Short communicationGastric mucosal irritation following oral exposure to sodium metabisulphite: A reproducible effect?

- A 7-day dose range-finding study of dietary sodium metabisulphite (SM) was conducted in male Sprague-Dawley rats.
- Rat feed with SM at concentrations of 0.25%, 0.5%, 1% or 4% (w/w) was prepared daily.
- Resulting group mean sulphite consumptions were 90, 198, 390 and 1478 mg SO2-equivalent/kg bodyweight/day respectively.
- Group mean feed consumption was marginally depressed in rats in the 4% group but bodyweight gain was markedly decreased.
- There was no histopathological evidence of treatment-related lesions of the gastric mucosa in any rats.
- These results challenge the reproducibility of stomach lesions following sulphites ingestion.

Sulphiting agents, such as sodium metabisulphite (SM), are used in food as bleaching agents and to prevent browning reactions. A 1972 repeat dose study in rats found that dietary sulphites caused irritation of the stomach with inflammation, hyperplasia and bleeding. We conducted a 7-day dietary study in rats to confirm that stomach lesions were the most sensitive toxicological endpoint. Rat feed was prepared daily with 0%, 0.25%, 0.5%, 1% or 4% (w/w) SM. Parameters included clinical signs, feed and water intake, bodyweight gain, haematology, serum protein chemistry, necropsy findings and gastrointestinal histopathology. There were no treatment-related clinical signs or gastrointestinal lesions. Mean bodyweight gain was markedly decreased in the 4% (w/w) SM group although feed consumption was marginally depressed. Slightly lower mean values for RBC, Hb, Hct, total WBC and lymphocyte count were observed in the 4% SM group with no evidence of compensatory haematopoiesis. The gastric lesions in rats observed in a 1972 study of dietary SM for 10-56 days could not be replicated. These findings create uncertainty around the most relevant toxicological endpoint to establish a suitable health based guidance value, which can only be overcome if a robust long-term dietary study is undertaken.