For the purpose to elucidate the type of mercury compounds present in agricultural products treated with organomercuric fungicides, behavior of phenylmercuric acetate and methylmercuric chloride within several kinds of young plants was studied. Both compounds were found to be decomposed, to some extent, to inorganic mercuric compound. It was shown by thin-layer chromatography in cooperation with X-ray fluorecence analysis that phenylmercuric compound was present in rice bran.
Decomposition mechanism of organomercuric fungicides in plants were studied from the pure chemical point of view. Thiol compounds such as cysteine, glutathione and dihydrothioctic acid were found to decompose organomercuric compounds to inorganic one. Mechanism of the reactions of thiols with phenylmercuric and alkylmercuric compounds seemed to be different from each other.
Decomposition mechanism of organomercuric fungicides in plants were studied from biochemical point of view. Phenyl- and alkylmercuric compounds were shown to be decomposed rapidly but with lag time, in the presence of tissue cultured wheat root. Pretreated root with an organomercuric compound reacts with the same reagent without lag time but not with other kinds of organomercuric compounds.
By the addition of nitrite as color fixative or preservative to marine fishes or fish roes which contain in high concentration of secondary amines, such as dimethylamine or diethylamine, the formation of nitrosamine in foods have to be presumed. The conditions in which dimethylnitrosamine was produced in vitro from sodium nitrite and dimethylamine hydrochloride were studied and it was found that the optimum pH for the production of dimethylnitrosamine in buffer solutions was near 3.6. Thirty minutes after oral dosage to rabbits, 5mg of dimethylnitrosamine was detected in stomach contents when 1, 000mg of sodium nitrite and 500mg of dimethylamine hydrochloride were administered. From the results of these experiments, the possibility of the formation of nitrosamines in foods was discussed which might occur in human stomach by the uptake of nitrite as food additive and when the foods which contain large quantities of nitrite and secondary amines were administered.
The precursors of nitrosamines which has been known as potent carcinogenic substance, were found as nitrite and secondary amines by the discovery during the storage of fishmeal preserved with nitrite. Although nitrite is used in foods as color fixative in many countries, it is also detected in natural products such as vegetables, fruits and other many kinds of foods. Secondary amines, the other precursor are detected in fishes especially in marine fishes and fish roes, but few data concerning the distribution of secondary amines in foods were reported. For the purpose of investigating on the toxicity of nitrosamines in foods, the distribution of secondary amines in common daily foods is important and it is necessary to establish a determination method of secondary amine. The authors modified the naphthylamine colorimetric method reported by Uno, and succeeded in obtaining good recovery and sensitivity.
It is necessary to research the distribution of secondary amines in foods which is one of the precursors of carcinogenic nitrosamines. In this report, rapid and not complicated extraction method of secondary amines from foods was described and over 98.6% of recovery was obtained by this method. For the identification of secondary amines in foods, thinlayer chromatography has been commonly used. But the chromatograms were sometimes disturbed with contaminated primary amines, ammonium salts or the other substances. To exclude the contaminants secondary amines were converted into nitroso compounds, purified, and carried out by thin-layer chromatography. By this procedure secondary amines extracted from foods could be clearly identified on the plate.
It is presumed that secondary amines contained in various foods were combined with nitrite which was added to the foods as the color fixative to form the carcinogenic nitroso compounds. And the possibility also must be discussed whether nitroso compounds were produced in human stomach when the foods whcih contained of high concentrations of secondary amines and nitrite respectively were successively administered, the animal experiments by use of rabbits being described in the first report of this series. Distribution and amounts of secondary amines in a few kinds of foods was already reported by some authors, though not in detail. In this report, distribution and amounts of secondary amines in foods, especially in Japanese proper foods, and the results of analyses of nitrosamines in foods were also described. Fishes, marine fishes and fish roes contained large quantities of secondary amines, i. s. dimethylamine and diethylamine, and the amounts in roasted fishes increased markedly. The amounts of secondary amines in meats, even in roasted meats, were trace, and nitrosamines were not detected in a kinds of foods by thin-layer chromatography.