Overview
This study measured total arsenic (tAs), inorganic arsenic (iAs), cadmium (Cd), lead (Pb), and mercury (Hg) in 33 rice samples purchased from Saudi Arabian markets, comparing locally grown Hassawi rice (n=9) against imported rice from India, USA, Australia, Pakistan, and Thailand (n=24), using HPLC-ICP-MS for arsenic speciation and ICP-MS for other metals. Among the five analytes, iAs was the primary concern, with imported rice showing significantly higher iAs than local Hassawi rice; Cd, Pb, and Hg levels in both rice types were well below WHO guidance values. Estimated lifetime carcinogenic risks from iAs in imported rice consumed in Najran city (high-consumption population) were within or slightly above the 1×10⁻⁴ threshold, suggesting that risk mitigation may be warranted for heavy consumers.
Key numbers
Imported rice (n=24, India, USA, Australia, Pakistan, Thailand):
- tAs: range 55–269 µg/kg (mean 140 µg/kg)
- iAs: range 45–120 µg/kg (mean 73±8 µg/kg)
- iAs/tAs proportion: mean 56%
- Cd: mean 23±1 µg/kg
- Pb: mean 32±3 µg/kg
- Hg: mean 4±3 µg/kg
Local Hassawi rice (n=9, Al-Ahsa, Saudi Arabia):
- tAs: range 42–103 µg/kg (mean 69 µg/kg)
- iAs: range 39–49 µg/kg (mean 43±5 µg/kg)
- iAs/tAs proportion: mean 67%
- Cd: mean 30±4 µg/kg
- Pb: mean 30±4 µg/kg
- Hg: mean 2±3 µg/kg
Statistical significance: Mann-Whitney U test confirmed iAs in imported rice was significantly higher than in local rice (P≤0.05, one-tailed). Cd, Pb, and Hg did not differ significantly between imported and local rice.
Exposure assessment (adult rice consumers in KSA):
- Mean adult rice consumption: 0.128–0.243 kg/person/day (general population to high-consumption city)
- EDI for iAs from imported rice: up to 0.3 µg/kg-bw/day in Najran city adults
- EFSA BMDL05 for skin cancer: 0.06 µg/kg-bw/day — mean imported rice exposure exceeds this
- WHO PTWI (withdrawn): 2.1 µg/kg-bw/day — imports within margin of safety
- Excess lifetime carcinogenic risk from iAs: 3×10⁻⁵–4×10⁻⁴ (overlapping or exceeding 1×10⁻⁴)
Individual sample range highlights (Table 5):
- USA rice (3 samples): tAs 141–269 µg/kg, iAs 52–120 µg/kg
- India rice (17 samples): tAs 55–216 µg/kg, iAs 55–102 µg/kg
- Brown long grain (India, sample 12): tAs 150 µg/kg, iAs 85 µg/kg
Reference material recovery: NIST 1568b — T-As 107%, Cd 103%, Pb 92%, Hg 85%, i-As 113%; LGC inter-laboratory — T-As 84–112%, i-As 84–88%.
Methods (brief)
Arsenic speciation by HPLC-ICP-MS (Agilent 1260 chromatography with Agilent 7700 ICP-MS) using PRP-X 110S anion exchange column; species measured: As(III), As(V), DMA, MMA. Total arsenic (As), Cd, and Pb by ICP-MS (Agilent 8900 Triple Quadrupole) after closed-vessel microwave digestion (8 mL sub-distilled concentrated HNO₃ + 1 mL H₂O₂). Total Hg by ICP-MS (Agilent 7700). Arsenic speciation used mild acid extraction (0.28 M HNO₃, 95°C, 90 min) to preserve species integrity. LOD approximately 1 µg/kg for tAs, Cd, Pb, Hg and 0.5 µg/kg for iAs.
Implications
Certification: iAs in imported rice sold in Saudi Arabia (mean 73 µg/kg) falls below the EU/Codex maximum of 200 µg/kg for polished rice but exceeds exposure thresholds for high rice-consumption populations. The iAs/tAs ratio (56–67%) is high, consistent with Asian-origin rice. The data anchors an iAs occurrence baseline for Middle Eastern markets, relevant for HMT&C standards discussion of rice-derived ingredients.
Courses: Demonstrates that the iAs/tAs split for rice is non-trivial (56–67% inorganic) and that HPLC-ICP-MS speciation is essential; total arsenic alone understates regulatory exceedance risk. High per capita rice consumption in Saudi Arabia (up to 0.243 kg/day in Najran) drives iAs exposure above EFSA skin-cancer benchmarks even at mid-range rice concentrations.
App: Hassawi rice (locally grown in Al-Ahsa) carries lower iAs than imported Asian rice, consistent with literature showing geographic variation by cultivar and growing conditions. The tAs/iAs ratio distinction is essential for the app’s per-ingredient risk model.
Related evidence
HMI reference use
Table 5 supplies 33 individual rice samples: 24 imported and nine local. Triplicate laboratory analyses remain one sample each. Reported-origin subgroup medians contribute to native-grain HMI references; the grain was ground without a documented dry-mass correction, so it is not pooled directly with dry-weight rice. Table values give an imported tAs mean of 137.4167 µg/kg versus the narrative’s rounded 140, and a maximum of 269 versus 223 in the prose. Original published row averages remain identified as such. Mercury values near zero with analytical dispersion around 3 µg/kg do not supply a resolved classification without clearer reporting limits.
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