Clinical Pharmacist and Master’s student in Clinical Pharmacy with research interests in pharmacovigilance, behavioral interventions in mental health, and AI applications in clinical decision support. Experience includes digital health research with Bloomsbury Health (London) and pharmacovigilance practice in patient support programs. Published work covers drug awareness among healthcare providers, postpartum depression management, and patient safety reporting. 
Clinical Pharmacist and Master’s student in Clinical Pharmacy with research interests in pharmacovigilance, behavioral interventions in mental health, and AI applications in clinical decision support. Experience includes digital health research with Bloomsbury Health (London) and pharmacovigilance practice in patient support programs. Published work covers drug awareness among healthcare providers, postpartum depression management, and patient safety reporting. What was studied
This study quantified nickel oral bioavailability in rice and wheat grown on naturally (geogenically) nickel-enriched soils, then used those bioavailability values to estimate real-world dietary exposure risk relevant to certification decisions. Researchers sampled paired soils and staple grains from a high–background nickel region in Xuyi County, Jiangsu Province, China, where nickel originates from ultramafic rock weathering rather than mining or smelting. They measured total nickel in soils and crops, characterized soil nickel fractions (to understand how tightly nickel is bound), and—most importantly for exposure assessment—measured oral relative bioavailability (RBA) using a newly developed mouse urinary nickel excretion bioassay benchmarked against soluble nickel sulfate (NiSO₄). The work explicitly compared two exposure routes that matter for programs like HMTC: food consumption (rice/wheat) versus incidental soil ingestion, with bioavailability used to avoid overestimating risk from total concentrations alone.
Who was studied
The primary “who” in this research was not human participants but a connected soil–crop–consumer system evaluated through field sampling and an in vivo bioassay. Field sampling included 58 farmland soils (29 wheat-season soils and 29 rice-season soils) and corresponding grain samples (29 wheat grains and 29 rice grains) collected across two campaigns (2016 and 2019) in the same agricultural landscape. For bioavailability testing, laboratory mice (BALB/c, ~16 g body weight) were used in metabolic cages to measure how much ingested nickel appeared in urine after consuming diets amended with real rice, wheat, or soil materials, with NiSO₄ as the reference compound. This design matters for HMTC-style interpretation because it links what is present in a crop to what is plausibly absorbed by a consumer, rather than assuming 100% absorption from measured nickel content.
Most important findings
For heavy metal certification, the headline is that rice combined higher nickel content with higher bioavailability, making it the dominant contributor to bioavailable nickel intake in this geogenic setting, while direct soil ingestion contributed little once low soil bioavailability was considered.
| Critical point | Details |
|---|---|
| Geogenic soils exceeded a key benchmark | Mean soil Ni was ~80.5 ± 23.0 mg/kg (n=58), about 1.34× higher than China’s agricultural soil risk control value of 60 mg/kg noted by the authors, while other metals (As, Cd, Pb, etc.) were well below their limits—isolating Ni as the main concern. |
| Rice accumulated ~2× more Ni than wheat | Rice grains averaged 2.66 ± 1.46 mg/kg Ni versus wheat at 1.32 ± 0.78 mg/kg, indicating crop type strongly affects contaminant loading even on similar soils. |
| Bioavailability was highest in rice | Mean Ni-RBA was ~85.9% in rice (n=9) versus ~46.1% in wheat (n=16), while soils were far lower (~14.8% overall; rice-soil and wheat-soil samples ~16.5% and ~13.0%). This is a certification-relevant reminder that “mg/kg in product” is not the same as “absorbed dose.” |
| Iron status appeared to drive consumer uptake | Ni-RBA negatively correlated with grain iron (r≈0.61), supporting a mechanism where low-Fe rice promotes higher nickel absorption via shared intestinal iron transport pathways—an insight for risk-based labeling and matrix-aware standards. |
| Rice dominated bioavailable daily intake | Using local adult consumption rates (255 g/day rice; 82 g/day wheat) and RBA, estimated Ni intake from rice averaged ~12.2 µg/kg-bw/day—about 14× higher than wheat (~0.84 µg/kg-bw/day); soil ingestion was negligible (~0.02 µg/kg-bw/day). |
Key implications
For HMTC decision-making, the regulatory impact is that geogenic nickel can create meaningful dietary exposure even without industrial pollution, so certification requirements should treat nickel oral bioavailability in rice as matrix- and nutrient-dependent rather than relying on total nickel alone. Industry applications include prioritizing rice-based ingredients from high-background regions for enhanced sourcing controls, adding iron-status or compositional context when interpreting risk, and using bioavailability-adjusted intake modeling to set practical pass/fail thresholds. Research gaps include human biomonitoring validation and standardized, program-ready bioavailability methods for nickel across food matrices. Practical recommendations are to implement region-of-origin screening, require commodity-specific nickel limits (rice tighter than wheat), and consider bioavailability-informed criteria where feasible.
Citation
Li H-B, Wang J-Y, Chen X-Q, Li Y-P, Fan J, Ren J-H, Luo X-S, Juhasz AL, Ma LQ. Geogenic nickel exposure from food consumption and soil ingestion: A bioavailability based assessment. Environmental Pollution. 2020;265:114873. doi:10.1016/j.envpol.2020.114873
Nickel is a widely used transition metal found in alloys, batteries, and consumer products that also contaminates food and water. High exposure is linked to allergic contact dermatitis, organ toxicity, and developmental effects, with children often exceeding EFSA’s tolerable daily intake of 3 μg/kg bw. Emerging evidence shows nickel crosses the placenta, elevating risks of preterm birth and congenital heart defects, underscoring HMTC’s stricter limits to safeguard vulnerable populations.
