Corn

Completeness scorecard

Deterministic gap audit — no score is composite, no cell is LLM-judged. Each chip is re-derivable by re-running tools/evidence/build-ingredient-scorecard.mjs. review: residuals and missing data are worked autonomously via data/evidence/ingredient-scorecard-review-flags.csv and wiki/completeness-gaps.md.

This ingredient stub was created during the FDA FY2018-FY2020 Total Diet Study element-results ingest so future source ingests have a stable destination for this food matrix. FDA reports this item as TDS Food 54, “Corn, frozen, boiled.” fda2022-tds-elements-fy2018-fy2020

Why this commodity accumulates heavy metals

Maize (corn) accumulates cadmium through root uptake from soil, a mechanism that is modulated by soil pH, organic matter content, and the competing presence of zinc. In acidic soils or soils with elevated cadmium from phosphate fertilizer application, maize grain can carry detectable cadmium, though whole-grain corn is generally a lower Cd accumulator than leafy vegetables or root vegetables because the grain is a reproductive structure with some buffering against cadmium translocation from vegetative tissue. romero-crespo2023-ecuador-mining-crops-metals documented substantially elevated cadmium, chromium, lead, and arsenic in maize grain grown near mining operations in Ecuador, where soil-to-plant transfer is driven by contaminated parent rock and tailings rather than agricultural inputs alone.

Arsenic in corn is typically low: the FDA TDS FY2018-FY2020 data report total arsenic below the 3 µg/kg reporting limit across all 27 composite samples for frozen boiled corn fda2022-tds-elements-fy2018-fy2020, and the primary corn-grain literature confirms a low but non-zero total-arsenic burden (Beijing retail corn flour 7 µg/kg, Nigerian corn grain at or below 10 µg/kg dry weight), consistent with corn not concentrating arsenic the way flooded-paddy rice does. Nickel shows episodic elevation in the TDS corn data, with a p90 of 54.4 ppb and a maximum of 160 ppb, indicating that some market-basket composites captured nickel from soil or processing sources at levels notably higher than typical. Lead, total mercury, total chromium, and uranium are all below their respective reporting limits across the FDA composites; those below-limit results are carried as left-censored bounds rather than as measured zeros, and the routed primary literature recovers low but non-zero lead, mercury, and chromium in corn grain (see the Synthesis basis and censoring treatment section).

Heavy metal contamination profile

Per-analyte snapshot derived from the machine-readable contamination_profile in the frontmatter above. data gap indicates the literature has been reviewed for this commodity-analyte combination and no usable occurrence data was found (a finding, not a placeholder). The Key sources column shows the top 2-3 contributing sources by year and sample size, with numbered wikilink aliases.

Synthesis basis and censoring treatment

The lead, total-arsenic, total-mercury, chromium, and uranium cells were resynthesized on 2026-06-11. The native basis for this page is corn grain as sold; FDA Total Diet Study Food 54 reports the matrix as “Corn, frozen, boiled” (whole-kernel corn), while most of the routed primary literature reports corn grain or corn flour on a dry-weight basis. Where dry-weight or corn-flour anchors are pooled against the FDA whole-kernel composite, the basis difference is stated rather than silently harmonized, and the mixed basis is recorded in the cell as corn-grain-as-sold-mixed-wet-and-dry-weight. Values below the analytical limit of detection or quantification are treated as left-censored, not as measured zeros.

The earlier profile reported lead, total arsenic, total mercury, chromium, and uranium at typical and 95th-percentile values of zero. Those figures were an artifact of the FDA Total Diet Study composite for frozen boiled corn (n=27), in which every sample fell below the reporting limit for each of these five analytes and the reported below-limit results were pooled as literal zeros (fda2022-tds-elements-fy2018-fy2020, reporting limits Pb 4, tAs 3, tHg 1, Cr 50, U 1 µg/kg). Cadmium and nickel were not part of this resynthesis: they carry genuine FDA detects (Cd p50 2.6 µg/kg, max 4.8; Ni p90 54.4 µg/kg, max 160) and remain as previously synthesized. The resynthesis replaces the literal zeros for the five censored analytes with a left-censored floor at the FDA reporting limit and recovers the upper distribution from the routed primary corn-grain occurrence literature, in which lead, total arsenic, total mercury, and total chromium are low but non-zero in corn grain.

