Inorganic contaminants and arsenic species contents in rice varieties consumed in Portugal

Rice (Oryza sativa L.) is the second largest cereal crop in the world, being responsible for feeding about half the world's population. Recent data shows that Portugal has a rice consume of 15.8 kg/capita/year, the largest in Europe, producing 168 300 tons of rice per year being the fourth largest producer in Europe. The aim of this work was to characterize whole grain rice, white rice and rice bran samples consumed in Portugal in terms of inorganic contaminants and arsenic species. A total of 21 samples cultivated in seven different locations were analysed. For each location 3 types of samples (whole grain rice, white rice and rice bran) were collected. Contents in Cr, Ni, As, Cd and Pb were quantified using ICP-MS. Samples with the highest content of arsenic were analyzed for arsenic speciation with HPLC-ICP-MS. All laboratorial work was carried out in compliance with the internal quality criteria established by the laboratory. Lead content was below the LOQ in all analysed samples. Cadmium was found above the LOQ only in one location; however it was present in all 3 sample types. Regarding the remaining elements bran was the type of sample with the highest levels. Arsenic content varied between 597-1527 µg/kg for bran, 266-593 µg/kg for whole grain, and 188-480 µg/kg for white rice. Speciation data showed that the arsenic species present were As (III), As (V) and DMA. In rice bran the inorganic species were predominant while in whole grain and white rice DMA was the most abundant species. This work demonstrates that, due to the toxicity of the species present, arsenic speciation studies are fundamental for characterize rice in terms of hazard identification. The content of all elements and species under study is in agreement with current legislation or available recommendations. This study also shows the need of powerful analytical techniques with very low detection limits to measure inorganic contaminants in foods.