Tin, Inorganic

Inorganic tin denotes tin in the +2 (stannous, Sn2+) and +4 (stannic, Sn4+) oxidation states bound to non-carbon ligands such as chloride, sulfate, or oxide. It is the form of tin overwhelmingly present in food packaged in tinplated metal cans, the dominant dietary tin pathway in modern food systems. Inorganic tin is the form HMTc certifies against under the analyte symbol Sn (per CLAUDE.md Part 14); when occurrence surveys report total tin without speciating, the wiki treats those values as inorganic tin in food matrices unless the matrix is one with documented organotin loading (seafood, drinking water from PVC pipes, food contact with PVC plastics). For the parent element page see tin; for the toxicologically distinct organotin compounds see organotins.

Toxicology

Inorganic tin’s principal toxic effect after ingestion is acute local irritation of the gastrointestinal mucous membrane producing nausea, vomiting, and diarrhea. The threshold for symptomatic effects in controlled human single-dose challenges is approximately 1,000 to 1,400 ppm tin in fruit juices (Benoy, Hooper, Schneider 1971). Below that concentration, single-dose ingestion is generally well tolerated; above it, gastrointestinal symptoms appear in a fraction of subjects that scales with concentration. Cats are somewhat more sensitive than humans and dogs: 1 of 11 cats vomited at 540 ppm, 20-30 percent at 1,370 ppm, up to 40 percent at 2,000 ppm.

Systemic absorption of inorganic tin from the gastrointestinal tract is limited. Approximately 99 percent of an ingested dose is recovered in feces in rat studies; urinary recovery is essentially zero. Bone is the primary tissue depot for the small absorbed fraction; tissue residues from prolonged dietary exposure are small. ATSDR derived an intermediate-duration oral MRL of 0.3 mg Sn per kg per day from a NOAEL of 32 mg/kg/day in animal studies of stannous chloride, applying an uncertainty factor of 100 (ATSDR 2005). The chronic effects identified in the supporting literature include anemia and reversible liver and kidney effects at sustained doses substantially above realistic dietary intake.

The mechanism distinction between inorganic tin (local gastrointestinal irritant) and organotins (systemic immunotoxicants and neurotoxicants at three-orders-of-magnitude lower doses) is the central toxicological fact about tin and is what makes the species split required for honest exposure assessment.

Typical exposure routes

Ingestion of canned food and canned beverage is the dominant inorganic tin exposure pathway. Acidic foods in tinplated cans dissolve elemental tin from the lining; the dissolution rate is governed by content pH, can lacquering status, oxygen partial pressure, and storage time and temperature. Light-colored fruits and fruit juices are historically packaged in unlacquered tinplate because elemental tin reacts with anthocyanin pigments to maintain product color; this category accounts for the highest-tin canned products in modern markets. More than 90 percent of food cans now use lacquered linings that suppress the food-tin reaction and keep finished-product tin below 25 ppm, versus up to 100 ppm in unlacquered cans (ATSDR 2005).

Other ingestion routes are minor: foods not packaged in metal cans contain tin generally below 2 ppm. Drinking water tin is typically below 0.003 mg per liter. Stannous fluoride in toothpaste contributes some oral exposure; pewter, bronze, and historic tinware leach inorganic tin into food in some legacy use contexts but are quantitatively minor in modern food systems. Inhalation exposure to tin oxide dust is an occupational concern in tin smelting and electronics manufacturing but is outside dietary scope.

Food sources and occurrence

Canned acidic foods are the dominant high-tin matrix. Reported tin levels in canned vegetable and fruit categories from Biego et al. 1999 (cited in ATSDR 2005 Table 6-2) range from approximately 24 to 156 mg/kg with category means in the high tens; canned alcoholic beverages around 4.5 mg/kg. Non-canned dietary staples (meats, milk, dairy, breads, pasta, mineral water) report tin at or below 0.003 mg/kg in the same survey, three orders of magnitude below the canned categories. The FDA Total Diet Study FY2018-FY2020 dataset includes prepared/composite-food tin values for many ingredient slugs and is integrated across the corresponding ingredient pages.

Tarigan, Silalahi, Muchlisyam 2016 reports the storage-time and pH dependence in three Indonesian canned beverage categories: tin concentrations between approximately 2.5 and 5.8 mg/kg across carbonated drinks, beer, and fruit juice, well below regulatory caps but with the expected pattern that lower pH and longer storage produce higher tin release. The Tarigan dataset is small and not benchmark-pool admissible but reinforces the underlying acidity-and-time mechanism.

Benoy 1971 documents historical canned-juice outbreaks at concentrations from 250 ppm (1967 Kuwait) to 7,300 ppm (1890 canned cherries), spanning the regulatory cap (200 ppm canned beverages, 100 ppm canned baby food) by an order of magnitude or more. Modern surveillance keeps observed tin in compliant canned product well below the symptomatic threshold.

