Inorganic arsenic speciation in baby rice cereals using HPLC-ICP-MS

Most people would automatically think of murder by poisoning when they hear about arsenic. Rumors persist that Napoleon Bonaparte’s final undoing was through arsenic poisoning, despite modern science failing to confirm whether poisoning caused his death. But despite its infamy, not all chemical forms of arsenic are poisonous. Arsenic is a naturally occurring substance found in water, air, soil, and food. The most abundant form found in fresh seafood is arsenobetaine, which is nontoxic to humans. However, inorganic arsenic (iAs), which occurs naturally in some rocks, soils, and groundwaters, is a known carcinogen and can cause toxic effects. Inorganic arsenic from human activity, such as the use of timber preservatives, or pesticides and insecticides in agriculture, can be released into the environment and accumulate in food. Some foodstuffs are susceptible to accumulating arsenic, with rice considered one of the main sources of inorganic arsenic consumed in the world’s diet.

Showing the levels of arsenic in a variety of foods

 

The different levels of toxicity in arsenic

ICP-MS is the technique of choice for total arsenic measurement in many sample types including foods. However, to quantify individual species, the ICP-MS must be combined with a chromatographic separation, typically using liquid chromatography (LC). To streamline this integration of LC with ICP-MS, Agilent provides a dedicated speciation kit.

It has long been known that significant levels of arsenic can be present in rice and rice-based food products. A 2012 publication by Jackson noted that infant formula, cereal bars, and energy shots can contain total arsenic up to 0.13 mg/kg (parts per million – ppm). This level is well above the WHO and EPA limit of 0.01 mg/L in drinking water.

In a report published in July 2014, the joint United Nations Food and Agriculture Organization (FAO) and WHO food standards body (Codex Alimentarius) recommended maximum levels of 0.2 mg/kg arsenic in rice. In 2016, the European Commission established maximum limits for inorganic arsenic (iAs) in rice and rice products. The regulation (EC) No 1881/2006 sets out limits of 0.20 mg/kg for white rice, and 0.25 mg/kg for brown rice. A lower level of 0.10 mg/kg is set for products intended for children, and a slightly higher limit of 0.30 mg/kg for certain puffed rice products.

In the US, through a draft guidance to industry, the FDA has proposed a limit or “action level” of 0.1 mg/kg (100 µg/kg (parts per billion – ppb)) for inorganic arsenic in infant rice cereal.

Following the introduction of the 2016 EC limits, consumer interest and scrutiny of infant food products has increased. Given the potential impact of arsenic exposure in infancy, it is important that manufacturers provide this vulnerable group with food products compliant with the limits.

Agilent study using HPLC-ICP-MS

Agilent conducted a research study with the Institute for Food Safety and Health at Illinois Institute of Technology to assess baby rice foods. The study used a modified HPLC-ICP-MS method specified in the FDA EAM (Elemental Analysis Manual) §4.11. The study was published in the Journal of Agricultural and Food Chemistry. It provided information on arsenic levels in rice and rice-based infant cereals to help understand the health risk to infants.

Speciation analysis was done using an Agilent 1200 Infinity LC system. The system consisted of a vacuum degassing unit, binary pump, autosampler, and a 10-port valve (two ports were plugged). An external pump was used for the internal standard spike introduction. The HPLC system was connected to an Agilent 7700x ICP-MS (using 1/16 × 0.0025 × 12 inch PEEK tubing. The ICP-MS was equipped with the standard MicroMist nebulizer and Scott-type double-pass spray chamber.

Baby rice samples were bought at different locations and various grocery stores in four US states. Seven different manufacturers produced the 31 infant rice cereals.

Study findings: speciation of inorganic arsenic in baby rice

A typical separation

The Analytical Solution Detection Limit (ASDL), Analytical Solution Quantitation Limit (ASQL), and method Limit of Detection (LOD) and Limit of Quantitation (LOQ) were determined for the arsenic speciation analysis in rice. The LOD values for As species ranged from approximately 0.9 ng/g to 1.8 ng/g and LOQ from 7 µg/kg to 14 µg/kg.

Results showed that levels of iAs varied greatly across all rice cereals. There was no substantial difference in iAs levels between organic and conventional rice cereals. In the baby rice cereals tested, the total arsenic concentration ranged from 79.9 to 277 ng/g. This wide variation suggests that the origin of the rice and the blend used (white rice, brown rice, organic versus nonorganic, and so on) makes a significant difference to the arsenic content of each product. Some of the levels seen in the study were well below the maximum limits allowed in the EU and recommended by the FDA, others were above the limits and action level. The iAs, as a percent of total arsenic, ranged from 23 to 81%. The major organic arsenic species detected was DMA, which is much less toxic than iAs.

The study demonstrated the successful application of the HPLC-ICP-MS method specified in the FDA EAM: §4.11 for the determination of arsenic species in infant rice cereals. The sensitivity (LODs and LOQs) and precision (%RSD) were sufficient to detect low levels of all arsenic species, including iAs levels that were below the levels previously found in baby rice cereals.

The result is new and much needed information for the assessment of arsenic levels in rice and rice-based infant cereals.

For more information, download the application note or view the Separation Science webinar.

For Research Use Only. Not for use in diagnostic procedures.

References

1. Hong Y-S, Song K-H, C J-Y, Health Effects of Chronic Arsenic Exposure, J Prev Med Public Health. 2014 Sep; 47(5): 245-252. Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4186552/ [accessed 15/12/2017]

 

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