Cadmium cause and effect: looking at renal function. (Science Selections).

Exposure to high concentrations of cadmium, as in industrial settings, can lead to renal failure, but kidney problems can arise even from low-level cadmium exposures. In this month's issue, a group of scientists led by Ing-Marie Olsson of the Swedish University of Agricultural Sciences investigates the relationship between cadmium intake from various sources, cadmium retention, and kidney function [EHP 110:1185-1190]. They found that, although most of the subjects had relatively low cadmium intake, the cadmium did appear to have an adverse effect on kidney function.

The study subjects were heterosexual couples living on farms in the Skane province of southern Sweden. The soil in this area is relatively high in cadmium. Some of the cadmium occurs naturally, some comes from phosphate fertilizers once used intensively in farming, and some comes from clouds of industrial pollution originating in central Europe.

Demographic and lifestyle factors may affect how people are exposed nonoccupationally to cadmium. For example, nonsmokers absorb most of their cadmium from food and water, but because tobacco draws cadmium from soil, smokers may absorb half their exposure from cigarettes. The researchers surveyed the subjects on their diets and smoking habits. They estimated the amount of cadmium the subjects ingested through foods and assigned cadmium values to these different eating patterns, based on existing literature. They also calculated the amount of cadmium the subjects got from water by measuring the metal in the subjects' wells and estimating the amount of water, tea, coffee, and juice they drank.

Even at the lowest exposure level, there was an indication of effect on kidney function, and higher concentrations of urine cadmium (UCd) correlated to reduced kidney performance. As expected, the researchers found that individuals with high blood cadmium (BCd) also had high UCd. However, cadmium consumption did not correlate with UCd or BCd, a finding that has been previously reported at low exposures. This may be because of the subjects' low average dietary intake of cadmium, because of variation in the bioavailability of the cadmium in the subjects' food and water, or because of uncertainties in the estimated intake of cadmium from food.

The women's BCd was about 1.4 higher than that of the men, and their UCd was about 1.6 times higher than the men's. In a subgroup of the sample--couples in which neither person had ever been a smoker--the women had lower intakes per body weight of cadmium than men, but had 1.8 times higher BCd and 1.4 times higher UCd. This may be due, the researchers say, to the lower iron status typical of premenopausal women, because lower iron levels have been linked to increased cadmium retention. In spite of the relationship between low iron status and higher cadmium levels, subjects who took vitamins, which usually contain iron, had higher BCd and UCd levels. The researchers suggest that the vitamins may have been contaminated with cadmium, as has happened before with vitamin-mineral supplements used for pig feed.

The researchers also compared cadmium levels in the kidneys of slaughtered pigs with the BCd and UCd of people living on the farms on which the animals were raised. Because the pigs were fed locally grown grain, their kidney cadmium levels was presumed to reflect the cadmium levels in the soil. But cadmium levels in the pigs did not predict cadmium levels in people living on the same farms. A possible explanation, the researchers say, is that much of the cereals and other foods that the subjects ate wasn't grown locally; another is that ingredients besides locally produced grain were contributing to the pigs' cadmium intake.