Concentration of Trace Metals in Some Major Edible Oils of Riyadh

Overview

Alrajhi and Idriss measured trace metals in 54 edible vegetable oil samples bought from supermarkets around Riyadh. The study is routeable occurrence evidence for the broad cooking-oils row because Table I reports sample-level and summary concentrations for Cd, Cr, Cu, Fe, Mn, Ni, Zn, Al, Pb, total As, and Se in finished edible oils on an mg/kg basis.

Key numbers

Table I reports all concentrations in mg/kg. The table lists 54 individual samples and then gives source-reported summary statistics:

Metal	Minimum	Maximum	Average	Standard deviation	Notes
Cd	0.001	0.011	0.0006	0.002	Detected in 14 of 54 samples; non-detects reported as LDL.
Cr	0.002	1.898	0.072	0.307	Discussion text gives an average of 0.026 mg/kg, conflicting with the summary table.
Cu	0.001	0.081	0.011	0.013	Source compares the range with a 0.002 mg/kg control sample.
Fe	0.025	7.861	0.362	1.256	Highest table value was sample 27 at 7.861 mg/kg.
Mn	0.001	0.128	0.006	0.020	Discussion text says detected in 43 of 54 samples.
Ni	0.002	1.215	0.065	0.196	Highest table value was sample 27 at 1.215 mg/kg.
Zn	0.001	0.511	0.047	0.077	Highest table value was sample 46 at 0.511 mg/kg.
Al	0.012	0.425	0.060	0.073	Source reports limited comparison data for Al in edible oils.
Pb	0.004	0.087	0.011	0.018	Discussion says Pb was detected in 16 of 37 samples; the study otherwise reports 54 samples.
Total As	0.010	0.975	0.170	0.229	ICP-OES total arsenic; not arsenic speciation.
Se	0.050	0.890	0.172	0.215	Strong source-reported correlation with total As.

The authors conclude that the measured concentrations were below the FAO/WHO limits they cite for edible oils, including Cd 0.5 mg/kg, Pb 0.1 mg/kg, and As 0.5 mg/kg. The study also reports strong correlations for Cr-Fe (0.998), Cr-Mn (0.994), Cr-Ni (0.985), Fe-Mn (0.994), Fe-Ni (0.985), Mn-Ni (0.978), and As-Se (0.997).

Methods (brief)

Samples were collected from supermarkets around Riyadh and described as soybean, palm, and olive oils. For each oil, 2 g sample was digested with 10 mL 65% nitric acid and 2 mL 30% hydrogen peroxide, held in a fume cupboard for two days, heated at 80 degrees C until transparent, filtered, and diluted to 45 mL.

Metals were measured by ICP-AES/ICP-OES using a Genesis ICP optical emission spectrometer with axial plasma observation. The paper reports element-specific detection limits of 0.0001 mg/kg for Cd and Zn, 0.001 mg/kg for Cr, Cu, Ni, and Al, 0.002 mg/kg for Fe, 0.003 mg/kg for Mn, 0.004 mg/kg for Pb, and 0.01 mg/kg for As and Se. Recovery was described as nearly quantitative, around 95%, with relative standard deviations below 10%.

Implications

Certification: This source adds Saudi-market edible vegetable oil occurrence data for the broad cooking-oils row. Because sample rows are not labeled by oil type in the extracted table, the values should not be split into soybean-oil, palm-oil, or olive-oil benchmark pools without additional source support.

App: Useful for showing that edible oil evidence can include both essential trace elements and toxic metals in the same ICP-OES panel. Total arsenic should remain separate from inorganic arsenic.

Courses: Useful for teaching non-detect notation, table-vs-text contradictions, and jurisdiction-aware product evidence routing.

Wiki pages this source may touch

Verification notes

This page was built from the full PDF, including Table I sample rows and summary statistics, the digestion and ICP-OES method description, the discussion sections for each metal, Table II correlations, and the conclusion. Three internal inconsistencies were retained rather than silently corrected: Table I reports an average Cr concentration of 0.072 mg/kg while the discussion text gives 0.026 mg/kg; the Mn discussion text on page 981 reports an average of 0.002 mg/kg while Table I gives 0.006 mg/kg; and the Pb discussion says “16 of the 37 samples” although the study and Table I describe 54 samples. This page follows the Table I summary statistics for concentration values and flags all three conflicts for audit. A separate paper-side typo where the Cd discussion paragraph opens with “Ca was detected in 14 of the 54 samples” is also noted; the paper clearly intends Cd given the surrounding numbers and FAO/WHO Cd limit.

Audit subagent 2026-06-02 flagged Se / selenium as outside the current Metals taxonomy (no metals/selenium.md page; selenium not in the snapshot’s Metals list). Verified — Se was dropped from metals: frontmatter and the [[metals/selenium]] bullet was removed from “Wiki pages this source may touch”. The selenium data in Table I (range 0.05-0.89 mg/kg, average 0.172 mg/kg, strong correlation with total As at 0.997) remains in the Key numbers table and is preserved here for the day a selenium metal page is added; flagging selenium as a proposed Metals slug addition for Karen.

Audit subagent 2026-06-02 flagged matrices: [edible-oil, vegetable-oil, soybean-oil, palm-oil, olive-oil] as over-specified because Table I sample rows are not labeled by oil type. Verified — the page’s own Implications already states that values should not be split into soybean-oil/palm-oil/olive-oil benchmark pools. Collapsed matrices to [edible-oil, vegetable-oil] per the system-prompt broad-scope rule.

[[testing/icp-oes]] is referenced in the “Wiki pages this source may touch” section but no wiki/testing/icp-oes.md exists yet. Retained because five other source pages use the same placeholder; flagging testing/icp-oes as a proposed testing-methods page (companion to the existing wiki/testing/icp-ms.md).

Update history

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