Saleem et al. 2025 — Metal concentrations and health risk assessment in locally grown vegetables, Grand Forks, North Dakota
This study measured 16 metals (Na, Mg, K, Ca, Fe, Se, Mn, Cu, Zn, Co, Hg, Cr, Ni, As, Cd, Pb) in 82 samples of 13 vegetable species from a local farmer’s market in Grand Forks, North Dakota, and assessed non-carcinogenic and carcinogenic health risks. Spinach showed the highest total metal burden and the highest concentrations of Cd, Cr, Pb, and Hg among the 13 species. Cadmium levels exceeded FAO/WHO maximum allowable concentrations in 100% of samples of tomato, green chili, white eggplant, capsicum, and spinach, and in 86% of onion, sugar beet, and potato samples. Non-carcinogenic target hazard quotients (THQ) exceeded 1 for Cd, Co, and As in most vegetable species; mean carcinogenic target cancer risk (TCR) values for Cr, Ni, As, and Cd all exceeded 1.0 × 10−4, indicating carcinogenic risk by USEPA criteria.
Key numbers
All concentrations reported as µg/g dry weight (DW). n values per vegetable shown in Table 2 of the source (total n = 82).
Mean concentrations across all 13 vegetables (µg/g DW):
- Pb: 0.019 (range 0.007–0.081, max in spinach = 0.081)
- Cd: 0.298 (range 0.006–0.985, max in spinach = 0.985)
- tAs (total arsenic): 0.083 (range 0.009–0.436, max in cucumber = 0.436)
- tHg (total mercury): 0.0030 (range 0.0008–0.0113, max in spinach = 0.0113)
- Ni: 0.736 (range 0.342–2.139, max in green bean = 2.139)
- Cr (total): 0.049 (range 0.014–0.179, max in kale = 0.114)
Selected per-vegetable concentrations (µg/g DW):
Spinach (n=5):
- Cd: 0.985 ± 0.223 (highest of all 13 species)
- Pb: 0.081 ± 0.013 (highest)
- Cr: 0.179 ± 0.063 (highest)
- Hg: 0.0113 ± 0.0035 (highest)
- Ni: 0.342 ± 0.070
Cucumber (n=6):
- tAs: 0.436 ± 0.145 (highest)
- Ni: 0.713 ± 0.274
Green bean (n=7):
- Ni: 2.139 ± 0.774 (highest)
Kale (n=5):
- Cr: 0.114 ± 0.088
- Cd: 0.105 ± 0.021
Corn (n=7):
- Cd: 0.006 ± 0.004 (lowest; below FAO/WHO limit of 0.05 µg/g for fruit vegetables)
FAO/WHO Cd exceedances (limits in µg/g FW; dry weight concentrations must be interpreted with caution for direct comparison):
- Fruit vegetables (tomato, chili, eggplant, capsicum, cucumber): limit 0.05 µg/g; exceeded in 100% of tomato, green chili, white eggplant, capsicum samples
- Leafy vegetables (kale, spinach, dill): limit 0.20 µg/g; exceeded in spinach (0.985 µg/g DW)
- Root/tuber and bulb vegetables (potato, onion, sugar beet): limits 0.05–0.10 µg/g; exceeded in 86% of onion, sugar beet, potato samples
- Note: source reports concentrations on DW basis; FAO/WHO limits are typically expressed on FW basis; direct comparison requires moisture correction not performed in this study
Non-carcinogenic risk (THQ > 1 threshold):
- Cd THQ range: 0.03 (corn) to 4.79 (spinach); above 1 in most species
- Co THQ range: 0.25 (onion) to 3.54 (green chili); above 1 in most species
- As THQ range: 0.14 (green bean) to 7.05 (cucumber); above 1 in most species
- HI (all metals combined): range 1.59 (corn) to 18.3 (spinach); all species above 1
Carcinogenic risk (TCR; acceptable threshold 1.0 × 10−4):
- Pb TCR: all vegetables below 1.0 × 10−6 (negligible for all species)
- Cr TCR range: 3.4 × 10−5 (potato) to 4.3 × 10−4 (spinach); mean above 1.0 × 10−4
- Ni TCR: all 13 vegetables above 1.0 × 10−4 (unacceptable for all species by USEPA criteria)
- As TCR: above 1.0 × 10−4 in 9 of 13 species
- Cd TCR: above 1.0 × 10−4 in 9 of 13 species
Methods (brief)
Samples collected from Town Square Farmer’s Market, Grand Forks, ND (mid-June through September); 2–3 sub-samples (~0.2–0.5 kg each) per species from different vendors combined. Washed with deionized water, air-dried 24 h, homogenized, oven-dried at 70–80°C to constant weight, stored in desiccators. Digestion: 0.5 g dried-ground sample in 5 mL concentrated HNO3, microwave-assisted (Milestone UltraWAVE), EPA method 3051A (Revision 1); ramp to 175°C over 5.5 min, hold 4.5 min, N2 pressure 35 bar; diluted to 50 mL with deionized water. ICP-MS: Thermo Scientific iCAP Qc in KED mode, EPA method 200.8 (Revision 5.4); internal standards Sc, Rh, Bi; all measurements in triplicate. Hg by direct solid-sample analysis: Milestone DMA-80 Tri Cell, EPA method 7473. QC: NIST SRM 1567b (wheat flour); recovery >85% for most elements; RPD of duplicates <20%. Detailed LOD, LOQ, blank spike recovery in supplementary Table S1.
Health risk parameters: EDI used body weight 70 kg, daily vegetable intake 0.34 kg/day. THQ reference doses (RfD) from ATSDR/USEPA-IRIS. TCR oral cancer slope factors from USEPA. Arsenic reported as total arsenic (tAs); speciation into inorganic arsenic (iAs) not performed; tAs values cannot be equated to iAs for regulatory comparison. Chromium reported as total Cr; no Cr-VI speciation.
Implications
Certification: The elevated Cd levels in spinach (0.985 µg/g DW) and multiple fruit-vegetable species in this North Dakota local-market survey suggest Cd is a material concern even in low-industrial agricultural areas of the US. The Ni TCR result (all 13 species above 1.0 × 10−4) and As TCR results highlight that Ni and As in common vegetables may collectively drive carcinogenic risk calculations in this population at standard consumption rates; however, the absence of iAs speciation limits direct regulatory comparison for arsenic, and total Cr should not be interpreted as Cr-VI for carcinogenicity purposes.
Courses: Illustrates the pattern that leafy vegetables (spinach, kale, dill) tend to accumulate more metals than fruit vegetables (corn, capsicum) due to larger surface area and higher transpiration; spinach consistently represents the high end of the distribution across metals.
App: Spinach should carry elevated-Cd and elevated-Pb flags. Cucumber should carry elevated-tAs flag (though iAs fraction unknown). Green bean should carry elevated-Ni flag. Corn presents the lowest total metal burden and is a low-risk ingredient for these analytes in this dataset.