximum concentrations were 0.0558 ± 0.0164 mg kg and 0.0480 ± 0.0213 mg kg, respectively. The maximum bioaccessibility of Th and U was 0.14 % and 0.93 %, respectively. Based on the assessment, the committed equivalent dose and committed effective dose of Th and U were below the United Nations Scientific Committee on the Effects of Atomic Radiation reference values. Overall, the DIN in vitro bioaccessibility method is feasible to estimate the solubility of Th and U from LC and WLP residue, and is also useful for monitoring and risk assessment purposes for environmental, health, and contaminated samples.