Conceptual problems in establishing the critical concentration of cadmium in human kidney cortex

Confusion about Cadmium Risks: The Unrecognized Limitations of an Extrapolated Paradigm

BACKGROUND

Cadmium (Cd) risk assessment presently relies on tubular proteinuria as a critical effect and urinary Cd (U-Cd) as an index of the Cd body burden. Based on this paradigm, regulatory bodies have reached contradictory conclusions regarding the safety of Cd in food. Adding to the confusion, epidemiological studies implicate environmental Cd as a risk factor for bone, cardiovascular, and other degenerative diseases at exposure levels that are much lower than points of departure used for setting food standards.

OBJECTIVE

The objective was to examine whether the present confusion over Cd risks is not related to conceptual or methodological problems.

DISCUSSION

The cornerstone of Cd risk assessment is the assumption that U-Cd reflects the lifetime accumulation of the metal in the body. The validity of this assumption as applied to the general population has been questioned by recent studies revealing that low-level U-Cd varies widely within and between individuals depending on urinary flow, urine collection protocol, and recent exposure. There is also evidence that low-level U-Cd increases with proteinuria and essential element deficiencies, two potential confounders that might explain the multiple associations of U-Cd with common degenerative diseases. In essence, the present Cd confusion might arise from the fact that this heavy metal follows the same transport pathways as plasma proteins for its urinary excretion and the same transport pathways as essential elements for its intestinal absorption.

CONCLUSIONS

The Cd risk assessment paradigm needs to be rethought taking into consideration that low-level U-Cd is strongly influenced by renal physiology, recent exposure, and factors linked to studied outcomes.

CITATION

Bernard A. 2016. Confusion about cadmium risks: the unrecognized limitations of an extrapolated paradigm. Environ Health Perspect 124:1-5; http://dx.doi.org/10.1289/ehp.1509691.

The effect of cadmium in combination with zinc and selenium on ovarian structure in Japanese quails

In this study the effect of cadmium, cadmium+selenium and cadmium+zinc administration on the ovarian structure in Japanese quails was studied. The morphometric analysis of the relative volume of primary follicles detected the highest value in control group with a similar value in the group with administration of cadmium with selenium. Lower relative volume is reported in group with cadmium and zinc administration and the group with simple cadmium administration (P < 0.05). The relative volume of growing follicles was very similar in all studied groups (11.33-15.35%), and the relative volume of stroma was very stable (82.59-86.45%). In the evaluation of the number of follicles undergoing atresia detected significantly higher number of atretic primary follicles as well as atretic growing follicles in the group with cadmium administration and cadmium with selenium administration in comparison with control group. In comparison of normal and atretic follicles we report the most negative effect of single cadmium administration on ovarian structure. Selenium co-administration shows protective effects but only the co-administration with zinc prevent significant cadmium ovarian alterations.

Apoptotic rate and metallothionein levels in the tissues of cadmium- and copper-exposed rats

It is well known that cadmium (Cd) has toxic and carcinogenic effects in rodents and humans, but the effects of Cd on apoptosis are still not clear. Although some studies have shown that Cd has apoptotic potential, other studies have shown that Cd can be antiapoptotic. Parameters such as sensitivity of the exposed organism or cells and the exposure conditions should be important in delineating the effect of Cd on apoptosis. In the present study, we aimed to determine the apoptotic index (AI) of Sprague-Dawley rat tissues that are loaded at a lower Cd concentration than the critical concentration (50 microg/g) for its toxic effects. Metallothionein (MT) levels of tissues were also determined and the experiments repeated with copper (Cu)-exposed rats. We detected decreases in the apoptotic index in liver and lung tissues of Cd-exposed groups accompanied with an increase in MT levels. Also, decreases of AI were detected in the liver tissues of Cu-exposed groups. These findings indicate that Cd can suppress apoptosis in vivo. The possible role of MT expression on the suppression of apoptosis and the importance of free-Cd ion concentration on switching antiapoptotic effects to proapoptotic effects are also discussed.

A meta-analysis of literature data relating to the relationships between cadmium intake and toxicity indicators in humans

The objective of the study was to determine the relationship between cadmium (Cd) intake and cadmium toxicity indicators by meta-analysis of literature data, in particular beta2-microglobulin (beta2MC), and to compare the results with the current Provisional Tolerable Weekly Intake (PTWI) set by FAO/WHO. The literature survey identified 79 feeding trials involving 27,537 people that were suitable for extraction of cadmium intake, levels in blood and urine and beta2-microglobulin in urine. There was an exponential increase in beta2-microglobulin with increases in cadmium intake above 302 micro g/day, which corresponds to a PTWI of 3.02 micro g/kg of body weight, when a safety margin of 10 is included. This compares with the current level set by FAO/WHO of 7 micro g/kg of body weight. Cadmium in blood and urine were also positively related to cadmium intake and participants' age. There were two principal components of variation in the data set, first: cadmium intake, concentrations of cadmium in blood, urine and beta2-microglobulin in urine, and second: duration and age of exposure.

