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Health risk assessment of eight heavy metals in nine varieties of edible vegetable oils consumed in China

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Overview

Zhu and colleagues measured eight heavy metals (Cu, Zn, Fe, Mn, cadmium (Cd), nickel (Ni), lead (Pb), total As) in 109 commercial edible vegetable oil samples spanning nine oil types (soybean, corn, peanut, sesame, rapeseed, cottonseed, olive, blend, sunflower) purchased from Chinese supermarkets during 2009-2010, using ICP-AES (Cu, Zn, Fe, Mn) and GF-AAS (Cd, Ni, Pb, As) after HNO₃/H₂O₂ microwave digestion. Iron was the dominant element across all oil types (16.2-45.3 µg/g), followed by zinc (0.742-2.56 µg/g) and copper (0.021-0.265 µg/g per Table 3 means; the abstract’s Cu range “0.214-0.875 µg g⁻¹” is anomalous and contradicts both the paper’s own body-text statement at §3 that “minimum and maximum values of copper in our samples were 0.021 and 0.265 µg g⁻¹” and every cell in Table 3, see Verification notes). Cadmium concentrations were higher in these Chinese oils than in most prior literature reports (2.64-8.43 ng/g; reported by the source at p.3083 as a comparative observation). Two-way ANOVA found that oil type had a highly significant effect on the concentrations of all measured metals except Pb (p = 8.66 × 10⁻⁴ per Table 3 notation 0.866E-3, still strongly significant) and Ni (p = 0.156, not significant); oil-source brand and type × source interaction were non-significant for every analyte. Estimated daily dietary intakes (EDDIs) from 25 g/day consumption and estimated weekly dietary intakes (EWDIs) from 175 g/week consumption fell well below the relevant IOM RDA/AL and UL, US EPA RfDo, JECFA PTWI, and WHO guideline values for a 70 kg adult.

Key numbers

Concentration ranges across the nine oil types, mean of n=11-14 samples per type (Table 3, µg/g unless noted):

  • Cu: 0.021 ~ 0.265 (corn 0.021 ± 0.002, range 0.017-0.026 lowest; olive 0.265 ± 0.018, range 0.248-0.276 highest; per-sample upper-bound across all 9 types is 0.276 in olive)
  • Zn: 0.742 ~ 2.56 (soybean 0.742 ± 0.061, range 0.671-0.804 lowest; corn 2.56 ± 0.211, range 2.23-2.85 highest)
  • Fe: 16.2 ~ 45.3 (corn 16.2 ± 0.9, range 15.1-16.8 lowest; peanut 45.3 ± 2.8, range 44.7-46.6 highest)
  • Mn: 0.113 ~ 0.556 (olive 0.113 ± 0.008, range 0.098-0.120 lowest; peanut 0.556 ± 0.043, range 0.543-0.613 highest)
  • Cd (ng/g): 2.64 ~ 8.43 (olive 2.64 ± 0.17, range 2.39-2.78 lowest; corn 8.43 ± 0.47, range 8.27-8.66 highest)
  • Ni: 0.026 ~ 0.075 (corn 0.031 ± 0.002, range 0.026-0.035; sesame 0.075 ± 0.005, range 0.066-0.083 highest)
  • Pb: 0.009 ~ 0.018 (corn 0.009 ± 0.001, range 0.007-0.012 lowest; sesame 0.018 ± 0.002, range 0.014-0.022 highest)
  • arsenic (As): 0.009 ~ 0.019 (corn 0.012 ± 0.001, range 0.007-0.015; sesame 0.019 ± 0.001, range 0.015-0.023 highest)

Per-oil-type mean ± SD, all eight metals (Table 3, µg/g except Cd in ng/g):

