RISK ASSESSMENT OF ARSENIC IN ARABIC AREA RICE USING ON-LINE LEACHING AND SPECIATION ANALYSIS BY ION EXCHANGE CHROMATOGRAPHY COUPLED TO INDUCTIVELY COUPLED PLASMA MASS SPECTROMETRY
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For the first time, a simple on-line continuous leaching method, where artificial gastrointestinal fluids are sequentially pumped through a mini-column of food while As is continuously monitored by inductively coupled plasma mass spectrometry (ICP-MS), is used to assess the bio-accessibility of As in Arabic area rice. This on-line leaching method offers several advantages over batch methods; most notably, it provides real-time leaching data and involves a shorter and simpler sample preparation, which reduces the risk of contamination. There was no significant difference between the bio-accessible As concentrations measured by on-line and batch methods, although, with the on-line method, the concentration sum of As leached and As left in the residue was closer to the total As concentration according to a Student’s t-test at the 95 % confidence level, which is commensurate with the batch method being more subject to contamination. Leaching with artificial saliva released As the most, followed by artificial gastric juice and intestinal fluid. Both the on-line and batch methods showed that 20%-95% of As in rice samples is bio-accessible. The results of As bio-accessibility in unwashed raw rice and in washed cooked rice after simply washing the rice with water prior to cooking were similar, indicating that cooking had no significant effect on As bio-accessibility. A method based on anion-exchange chromatography with on-line detection by ICP-MS was also used for the speciation analysis of As. For better risk assessment, speciation analysis was performed on washed and cooked samples. Because saliva leached the most As, the determination of As species was only conducted in saliva leachates. The results revealed that the concentration of inorganic As species in rice varies to some extent according to the samples' location. In general, As(V) predominated over As(III), monomethylarsonic acid (MMA), and dimethylarsinic acid (DMA). Although As(V) is considered to be more toxic than MMA and DMA, this investigation indicates that the concentration of As(V) can be reduced significantly by washing rice several times, thereby decreasing the risk of arsenic poisoning.