Heavy Metal Index
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Determination, distribution, and health risk assessment of 12 heavy metals in various edible oils in Taiwan

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Overview

Lin and colleagues measured 12 heavy metals (As, lead (Pb), cadmium (Cd), nickel (Ni), V, chromium (Cr), Co, Cu, Fe, Zn, Mn, Ba — mercury was not analysed) in 50 commercial edible-oil samples representing 24 oil types (12 refined, 12 unrefined) sold in Taiwan, using ICP-MS after microwave digestion. None of the sampled oils exceeded Taiwan, CODEX, IOC, or EU limits for any analyte. Unrefined (cold-pressed and virgin) oils carried significantly higher concentrations than refined counterparts for 8 of 12 metals, with the largest fold-changes in Mn (468-fold), Ba (23-fold), and Zn (11-fold). Olive oil was the consistent exception: per the source text (page 177), refined olive oil carried higher metal concentrations than unrefined extra-virgin olive oil for every measured metal except Pb, Cr, and Co (note: Table 1 vs Table 2 values in fact show refined > unrefined for Pb and Cr in olive; this paper-internal text-vs-table inconsistency is flagged in Verification notes rather than silently re-synthesised here). Incremental lifetime cancer risk from arsenic exceeded 10⁻⁶ for unrefined oils in every age group except 19–65 years, with the unrefined-sesame-oil ILCR in the 0–3 year group also exceeding 10⁻⁶.

Key numbers

Refined oils, concentration ranges across the 12 oil types (µg/kg, page 177):

  • arsenic (As): 0.325 ~ 2.811
  • Pb: <LOQ ~ 3.338
  • Cd: <LOQ ~ 0.115
  • Ni: <LOQ ~ 14.072
  • V: <LOQ ~ 0.553
  • Cr: <LOQ ~ 7.038
  • Co: <LOQ ~ 0.329
  • Cu: <LOQ ~ 90.123
  • Fe: <LOQ ~ 191.054
  • Zn: 40.506 ~ 128.143
  • Mn: 0.892 ~ 26.315
  • Ba: <LOQ ~ 9.905

Unrefined oils, concentration ranges across the 12 oil types (µg/kg, page 177):

  • As: 0.262 ~ 12.262
  • Pb: 1.516 ~ 45.226
  • Cd: <LOQ ~ 2.512
  • Ni: 0.721 ~ 40.173
  • V: <LOQ ~ 1.449
  • Cr: <LOQ ~ 8.316
  • Co: <LOQ ~ 0.495
  • Cu: 2.075 ~ 111.840
  • Fe: <LOQ ~ 1367.566
  • Zn: 66.768 ~ 128.143
  • Mn: 2.038 ~ 15,105.418
  • Ba: 5.090 ~ 799.567

Refined-oil values for the ingredients with HMI ingredient pages (mean ± SD, µg/kg, Table 1):

  • Corn oil (n=2): As 1.261 ± 0.021; Pb 3.198 ± 0.984; Cd 0.115 ± 0.051; Ni 0.833 ± 0.341; Fe 32.789 ± 20.047; Zn 69.612 ± 16.344; Mn 2.743 ± 0.191; Ba 9.905 ± 0.329
  • Rice bran oil (n=2): As 2.469 ± 0.470; Pb 2.578 ± 0.186; Cd 0.079 ± 0.001; Ni 0.973 ± 0.371; Fe 30.742 ± 2.404; Zn 101.367 ± 39.665; Mn 2.446 ± 0.931; Ba 9.526 ± 3.212; Cu 21.080 ± 3.638
  • Olive oil refined (n=3): As 2.115 ± 0.755; Pb 3.338 ± 3.611; Ni 14.072 ± 18.474; Cr 7.038 ± 5.888; Co 0.329 ± 0.399; Cu 10.566 ± 5.483; Fe 56.122 ± 10.077; Zn 88.288 ± 20.525; Mn 6.122 ± 3.087; Ba 8.310 ± 5.176
  • Sunflower oil refined (n=3): As 0.551 ± 0.288; Pb 0.675 ± 0.368; Cd 0.079 ± 0.116; Ni 1.201 ± 0.388; V 0.155 ± 0.116; Cu 3.223 ± 1.361; Fe 90.123 ± 6.878; Zn 69.607 ± 25.511; Mn 2.296 ± 1.008; Ba 6.470 ± 0.447
  • Canola oil refined (n=3): As 0.678 ± 0.084; Pb 1.000 ± 0.420; Ni 0.273 ± 0.321; Cu 9.821 ± 10.686; Fe 65.364 ± 29.503; Zn 77.171 ± 6.464; Mn 0.892 ± 0.419; Ba 9.092 ± 1.162 (routed to rapeseed-oil slug)
  • Soybean oil refined (n=3): As 1.589 ± 0.870; Pb 1.126 ± 0.698; Ni 0.967 ± 0.167; Cu 4.442 ± 3.991; Fe 55.404 ± 8.561; Zn 95.038 ± 26.591; Mn 1.964 ± 0.441; Ba 6.470 ± 1.793

