Arsenic species in rice: A new Australian reference material

Inorganic arsenic is a known carcinogen, and long-term oral exposure to high levels of inorganic arsenic is associated with developmental defects, cardiovascular disease, neurotoxicity, and diabetes, according to the World Health Organization. Worldwide, drinking water and foodstuffs are the two main sources of inorganic As. While today there is very limited legislation limiting the acceptable arsenic content in food, it is very likely that specific legislation will be introduced for inorganic arsenic concentrations in rice in Europe, USA, Australia and elsewhere. Food safety organizations in Europe (EFSA), USA (FDA) and Australia (FSANZ) are in the process of discussing the acceptable levels for inorganic arsenic that is expected to be set at 0.2–0.3 µg/g. This will require producers of rice to certify that their rice has acceptable inorganic As concentrations.

Measurement of inorganic As in food is demanding both with respect to methodology and required instrumentation. First, inorganic Arsenic  must be quantitatively extracted from rice and separated from other arsenic species such as monomethylarsenic (MMA) and dimethylarsenic (DMA), to avoid overestimation of inorganic As. Commonly, high performance liquid chromatography (HPLC) coupled to inductively coupled mass spectrometry (ICPMS) is used for this purpose, but care must be taken that co-elution of arsenic species and/or losses from adsorption to column packing material doesn't occur. Also, arsenic determination by ICPMS can suffer from matrix interference such as carbon enhancement in the ICP torch and isobaric interferences in the mass spectrometer, leading to an overestimation in arsenic concentration. Precautions must be taken to ensure the quality of results.

New reference material:
In order to support the quality assurance of such speciation analysis, people at the Ecochemistry Laboratory at the University of Canberra, have produced a rice reference material. For that purpose, rice flour was sterilised by gamma irradiation and homogeneity tests were conducted using a suite of other elements present in the rice flour.

For the speciation analysis, aliquots of the rice flour were extracted with 2% nitric acid; total arsenic was measured by ICPMS and inorganic As and DMA by HPLC-ICPMS by a method verified by analysis of eight international rice flour reference materials and XANES. The rice flour contains 0.192 ± 0.006 µg/g dry mass total As, 0.040 ± 0.004 µg/g dry mass AsIII, 0.068 ± 0.003 µg/g dry mass AsV and 0.085 ± 0.004 µg/g dry mass DMA.  The analysis of reference material and obtaining satisfactory results gives confidence in arsenic concentrations being reported by the Ecochemistry Laboratory.

The reference material is available, free of charge, by sending a stamped, self-addressed envelope to Ecochemistry Laboratory, University of Canberra, Bruce, ACT 2601. For more information, contact Bill Maher at the University of Canberra.