  • Soybean oil (n=13): Cu 0.053 ± 0.004 (0.048-0.056); Zn 0.742 ± 0.061 (0.671-0.804); Fe 22.5 ± 1.4 (21.6-23.1); Mn 0.154 ± 0.012 (0.145-0.164); Cd 4.36 ± 0.32 ng/g (4.13-4.52); Ni 0.053 ± 0.003 (0.043-0.064); Pb 0.015 ± 0.001 (0.012-0.018); As 0.015 ± 0.001 (0.010-0.018)
  • Corn oil (n=12): Cu 0.021 ± 0.002 (0.017-0.026); Zn 2.56 ± 0.211 (2.23-2.85); Fe 16.2 ± 0.9 (15.1-16.8); Mn 0.327 ± 0.026 (0.305-0.346); Cd 8.43 ± 0.47 ng/g (8.27-8.66); Ni 0.031 ± 0.002 (0.026-0.035); Pb 0.009 ± 0.001 (0.007-0.012); As 0.012 ± 0.001 (0.007-0.015)
  • Peanut oil (n=14): Cu 0.166 ± 0.022 (0.146-0.173); Zn 1.30 ± 0.09 (1.18-1.42); Fe 45.3 ± 2.8 (44.7-46.6); Mn 0.556 ± 0.043 (0.543-0.613); Cd 3.81 ± 0.25 ng/g (3.65-3.91); Ni 0.026 ± 0.002 (0.019-0.031); Pb 0.012 ± 0.001 (0.007-0.015); As 0.013 ± 0.001 (0.010-0.017)
  • Sesame oil (n=12): Cu 0.039 ± 0.003 (0.028-0.045); Zn 0.883 ± 0.067 (0.789-0.981); Fe 38.5 ± 2.3 (37.9-40.4); Mn 0.184 ± 0.014 (0.171-0.195); Cd 5.44 ± 0.28 ng/g (5.27-5.64); Ni 0.075 ± 0.005 (0.066-0.083); Pb 0.018 ± 0.002 (0.014-0.022); As 0.019 ± 0.001 (0.015-0.023)
  • Rapeseed oil (n=11): Cu 0.187 ± 0.014 (0.177-0.196); Zn 1.57 ± 0.12 (1.42-1.69); Fe 27.6 ± 1.6 (26.8-28.4); Mn 0.121 ± 0.009 (0.116-0.125); Cd 6.33 ± 0.31 ng/g (6.11-6.45); Ni 0.048 ± 0.003 (0.041-0.056); Pb 0.012 ± 0.001 (0.007-0.016); As 0.015 ± 0.001 (0.012-0.020)
  • Cottonseed oil (n=12): Cu 0.033 ± 0.003 (0.025-0.039); Zn 1.64 ± 0.12 (1.48-1.82); Fe 36.8 ± 2.1 (35.1-37.6); Mn 0.227 ± 0.017 (0.206-0.238); Cd 4.62 ± 0.25 ng/g (4.39-4.82); Ni 0.038 ± 0.003 (0.032-0.048); Pb 0.011 ± 0.001 (0.007-0.015); As 0.008 ± 0.001 (printed range 0.016-0.022 — mathematically inconsistent with the mean ± SD, preserved as printed; see Verification notes)
  • Olive oil (n=12): Cu 0.265 ± 0.018 (0.248-0.276); Zn 1.41 ± 0.08 (1.24-1.58); Fe 34.1 ± 2.1 (32.8-35.4); Mn 0.113 ± 0.008 (0.098-0.120); Cd 2.64 ± 0.17 ng/g (2.39-2.78); Ni 0.053 ± 0.003 (0.046-0.061); Pb 0.013 ± 0.001 (0.009-0.016); As 0.012 ± 0.001 (0.008-0.015)
  • Blend oil (n=11, admixture of sunflower + rapeseed + soybean): Cu 0.053 ± 0.003 (0.042-0.059); Zn 0.965 ± 0.073 (0.852-1.11); Fe 27.3 ± 1.5 (25.7-28.5); Mn 0.388 ± 0.031 (0.368-0.412); Cd 4.12 ± 0.26 ng/g (3.91-4.32); Ni 0.026 ± 0.003 (0.022-0.035); Pb 0.015 ± 0.001 (0.009-0.021); As 0.009 ± 0.001 (0.006-0.012)
  • Sunflower oil (n=12): Cu 0.066 ± 0.005 (0.052-0.068); Zn 1.23 ± 0.06 (1.04-1.33); Fe 29.2 ± 1.7 (27.3-29.8); Mn 0.445 ± 0.035 (0.413-0.471); Cd 3.51 ± 0.23 ng/g (3.34-3.75); Ni 0.034 ± 0.002 (0.028-0.041); Pb 0.010 ± 0.001 (0.006-0.015); As 0.011 ± 0.001 (0.007-0.014)

Concentration ranges restated in µg/kg (ppb) for cross-source comparability (Table 3 means; per-sample upper bounds in parentheses where they differ):

