Hu et al. 2023 — Heavy metals in Heijing 5 rice grain at high latitude (Sweden vs China)
This study evaluates Heijing 5, a japonica rice cultivar from Heilongjiang province China, for low methane emissions and its performance at high-latitude growing conditions. As part of field trials in Uppsala, Sweden (59.81°N) and Nanjing, China (32.05°N), the authors measured total As, Pb, and Cd in mature rice grains from both sites using ICP at an accredited laboratory (Eurofins Sweden). The Swedish cultivation produced grains with notably lower heavy metal concentrations than literature values for rice from Asia, attributed to the low background contamination of Swedish paddy soils. All values were substantially below FAO/WHO Codex limits.
Key numbers
Uppsala (Sweden) rice grain concentrations (mean ± SD), n≥4, dry weight:
- Total As: 0.064 ± 0.011 mg·kg⁻¹ (64 ± 11 ppb)
- Total Pb: <0.02 mg·kg⁻¹ (<20 ppb, below detection)
- Total Cd: 0.055 ± 0.025 mg·kg⁻¹ (55 ± 25 ppb)
Uppsala paddy soil (mg·kg⁻¹ dry weight):
- Total As: 6.0 ± 0.51
- Total Pb: 20.75 ± 1.89
- Total Cd: 0.94 ± 0.83
FAO/WHO Codex limits cited (mg·kg⁻¹):
- Total As: 0.35 (Codex CXS 193-1995)
- Pb: 0.2
- Cd: 0.4
Comparative literature data compiled by authors (Table 1, total As / total Pb / total Cd, all mg·kg⁻¹):
- Bangladesh: 0.137 / 0.375 / 0.088
- India: 0.066 / 0.267 / —
- China: 0.187 / 0.28±0.06 / 0.229
- Thailand: 0.137 / 0.419 / 0.329
- Italy: 0.275 / 0.317 / 0.034±0.007
- Australia: 0.27 / 0.375 / —
Methods (brief)
Mature raw rice grains from field trials analyzed for total As, Cd, and Pb at Eurofins Sweden (accredited laboratory, ISO/IEC 17025:2005 SWEDAC 1125). Methods follow Fei et al. (2020). Speciation not reported; values are total arsenic. All values reported as dry weight. Sample size n≥4 per site.
Limitation: Nanjing (China) grain values are not reported separately for this paper’s field trials; the paper presents only Uppsala values as primary data and uses published literature for the comparative table. The Chinese site data for this cultivar under field conditions were measured and are summarized as “within ranges” but exact values for Nanjing under this study’s conditions are not individually tabulated.
Implications
Certification: The Swedish cultivation data provide a reference for Heijing 5 rice grown in unpolluted temperate soil. Total As of 64 ppb is well below any proposed threshold; Cd of 55 ppb is also well below thresholds. Pb was below LOD (<20 ppb). These are among the cleanest rice grain values in the comparative literature.
Courses: Illustrates how soil background contamination is the primary driver of rice grain heavy metal concentrations; the same cultivar in Swedish (unpolluted) vs Asian (higher background) soils shows dramatically different grain values.
App: Supports low-risk classification for rice grown in Scandinavian/northern European cultivation systems. Does not generalize to typical commercial rice supply chain.
Microbiome: Not applicable.