Seyfferth et al. 2024 — Cadmium and lead in U.S. spinach: comprehensive review
This review synthesizes U.S. occurrence data and soil-plant mechanisms for Cd and Pb in spinach, using paired data from the 1980s USDA-FDA-EPA national survey and the FDA Total Diet Study (TDS) to document concentrations, trends over time, and the practicality of mitigation strategies. Cd in U.S. spinach ranges approximately 2 orders of magnitude (0.01–1.1 mg/kg fresh weight) and is higher in newer TDS data than in 1980s samples, likely reflecting geographic shift toward the Salinas Valley growing region. Pb in U.S. spinach has declined substantially over time, consistent with the phase-out of leaded gasoline, though approximately 15–30% of recent TDS samples still exceed the FDA draft guidance limit for vegetables in baby and young-child foods. The review is directly relevant to FDA Closer to Zero action plan implementation and proposes mitigation strategies including chloride reduction in irrigation to limit Cd bioavailability.
Key numbers
Cd in U.S. spinach:
- 1980s USDA-FDA-EPA survey (4 states: CA, MD, NJ, TX): range 0.012–0.195 mg/kg FW; geometric mean 0.065, median 0.061 mg/kg FW (Wolnik et al. 1985, n reported by state, CA and MD lowest, TX and MD highest).
- FDA TDS 1991–2017 (boiled fresh/frozen, 4 regions, 4×/yr): range 0.03–1.09 mg/kg FW; mean 0.16, median 0.11 mg/kg FW.
- FDA TDS 2018–2020 (raw spinach, 6 regions): range 0.1–0.4 mg/kg FW; mean 0.222, median 0.200 mg/kg FW.
- EU limit for spinach: 0.2 mg/kg FW. Under this limit, 0% of 1980s samples would fail; 40–50% of recent CA/AZ samples would fail; 37% of 2018–2020 TDS samples would fail.
Pb in U.S. spinach:
- 1980s USDA-FDA-EPA survey: range 0.016–0.166 mg/kg FW; mean 0.045, median 0.038 mg/kg FW.
- FDA TDS 1991–2017 (boiled): below detection to 0.062 mg/kg FW; mean and median 0.008 mg/kg FW. ~30% of samples exceed FDA draft guidance limit for Pb in vegetables (0.01 mg/kg FW) for baby/young-child foods.
- FDA TDS 2018–2020 (raw): below detection to 0.018 mg/kg FW; mean and median 0.006 mg/kg FW; ~15% of samples exceed 0.01 mg/kg FW draft limit.
Dry-weight conversion factor: spinach 7.7% dry matter (92% water); to convert mg/kg dw to mg/kg FW, multiply by 0.077.
Methods (brief)
This is a review paper synthesizing existing U.S. occurrence datasets plus stakeholder interviews on mitigation feasibility. Primary underlying datasets: (1) Wolnik et al. 1985 paired soil-plant national survey; (2) FDA Total Diet Study composite market-basket samples 1991–2017 and 2018–2020; (3) Brierley & Sanchez 2017 non-peer-reviewed California/Arizona survey. Limitations: limited paired soil-plant data for modern U.S. spinach production; TDS samples composited by region and do not include paired soil data; very limited data on speciation (all values are total Cd and total Pb). Published in GeoHealth, AGU journal.
Implications
Certification: Spinach and other leafy greens are a clear source of Cd exposure for infants and young children (Pokharel & Wu 2023 cited in review). The FDA Closer to Zero spinach Cd picture is actively debated and lacks a formal action level as of publication date. This review provides the most comprehensive synthesis of U.S. spinach Cd and Pb occurrence available as of 2024.
Courses: Excellent primary source for explaining why Cd and Pb behave differently in soil-plant systems and why one-size-fits-all mitigation fails. Review distinguishes root-to-shoot mobility (Cd accumulates in leaves; Pb does not) as the mechanistic reason for their different occurrence patterns in leafy vegetables.
App: Spinach flagged for high Cd, lower Pb. Regional variance is substantial; CA desert (Salinas Valley, AZ) shows systematically higher Cd than NJ or TX 1980s data; modern CA/AZ samples 40–50% would fail EU limit.
Microbiome: Not addressed.