Arsenic (As), a naturally occurring metalloid, is widely distributed in air, soil and groundwater in both organic and inorganic forms. Current knowledge indicates that organic forms of As have relatively low toxicity, but inorganic As (iAs) is a non-threshold human carcinogen [1
]. In South-East Asia (e.g., Bangladesh, West Bengal and Vietnam) where groundwater is a major source of As contamination; it has adversely affected tens of millions of people [2
]. In addition to exposure through As-contaminated drinking groundwater, people can also be exposed to As through food ingestion, particularly rice [3
Rice (Oryza sativa
) plants accumulate As more than similar cereal crops [5
]. It has been suggested that rice’s high As absorption is due to a high-affinity phosphate/arsenate uptake system [6
]. Additionally, the anaerobic paddy soil culture of rice plant also contributes to high As accumulation in rice because phosphate uptake in saturated soil environments does not have the diffusion limitations observed in drier soil [5
]. The predominant As species found in rice are arsenate (As (V)), arsenite (As (III)) and dimethylarsinic acid (DMA) [8
Rice and rice-based baby foods are frequently used to feed infants and young children due to the bland taste, iron fortification and relatively low allergic potential [11
]. Thus, there is the potential for higher levels of As exposure in infants and young children than the general population. Infants and toddlers have a higher food consumption rate per body weight basis, which further exacerbates the risks of dietary exposure to As via rice for this age group [12
Researchers have also reported that brown rice has higher concentrations of total arsenic (tAs) and iAs than white rice [9
], with As being localized at the surface of brown rice compared with being dispersed throughout the grain in white rice [15
]. In addition, organic rice has been shown to have higher iAs than inorganic rice, which could be associated with the inclusion of wholegrain rice in the organic product. This is of particular concern because baby food companies are increasingly shifting to organic products due to the association of organic food and being healthier and more nutritious [11
Studies of As concentrations in infant rice-based products have reported elevated As exposure to infants and young children in many countries [9
]. Despite the potential risk of As in infant rice-based food globally, there were no As guidelines developed specifically for this vulnerable age group until 2016, when the European Union set a maximum level iAs of 0.1 mg kg−1
for rice used in the production of food for infants and young children [22
] (Table 1
). In comparison, the current maximum level in Australia only includes tAs and was developed for adults. In addition, in Australia only one published study has investigated As in one baby rice-based product amongst general rice-based foods and found that >53% of tested products exceeded the European Union maximum level of 0.1 mg kg−1
Therefore, there is a need for further evaluation of As concentrations in infant foods that are available in Australia as well as to determine the potential infant exposure in order to ensure the protection of Australian children.
Hence, the objectives of this study were:
to determine the tAs and iAs concentrations in rice-based infant foods for sale in Australia;
to investigate how the characteristics of rice-based products (i.e., rice content, rice texture and origin) are related to arsenic concentrations;
to calculate the dietary intake and exposure of infants to examine the potential As exposure risk to Australian infants.
2. Materials and Methods
2.1. Sample Collection
Thirty-nine samples representing four infant food categories: rice milk powder, rice cereal (including rice porridge and rice congee), rice crackers (including rice cakes and rice biscuits) and rice pasta were purchased from supermarkets in Melbourne Australia between April and May 2017. For rice milk powder and rice pasta, only one brand was found, thus, 6 samples of milk powder and wheat pasta with no rice content were purchased for comparison. Different supermarkets were selected so that three different batches of the same type of food were bought to maximise sample representativeness. Manufacture and expiry date of all samples were also recorded to ensure replicates of products were from different batches. The selection of products covered 11 brands from 6 countries of origin as well as various rice types, including brown, white, organic and inorganic rice. It was not possible to trace the origin(s) of samples labelled as “made in Australia from local and imported ingredients”. Therefore, they were separated as “Australia (mix)”.
2.2. Sample Preparation and Chemical Analysis
The food samples were dried in an oven at 60 °C for 48 h and homogenously ground using a ceramic mortar where necessary. Dry weight results were converted to fresh weight through moisture content. Moisture content was calculated by weight difference before and after drying divided by initial weight. Analytical results are expressed as fresh weight throughout this paper, unless specifically stated.
The experimental procedure for tAs testing was designed following the method of Fransisca et al. [29
] with minor modifications. Briefly, 1.0 g dried and ground sample was weighed directly into a digestion tube and 6.0 mL 70% nitric acid (AR grade) was added. The samples were then heated at 100 °C for 2 h, then left to cool to room temperature before being diluted to 25 mL with ultrapure water (18 MΩ.cm), filtered through a 0.45 μm pore size cellulose acetate syringe filter (Membrane Solutions) and stored in polypropylene vials. A 1.25 mL aliquot of each sample was diluted with ultrapure water to a total volume of 10 mL before analysis by inductively coupled plasma mass spectrometer (ICP-MS, Agilent Technologies, California, USA, 7700× Analyser) for total As.
