Arsenic Speciation in Rice Cereals for Infants

Arsenic occurs either naturally in the environment (in soil or from atmospheric inputs due to volcanism) or has been introduced into the soil as the result of human activity such as the use of arsenic-based pesticides or the use of seaweed as a fertilizer. Processes within the soil can transform arsenic species into forms that are bioavailable for plant uptake, which allow it to enter the food supply.

Rice plants are especially efficient at accumulating arsenic from their anaerobic environment because the paddy cultivation in flooded areas enhances bioavailability of arsenic compounds. For this reason,  rice can be a significant source of arsenic for consumers. The toxicity of arsenic in foods depends on its chemical form and bioaccessibility.

Inorganic arsenic is classified as cancerogen and human exposure through the food should be avoided or at least minimized. However, up to now, neither the United States nor the European Union have set limits for arsenic in food products, including rice. Since it is not clear how harmful arsenic in rice may be to the human population,  new data especially on the speciation of arsenic in food could aid in risk assessment. On September 19, 2012, the FDA released the first analytical results of nearly 200 samples of rice and rice products collected in the U.S. marketplace (see the News below). Rice samples from the US have shown higher total arsenic levels when compared to other samples from around the world. Brown rice from all locations was shown to contain more arsenic than white rice. Infants may be at higher risk because they are more susceptible to the harmful effects of arsenic than adults.


The new study:
The aim of this new study was to conduct a survey of arsenic content in rice cereals for infants. The analytical method was based on the FDA Elemental Analysis Manual (EAM 4.11) which is using an inductively coupled plasma mass spectrometer (ICP-MS) to determine total As. The same ICP-MS coupled to a high-performance liquid chromatograph (HPLC) was used to perform As speciation analysis.  Ion exchange chromatography was used for species separation, with the advantage of a simple buffer systems and isocratic conditions, allowing for simple connection of these separation systems to ICP, without having any system or chemical modification to change for the detection of the arsenicals. Using this HPLC-ICP-MS approach, the total and speciated arsenic was determined in 31 different infant rice cereals sold in U.S. supermarkets.

The mass fraction of total inorganic As (iAs; sum of arsenite As(III) and arsenate As(V)) concentrations ranged between 55.5 ± 1.3 and 158.0 ± 6.0 µg/kg. The average total arsenic and iAs concentrations in infant rice cereal were 174.4 and 101.4 µg/kg, respectively. There was no substantial difference in iAs levels between organic and conventional rice cereals and the mixed-grain rice cereal contained the least total (105 µg/kg) and inorganic arsenic (63 µg/kg).  The major detected organoarsenical species was dimethylarsinic acid (DMA). Monomethylarsonic acid (MMA) was not detected, or only trace levels were found.  While total As concentrations as high as 272 µg/kg were observed, the Chinese maximum allowed concentration of 150 µg/kg iAs in rice was slightly surpassed by only one American rice cereal (organic whole grain rice cereal).