Overview
This Food Chemistry study characterized total arsenic (tAs) and inorganic arsenic (iAs) speciation across eight main rice-producing regions of the Iberian Peninsula (Andalucía, Aragón, Catalunya, Extremadura, Murcia, Navarra, Portugal, Valencia) using soil (n=40), shoot (n=40), field-collected grain (n=20), and commercial rice (n=144: 20 brown, 11 parboiled, 113 polished) samples. IC-ICP-MS speciation revealed significant regional differences in iAs in commercial polished rice: Extremadura/Portugal had the highest iAs (median 0.087–0.088 mg/kg), while Andalucía had the lowest (0.054 mg/kg). About 26% of commercial rice samples exceeded the EC permissible concentration for infant food production (0.100 mg/kg iAs). Soil arsenic had a geogenic/mining origin. Cadmium concentrations in rice grain were consistently low and near the LOD.
Key numbers
- Commercial polished rice (n=113 total):
- Entire dataset median iAs: 0.071 mg/kg; range 0.027–0.175 mg/kg
- By region (median iAs, mg/kg):
- Andalucía (n=20): 0.054 (range 0.027–0.130)
- Aragón/Navarra (n=10): 0.067 (range 0.044–0.154)
- Catalunya (n=14): 0.080 (range 0.044–0.147)
- Extremadura/Portugal (n=23): 0.087 (range 0.066–0.138)
- Murcia (n=11): 0.057 (range 0.039–0.075)
- Valencia (n=29): 0.063 (range 0.028–0.175)
- Significant regional differences (Kruskal-Wallis P < 0.001)
- ~26% of polished rice samples exceeded EU 100 µg/kg infant production ML
- Brown rice: higher median iAs than polished; median iAs (all Spain/Portugal brown) 0.157 mg/kg (range 0.083–0.247)
- Parboiled rice: median iAs 0.083 mg/kg (range 0.022–0.170)
- Commercial rice iAs vs. tAs regression: slope 0.186, R² = 0.38 across entire polished dataset
- DMA (dimethylarsinic acid) in polished rice: median 0.055 mg/kg (range 0.003–0.291)
- Highest median DMA: Extremadura/Portugal 0.139 mg/kg; lowest: Murcia 0.009 mg/kg (P < 0.001)
- iAs percentage of ΣAs in polished rice: median 57% (range 14–95%); Murcia 87% iAs proportion (highest), Extremadura/Portugal lowest (41%)
- Soil tAs (8 paddy regions): range 2.3–17 mg/kg; Portugal highest (median 15 mg/kg)
- Shoots iAs: range 0.257–17.1 mg/kg (dry weight); Extremadura highest (11.0 mg/kg median), Murcia lowest (1.4 mg/kg median)
- Cadmium in all rice grain samples: consistently low, near LOD (LOD for Cd analysis 0.009 mg/kg)
- Field-collected grain iAs: median iAs percentage 85% (41–97%), range 0.052–0.161 mg/kg; Extremadura highest (0.100, 0.061–0.130), Murcia lowest values
- LOD: Cd 0.009 mg/kg (soil CRM), As speciation 0.002 mg/kg (rice CRM from DMA calibration)
Methods (brief)
Soil (n=40), shoot (n=40), field grain (n=20) collected September 2014 from 8 paddy regions (5 replicates per region). Commercial rice (n=144) purchased from supermarkets and local shops. IC-ICP-MS for As speciation (Thermo IC5000 + Thermo AG7 guard column + Thermo ICAP Q ICP-MS); ICP-MS direct acquisition for tAs and Cd. Freeze-dried, ball-milled samples; 1% HNO₃ microwave digestion (55°C/75°C/95°C). CRM: NIST 1568b rice flour (As species and Cd certified). Statistical: Kruskal-Wallis rank non-parametric; R statistical software.
Limitations
Commercial rice samples (n=113 polished) do not uniformly represent all Spanish rice-growing regions — Valencia n=29 is well-represented, Extremadura n=3 in field-collected grain is small. Regional commercial rice samples were purchased from supermarkets and include rice of uncertain origin within the labeled region. The very high DMA proportion in Extremadura/Portugal rice (which reduces the iAs% of total arsenic while maintaining absolute iAs near the top) reflects complex soil-plant arsenic speciation interactions not fully explained. Cadmium data for commercial rice grain are largely below LOD, providing little quantitative information for Cd risk assessment.
Implications
- Certification: The regional breakdown of Spanish polished rice iAs (Andalucía lowest 54 µg/kg; Extremadura/Portugal highest 87 µg/kg) is directly usable as a geographic_breakdown entry for the rice ingredient page. The finding that ~26% of commercial rice exceeded the EU infant food ML of 100 µg/kg is a supply-chain risk signal. Sourcing from Andalucía or Murcia within Iberia provides a lower-iAs baseline.
- Courses: Strong case study for geographic variance within a single agricultural region. Soil tAs gradient (Portugal/Catalunya highest, Murcia/Extremadura lowest as Murcia) driving plant uptake demonstrates the soil → shoot → grain pathway.
- App: For Spanish/Portuguese market rice ingredients, regional origin matters. Andalucía (54 µg/kg median) and Murcia (57 µg/kg median) polished rice are substantially lower than Extremadura/Portugal (87 µg/kg) or Valencia (63 µg/kg). Brown rice median of ~157 µg/kg is the relevant figure for brown rice ingredient scoring.
- Microbiome: Not primary topic.
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Update history
The five most recent substantive edits to this page, classified major (evidence or structure moved), correction (a published value or statement was wrong and has been fixed), or minor (narrative rewritten without changing the underlying evidence). Each description is derived from what the edit did to this page; the linked commit is the authoritative record, routine regeneration passes are excluded, and the full version history lives in git. When DOI minting comes online (see schema docs), each entry below will also link to a version-pinned DataCite DOI.
| Commit | Date | Change | Description |
|---|---|---|---|
| a8052bb | 2026-08-09 | major | 7 sections added; narrative text revised |