Regulatory limits

The single loaded regulatory page is 915, which sets binding maximum levels for inorganic tin: 200 mg/kg in canned food other than canned beverages; 100 mg/kg in canned beverages; 50 mg/kg in canned infant formula and follow-on formula and canned young-child formula; 50 mg/kg in canned baby food and canned processed cereal-based food; 50 mg/kg in canned infant and young-child medical foods. The infant and baby-food rows are tightened by an order of magnitude relative to general canned beverages.

The U.S. has no equivalent FDA action level or maximum level for tin in food at the federal level; FDA addresses tin primarily through Total Diet Study surveillance and contact-material guidance rather than a numeric food limit. Codex Alimentarius CXS 193-1995 sets a 250 mg/kg general food maximum for inorganic tin in canned foods other than canned beverages and 150 mg/kg for canned beverages; the Codex tin limits are looser than the EU 2023/915 limits.

Drinking-water inorganic tin is not a primary public-health concern in most jurisdictions because tin’s water solubility is limited and drinking-water tin is typically far below any health-based threshold.

Testing methods

Atomic absorption spectrophotometry (AAS) at 286.3 nm with air-acetylene flame is the historical workhorse for inorganic tin in food; ICP-MS is now the routine multi-element method and produces total-tin values that, in canned food matrices, are appropriately treated as inorganic tin. Speciation methods that separate Sn2+ from Sn4+ are uncommon in routine occurrence work because the toxicological distinction between stannous and stannic forms is small compared to the inorganic-versus-organotin distinction. Speciation methods that separate inorganic tin from organotin compounds (gas-chromatographic or HPLC separation with ICP-MS or ETV-AES detection) are essential for any matrix where organotin loading is suspected, especially seafood and drinking water from PVC distribution.

Benoy 1971 establishes that 24-hour fecal collection is sufficient to characterize inorganic tin absorption-and-excretion in animal challenge experiments because urinary excretion is essentially absent. This metabolic pattern matters for biomonitoring choices: blood and tissue tin reflect organotin and not inorganic tin in mixed exposures, so urinary or fecal measurement is the route of choice for ingested inorganic tin assessment.

Microbiome effects

The current corpus is essentially silent on inorganic-tin effects on the gut microbiome. The local-irritation mechanism documented in Benoy 1971 implies real interaction with the small-intestinal and gastric mucosa, but no taxon-level or functional metals-microbiome study with inorganic tin as the primary exposure is loaded on the wiki. This is a candidate gap for WikiBiome crosswalk when source material is identified.

Vulnerable populations

Infants and young children fed canned baby food are the principal inorganic-tin dietary vulnerable group, which is why EU 2023/915 sets the 50 mg/kg infant/baby-food limit at one quarter of the general canned-food limit. Body-weight-normalized intake of tin from canned baby food can be substantially higher than adult intake of tin from canned beverages, even at lower per-product concentrations, because small infants consume larger fractions of body weight per serving.

Acidic-food-heavy diets (canned tomato products, citrus juice, fruit cocktails, sauerkraut, pickles) produce higher inorganic tin intake than typical Western mixed diets. The FDA Total Diet Study FY2018-FY2020 includes canned-corn, canned-fruit-cocktail, canned-green-beans, canned-mushrooms, canned-tomatoes, ketchup, tomato-soup, and similar acidic-and-canned matrices in its ingredient roster; the per-ingredient tin values are integrated on the corresponding ingredient pages.

Open questions

What is the current US-market distribution of inorganic tin in canned acidic foods, particularly canned tomato products and canned fruit juices? Surveillance updates since the early 1990s are limited in the loaded corpus; the 2024-2025 FDA TDS and any successor surveys would be useful to ingest.

How does the introduction of plant-derived can-lining lacquers (replacements for BPA-containing epoxy linings) affect tin release in acidic canned foods? Lacquer chemistry has shifted substantially in the past decade, and tin release behavior under newer linings is not characterized in the loaded corpus.

What is the dietary tin intake for infants on heavy reliance on canned commercial baby food (versus home-prepared or pouched alternatives)? The 50 mg/kg EU canned-baby-food limit prevents acute exposures but does not prevent chronic body-burden from frequent canned-product feeding; a body-weight-normalized exposure assessment is missing from the loaded corpus.

Sources

• ATSDR 2005 — Comprehensive ATSDR Toxicological Profile for Tin and Tin Compounds. Source for inorganic-tin MRLs (intermediate oral MRL 0.3 mg Sn/kg/day for stannous chloride), food occurrence summary, exposure-route discussion, and toxic-mechanism characterization.
• Benoy, Hooper, Schneider 1971 — Primary controlled-dose canned-juice toxicity study; establishes the 1,000-1,400 ppm symptomatic threshold and the local-irritation absorption-limited mechanism.
• Tarigan, Silalahi, Muchlisyam 2016 — Indonesian canned-beverage tin occurrence with pH-and-storage-time dependence; supporting evidence on the release mechanism.
• Schafer & Femfert 1984 — Historical European synthesis review establishing the species-distinction principle the wiki and HMTc both maintain.
• 915 — Binding maximum levels for inorganic tin in canned food, canned beverages, and canned infant/young-child foods.