Lead rests on the FDA censored floor for the low bound and on commercial-market corn anchors for the central and upper distribution. Beijing retail corn flour carried lead at 60 µg/kg (Liang et al. 2019); Kermanshah retail corn ran 93 to 146 µg/kg dry weight across three markets (Ataee et al. 2016); and an industrial-region Chinese cereal survey reported a mean of 45 µg/kg with a maximum of 284 µg/kg (Wang et al. 2023). The clean-platform floor is corroborated by Egyptian freshwater-irrigated maize, which ran below detection to 40 µg/kg at all five Nile-irrigated sites (El-Hassanin et al. 2020). The pooled lead typical of [0, 60] takes the FDA censored floor as the low bound and the Beijing retail-flour and Kermanshah lower-market values as the upper central; the 95th-percentile of 130 µg/kg is anchored to the elevated commercial-market tail (Ataee 146 µg/kg, Wang 284 µg/kg maximum). Confidence is held at medium: the pool is deep, but the contributors mix whole-kernel, dry-weight, and corn-flour bases and span commercial markets of differing background burden.

Total arsenic is genuinely low in corn, in contrast to flooded-paddy rice, because corn is not grown under the anaerobic conditions that mobilize arsenite into grain. The honest floor is the FDA 3 µg/kg reporting limit; the central rests on Beijing retail corn flour at 7 µg/kg (Liang et al. 2019) and on Nigerian cement-vicinity corn grain, in which total arsenic was uniformly at or below 10 µg/kg dry weight across all sites including the contaminated downwind farmlands (Abatemi-Usman et al. 2023). The pooled typical of [0, 7] and 95th-percentile of 10 µg/kg reflect this narrow low-arsenic band. Confidence is low because only two primary anchors report an extractable positive corn total-arsenic value. Total arsenic is held distinct from inorganic arsenic, which remains a reviewed data gap for this commodity; no speciated corn-arsenic measurement exists in the corpus, and the inorganic fraction is never inferred from total arsenic.

Total mercury rests on the FDA censored floor and two primary anchors. Guangxi maize grain carried total mercury at a mean of about 1 µg/kg with a maximum of 33 µg/kg (Gu et al. 2019), and Beijing retail corn flour carried total mercury at 18 µg/kg (Liang et al. 2019). The pooled typical of [0, 1] spans the FDA reporting-limit floor to the Guangxi central; the 95th-percentile of 18 µg/kg is the Beijing retail-flour value, which sits at the top of the ordered pooled set. Confidence is low: only two single-region positive contributors exist. Total mercury is held distinct from methylmercury and is not derived from it.

Chromium is reported as total chromium only, and no corn hexavalent-chromium measurement exists in the corpus, so no Cr-VI value is inferred. Total chromium is the standout analyte in commercial corn-derived products: an independent Lebanese retail survey of 42 cornflake products found chromium at the highest mean concentration of the five metals measured (Hassan et al. 2025). The honest floor is the FDA 50 µg/kg reporting limit; the central and upper distribution rest on Beijing retail corn flour at 76 µg/kg (Liang et al. 2019), an industrial-region Chinese cereal mean of 256 µg/kg with a maximum of 770 µg/kg (Wang et al. 2023), and Kermanshah retail corn at 740 µg/kg (Pirsaheb et al. 2015). The pooled typical of [0, 256] and 95th-percentile of 740 µg/kg span the FDA floor to the Wang and Pirsaheb commercial-market central-to-upper values. Confidence is low because total chromium carries no speciation, the contributors mix whole-kernel and dry-weight bases, and the distribution is wide.

