Overview
Manousi and colleagues developed an autoclave digestion and ICP-AES method for walnut oil and applied it to 20 oils pressed from Greek Chandler walnuts, half from conventional and half from organic farming. Cadmium, lead, nickel, chromium, aluminum and several other elements were not detected in any oil. Calcium, iron, magnesium and zinc were quantified per sample.
Key numbers
- Cadmium and lead: “nd” in all 20 oils, with detection limits of 1.53 and 2.43 µg/g (Table 5; Table 2).
- Zinc 8.1 to 14.7 µg/g in conventional and 6.4 to 15.6 µg/g in organic oils (Table 5).
- Iron up to 13.8 µg/g in conventional and 45.6 µg/g in organic oils (Table 5).
Methods (brief)
100 mg oil digested with nitric acid in Teflon autoclaves under heat and pressure, then ICP-AES. Accuracy checked with BCR 278-R and spiked oils (recoveries 85.0 to 110.2%). Each oil analysed in triplicate.
Evidence Fitness
Twenty authentic oils from one region and one walnut variety, not retail products. The detection limits for cadmium and lead are in the microgram-per-gram range, far above typical oil levels, so the non-detects show only that levels were below about 1.5 to 2.4 mg/kg. Arsenic and mercury were not measured, although the text mentions mercury. Walnut oil is a proxy for rice-bran-oil: the paper does not measure rice bran oil, so it is not linked to that page.