Beans

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.

Beans — the broad legume category covering dried and canned pulses (kidney, black, pinto, navy, cannellini, fava, pinto, chickpeas, lentils as a distinct sub-category) — sit at the middle of the food-system heavy-metals risk distribution. The defining feature of the legume category is nickel accumulation: leguminous plants harbour nitrogen-fixing Rhizobium bacteria in root nodules that require nickel for their urease enzyme machinery, so legumes consistently carry higher Ni than non-legume crops. Beans also accumulate Cd at modest rates and inherit canning-source Pb when sold in cans rather than dried. The current corpus loads 4 sources directly: Abdolahpour 2023 Iranian Babol-city vegetable Pb-Cd (n=32, abdolahpour2023-heavy-metals-babol-vegetables), Alzabadi 2018 Palestinian canned-foods including canned beans (n=16, alzabadi2018-canned-foods-palestine-cd-pb-cu-zn), Bora 2022 Romanian fruit-and-vegetable washing intervention covering bean baseline (n=80, bora2022-heavy-metals-fruits-vegetables-romania-vinegar-washing), Sandil 2023 bean-and-lettuce arsenic uptake mechanism (sandil2023-arsenic-bean-lettuce); plus the ATSDR 2005 Tin Toxicological Profile relevant to canned-bean Sn (atsdr2005-tin-toxicological-profile) and the broader vegetable-and-legume corpus reachable through the routing layer.

Why this commodity accumulates heavy metals

Beans accumulate metals through root uptake into the seed-pod and seed tissues, with rates varying by species and soil chemistry. The legume-specific nickel accumulation is driven by Rhizobium nitrogen-fixation biochemistry: the bacterial urease enzyme requires nickel as a cofactor, so the plant actively concentrates Ni into the root nodule and into the seed. The Sandil 2023 work documented arsenic uptake into bean tissue at developmental-stage-dependent rates, with mature beans carrying more total arsenic than younger plant tissue (sandil2023-arsenic-bean-lettuce). Cadmium uptake follows the standard plant pathway driven by soil Cd-to-Zn ratio. The canning step is the dominant downstream contamination event for canned beans specifically: traditional tin-plate cans contribute Sn through corrosion of the tinplate over shelf life, particularly for acidic bean products (chili beans, baked beans in tomato sauce); historical lead-soldered cans (largely phased out globally but persisting in some markets) contributed Pb. The Alzabadi 2018 Palestinian canned-foods survey found Cd-and-Pb in canned beans at retail levels of concern in some samples, with the canning step the most plausible explanation for the elevation relative to dried bean baseline (alzabadi2018-canned-foods-palestine-cd-pb-cu-zn).

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.

Ranges by source, region, and variety

The corpus characterises bean metals through directly-routed studies plus broader vegetable surveys reachable via the routing layer. The Palestinian Alzabadi 2018 canned-foods survey (n=16 including canned beans, fava beans, and related canned product) documented Cd-and-Pb concentrations approaching Codex limits in a meaningful fraction of canned-bean product, with the canning step implicated as the dominant pathway (alzabadi2018-canned-foods-palestine-cd-pb-cu-zn). The Romanian Bora 2022 work characterised bean baselines (within the broader fruit-vegetable n=80 panel) and tested vinegar-wash interventions for surface metals (bora2022-heavy-metals-fruits-vegetables-romania-vinegar-washing). The Hungarian Sandil 2023 bean-and-lettuce arsenic uptake mechanism work documented developmental-stage-dependent As accumulation in bean tissue (sandil2023-arsenic-bean-lettuce). Variety-level pattern: kidney beans, black beans, pinto beans, and navy beans have similar metal profiles within commodity-grade product; soybeans (technically a legume but covered separately as oilseed) accumulate Cd at higher rates than other beans. Origin: US, Canadian, Mexican, Brazilian commodity beans are broadly equivalent on heavy metals; specific-origin specifications add cost without meaningful metal-load shift for the broader bean category. Canned beans consistently carry higher Pb-Cd-Sn than the dried equivalent due to canning-step contributions.