The mining-area, industrial, and wastewater-irrigated corn anchors are deliberately excluded from the headline percentiles above and recorded as a separate contamination stratum. Maize grown adjacent to a Chongqing manganese mining and smelting area, in an oil-industry zone of Khuzestan Province (lead mean 1,840 µg/kg, total arsenic 1,570 µg/kg, chromium 4,920 µg/kg), in the industrialized Chengdu Plain (maize lead mean 290 µg/kg), near the Obajana cement plant (corn lead 230 to 380 µg/kg dry weight downwind, chromium 2,080 to 3,560 µg/kg), and on Egyptian sites irrigated with mixed sewage and industrial effluent (maize lead 260 to 550 µg/kg, 19 to 30-fold above the freshwater-irrigated controls) all carried metal burdens far above commercial-market corn (Zhang et al. 2026; Gholami et al. 2025; Liu et al. 2022; Abatemi-Usman et al. 2023; El-Hassanin et al. 2020). These define an upper bound for industrially or geologically anomalous origins and are not representative of the general commercial corn supply.

Uranium is recorded as a reviewed data gap. The only corn uranium measurement in the corpus is the fully censored FDA Total Diet Study cell (all 27 frozen-boiled-corn composites below the 1 µg/kg reporting limit), and no routed primary source reports an extractable quantitative corn-grain uranium value. The FDA cornbread composite carries detectable uranium (2.2 to 2.7 µg/kg), but cornbread is a flour-and-leavening derivative, not corn grain, and its value is not relabeled as corn. With no positive corn-grain anchor, no distribution is published, following the rice-uranium precedent.

FDA TDS FY2018-FY2020 Evidence

The normalized row-level data for this TDS food is stored in data/evidence/fda_tds_fy2018_2020_element_results_samples.csv, with per-food/per-analyte summaries in data/evidence/fda_tds_fy2018_2020_summary_by_food_analyte.csv. Concentrations are retained as FDA reported them, with the reporting-limit column preserved separately; reported zeroes are not rewritten as <LOD unless a source explicitly says to do so. fda2022-tds-elements-fy2018-fy2020

Routing

This node is linked from the ingredient index and the FDA TDS source routing table.

Contamination Profile State

The machine-readable contamination profile is in_progress for analytes measured in the TDS file and pending for profile metals not measured by this source. Ingredient-level values belong here once cross-source synthesis is reviewed; product-category values belong on the relevant product page.

FDA TDS FY2018-FY2020 Occurrence Values

FDA Total Diet Study FY2018-FY2020 reports prepared/composite-food concentration distributions for this ingredient as TDS food “Corn, frozen, boiled” (fda2022-tds-elements-fy2018-fy2020). Values are in ppb-equivalent on the basis FDA reported. The full sample-level data are stored in data/evidence/fda_tds_fy2018_2020_element_results_samples.csv; per-analyte distributions in data/evidence/fda_tds_fy2018_2020_summary_by_food_analyte.csv. These distributions count as one source under persistent-wiki-ingest-rule synthesis discipline; numerical values stay in body scratch until a second independent source is integrated.

Ranges by source, region, and variety

The FDA TDS FY2018-FY2020 market-basket survey of frozen boiled corn (n=27) shows Cd at a median of 2.6 ppb and a maximum of 4.8 ppb, with Pb and tAs at zero across all samples fda2022-tds-elements-fy2018-fy2020. This represents the commercial US market baseline for a composite of diverse origin corn. By contrast, romero-crespo2023-ecuador-mining-crops-metals measured substantially higher metal concentrations in maize grain from agricultural plots adjacent to mining operations in Ecuador, where contamination from ore processing and tailings runoff is the dominant input. This contrast between market-basket and mining-area concentrations reflects the origin dependence that is critical to understanding corn’s metal risk profile: under normal US or EU agricultural conditions the risk is low, but sourcing from mining-adjacent or industrially contaminated regions can elevate cadmium, lead, arsenic, chromium, and nickel well above market-basket levels.

Corn variety also influences metal accumulation, though varietal differences are less studied than origin effects. Field corn versus sweet corn versus popcorn varieties have different grain morphologies and growing conditions, and these differences can translate into different metal concentrations per unit of edible tissue. No cross-varietal comparison is yet integrated into this corpus.

Processing effects

Milling removes the bran and germ fractions of the corn kernel, concentrating the starchy endosperm in refined products (corn flour, masa, starch) and leaving the metal-concentrated outer layers behind. Cadmium in corn grain, like in wheat, tends to partition into the bran and germ rather than the endosperm, so degermination and milling reduce Cd in refined corn products relative to whole-grain corn. Wet milling for corn starch and corn syrup production removes essentially all mineral content, including trace metals, so these highly refined corn derivatives carry negligible metals.