Meta-analysis for deriving age- and gender-specific dose-response relationships between urinary cadmium concentration and beta2-microglobulinuria under environmental exposure

A meta-analysis was conducted to derive age- and gender-specific dose-response relationships between urinary cadmium (Cd) concentration and beta2-microglobulinuria (beta2MG-uria) under environmental exposure. beta2MG-uria was defined by a cutoff point of 1000 microg beta2-microglobulin/g creatinine. We proposed a model for describing the relationships among the interindividual variabilities in urinary Cd concentration, the ratio of Cd concentrations in the target organ and in urine, and the threshold Cd concentration in the target organ. The parameters in the model were determined so that good agreement might be achieved between the prevalence rates of beta2MG-uria reported in the literature and those estimated by the model. In this analysis, only the data from the literature on populations environmentally exposed to Cd were used. Using the model and estimated parameters, the prevalence rate of beta2MG-uria can be estimated for an age- and gender-specific subpopulation for which the distribution of urinary Cd concentrations is known. The maximum permissible level of urinary Cd concentration was defined as the maximum geometric mean of the urinary Cd concentration in an age- and gender-specific subpopulation that would not result in a statistically significant increase in the prevalence rate of beta2MG-uria. This was estimated to be approximately 3 microg/g creatinine for a population in a small geographical area and approximately 2 microg/g creatinine for a nationwide population.

Metal levels in body tissues, forage and fecal pellets of elk (Cervus elaphus) living near the ore smelters at Sudbury, Ontario

Ontario's only free-ranging elk herd located at Burwash-French River has been subjected to the influence of historic copper-nickel-iron (Cu-Ni-Fe) ore smelting operations within the Sudbury area. Metal levels in selected body tissues, preferred forage items and fecal pellets were determined, and their potential effects on health and reproductive viability assessed. Significant age effects were apparent in 13 out of 31 tissue metal values obtained, with most age-related differences attributable to elevated concentrations in fetal tissues. Cu and zinc (Zn) levels were four to six times higher in livers and one and a half to two times higher in the bones of fetuses as compared to post-natal animals. Enhanced pre-natal tissue burdens were also noted for cobalt (Co), Ni and lead (Pb) in muscles. However, mean cadmium (Cd) levels in kidney, liver and muscle tissues, as well as hepatic Fe concentrations, showed significant increases with age. Although Cd levels in the kidneys of older elk were still well below the reported threshold for irreversible organ damage, and not considered to be health-threatening, detailed histological study of the cortical tissues for subtle pathotoxicological effects may be warranted. Unlike renal and hepatic tissues, Cd concentrations in skeletal muscle were minimal and within levels considered acceptable for human consumption. Forage species collected in the elk range generally showed higher (two to eight times) Ni and Fe levels than the corresponding plants from a non-contaminated reference site. The highest Ni and Fe burdens were carried by eastern white cedar, a preferred winter food item for elk. No consistent site-related trends were demonstrated by Cu, Zn, Co, Pb, chromium (Cr) and Cd forage levels. Mean metal concentrations in fecal pellets generally exceeded the mean composite forage levels by a factor of 3, except for Ni, which was five times more concentrated in feces. Significantly elevated Ni and Fe levels in preferred browse species and fecal pellets of the Sudbury-area elk could be of concern and warrant further investigation.

Risk assessment of nephrotoxicity of cadmium

Cadmium as an environmental or occupational toxin has been well studied. Exposure can fairly easily be detected by analysis of cadmium in biological material. Different routes of cadmium uptake, such as via airborne particles, cigarette smoke or contaminated food, have been identified. Urinary concentrations associated with renal effects vary, depending on urinary marker of effect, and are as low as 2 micrograms cadmium/g creatinine. Different segments of the nephron are affected by cadmium. Urinary enzymes and serum derived proteins, mainly low-molecular weight proteins, as well as eicosanoids or glycosaminoglycans are among the tubular or glomerular markers of effect. Predisposing factors, such as smoking, dietary habits and low body iron stores have been described. It is concluded that even for low level cadmium exposure effects can be detected with sensitive diagnostic tools.

alpha-1-Microglobulin: epidemiological indicator for tubular dysfunction induced by cadmium?

OBJECTIVES

To evaluate the suitability of alpha-1-microglobulin as a marker for cadmium induced renal dysfunction.

