Toxicological evaluation in rats and mice of the ingestion of a cheese made from milk with added formaldehyde

Male Swiss albino mice (CD-1) and male Sprague-Dawley rats were given single oral doses of 0.5 g (4.0 μCi) and 2.2 g (18 μCi) 14C-labelled grana cheese, respectively. The cheese was made by the normal process but using milk with added [14C]formaldehyde. The plasma and tissue kinetics of the radiolabelled cheese were studied by monitoring the decay of radioactivity in the plasma, gastrointestinal tract, liver, kidney, lung, testes, spleen, brain, muscle and adipose tissue. The faeces and urine of animals placed in individual metabolism cages were collected between 4 and 64 hr after dosing for rats and between 2 hr and 12 days for mice. Within 32 hr of administration 63-67% of the radioactivity had been excreted in the faeces and urine and 24-28% of the radioactivity had been exhaled as 14CO2, in both species. Maximum concentrations, corresponding to 0.07% and 0.3% of the dose per ml of blood were reached respectively within 8 hr for rats and 2 hr for mice. The toxicokinetic profile appears to be similar in mice and rats because of the similarity of the half-lives of the elimination phase, 27.8 and 26.4 hr respectively, and suggests that accumulation of the 14C-activity does not occur in any of the tissues of either species. The low levels of radioactivity still present 32 hr after the administration of 14C-grana cheese are probably due to the residues of labelled fractions of milk protein not completely metabolized.