Boiling corn does not meaningfully reduce metal concentrations in the grain, since most metal is structurally bound within the kernel’s cell walls and is not water-extractable. The TDS data for frozen boiled corn therefore reflects an as-consumed metal burden that is substantially similar to the raw grain’s metal content adjusted for moisture change.

Ingredient-derivative risk

Corn is processed into a wide range of derivative ingredients with different metal profiles. Whole-grain corn flour and masa harina retain the bran fraction and carry the highest cadmium and mineral content of any corn-derived product. Degerminated corn meal removes the germ and has lower cadmium than whole-grain flour. Corn starch and corn syrup are highly refined and carry negligible metals. Corn oil, extracted from the germ fraction, concentrates any lipid-soluble contaminants present in the germ, though heavy metals are largely hydrophilic and do not preferentially partition into oil; corn oil is therefore a low-risk derivative for the analytes tracked in this wiki. Popcorn, which retains the pericarp and germ, carries a metal burden more similar to whole-grain corn than to degerminated products.

Mitigation options

Sourcing levers

Origin selection is the dominant mitigation lever for corn. Avoiding procurement from mining-adjacent regions or areas with documented soil cadmium elevation (for example, from legacy phosphate fertilizer overuse or industrial contamination) is the most effective strategy. romero-crespo2023-ecuador-mining-crops-metals illustrates the magnitude of the origin effect: mining-area maize carried metals far exceeding the levels in US commercial market-basket corn fda2022-tds-elements-fy2018-fy2020. Supplier specification requiring origin documentation and soil-cadmium pre-screening is the procurement-side implementation of this lever.

Agronomic levers

Soil pH management reduces cadmium bioavailability; liming acidic soils to raise pH above 6.5 reduces cadmium uptake by corn. Zinc application competes with cadmium at the same root transporter, potentially reducing cadmium uptake, though excess zinc application carries its own environmental costs. These levers are most relevant for farmers supplying to buyers with contractual metal specifications.

Processing levers

Degermination and milling to remove bran and germ reduces cadmium in refined corn products. For whole-grain corn products, this lever is not applicable by definition. Washing or blanching corn prior to processing has minimal effect on grain-incorporated metals but may reduce surface-deposited particulate contamination.

Formulation levers

For food manufacturers concerned about cadmium or nickel, substituting degerminated corn products for whole-grain corn in formulations will reduce the metal burden per serving without eliminating corn as an ingredient.

Testing and QC levers

Given that nickel in the TDS corn dataset reaches 160 ppb maximum across 27 samples fda2022-tds-elements-fy2018-fy2020, lot-level nickel testing is warranted for brands with high-corn-content products sold to sensitive populations. Cadmium testing at the incoming ingredient level is appropriate for any product using whole-grain corn from origins with uncertain soil histories.

Packaging and storage levers

No quantified data on packaging or storage effects on heavy metal content in corn is in the current corpus; section will be expanded when relevant evidence is ingested.

Regulatory limits that apply

The European Union under eu2023-contaminants-maximum-levels sets a maximum level for cadmium in cereals (including corn) of 0.10 mg/kg (100 ppb) wet weight. For lead in cereals, the EU limit is 0.20 mg/kg (200 ppb). Codex Alimentarius (CXS 193-1995 and revisions) sets a maximum level of 0.10 mg/kg for cadmium in grain crops including maize and 0.20 mg/kg for lead. The US TDS market-basket Cd maximum of 4.8 ppb and Pb at zero are well below these regulatory limits for the sampled commercial products. No US federal maximum level for cadmium or lead in corn grain has been finalized for the general food supply as of 2026.

Sources

Auto-generated from source-page frontmatter. The “Used on this page for” column is populated by the orchestrator’s POPULATE-SOURCE-LEGEND action; pending entries appear as *[awaiting synthesis]*.

Page history

The five most recent substantive edits to this page. The full version history lives in git; when DOI minting comes online (see schema docs), each entry below will also link to a version-pinned DataCite DOI.