Survey of total Arsenic and Arsenic species in Italian rice.

Arsenic toxicity depends on the chemical form. Inorganic arsenic is more toxic than organic arsenic and trivalent arsenite is more toxic than pentavalent and zero-valent arsenic. Generally rice, unlike food products of terrestrial origin, contains significant amounts of inorganic arsenic. Recently some Government Organizations (e.g. EFSA) debated the possibility to set an upper limit for total and inorganic arsenic in rice. Arsenic speciation was realized in 70 Italian rice samples from different representative cultivation conditions. The adopted method was effective in preserving the arsenic species and suitable for routine analysis of large numbers of samples. Pulverized rice grains (approx. 1.5 g) were mineralized using HNO3 0,28 M at 95°C for 90 min in a heating block system. The digested samples were filtered under vacuum-assisted sample filtration in order to obtain a faster and more complete filtration, with lower sample preparation time and sample manipulation. The HPLC-ICP-MS technique was used to measure the different arsenic species [arsenite (As(III)), arsenate (As(V)), monomethylarsonic acid (MMA) and dimethylarsinic acid (DMA)], which were separated using an anion-exchange column. It was possible to separate and analyze the four arsenic species in only 9 minutes. The sum of As(III) and As(V) is known as inorganic arsenic. Total As concentration in samples was determined directly by ICP–MS. Certified reference material, NIST 1568a rice flour and IMEP 107, for total and inorganic As in rice, were included for quality assurance. Moreover, the sum of As(III), As(V), MMA, and DMA was compared with total arsenic and resulted similar. The most abundant species in rice were As(III) and DMA. Total arsenic levels in the 70 Italian rice samples averaged 0.16 µg g-1 (range 0.06-0.60 µg g-1); inorganic arsenic averaged 0.10 µg g-1 (range 0.04-0.16 µg g-1). The percentage of inorganic arsenic tended to decrease with increasing the total arsenic.