Cadmium, Environmental Exposure, and Health Outcomes

Soisungwan Satarug; Scott H. Garrett; Mary Ann Sens; Donald A. Sens


Environ Health Perspect. 2010;118(2):182-90. 

In This Article

Cadmium Sources and Bioavailability

Mollusks and Crustaceans

Bivalve mollusks and crustaceans are filter feeders that accumulate metals from the aquatic environment independent of environmental pollution, and contaminated waters could further increase the content of metals (Whyte et al. 2009). Cadmium content of some Pacific oysters was found to be 13.5 mg/kg dry weight, whereas 2-fold higher cadmium content was reported for some New Zealand bluff oysters (Copes et al. 2008). A bioavailability study was conducted on 57 men and 19 women 2075 years of age who were associated with the oyster industry (McKenzie et al. 1986). The subjects were divided into groups 1, 2, 3, and 4, according to their average weekly oyster consumption rate at < 6, 624, 24 to < 72, and ≥ 72 oysters, respectively. The estimated cadmium intake for subjects in groups 1, 2, 3, and 4 was 34, 75, 116, and 250 µg/day, respectively. The estimated consumption for all groups, except group 1, exceeded the FAO/WHO safe guideline. The blood cadmium was higher among smokers than among nonsmokers. For the nonsmokers in group 4 (the highest consumption rate), the increase in blood cadmium attributable to oyster consumption was 1.2 µg/L. Blood selenium was also elevated by oyster consumption, but no effect on serum zinc or copper levels was observed. Urinary cadmium, zinc, and β2-microglobulin (β2-MG) levels were not affected, and no relationship was found between cadmium intake and adverse renal effects, defined as glycosuria or proteinuria. In addition, no effect was observed on levels of cadmium, zinc, and copper in hair. McKenzie et al. (1986) concluded that interactions with selenium and other metals in oysters may result in diminished cadmium absorption. This study is extremely important because it has been used as the basis for assigning high cadmium ML values to allow the marketing of oysters and their products that contain naturally high levels of cadmium. It is important to note that no distinction is made between toxicity of natural versus anthropogenic cadmium. In our opinion, this study had several flaws. For example, although dietary selenium and zinc were measured in the analysis, other determinants of cadmium absorption were not considered, such as body iron stores and the older age of the subjects. Furthermore, evidence ( Table 1 , Table 2 , Table 3 , Table 4 , and Table 5 ) now indicates that the blood cadmium 1.2 µg/L attributed to oyster consumption among nonsmokers in group 4 can be considered at risk, because blood cadmium levels of < 1 µg/L have been associated with adverse effects ( Table 2 and Table 3 ).

Recently, Copes et al. (2008) and Clark et al. (2007) reexamined the bioavailability of cadmium in oysters and showed the effects of consuming oysters on cadmium body burden and serum elemental composition (selenium, zinc, copper). Copes et al. (2008) considered the potential confounding effects of age and cigarette smoking and restricted their study to nonsmokers (33 men, 28 women) between 33 and 64 years of age (mean age, 47.3 years). They estimated that the cadmium intake from oysters was 174 µg/week (24.8 µg/day). Significant increases in blood and urinary cadmium levels were found to be associated with the duration of oyster farming of at least 12 years during which time the on average consumption rate was 18 oysters/week (87 g/week). For the study participants, the average (range) blood cadmium was 0.83 (0.342.27) µg/L, and the average urinary cadmium (range) was 0.76 (0.164.04) µg/g creatinine. The mean urinary cadmium 0.76 µg/g creatinine was 2.5-fold greater than that of U.S. female nonsmokers, mean age 55 years, as defined in the study by McElroy et al. (2007). Cadmium in a shellfish diet was shown to be bioavailable in the study by Vahter et al. (1996) who found cadmium intake to be 11 µg/day for women in the mixed-diet group and 28 µg/day for those in the high-shellfish diet group. No differences in blood or urine cadmium levels were observed between the two groups. However, an increase in blood cadmium of 63% and an increase in urinary cadmium of 24% were found among those consuming the high-shellfish diet who had plasma ferritin levels < 20 µg/L when compared with those who consumed mixed diets and had the same low body iron stores. Thus, these studies strongly suggest that cadmium in oysters and shellfish is bioavailable and that long-term oyster consumption does result in a higher body burden of cadmium.


Sunflower seeds, peanuts, flaxseed, and linseed accumulate cadmium from the soil in a manner similar to that of tobacco. Cadmium levels in sunflower kernels range from 0.2 to 2.5 mg/kg. Reeves and Vanderpool (1997) conducted a study on 75 male and female nonsmokers who were 3070 years of age. Using a self-reported food-frequency survey, those subjects who reported consuming > 28 g of sunflower kernels per week were considered high consumers. An analysis of a duplicate diet among controls showed that on average cadmium intake was 36 µg/day, but intake was not determined for any of the high consumers. Blood and urinary cadmium levels were used as indicators of cadmium body burden. The expected increased cadmium body burden could not be demonstrated, probably because of the limited number of subjects and the short time frame of the study. However, evidence for kidney effects, reflected by urinary β2-MG and N-acetyl-β-D-glucosaminidase (NAG) levels, was found among high consumers of sunflower seeds. These data may indicate that cadmium in sunflower kernels possess a high nephrotoxic potential. Alternatively, they may indicate increased sensitivity to cadmium renal toxicity in the high sunflower-kernel consumers.


High cadmium levels (776 mg/kg wet weight) were found in the offal of dugongs and turtles that constituted the diet in the Torres Strait (Australia). Haswell-Elkins et al. (2007a) examined cadmium body burden in relation to offal consumption among residents in two communities with varying dugong and turtle catch statistics. Of the 182 subjects, 12% had urinary cadmium > 2 µg/g creatinine, and the group mean urinary cadmium was 0.83 µg/g creatinine. Age accounted for 46% of total variation in urinary cadmium levels, and sex (female) and current smokers accounted for 7% and 4.7% of variation, respectively. In a second study, Haswell-Elkins et al. (2007b) found high cadmium body burden associated with higher consumption of turtle liver and kidney and with locally gathered clams, peanuts, and coconuts. The sum of these foods, heavy smoking, age, and waist circumference accounted for 40% of variation in cadmium body burden (p < 0.05). Thus, this study showed that local offal consumption is linked with high cadmium body burden.

Cadmium levels are higher in liver and kidney than in muscle and older animals (Prankel et al. 2005). Average cadmium in the liver and kidney of wild moose was 2.11 and 20.2 µg/g wet weight, respectively (Arnold et al. 2006). Notably, chronic, low-dose exposure situations produce 10- to 20-fold higher cadmium in kidney than liver. It is worth noting that no difference was observed in bioavailability of ionic cadmium versus protein bound cadmium. In the human gastrointestinal tract, the protein bound to cadmium is digested and ionic cadmium released; thus speciation of cadmium in food would not be a basis for assigning high cadmium MLs for marketing purposes (Francesconi 2007). There has been no indication of decreases in food cadmium content over the past decade or any drastic change in dietary habits. In a British study, Lyon et al. (1999) showed that human kidney cadmium levels were static over a period of 16 years (19781993) but were higher than those found in studies conducted in the early 20th century. The distribution of kidney cadmium concentrations was skewed, with about 3.9% of the 2,700 samples > 50 µg/g kidney cortex wet weight, although the population mean was only 19 µg/g wet weight (Lyon et al. 1999).


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