Unrefined-oil values for the ingredients with HMI ingredient pages (mean ± SD, µg/kg, Table 2):

  • Olive oil unrefined (extra virgin, n=5): As 0.467 ± 0.455; Pb 1.516 ± 0.509; Ni 0.721 ± 0.285; Cr 2.530 ± 0.547; Cu 6.328 ± 2.381; Zn 66.768 ± 17.405; Mn 2.038 ± 0.849; Ba 5.090 ± 1.722
  • Sunflower oil unrefined (n=1): Pb 13.641 ± 9.368; Ni 6.550 ± 3.884; V 0.386 ± 0.205; Cr 4.812 ± 4.661; Co 0.495 ± 0.340; Cu 53.349 ± 31.253; Fe 271.430 ± 49.252; Zn 143.134 ± 23.400; Mn 14.079 ± 2.470; Ba 10.895 ± 6.012
  • Peanut oil unrefined (n=3): As 4.919 ± 1.237; Pb 17.739 ± 4.047; Cd 1.408 ± 1.097; Ni 40.173 ± 62.106; V 0.209 ± 0.126; Cu 101.181 ± 7.608; Fe 910.367 ± 600.046; Zn 513.946 ± 464.134; Mn 350.365 ± 179.116; Ba 23.479 ± 13.708
  • Sesame oil unrefined (n=5): As 12.262 ± 14.574; Pb 6.670 ± 1.689; Cd 0.129 ± 0.079; Ni 2.907 ± 1.256; V 1.449 ± 2.791; Cr 2.906 ± 0.981; Co 0.069 ± 0.025; Cu 106.273 ± 4.700; Fe 265.255 ± 363.774; Zn 204.854 ± 211.290; Mn 26.946 ± 55.366; Ba 83.162 ± 172.522

Pb-vs-Taiwan-upper-limit (0.1 mg/kg = 100 µg/kg) ratios in unrefined oils (page 181): camellia 45.2 %, peanut 17.7 %, sunflower 16.2 %. The authors flag camellia oil specifically for ongoing Pb monitoring.

Refined-vs-unrefined comparison, same oil type (page 177):

  • Refined oils contained significantly lower metal concentrations than their unrefined counterparts for 8 of 12 metals (p < 0.05).
  • Largest fold-decreases in sesame oil: Mn 468.4-fold, Ba 23.2-fold, Zn 11.2-fold lower in refined than unrefined.
  • Olive oil reverses the pattern as the source describes it (page 177): “Concentrations of all of the heavy metals in refined olive oil were higher than those in the unrefined oil, except for Pb, Cr, and Co.” (Table 1 vs Table 2 olive rows in fact show refined > unrefined for Pb and Cr; this paper-internal contradiction is preserved as-written and flagged in Verification notes rather than silently re-synthesised.)

Principal-component / cluster analysis (page 181): PC1 (52.24 % variance) was driven by Cd, Ba, Fe, Pb, Co, Zn, and Mn; PC2 (15.80 %) by As and V. Cluster analysis grouped the 19 oil types into five clusters: (1) corn + safflower + olive + coconut + rice bran (higher Ba, Fe, Zn); (2) canola + cottonseed + soybean + avocado + linseed (lower Mn, As, Ni); (3) palm + peanut (higher Co, As, Ni); (4) sunflower + sesame (lower Mn, Ni); (5) camellia + tea seed (higher Ba, Fe, Mn, Cu).

