Characterization of inorganic contaminants present in rice varieties consumed in Portugal

Recent data shows that Portugal has a rice consume of 15.8 kg/capita/year, the largest in Europe. The Sado estuary, located in the West Coast of Portugal, is a major area for rice production in Portugal. Although this area is partially classified as a natural reserve, it is also threatened by many sources of anthropogenic pressure and runoff from agriculture grounds, originating a moderately contaminated estuary in some hot-spot areas. The present work aims at evaluating the level of inorganic contaminants present in different rice varieties including whole grain, white rice, husk and bran. A total of 33 samples were obtained from Sado region and from distribution stores. Contents in manganese, copper, zinc, vanadium, chromium, cobalt, nickel, arsenic, selenium, strontium, cadmium and lead, were evaluated using an ICP-MS. Samples with the highest content of arsenic, were analyzed for arsenic speciation by coupling an HPLC to the ICP-MS. Samples were analyzed in compliance with the internal quality criteria established by the laboratory. In most samples levels of lead, cadmium, cobalt, and vanadium were below or near to the LOQ. Arsenic content varies between 98 and 250 µg/kg. Speciation data, showed that the species present were mainly arsenite (AsIII), representing about 80% of total arsenic, and dimethylarsinic acid (DMA). After comparing this data with other analytical results used in risk assessment studies we can infer that inorganic contaminants in samples are not a matter of concern. This study also shows the need of powerful analytical techniques with very low detection limits to measure inorganic contaminants in foods.

This work was completed on behalf of project “23290 – ValCAP” funded by the Portuguese Innovation Agency (ADI) and project “ORQUE SUDOE”, Ref. SOE3/P2/F591. Sandra Gueifão acknowledges the financial support from the project “ORQUE SUDOE” in the frame of students Exchange.