Meharg et al. 2009 — Geographical variation in total and inorganic arsenic in white rice (n=901, 10 countries)
This landmark Environmental Science & Technology paper reports total arsenic (tAs) and inorganic arsenic (iAs) speciation data on 901 polished (white) rice samples from 10 countries across 4 continents (Bangladesh, China, Egypt, France, India, Italy, Japan, Spain, Thailand, USA), all collected from markets or supermarkets and designated for human consumption. It is one of the largest and most geographically comprehensive market-basket surveys of rice arsenic ever conducted. Median tAs varied 7-fold across countries (Egypt 0.04 mg/kg to USA 0.25 mg/kg and France 0.28 mg/kg); iAs was speciated for a subset of 63 samples. The relationship between iAs and tAs differed significantly by country: Bangladesh and India had the steepest linear regression slope (most tAs manifesting as iAs), while US rice had the shallowest slope. Using country-specific rice consumption rates, the modeled global risk of dietary iAs from rice ranged 30-fold across the 5 speciated countries.
Key numbers
Total arsenic in white rice by country (dry weight basis):
| Country | N | Mean tAs (mg/kg) | Median tAs (mg/kg) | Min | Max |
|---|---|---|---|---|---|
| Bangladesh | 144 | 0.13 | 0.13 | 0.02 | 0.33 |
| China | 124 | 0.14 | 0.14 | 0.02 | 0.46 |
| Egypt | 110 | 0.05 | 0.04 | 0.01 | 0.58 |
| France | 33 | 0.28 | 0.23 | 0.09 | 0.56 |
| India | 133 | 0.07 | 0.07 | 0.31 | 0.18 |
| Italy | 38 | 0.15 | 0.13 | 0.07 | 0.33 |
| Japan | 26 | 0.19 | 0.18 | 0.07 | 0.42 |
| Spain | 76 | 0.20 | 0.14 | 0.05 | 0.82 |
| Thailand | 54 | 0.14 | 0.13 | 0.01 | 0.39 |
| USA | 163 | 0.25 | 0.25 | 0.03 | 0.66 |
| All | 901 | 0.15 | 0.13 | 0.01 | 0.82 |
Inorganic arsenic in white rice (speciated subset, n = 63):
| Country | N | Mean iAs (mg/kg) | Median iAs (mg/kg) | Min | Max |
|---|---|---|---|---|---|
| Bangladesh | 15 | 0.08 | 0.07 | 0.01 | 0.21 |
| China | 21 | 0.16 | 0.12 | 0.07 | 0.38 |
| India | 12 | 0.03 | 0.03 | 0.02 | 0.07 |
| Italy | 5 | 0.11 | 0.12 | 0.07 | 0.16 |
| USA | 10 | 0.10 | 0.10 | 0.05 | 0.15 |
- Linear regression (iAs vs. tAs) slope by country: Bangladesh 0.719 (r²=0.912), China 0.599 (r²=0.951), India 0.796 (r²=0.796), Italy 0.506 (r²=0.819), USA 0.275 (r²=0.370)
- USA lowest slope: proportionally less of total arsenic is inorganic; possibly due to methylated arsenical pesticide use history in south-central US rice paddies or genetic/methylation differences
- Global distribution modeled by weighting each country’s distribution by % contribution to global rice production
- Modeled global cancer risk (100 g/day rice consumption at country-specific rice consumption, EPA cancer slope 3.67 (mg/kg/d)⁻¹): range 3.6 per 10,000 (India) to 7.0 per 10,000 (China) for 100 g/day consumption; Bangladesh country-specific consumption → 22.1 per 10,000 excess cancer risk
- French rice (Camargue region, 0.28 mg/kg mean tAs) and US rice (0.25 mg/kg) had highest tAs concentrations among the surveyed countries — both non-traditionally-high-arsenic regions
- iAs ~90% bioavailable in white rice (based on prior swine feeding studies cited)
Methods (brief)
Analytical methods identical to prior publications (Williams et al.; ICP-MS for tAs; HPLC-ICP-MS for speciation). White rice selected as most popularly consumed, excluding brown rice (elevated arsenic in bran). Samples collected from markets and supermarkets; not collected from arsenic-contaminated areas specifically. US south-central/California sampling proportional to regional rice production. China data from Zhu et al. (2008), 8 major urban conurbations. Bangladesh from major town/city markets. France from Camargue rice-growing region. India dominated by basmati. Spain from Valencia/Ebro rice regions.
Limitations
iAs speciation available for only 5 of 10 countries (63 samples), limiting direct iAs comparison across the full dataset. Egyptian and French, Spanish, Thai, Japanese country data are total arsenic only — iAs must be inferred from regression relationships with associated uncertainty. US regression slope highly uncertain (r²=0.370); US rice contains a low-inorganic arsenic type not seen in South/Southeast Asian rice, complicating global modeling. Market basket survey integrates inherent field-to-field variation. Brown rice excluded.
Implications
- Certification: This is the foundational geographic reference for rice arsenic variability. The 7-fold range in median tAs across countries and the country-specific differences in iAs/tAs ratio are load-bearing for geographic_breakdown sub-fields on the rice ingredient page. The France Camargue and US data are particularly important for European and US supply-chain defensibility arguments.
- Courses: One of the most-cited papers on geographic arsenic variation in rice. The EPA cancer risk modeling (30-fold variation across countries) makes the policy-relevant argument for country-of-origin controls.
- App: Country-level iAs and tAs medians from this paper are the primary data inputs for the rice geographic_breakdown sub-fields in the contamination_profile. Particularly relevant for ingredients labeled by origin.
- Microbiome: Not primary topic.