Overview
Thompson-Morrison and colleagues measured pseudo-total element concentrations in oil palm plant tissues (leaves, mesocarps, endosperms) from three Sumatra plantation sites and in a commercially refined palm oil product using ICP-MS after microwave digestion (EPA Method 3051A). The study covered 23 elements across cadmium, lead, arsenic, mercury, chromium, nickel, aluminium, and 16 additional elements. In the refined palm oil, arsenic, mercury, and zinc were below the instrument LOQ (0.01 mg/kg). Cadmium was 0.015 mg/kg, lead was 0.075 mg/kg, chromium was 0.080 mg/kg, and nickel was 0.040 mg/kg. Aluminium was 159 mg/kg, unusually high and attributed by the authors to soil or dust contamination and possibly aluminium-containing clay flocculants used in processing. At a consumption of 37.1 g/day palm oil, no element exceeded the tolerable weekly intake or maximum dietary reference intake. The paper identifies low bioaccumulation from soil to mesocarp for lead (BAC 0.001 to 0.003), cadmium (0.10 to 0.13), and arsenic (below LOQ).
Key numbers
Refined palm oil (Table 6, mean with standard error, mg/kg, n = 10 replicate digests):
All values wet weight. LOQ = 0.01 mg/kg throughout.
Converting to micrograms per kilogram (ppb): cadmium (Cd) approximately 15 µg/kg, lead (Pb) approximately 75 µg/kg, chromium (Cr) approximately 80 µg/kg, nickel (Ni) approximately 40 µg/kg, aluminum (Al) approximately 159,000 µg/kg.
Mesocarp (Table 4, representative of unrefined fruit flesh, mean or single value, dry weight, mg/kg):
- Cr: 3.8 to 4.0 across sites
- Ni: 2.1 to 2.0
- arsenic (As): below LOQ
- Cd: 0.014 to 0.010
- mercury (Hg): below LOQ
- Pb: 0.053 to 0.060
Bioaccumulation coefficients (BAC = plant tissue / soil concentration, Table 5):
- Cd mesocarp: 0.10 to 0.13
- Pb mesocarp: 0.0012 to 0.0033
- As mesocarp: below calculation limit (As in fruit below LOQ)
- Cu mesocarp: 0.37 to 2.5
Tolerable intakes at 37.1 g/day palm oil (Table 6):
- Al: maximum consumed 0.59 mg/day vs tolerable weekly intake 1 mg/kg bw/wk (not exceeded for a 60 kg adult)
- Cd: maximum consumed below 0.0001 mg/kg bw/wk vs tolerable weekly intake 0.007 mg/kg bw/wk
- Hg: below LOQ vs tolerable weekly intake 0.016 mg/kg bw/wk
- Pb: below 0.0001 mg/kg bw/wk vs tolerable weekly intake 0.025 mg/kg bw/wk
The authors state: “elemental concentrations in refined palm oil were lower than food safety standards and posed no risk of elemental toxicity.”
Methods (brief)
Pseudo-total digestion by EPA Method 3051A microwave (HNO3, closed vessel). ICP-MS (not stated which instrument). LOQ 0.01 mg/kg (dry weight for plant tissue; wet weight for oil). Two CRMs run with every 11 samples; recovery data in Supplementary Table S1. Sample n: oil 10 replicate digests of one commercial product. Plant tissues: 10 samples Site A, 7 Site B, 3 to 4 Site C (varying by tissue type). Speciation: total elements throughout; arsenic and mercury are reported as totals, not speciated. All oil values are wet weight; plant tissue values are dry weight.
Implications
Certification: This is the most methodologically robust direct measurement of refined palm oil in this deposit (ICP-MS, CRM-validated, published recoveries). Lead at 75 µg/kg wet weight is below the Codex maximum level of 100 µg/kg for edible fats and oils (CXS 193-1995 as amended). Cadmium at 15 µg/kg is below the Codex maximum of 100 µg/kg. Arsenic and mercury were below the 10 µg/kg LOQ, so these values bound the upper end of the range rather than establishing a central estimate. Aluminium at 159 mg/kg is a process-contamination finding rather than a soil-transfer signal; the authors discuss flocculant and soil/dust routes.
Courses: This paper is a useful worked example of the difference between soil-to-plant and plant-to-oil transfer pathways, the role of bleaching earths and clays in modifying trace element content during refining, and the difference between total and speciated arsenic and mercury.
App: Pb 75 µg/kg and Cd 15 µg/kg are point estimates for one Indonesian refined palm oil product. As and Hg are bounded above 10 µg/kg. These should be combined with the Bangladesh retail composite data from Shaheen et al. 2024 for a multi-source estimate.
Related evidence
- Palm oil
- Other cooking oils (canola, sunflower, coconut, avocado, sesame)
- Lead
- Cadmium
- Arsenic
- Mercury
- Nickel
- Aluminum
- Chromium
Update history
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