  • Cu: 21 ~ 265 µg/kg (per-sample upper bound 276 µg/kg in olive)
  • Zn: 742 ~ 2,560 µg/kg
  • Fe: 16,200 ~ 45,300 µg/kg
  • Mn: 113 ~ 556 µg/kg
  • Cd: 2.64 ~ 8.43 µg/kg
  • Ni: 26 ~ 75 µg/kg
  • Pb: 9 ~ 18 µg/kg (per-sample upper bound 22 µg/kg in sesame; per-sample upper bound 21 µg/kg in blend)
  • As (total): 8 ~ 19 µg/kg (per-sample upper bound 23 µg/kg in sesame; printed cottonseed per-sample range 16-22 is paper-internally inconsistent with cottonseed mean ± SD of 0.008 ± 0.001 — see Verification notes)

Two-way ANOVA p-values for oil-type effect (Table 3): Cu 2.56 × 10⁻¹⁵; Zn 1.08 × 10⁻¹⁷; Fe 2.67 × 10⁻¹⁹; Mn 8.99 × 10⁻²⁵; Cd 1.29 × 10⁻²²; Ni 0.156 (not significant); Pb 8.66 × 10⁻⁴ (Table 3 prints “0.866E−3” = 0.000866); As 2.57 × 10⁻⁷. Oil source (brand) and type × source interaction were not significant for any of the eight metals (all p > 0.10).

Method validation (Table 2, n=3 CRM replicates):

  • GBW10018 (chicken) recoveries: Cu 97 %, Zn 96 %, Fe 103 %, Mn 98 %, Ni 106 %, Pb 96 %, As 99 %.
  • GBW08551 (porcine liver) recoveries: Cu 97 %, Zn 101 %, Fe 103 %, Mn 99 %, Cd 97 %, Pb 96 %, As 98 %.
  • Detection limits (mg/L): Cu 0.018, Zn 0.010, Fe 0.016, Mn 0.020, Cd 0.09, Ni 0.35, Pb 0.18, As 0.17. RSDs < 10 % for every analyte.

Estimated daily dietary intake (EDDI) from 25 g/day consumption, % of IOM AL or UL (Table 4):

  • Cu: EDDI 0.525-6.63 µg/day per 70 kg adult; % of IOM RDA/AL 990 µg/day = 0.053-0.670 %; % of IOM UL 10,000 µg/day = 0.005-0.066 %. Olive oil EDDI 6.63 µg/day is the highest among the nine types but contributes only 0.670 % of the AL.
  • Zn: EDDI 18.6-41.0 µg/day; % AL (11,000 µg/day) = 0.17-0.582 %; % UL (40,000 µg/day) = 0.047-0.160 %.
  • Fe: EDDI 405-1,132.5 µg/day; % AL (8,000 µg/day) = 5.06-14.2 %; % UL (45,000 µg/day) = 0.900-2.52 %. Peanut oil contributes the largest fraction (Fe AL 14.2 %, UL 2.52 %).
  • Mn: EDDI 3.03-13.9 µg/day; % AL (2,300 µg/day) = 0.123-0.604 %; % UL (11,000 µg/day) = 0.026-0.126 %.
  • Ni: EDDI 0.775-1.88 µg/day; % UL (40,000 µg/day) = 0.002-0.005 %.

Estimated weekly dietary intake (EWDI) from 175 g/week consumption, % of WHO/JECFA guidance (Table 5):

  • Cd: EWDI 0.007-0.021 µg/kg bw per week (computed against 70 kg bw); % JECFA PTWI 7 µg/kg bw/wk = 0.100-0.300 %. Highest contributor is corn oil (0.021 µg/kg bw/wk, 0.300 % of PTWI).
  • Pb: EWDI 0.023-0.045 µg/kg bw/wk; % JECFA former PTWI 25 µg/kg bw/wk = 0.092-0.180 %. (JECFA 2010 withdrew the lead PTWI; the source uses the pre-2010 value, see Verification notes.)
  • As (total): EWDI 0.023-0.048 µg/kg bw/wk; % JECFA PTWI 15 µg/kg bw/wk (general inorganic, withdrawn 2010) = 0.153-0.320 %.
  • Cu: EWDI 0.053-0.663 µg/kg bw/wk; % JECFA PTWI 3,500 µg/kg bw/wk = 0.002-0.019 %.

