Determination of some inorganic metals in edible vegetable oils by inductively coupled plasma atomic emission spectroscopy (ICP-AES)

Overview

This study determined nine metals (Cu, Fe, Mn, Co, Cr, Pb, Cd, Ni, Zn) in 17 edible vegetable oil samples from Turkish markets using ICP-AES after direct acid extraction with dilute nitric acid. The study demonstrates a simple sample preparation approach — 2–3 g oil + 1 mL 10% HNO3, shaken and incubated 2 h at 50°C, then centrifuged — that avoided the losses associated with wet digestion or dry ashing. Lead concentrations were below the EC 466/2001 vegetable-oil Pb limit cited by the authors; the paper does not provide vegetable-oil regulatory limits for most other measured metals. Virgin olive oil had the highest lead among oil types (0.0074 mg/kg), and almond oil showed the highest values for Cu, Cr, Ni, and Zn.

Note on evidence tier: downgraded from A to B. The study is older (2008), uses ICP-AES without speciation, and the variety of oil subtypes within a single category (e.g., 5 sunflower oil brands) means per-variety n=1. Total chromium is reported; this cannot be treated as Cr-VI.

Key numbers

All values in mg/kg wet weight. n=17 total; analysis in triplicate.

Selected maximum concentrations by oil type:

Cu: almond oil 0.0850 mg/kg (highest); corn oil-c 0.0082 mg/kg (lowest)
Fe: corn oil-c 0.0352 mg/kg (highest); corn oil-a 0.0039 mg/kg (lowest)
Mn: soybean oil 0.0220 mg/kg (highest); riviera olive-a 0.0007 mg/kg (lowest)
Co: sunflower oil-b and almond oil 0.0040 mg/kg (highest)
Cr (total): almond oil 0.0010 mg/kg (highest); sunflower oil-d 0.0005 mg/kg (lowest) — note: total Cr, not Cr-VI
Pb: virgin olive oil 0.0074 mg/kg (highest); many oils at or near 0 mg/kg
Cd: sunflower oil-e 0.0045 mg/kg (highest); Table 4 reports corn oil-a 0.0002 mg/kg as lowest, despite discussion prose naming almond oil 0.0003 mg/kg
Ni: almond oil 0.0254 mg/kg (highest); natural olive oil 0.0013 mg/kg (lowest)
Zn: almond oil 0.2870 mg/kg (highest); sunflower oil-e 0.0184 mg/kg (lowest)

Key per-oil-type summary (mg/kg, mean ± SD from Tables 2–4): Olive oils (natural, riviera a/b/c, virgin, frying):

Pb: 0.0000–0.0074 (virgin highest); Cd: 0.0009–0.0033; Ni: 0.0013–0.0041; Cu: 0.0097–0.0194; Fe: 0.0125–0.0295 Sunflower oils (a–e):
Pb: 0.0000–0.0026; Cd: 0.0007–0.0045; Ni: 0.0015–0.0060 Corn oils (a–c):
Pb: 0.0000; Cd: 0.0002–0.0013; Fe: 0.0039–0.0352 Soybean oil:
Pb: 0.0000; Cd: 0.0013; Mn: 0.0220; Cu: 0.0273

EU regulatory limit (Regulation EC 466/2001, as noted by authors): Pb 0.10 mg/kg for vegetable oils. All Pb values were below this limit. The authors state that no legislation existed for Cd, Cu, and Zn in vegetable oils at the time of publication; the paper does not identify vegetable-oil limits for the other measured metals.

Recovery: the authors state that average standard-addition recoveries were higher than 95% for all metal ions, although Table 1’s added/found central values are lower for some low-level spikes. Precision: RSD below 10% for Cu, 5% for Fe, 15% for Mn, 8% for Co, 10% for Cr, 20% for Pb, 5% for Cd, 16% for Ni, and 11% for Zn.

Methods (brief)

ICP-AES (Varian Vista). Acid extraction: 2–3 g oil + 1 mL 10% HNO3; shaken at 50 Hz for 60 s; incubated in shaking water bath at 50°C for 2 h; centrifuged at 2800 rpm for 10 min; aqueous layer diluted to 25 mL. No microwave digestion — direct extraction method. Wavelengths: Al 396.152, Cd 228.802, Cu 324.754, Fe 259.940, Mn 257.610, Co 238.892, Cr 257.716, Pb 220.353, Ni 231.604, Zn 213.857 nm. Working range 0.001–0.1 ppm for all metals. No speciation performed: total Pb, total Cd, total Cr. Data collected from Turkish food markets, specific city/date not stated. Study published in Grasas y Aceites (Spain), received 2/2/06, accepted 7/2/08.

Limitation: This is a 2008 study with no speciation. The method is dilute-acid extraction rather than total microwave digestion or dry ashing, so comparisons with digestion-based studies should preserve the sample-preparation difference. Per-oil n=1–5 across 17 total samples, with several oil subtypes represented by one sample.

Implications

Certification (HMTc): Provides historical Turkish market baseline values for Pb and Cd in edible vegetable oils. Values are low in this 17-sample set (Pb maximum 0.0074 mg/kg in virgin olive oil, Cd maximum 0.0045 mg/kg in sunflower oil-e) and sit well below the EC 466/2001 Pb limit cited by the authors.
Courses: Useful as an older reference illustrating the acid-extraction methodology for ICP-AES and the range of metals determinable in a single run. Also illustrates that total Cr data (not Cr-VI) does not enable toxicological assessment for the hexavalent form.
App: Values are low and relatively dated (2008, Turkish market). Use only for broad order-of-magnitude framing; prefer more recent and larger-n studies for ingredient profiling.

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Verification notes

2026-05-17 Codex merge-enhance: identity checked against the manual-fetch PDF; corrected legacy raw_handle/truncated path, replaced the erroneous products/nuts-seeds-other route with products/olive-oil and products/cooking-oils-other, changed legacy headings to current source-page headings, and removed the non-taxonomy testing/icp-oes wikilink.
Source reports total Cr by ICP-AES, not Cr-VI; the page therefore uses Cr and links [[metals/chromium]].
olive-oil, sunflower-oil, corn-oil, soybean-oil, hazelnut-oil, almond-oil, and edible-oil are source-specific matrix descriptors used for routing/context; ingredient and product declarations use existing wiki slugs.
2026-05-18 Codex DOI cleanup: DOI, access URL, license, and raw SHA-256 verified against article metadata and the local manual-fetch PDF. The local PDF does not print the DOI, so DOI provenance is from the article metadata rather than the PDF body.
2026-05-18 Codex regulation cleanup: created Commission Regulation (EC) No 466/2001 setting maximum levels for certain contaminants in foodstuffs as the historical regulation node for the EC 466/2001 citation; the paper’s Pb 0.10 mg/kg vegetable-oil benchmark is preserved as an author-cited comparison.
2026-05-18 Cross-vendor audit (Codex) tightened regulatory framing: the paper supports the EC 466/2001 Pb comparison and explicitly says no legislation existed for Cd, Cu, and Zn, but it does not support a broad all-metals “within regulatory limits” statement or a Ni no-limit claim.
Source-internal note: the Discussion prose says the lowest Pb value was 0.012 mg/kg for sunflower oil (c), but Table 3 reports 0.0012 mg/kg for sunflower oil (c) and several 0.0000 entries; this page follows Table 3. The prose also says the lowest Cd value was 0.0003 mg/kg in almond oil, while Table 4 reports 0.0002 mg/kg in corn oil (a); this page follows Table 4.

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
e317189	2026-08-11	correction	7 sections added; narrative text revised