AbdElgawad et al. 2023 — Chromium accumulation in rice grain under elevated CO2
This controlled experiment examines chromium (Cr, as Cr6+) toxicity and grain accumulation in two Egyptian rice cultivars (Sakha 106 and Giza 181) grown in soil spiked with 200 and 400 mg Cr(VI)/kg. The study tests whether elevated CO2 (eCO2) mitigates chromium stress and grain accumulation. Results show that eCO2 reduced Cr uptake in rice grain and improved plant physiology under Cr stress, with potential climate-change implications for managing chromium contamination in rice cultivation.
Key numbers
Soil Cr concentrations tested: 200 and 400 mg Cr(VI)/kg soil (severely contaminated scenario, above normal agricultural soil). These are experimental spiking levels, not field measurements.
Grain Cr concentrations: at 200 mg/kg soil Cr, grain Cr accumulation in Sakha 106 was approximately 3–5 mg/kg (dry weight) under ambient CO2; eCO2 reduced this by approximately 30–40%. At 400 mg/kg soil Cr, grain accumulation increased substantially. Exact values per table require confirming in the full paper figures.
Cultivar differences: Sakha 106 showed higher Cr uptake efficiency than Giza 181 under the same soil conditions.
eCO2 effect: elevated CO2 (700 ppm vs. 400 ppm ambient) consistently reduced both shoot Cr concentration and grain Cr concentration, associated with reduced oxidative stress markers and enhanced antioxidant capacity.
Methods (brief)
Pot experiment with Egyptian sandy clay loam soil spiked with K2Cr2O7 to achieve target soil Cr levels. Two cultivars; two CO2 levels (ambient 400 ppm; elevated 700 ppm); two Cr doses (0, 200, 400 mg/kg). Grain and shoot samples analyzed by ICP-OES for total chromium (not speciated for Cr-VI vs. Cr-III in grain). Biochemical assays for oxidative stress markers, antioxidant enzymes.
Limitation: experimental contamination levels (200–400 mg/kg soil) far exceed typical agricultural soil Cr backgrounds (5–50 mg/kg). Results indicate directional effects under extreme contamination; cannot be directly extrapolated to field concentrations. Total Cr reported, not hexavalent Cr-VI.
Implications
Certification: Documents Cr accumulation in rice grain under severe soil contamination. The Cr data should be flagged as experimental-spiking scenario, not representative of market rice concentrations. The Cr-VI vs total Cr distinction is critical (Part 14 convention: total Cr in ingredient profile; Cr-VI evidence belongs on metals/chromium-hexavalent).
Courses: Useful for the supply-chain module on agronomic levers — illustrates that CO2 level and cultivar selection affect Cr accumulation, though the practical takeaway for current agriculture is limited without field validation.
App: Experimental spiking study. Does not contribute to contamination_profile typical_ppb values for market rice; values are specific to severely contaminated soil conditions.
Microbiome: Not applicable.