Health-risk metrics (page 181):

  • All non-carcinogenic hazard quotients < 1 across all age groups for both refined and unrefined oils.
  • Incremental lifetime cancer risk (ILCR, using US EPA oral slope factor 1.5 (kg/day)/mg for inorganic As) from arsenic across both refined and unrefined oils ranged 1.718 × 10⁻⁶ to 1.770 × 10⁻⁸ across age groups; unrefined-sesame ILCR in the 0–3 year group and unrefined oils in all age groups except 19–65 years exceeded the 10⁻⁶ threshold.
  • All other heavy-metal exposure proportions fell well below JECFA PTWI (Cu, Cd, Fe, Zn) and EPA PTDI (As, Pb, Cu, Cd, Ni, Fe, Zn, Mn) reference levels (figure 3, all age groups).

Regulatory limits referenced (mg/kg, page 177): Taiwan: Pb 0.1, As 0.1. CODEX: Pb 0.1, As 0.1, Fe 0.4, Cu 0.4. IOC (olive oils): Pb 0.1, As 0.1, Cu 0.1. EU: Pb 0.1. None of the 50 sampled oils exceeded any of these caps.

Methods (brief)

ICP-MS (Agilent 7800, Tokyo, Japan) after microwave digestion (Multiwave Pro, Anton Paar, Graz, Austria). 0.4-g aliquot of each oil sample digested with 2 mL of 65 % HNO₃ (ultrapure, J.T. Baker) at 800 W for 15 min then 1100 W for 40 min, diluted to 10 mL with deionised water, filtered through 0.45-µm ANPEL filters. Calibration range 0.05 ~ 100 µg/kg from a 100 g/L multi-element AccuStandard stock in 2 % HNO₃; correlation coefficients all > 0.995. Quality control by certified reference material (Merck 109460 Multi-element Standard II Oil Dissolved) analysed at 4 µg/kg in triplicate: recoveries 87 ~ 117 %, coefficients of variation 1.332 ~ 3.128 %. Plasma 1450 W; argon 18 L/min; auxiliary 1.2 L/min; nebuliser 0.96 L/min. Statistical analysis in SPSS 19.0 and Minitab 17; one-way ANOVA with p < 0.05 significance, plus principal component analysis and cluster analysis.

Arsenic is reported as total arsenic (no speciation between inorganic and organic forms); the ILCR calculation conservatively treats the total-As measurement as inorganic-As for risk purposes using the EPA oral slope factor of 1.5 (kg·day)/mg. Mercury (any species) was not analysed in this study because of analytical-method incompatibility with the other 11 metals on the same instrumental run. Chromium is reported as total chromium with no speciation between Cr(III) and Cr(VI).

Implications

Certification: Provides primary measurements for Pb, total arsenic (tAs) (total As), Cd, Ni, Cr (total), and Cu in 24 commercial edible oil types sold in Taiwan, with both refined and unrefined samples for each oil type where market availability permitted. The dataset is directly routeable to products/olive-oil (HMTc Cat 7 Row 1) and products/cooking-oils-other (HMTc Cat 7 Row 2) as primary literature evidence for refined-vs-unrefined heavy-metal occurrence in commercial edible oils.

Courses: The dataset is a strong teaching example of how refining (degumming, deacidification, bleaching, deodorisation) removes heavy metals from edible oils for most oils but not for olive oil, and of how PCA can cluster oils by contamination profile. The 468-fold Mn reduction in refined sesame oil and the camellia-oil Pb monitoring flag are useful single-finding hooks.

App: Unrefined oils carry materially higher heavy-metal loads than refined counterparts for most edible-oil types, with camellia oil, peanut oil, and sunflower oil showing the highest unrefined Pb levels (45.2 %, 17.7 %, and 16.2 % of the Taiwan 0.1 mg/kg cap respectively, page 181). For consumer-facing risk context the app can convey that “cold-pressed/virgin” oils — generally marketed as a premium attribute — also carry higher concentrations of multiple heavy metals than their refined counterparts.

Speciation caution: Arsenic figures are total arsenic. The ILCR calculation treats total As as inorganic As, which is an over-estimating assumption when organic-As fractions are non-trivial; the authors flag the lack of speciation as a limitation. Chromium figures are total chromium with no Cr(VI) discrimination.

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