Comparison with regulatory limits (Section 3 discussion):

  • Cu in peanut, rapeseed, and olive oils (0.166, 0.187, 0.265 µg/g respectively) exceeds the 0.1 µg/g cap that the source attributes to Kowalewska et al. 2005 (paper p.3082-3083 lists approved contents as “1-1.5 µg g⁻¹ (Fe), 0.2 µg g⁻¹ (Ni), 0.1 µg g⁻¹ (Cu, Pb, As) and 0.05 µg g⁻¹ (Cd) (Kowalewska et al., 2005)”).
  • Fe in all nine oil types (mean 16.2-45.3 µg/g) exceeds the 1-1.5 µg/g Kowalewska-2005 cap by at least one order of magnitude; the source’s body text discusses this exceedance for peanut and other types without explicitly flagging that all nine exceed the cap.
  • Pb in every oil type is below the Chinese hygienic standard for edible vegetable oil (MOH 2005, GB2716-2005) maximum of 0.1 mg/kg.
  • Cd was lower than legal limits in every oil type.

Methods (brief)

ICP-AES (Perkin Elmer Optima 2100 DV) for simultaneous multi-element detection of Cu, Zn, Fe, and Mn at wavelengths 327.4, 206.2, 238.2, and 257.6 nm respectively, plasma RF 1,200 W, argon flows 18 L/min coolant + 0.6 L/min auxiliary + 0.8 L/min nebuliser, sample uptake 1.5 mL/min, axial torch. Graphite-furnace AAS (Perkin Elmer Analyst 700 with HGA graphite furnace, AS-800 autosampler, Perkin Elmer B3 001264 pyrolytic-coated graphite tubes) for Cd, Ni, Pb, and As. Microwave digestion (Xintuo XT-9912 system, PTFE vessels) of 1.000 g oil aliquots with 6 mL 65 % HNO₃ + 2 mL 30 % H₂O₂ for 32 min total (3 min at 500 W, 5 min at 800 W, 8 min at 1,000 W, 10 min at 1,300 W, 8 min venting); digest diluted to 10 mL with 2 % HNO₃. Reagent-grade HNO₃ and H₂O₂ (E. Merck), double-deionised water (Milli-Q 18.2 MΩ·cm), Nssrc certified single-element standards diluted from 1,000 mg/L to working solutions. Method validation against certified reference materials GBW10018 (chicken) and GBW08551 (porcine liver) with n=3 replicates each. Statistical analysis in SPSS 17.0 with two-way ANOVA across oil types and oil-source brands; significance threshold p < 0.05.

Arsenic is reported as total arsenic with no speciation between inorganic and organic forms; the EWDI vs JECFA PTWI comparison conservatively treats total-As as the basis for risk assessment. Mercury (any species) was not analysed. Chromium was not analysed.

Implications

Certification: Provides A-tier primary measurements for Cu, Zn, Fe, Mn, Cd, Ni, Pb, and total As in nine commercial edible vegetable oil types sold in China during 2009-2010. 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 heavy-metal occurrence in Chinese-market edible oils. The two-way ANOVA result that oil type strongly drives Cu, Zn, Fe, Mn, Cd, Pb, and As while oil-source brand does not is a useful design observation for category-level pooling: per-oil-type pooling across brands is statistically defensible in this dataset.

Courses: The dataset is a useful teaching example of (a) ICP-AES vs GF-AAS analyte allocation by sensitivity requirement (lighter metals at ppm levels on ICP-AES, lower-concentration metals at ppb levels on GF-AAS), (b) CRM-based method validation using two complementary biological-tissue CRMs, and (c) dietary-intake-vs-regulatory-guideline arithmetic for a single food category. The Cu and Fe excedances of the FAO/WHO recommended caps in peanut, rapeseed, and olive oils are a useful single-finding hook for processing-vs-occurrence discussions.

App: Iron and zinc concentrations in vegetable oils — though useful as essential-mineral contributors at the population level — are also above some recommended caps for Cu and Fe (peanut, rapeseed, and olive oils). For consumer-facing risk context the app can convey that at typical consumption levels (25 g/day or 175 g/week) the eight measured metals from Chinese-market edible vegetable oils contribute well under 1 % of the IOM RDA/AL or UL for Cu, Zn, Mn, Ni, and well under 1 % of the JECFA PTWI for Cd, Pb, and As — but Fe from peanut-oil consumption reaches 14 % of the IOM AL, which is a meaningful contribution if peanut oil is the household primary.

Speciation caution: Arsenic figures are total arsenic. The EWDI-vs-PTWI comparison uses total As against the (pre-2010-withdrawn) JECFA inorganic-As PTWI of 15 µg/kg bw/wk, which is an over-estimating assumption when organic-As fractions are non-trivial; the authors do not discuss speciation explicitly. No mercury (any species) was analysed. No chromium was analysed.

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