The majority of samples were further analysed for iAs after tAs analysis; however, rice cereal samples were not analysed for iAs due to low tAs concentration as consumed. The iAs analysis method was adapted from Holak and Specchio [30
]. Briefly, 1 g of homogenised sample was weighed into a polypropylene tube and extracted with 7 mL 50% perchloric acid (AR grade) by heating on a hot block at 80 °C for 1 h. After extraction, 5 mL of sample extraction solution was transferred to a polypropylene tube and 4 mL 10 M hydrochloric acid (AR grade), 0.5 mL 48% hydrobromic acid (AR grade) and 0.5 mL 3% hydrazine sulphate were added. The solution was then determined by ICP-MS (Perkin Elmer Elan DRC II) with an interfaced hydride generation system.
2.3. Quality Control
For tAs determination, the instrumental limit of detection (LOD) for the ICP-MS was 0.02 µg kg−1, which was determined by 3 times the standard deviation of the counts in a blank solution. This gave a corresponding dry sample LOD of 0.004 mg kg−1. Four reagent blanks were included in each of the three batches of sample digestion and all 12 blanks were below LOD. Each food sample was analysed in duplicate. For 85% of samples, the relative percent difference (RPD) was within 10%. The rest of samples were within 25% except one sample (one non-rice pasta sample out of three replicates) which had a RPD of 42%. This high RPD was mostly likely due to higher errors as a result of the concentration being close to the LOD. The certified reference material (NCS ZC73031 Carrot) gave a recovery of 74% of the tAs certified concentrations (0.11 ± 0.02 mg kg−1).
For iAs determination, the sample LOD was 0.05 mg kg−1, which was determined through repeated analysis (approx. 10 measurements) of blank solutions and spiked solutions. One reagent blank was included in the iAs analysis and it was measured below the LOD. Samples were analysed in duplicate and the RPD was less than 5%. The recovery of reference material (AGAL40) and matrix spike were 105% and 97%, respectively. The iAs concentration of reference material (AGAL40) is 6.43 ± 0.22 mg kg−1.
2.4. Dietary Exposure Estimations
Dietary exposure estimates followed the method used by FAO/WHO [31
]. Briefly, the principle equation for determining dietary intake was
DI = dietary intake (μg person−1 day−1),
C = concentration of contaminants (μg kg−1) and
CR = food consumption rate (kg person−1 day−1).
Dietary exposure was calculated using the following equation.
DE = dietary exposure (μg kg−1 b. wt. day−1)
DI = dietary intake (μg person−1 day−1) and
BW = mean individual body weight (kg)
According to the 23rd Australia Total Diet Study (ATDS), mean rice and rice products consumption for 9 month-old infants was 8.6 g day−1
and for 2–5 year-old children, was 28 g day−1
]. Mean body weight was 8.9 kg for 9 month-old infants and 18 kg for 2–5 year-old children [32
]. The upper 90th percentile for exposure was calculated at twice the mean exposure [31
2.5. Reference Values for Comparison
The Australian current maximum level for tAs in rice (1.0 mg kg−1
) is more than 3 times higher than the proposed WHO maximum levels for tAs (0.3 mg kg−1
]. Hence, we used the proposed WHO maximum levels as a tAs reference point in this study to compare to our results. However, it should be noted that the proposed maximum levels of 0.3 mg kg−1
for tAs was established for adults, which may not be protective for infants and young children. For iAs, the maximum iAs level (0.1 mg kg−1
) that was specifically developed for infant rice products was used as an iAs reference point in our study [22
For dietary exposure, there were no values relevant to infants and young children available worldwide; hence, we adopted the European benchmark dose lower confidence limit (BMDL) of 0.3 to 8 μg kg−1
b.w. per day [12
]. It was developed by modelling the dose-response date from key epidemiological studies and using 1% extra risk as a benchmark response. Again, it should be noted that dietary exposure for infants and children can be 2–3 fold higher than that of adults [12
] and thus, the BMDL may not be fully protective for infants and children.
2.6. Statistical Analysis
Statistical analyses were performed using Minitab®
Statistical Software (version 17, Minitab, LLC., Pennsylvania, USA) including descriptive statistics and box and whisker plots. Data were further evaluated via analysis of variance (ANOVA) and Fishers Least Significant Difference (LSD) to determine significant differences (p
< 0.05) between treatment means. Regression lines were not included in figures where p
> 0.05. Where As concentrations were <LOD, half of the sample LOD was used for statistical analysis [33
Rice-based products are widely used to feed infants and children due to a number of advantages, including its bland taste, fortified iron and low allergic potential. However, the research presented here demonstrates that the concentrations of iAs and tAs in some rice-based infant foods sold in Australia are concerning for children consuming multiple serves of these products on a regular basis. In addition, the current Australian guidelines for As in food are based on adult consumption and are not protective of high-sensitivity consumers like infants and young children. This study concludes that there may be unacceptable risks due to elevated As consumption for Australian infants consuming a large amount of rice-based products, especially rice pasta and rice crackers, in their diet.