Processing effects

Dried beans require soaking and cooking before consumption. Soaking in fresh water leaches a fraction of soluble metals (Cd, some Ni) into the soak water; discarding the soak water reduces per-serving exposure of these soluble forms. Cooking by boiling leaches additional Cd and tAs into the cooking water; discarding the cooking water further reduces exposure. The traditional Mediterranean-and-Middle-Eastern practice of multiple-soak-and-rinse cycles is documented in food-safety literature as a meaningful reduction intervention for Cd and Ni in legumes. Canning introduces the can-source Pb and Sn pathway and is the single largest processing-driven contamination event for canned bean product. Pressure cooking and slow cooking do not affect metal load differently from boiling. Fermented bean products (miso, tempeh, natto from soybeans; fermented bean paste from black beans) carry the parent bean’s metal load with negligible processing-driven change.

Ingredient-derivative risk

Dried beans cooked at home in fresh water with discarded soak-and-cook water represent the lowest-metal-load consumption form. Canned beans carry elevated Pb-Cd-Sn relative to the dried equivalent; the Alzabadi 2018 Palestinian data document the magnitude. Bean flour (chickpea flour, black bean flour, etc., used in gluten-free baking) carries the parent bean’s metal load on a dry-weight basis without the soak-and-cook reduction. Bean protein isolate (used in plant-based meat alternatives and supplement applications) concentrates protein and any protein-bound metals. Refried beans and pre-cooked bean preparations sold in pouches inherit the canning or pouch-source metal contributions. Bean dips, hummus, and finished-product applications carry the bean’s metal load at the inclusion ratio.

Mitigation options

Sourcing levers

For dried beans, sourcing from suppliers with documented soil-and-water screening provides upstream metal-load control. Avoid sourcing from regions with documented mining-corridor or industrial-corridor soil contamination. For canned beans, source from canners using modern fully-welded steel cans with food-grade interior coatings; avoid lead-soldered cans (largely phased out but persisting in some markets) and avoid tinplate cans with damaged coatings for acidic bean products.

Agronomic levers

For brand-controlled-supply operations, soil pH management around 6.5 reduces Cd bioavailability. Avoid phosphate fertilisers with elevated Cd impurity. Rhizobium-inoculated nitrogen-fixation reduces the need for external nitrogen fertilisers and the associated Cd-contamination risk. Most agronomic interventions live with bean producers rather than ingredient buyers.

Processing levers

Soaking-and-discarding-water plus cooking-and-discarding-water reduces Cd and soluble metals by 20-40% from the dried baseline. For canners, modern can technology (fully welded steel with food-grade interior coatings, glass jar alternative) eliminates the Pb-and-Sn pathway. Pressure-cooked product does not differ meaningfully from boiled product on metal removal.

Formulation levers

For finished products using beans as an ingredient (chili, soups, dips, ready-meals), the inclusion ratio caps per-serving exposure. Substitution between bean varieties does not meaningfully change the Pb-Cd profile; substitution with lentils (typically lower-Cd) shifts the per-serving Cd modestly lower.

Testing and QC levers

Lot-level ICP-MS testing for Pb (detection floor ≤ 5 ppb), Cd (≤ 1 ppb), Sn (≤ 50 ppb for canned), and Ni (≤ 50 ppb) icp-ms is the standard intervention.

Packaging and storage levers

Glass jars eliminate the can-leaching pathway entirely. Modern fully-welded steel cans with food-grade interior coatings are acceptable. Lead-soldered cans (historical risk) and tinplate cans with damaged coatings for acidic bean products are the historical packaging risks. Pouches do not contribute meaningfully to the metal load.

Regulatory limits that apply

The Codex Alimentarius General Standard CXS 193-1995 sets a Pb maximum of 0.10 mg/kg fresh weight for legumes (dry) and 0.10 mg/kg for canned vegetables; Cd at 0.10 mg/kg for legumes. The EU Regulation 2023/915 sets the legume Pb maximum at 0.10 mg/kg and Cd at 0.040 mg/kg for legumes (tighter than Codex). The Codex Sn maximum of 250 mg/kg applies to canned beans alongside the broader canned-food category. The FDA has not set bean-specific action levels but has issued recall notifications for canned-bean products with elevated Pb tied to historical packaging issues.

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.