The antimicrobial activity of silver ions has been well known for a long time. Products in which zeolite ions are replaced with silver ions - taking advantage of the ease with which zeolite ions can be exchanged in this way - are used in simple water purifying equipment, for example. In recent years, moreover, they have also been adapted for use as plastic additives for use in the manufacture of a growing range of products including kitchen utensils, hospital pencils and telephone ear and mouthpieces - a class of goods now generally referred to as antimicrobial goods. Other applications as indirect additives for use, for example, in the manufacture of containers designed to prevent food from going off are also currently under consideration. In light to the above, the authors decided to examine the growing use of zeolites with silver content in the manufacture of household equipment from the point of view of the possible effects of such equipment on public health. To this end, and in strict adherence to the international rules of experimentation, we carried out a series of experiments designed to evaluate the long-term toxicity and carcinogenic characteristics of this type of product. For the purpose of our experiments, we selected silver, zinc and ammonium composite substitute type A zeolites with high silver and zinc content. The average silver content of the materials used was 2.6% and the average zinc content 14.5%. We tested the selected materials on 600 four week old B6C3F1 mice (300 males and 300 females) and on 700 four week old Fischer 344 rats (350 males and 350 females). We monitored the groups by selecting and dissecting 10 animals from each group at the end of the third, sixth and 12th month. The rest was used as the breeding group for a period of 24 months. THe doses for the experimental groups were determined in accordance with experiments on the subchronic toxicity of silver composite zeolites which were carried out separately. The mice were divided into three dose groups which were administered 0.1%, 0.3% and 0.9% dose levels respectively of the test substance mixed in with their feed. The rats were divided into four experimental groups which were similarly administered doses of 0.01%, 0.03%, 0.1% and 0.3% of the test substance, respectively. The results of our experiments are summarized below. 1. In terms of factors such as survival rates and weight change, there was no observable difference between the control and experimental groups of both mice and rats and similar control group (0%) of mice and rats. There was equally no significant change observed in the general physiological condition of the rats and mice in the control and experimental group. However, although increases in body weight were found to be inhibited in the medium and high dose male mice, in all the male rat groups and in the highest dose female rat group throughout the experimental period, a simultaneous tendency towards long-term reduction of the amount of intake was observed only in the male rats during their fastest growth phases. The tendency amongst rodents that have taken in large amounts of silver and zinc over long periods to reduce intake and so to suffer growth retardation has, in fact, been previously reported (see Figure 1-1, 1-2, 2-1, 3-1, 3-2, 4-1 and 4-2). 2. In clinical biochemical tests on the rats' serum, there was little evidence of changes in the rats' serum protein and albumin levels and pathological tests showed no evidence whatsoever of organic change in the form, for example, of inflammation or decidua of the intestinal membranes. Although a tendency to anemia was identified in the medium and high dose male mice and also in the highest dose female rats, there was no evidence of an increase in thrombocytes or of abnormalities in the shapes of the red blood cells. In the case of animals that were given zinc orally, the ensuing competition
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