A non-essential metal with a dual toxicological profile: inorganic tin (from canned foods) causes primarily gastric irritation at high concentrations, while organotin compounds (tributyltin, trimethyltin) are far more toxic, acting as endocrine disruptors and neurotoxins. Tin exposure is nearly ubiquitous in the US population and is primarily a food safety concern rather than an occupational or environmental one for the general public.
Chemical Properties
- Post-transition metal (Group 14); two common oxidation states: Sn2+ (stannous) and Sn4+ (stannic).
- Density 7.3 g/cm3; melting point 232 C.
- Inorganic tin salts are poorly absorbed from the GI tract and mainly excreted in feces [eu scf 2001 tin canned foods].
- Organotin compounds (R-Sn bonds) are lipophilic and far more bioavailable than inorganic forms.
- Listed on the CERCLA National Priorities List of hazardous substances [atsdr 2005 tin toxicological profile].
Sources of Exposure
Canned Foods (Primary Route)
Canned foods in unlacquered or partially lacquered tinplate cans are the principal source of inorganic tin exposure for the general population:
- Tin leaches from can walls into acidic food contents (tomatoes, citrus juices, fruits).
- Adverse reactions reported from canned beverages (100-490 mg/kg tin) and canned tomato juice (140-400 mg/kg tin) [eu scf 2001 tin canned foods].
- Modern lacquered cans substantially reduce leaching, but damage or incomplete coating allows migration.
Baby Food and Infant Formula
- Baby food jars from Spain contained measurable tin; part of the multi-element risk assessment showing baby food consumption scenarios are not safe for some elements [gonzalez suarez 2022 baby food jars essential toxic elements].
- Tin detected in Brazilian infant formulas as part of toxic metal screening [de almeida 2022 toxic metals infant formula brazil].
Other Sources
- Organotin compounds: tributyltin (TBT) used as antifouling paint on ships (now largely banned); PVC stabilizers; agricultural fungicides.
- Fruit juices from Nigeria showed detectable tin among other trace metals [onyeneto 2015 trace metals fruit juices nigeria].
Population Exposure
US population data from NHANES 2011-2014 provides the most comprehensive exposure assessment [lehmler 2018 tin exposure nhanes us population]:
- Detection frequency: 87% in adults, 91% in children -- exposure is nearly ubiquitous.
- Median urinary tin: 0.42 ug/L in adults; 0.60 ug/L in children.
- Age: The strongest predictor; levels in the >=60 year group are ~2-fold higher than the 20-39 group, suggesting bioaccumulation.
- Children: 6-11 year olds have ~2-fold higher levels than 12-19 year olds.
- Race/ethnicity: Non-Hispanic Black individuals have the highest levels (0.74 ug/L).
- Income: Inverse association; low-income groups have significantly higher tin levels.
- Canned food consumption: Surprisingly, not consistently associated with urinary tin levels in this study, suggesting other exposure routes or that total urinary tin does not distinguish organic from inorganic forms [lehmler 2018 tin exposure nhanes us population].
Health Effects
Inorganic Tin -- Gastric Irritation
The primary health effect of inorganic tin exposure is acute GI disturbance:
- Tin salts are corrosive; acute toxicity manifests as gastric irritation, nausea, vomiting, abdominal discomfort, and diarrhea within 0.5-3.0 hours of ingestion, resolving within 48 hours [eu scf 2001 tin canned foods].
- Toxicity depends more on tin concentration in the foodstuff than on total tin intake per body weight [eu scf 2001 tin canned foods].
- Regulatory thresholds: The EU SCF concurs with JECFA that tin levels of 150 mg/kg in beverages or 250 mg/kg in other canned foods may cause gastric irritation in some individuals [eu scf 2001 tin canned foods].
- No data available on whether infants are more sensitive than older children and adults [eu scf 2001 tin canned foods].
- Low oral absorption means systemic toxicity from inorganic tin is rare.
Organotin Compounds -- Endocrine Disruption and Neurotoxicity
Organotin compounds are orders of magnitude more toxic than inorganic tin:
- Tributyltin (TBT): Endocrine disruptor; causes imposex in gastropod mollusks at ng/L concentrations; obesogen (promotes adipogenesis via PPARgamma/RXR activation); immunotoxic.
- Trimethyltin (TMT): Potent neurotoxin targeting the hippocampus and limbic system; causes seizures, cognitive impairment, and neuronal death.
- ATSDR profile covers both inorganic and organotin health effects across inhalation, oral, and dermal routes at acute, intermediate, and chronic durations [atsdr 2005 tin toxicological profile].
Cancer
- Tin was included in the 15-metal toenail panel in the Sister Study: no significant association with breast cancer risk [niehoff 2021 metals breast cancer toenail].
Regulatory Framework
- EU SCF: Tin levels of 150 mg/kg (beverages) and 250 mg/kg (other foods) as thresholds for gastric irritation [eu scf 2001 tin canned foods].
- ATSDR: Comprehensive toxicological profile prepared under CERCLA/Superfund mandates [atsdr 2005 tin toxicological profile].
- EU Drinking Water Directive: Tin included in monitoring parameters [eu 2020 drinking water directive].
- Codex Alimentarius: Maximum level of 250 mg/kg for canned foods (general) and 150 mg/kg for canned beverages.
Connections
- food safety -- tin in canned foods is the primary exposure route; regulatory limits are food-specific
- breast cancer -- measured in toenail biomarker study; no association found
- dietary metal exposure -- canned food as primary route for general population
- iron, aluminum -- co-measured in baby food and canned food safety assessments
- cadmium, lead -- co-contaminants in food matrices
- endocrine disruption -- organotin compounds (TBT) are established endocrine disruptors