Abstract

Two experiments with day-old chicks and one experiment with weanling rats were conducted to determine: (1) whether low levels of mercury found in some feedstuffs would result in hazardous accumulations of mercury in their tissues, and (2) the effects of feeding various dietary levels of methyl mercury to chicks and rats. Data show that feeding animal protein (fish meal) containing higher than normal levels of mercury did not result in the concentration of mercury in poultry tissues that exceeded FDA guideline levels. In fact, breast muscle concentration of mercury averaged only 0.1 p.p.m. even when the fish meal made up 17% of the diet. Significant amounts of mercury were deposited in the feathers of the test birds. At 16.9 p.p.m. dietary mercury as methyl mercuric chloride, all chicks succumbed to mercury toxicity by 17 days of age. Total mercury dose was 28.3 mg./kg. body weight. At this level of dietary mercury, brain, liver, and breast tissue of chicks at death contained 19, 47, and 15 p.p.m., respectively. Within limits, tissue concentrations of mercury were proportional to dietary levels. After 7 weeks of mercury exposure chicks retained an average of 63% of the mercury consumed. During a 21-day depletion period, chicks excreted an average of 0.66% of the total body burden of mercury per day. Thus biological half-lives can be calculated to average about 97 days for all dietary levels. Rats fed diets containing 16 p.p.m. mercury did not show outward signs of toxicity until the 6th week of treatment. After 12 weeks of mercury exposure, the total mercury dose was 84 mg./kg. body weight. None of the rats receiving lower levels of mercury showed symptoms of toxicity. Liver and brain mercury levels in rats fed 16 p.p.m. mercury averaged 26 and 12 p.p.m., respectively. Male rats generally had higher tissue levels of mercury than females. In general, rats tolerated the highest level of dietary methyl mercury for a longer period of time than chicks which consumed three times as much mercury and deposited less mercury in their tissues.

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