HYPERTENSION AND THE GEOCHEMICAL ENVIRONMENT

Human health effects of exposure to cadmium

The health effects of human exposure to cadmium are discussed with emphases on intake, absorption, body burden, and excretion; osteomalacia in Japan; hypertension; and proteinuria, emphysema, osteomalacia, and cancer in workers. Elevated blood pressure has not been observed as a result of excessive exposures to cadmium in Japan or the workplace. Renal tubular dysfunction and consequent proteinuria is generally accepted as the main effect following long-term, low-level exposure to cadmium. Studies of workers show that proteinuria may develop after the first year of exposure or many years after the last exposure. Proteinuria and deterioration of renal function may continue even after cessation of exposure. The immediate health significance of low-level proteinuria is still under debate. However, there is evidence that long-term renal tubular dysfunction may lead to abnormalities of calcium metabolism and osteomalacia. The few autopsy and cross-sectional studies of workers do not permit conclusions to be drawn regarding the relationship between cadmium exposure and emphysema. Retrospective and historical-prospective studies are needed to settle this important question. No conclusive evidence has been published regarding cadmium-induced cancer in humans. However, there is sufficient evidence to regard cadmium as a suspect renal and prostate carcinogen. Because of equivocal results and the absence of dose-response relationships, the studies reviewed should be used with caution in making regulatory decisions and low-dose risk assessments.

Augmented depression and reduced excitability of the central nervous system (CNS) by cadmium in the rat

Reports indicating that low doses of cadmium caused vasodilation, but that larger quantities elicited a pressor response, apparently mediated by a CNS reflex, prompted an examination of cadmium-induced changes in CNS responsiveness and activity. Rats were injected intraperitoneally with either 2 mg/kg or 4 mg/kg of CdCl2 solution, after which the CNS was either depressed by pentobarbital or excited by strychnine at different dose levels. Cadmium treatment, administered before pentobarbital, decreased the time required for sleep induction and prolonged sleep duration at doses of either 20 mg/kg or 30 mg/kg: at 40 mg/kg only induction was affected and at 60 mg/kg neither was influenced. At a dosage of 60 micrograms/kg, strychnine caused convulsions in all control animals, but in none pretreated with CdCl2. When either 75 or 120 micrograms/kg of strychnine was used, cadmium at either dosage failed to prevent convulsions, although the onset was delayed and duration curtailed. The rapidity with which Cd modified CNS activity indicated that the effect can not depend upon cadmium-induced synthesis of metallothionine, but represents a direct effect of Cd on the CNS. Cadmium treatment did not substantially improve the survival of rats that convulsed when treated with strychnine.

Human health effects of exposure to cadmium

The health effects of human exposure to cadmium are discussed with emphasis on intake, absorption, body burden, and excretion; osteomalacia in Japan; hypertension; and proteinuria, emphysema, osteomalacia, and cancer in workers. Elevated blood pressure has not been observed as a result of excessive exposures to cadmium in Japan or the workplace. Renal tubular dysfunction and consequent proteinuria is generally accepted as the main effect following long-term, low-level exposure to cadmium. Studies of workers show that proteinuria may develop after the first year of exposure or many years after the last exposure. Proteinuria and deterioration of renal function may continue even after cessation of exposure. The immediate health significance of low-level proteinuria is still under debate. However, there is evidence that long-term renal tubular dysfunction may lead to abnormalities of calcium metabolism and osteomalacia. The few autopsy and cross-sectional studies of workers do not permit conclusions to be drawn regarding the relationship between cadmium exposure and emphysema. Retrospective and historical-prospective studies are needed to settle this important question. No conclusive evidence has been published regarding cadmium-induced cancer in humans. However, there is sufficient evidence to regard cadmium as a suspect renal and prostate carcinogen. Because of equivocal results and the absence of dose-response relationships, the studies reviewed should be used with caution in making regulatory decisions and low-dose risk assessments.

The effect of body protein supply on resistance to cadmium

Six groups of 15 rats were fed on three diets, each differing in the quantity and quality of protein (17.87 as opposed to 8.85 g%, with or without the addition of 0.5 g methionine), one group of each pair of animals being injected subcutaneously with 0.3 mg Cd/kg body weight/day, for 13 weeks. The low protein diet increased the effects of cadmium, rendering them significantly more harmful than in animals which were given the normal protein diet. The incorporation of 0.5 g% DL-methionine in the low protein diet, without increasing the total nitrogen content, diminished the most marked effects induced by the same amounts of cadmium, so that their mean values were not significantly different from those found in the normal protein group treated with the same dose of the metal. The results show that a quantitatively and qualitatively adequate protein supply increased the resistance of the organism to cadmium, diminishing significantly the severity of symptoms induced by the metal.

Possible toxic water factor in coronary heart-disease

Many reports indicate a significant negative correlation between death-rates for coronary heart-disease (C.H.D.) and water hardness. A reverse situation exists in the twin Kansas cities, U.S.A. Kansas City, Kansas, has water which is more than twice as hard as the softened water of Kansas City, Missouri, from the same source. Serum cholesterol and triglyceride levels were similar, but blood-pressure was higher in Kansas City, Kansas, and this correlated with higher serum-sodium, lower serum-potassium, and a tenfold higher serum-cadmium. Serum calcium and magnesium levels were higher in Kansas, while copper, chromium, cobalt, and zinc were higher in Missouri. The serum studies were con ducted on two matched groups of 260 adults from each of the sample cities. Hypertension may account for the reverse C.H.D. rate noted and be cadmium related.