Risk assessment of bioaccessible arsenic and cadmium exposure through rice consumption in local residents of the Mae Tao Sub-district, Northwestern Thailand.

Consumption of contaminated rice is a toxin exposure route in Asian populations. Since total concentrations generally overestimate health risks, the objectives of this study were to determine the levels of bioaccessible As and Cd in rice cultivated in the Mae Tao, Tak Province and evaluate their potential health impacts in local adults. In total, 59 locally grown rice samples were analyzed for their total and bioaccessible concentrations. Bioaccessible concentrations were obtained from an in vitro digestion process. Inorganic As concentrations were estimated assuming that 63.2-63.5% of the total As is inorganic As. Rice contained inorganic As (45.2% of white rice and 57.1% of sticky rice) and Cd (51.6% of white rice and 32.1% of sticky rice) levels exceeding the Codex standards. The bioaccessibilities of As (16.3-70.0%) and Cd (Null to 83.7%) in rice varied widely. The concentrations of bioaccessible As, which were 1-1.2 times greater than those of bioaccessible Cd, indicate a higher possibility of As absorption into the human body. Positive significant relationships were found between total and bioaccessible As (R2  = 0.568 for white rice and R2  = 0.704 for sticky rice) and Cd (R2  = 0.874 for white rice and R2  = 0.862 for sticky rice). The hazard quotient (HQ) of inorganic As exposure accounted for approximately 93.4% of hazard index (HI). Approximately 2-6 in 10,000 residents over a lifetime of 75 years could suffer from cancer as a result of daily rice consumption. Therefore, the consumption of the home-grown rice in this study should be limited.