Bachelor Thesis

Indian rice often contains high proportions of arsenic because of the arsenic content in the irrigation water which is geogenically increased. This concerns other countries, which import contaminated Indian rice like Iran which imported large amounts of a variety of Indian rice in September 2009. For this thesis 15 rice samples were bought in Iran, 12 of them coming from India and 3 being grown in Iran. In these samples the total concentration of arsenic, lead and cadmium were determined by microwave digestion with HNO₃ and H₂O₂ and analyzed using ICP-MS. For arsenic speciation analysis using IC-ICP-MS, two extraction methods were investigated and compared: (i) microwave extraction with 0.28 M HNO₃ at 95 °C for 90 min which provided a better extraction efficiency (108 ± 19 %) than (ii) extraction with diluted formic acid (50 ± 23 %). The total arsenic concentrations ranged from 61 to 168 μg/ kg and only one sample exceeded the recommended arsenic concentration limit of 150 μg/kg, but almost all samples exceeded the recommended limit of 200 μg/kg for Cadmium. Concerning the lead content all samples can be classified as harmless, none of them reached the limit of 200 μg/kg. Speciation of arsenic in the rice revealed that arsenite was the predominant species (41-78%), followed by the less toxic species arsenate (2-41 %), monomethylarsenate (< LOD 1,5 %) and dimethylarsenate (5-26 %). The obtained results show that rinsing the rice after cooking can reduce the arsenic content significantly, but arsenite remains the predominant species. These results indicate that rice analysis is still necessary but not only the arsenic, but also the heavy metal content has to be examined.