Benoy, Hooper, Schneider 1971 — Tin toxicity in canned fruit juices and solid foods
Summary
This 1971 paper from the Department of Clinical Pharmacology at the University of Birmingham investigates the toxicity of tin dissolved into canned fruit juices and solid foods, motivated by a 1967 outbreak in Kuwait associated with canned orange and apple juice containing 250-385 ppm tin. The authors fed authenticated outbreak juices and laboratory-spiked tin solutions to pigeons, cats, dogs, rats, and five human volunteers, and concluded that vomiting and diarrhea begin in cats at approximately 540 ppm tin (single cat) and 1,370 ppm (20-30 percent of cats), with humans showing gastrointestinal disturbance only at 1,370 ppm and above. The mechanism is local irritation of the alimentary mucous membrane, not systemic absorption: 99 percent of an ingested dose is recovered in rat feces and no tin is recovered in urine, with only minute amounts detectable in tissues outside the alimentary tract after seven days of ad libitum feeding.
Key numbers
| Subject group | Dose (ppm tin in juice) | Vomiting / GI symptoms |
|---|---|---|
| Cats (n=11), Kuwait outbreak juice | 250-385 | None |
| Cats, modified juice | 540 | 1 of 11 (one vomited) |
| Cats | 1,370 | 20-30 percent vomited |
| Cats | 2,000 | Up to 40 percent vomited |
| Dogs | 1,370 | None affected |
| Rats | up to 995 (added tin salts) | No toxic signs |
| Rats and cats | up to 1,200 (aqueous tin salts in citric acid) | No toxic signs |
| Solid foods, dogs and cats | up to 470 (tin from container) | No toxic effect |
| Human volunteers (n=5) | 498, 540, or 730 | No toxic signs |
| Human volunteers (n=5) | 1,370 | All 5 had GI disturbance; repeat dose: 4 of 5 unaffected, 1 mild |
Methods (brief)
Outbreak juices were obtained from the residual batches of the 1967 Kuwait incident and assayed for tin. Laboratory-tin-enriched juices were prepared by deliberate addition of stannous salts in citric acid. Animals received single oral doses; human volunteers drank single test servings. Absorption was assessed by 24-hour fecal and urinary collection in rats and cats, and by tissue analysis in one rat fed tin-rich orange juice ad libitum for seven days.
Historical context
The paper compiles prior outbreak reports from 1888-1967 and is the first controlled-dose human and animal challenge in the tin-canned-food literature. Reported outbreak tin concentrations include: Luff and Metcalfe 1890 canned cherries 7,300 ppm; Warburton et al. 1962 vodka punch in retinned milk container 2,000 ppm; Omori 1966 canned orange-based drink (1,838 affected) 452 ppm; Kuwait 1967 canned orange/apple juice 250-385 ppm; Kwantes 1966 canned salmon, fruit salad, rhubarb 250-650 ppm. These earlier outbreaks at lower tin levels were generally attributed to other co-contaminants or to special conditions (re-tinned containers, prolonged storage), and Benoy 1971’s controlled experiments support the conclusion that the symptomatic threshold from tin alone is in the high hundreds to low thousands of ppm rather than the low hundreds historically reported.
Implications
- Certification: This is the foundational primary-literature source for the local-irritation mechanism of inorganic tin in canned juice. The 1,000-1,400 ppm symptomatic threshold sits at roughly five to seven times the EU 2023/915 maximum level for inorganic tin in canned beverages (200 ppm), which builds in a meaningful safety margin. HMTc certification thresholds for tin in canned product categories should reference Benoy 1971 for the toxicology floor and EU 2023/915 for the regulatory cap.
- Courses: Strong example of a local-action versus systemic-absorption distinction. Tin is one of the few heavy metals where the principal acute effect is gastrointestinal irritation rather than systemic toxicity, and where measured fecal recovery confirms the absorption-limited mechanism.
- App: Supports per-product caution flags for canned juices and canned solids stored in unlacquered tinplate, especially after extended storage or after a can has been opened.