METHODS

alpha-1-Microglobulin was studied in a cross sectional survey in relation to the body burden of cadmium. Concentrations of alpha-1-microglobulin in 24 h urine of 831 people aged 2-87 years were analysed in association with urinary cadmium excretion, cadmium blood concentration, age, sex, occupational and smoking history, and estimated creatinine clearance. Participants came from a population residentially exposed to cadmium and from two control populations matched for socioeconomic status.

RESULTS

The excretion of alpha-1-microglobulin/24 h ranged from 0.1 mg to 176.3 mg and 44.4% of samples showed concentrations near the detection limit. Ordinal logistic regression analysis of people of all ages identified a high risk only for males compared with females (odds ratio (OR) 2.14; 95% confidence interval (95% CI) 1.56 to 2.94), age group, and duration of living on contaminated soil (OR 1.03/year; 95% CI 1.02 to 1.04), but not urinary cadmium excretion (OR 1.30; 95% CI 0.96 to 1.77) as significant predictors. For people < or = 50 years of age a weaker effect of sex (OR 1.76; 95% CI 1.13 to 2.73) and age group and an effect of similar magnitude for the duration of soil exposure (OR 1.03; 95% CI 1.01 to 1.04) were found. Also, the urinary cadmium excretion (OR 2.26; 95% CI 1.38 to 3.70) and occupational exposure (OR 1.71; 95% CI 1.03 to 2.83) were found to be significant in this younger age group. The estimated creatinine clearance had no significant impact on the alpha-1-microglobulin excretion.

CONCLUSION

alpha-1-Microglobulin is a suitable marker for early tubular changes only for people < or = 50 years. It may not be sufficiently specific for cadmium, and therefore not a suitable surrogate for cadmium exposure in epidemiological studies.

Cadmium in kidneys in Swedes measured in vivo using X-ray fluorescence analysis

An X-ray fluorescence (XRF) technique using plane polarized X-rays for excitation was used for in vivo measurements of cadmium in the kidney cortex among non-occupationally exposed members of the general population in southern Sweden. The measured concentrations of cadmium in the kidney cortex of smokers (median 28 micrograms/g, n = 10) were significantly higher (P = 0.0036) as compared to those in non-smokers (median 8 micrograms/g, n = 10), and so were the cadmium concentrations in blood and urine. The results show that smoking considerably increases the cadmium concentration in the kidney cortex and that smoking is a major source of cadmium exposure in the general population of Sweden. Except in the presence of very deeply situated kidneys, where the minimum detectable concentration is high, non-invasive in vivo XRF analysis of kidney cadmium should be a useful tool for evaluating the effects of long-term low-level exposure to cadmium and the risk of kidney damage.

Effects of acidification on the availability of toxic metals and calcium to wild birds and mammals

The effects of acidification on wildlife inhabiting aquatic or semi-aquatic environments are reviewed, with particular reference to the possibility for increased dietary exposure to Hg, Cd, Pb and/or Al, and decreased availability of essential dietary minerals such as Ca. It is concluded that: (1) piscivores risk increased exposure to dietary methyl-Hg in acidified habitats, and Hg concentrations in prey may reach levels known to cause reproductive impairment in birds and mammals; (2) piscivores do not risk increased exposure to dietary Cd, Pb or Al because these metals are either not increased in fish due to acidification, or increase are trivial from a toxicological perspective; (3) insectivores and omnivores may, under certain conditions, experience increased exposure to toxic metals in some acidified environments. Exposure levels are likely to be sufficiently low, however, that significant risks to health or reproduction are unlikely. More importantly, these wildlife species may experience a drastic decrease in the availability of dietary Ca due to the pH-related extinction of high-Ca aquatic invertebrate taxa (molluscs, crustaceans). Decreased availability of dietary Ca is known to adversely affect egg laying and eggshell integrity in birds, and the growth of hatchling birds and neonatal mammals. Acidification-related changes in the dietary availability of other essential elements, such as Mg, Se and P, have not been established and require further investigation; (4) herbivores may risk increased exposure to Al and Pb, and perhaps Cd, in acidified environments because certain macrophytes can accumulate high concentrations of these metals under acidic conditions. The relative importance of pH in determining the metal concentrations of major browse species, and the toxicological consequences for herbivores wildlife, is not well established and requires further study. A decreased availability of dietary Ca is also likely for herbivores inhabiting acidified environments.

Total body burdens and tissue concentrations of lead, cadmium, copper, zinc, and ash in 55 human cadavers

Trace metal contents of human tissues and total body burdens are useful for studies of nutrition and certain diseases. Data are summarized and analyzed for individuals exposed to the normal Cincinnati environment, for 29 tissues from 55 cadavers for lead and ash concentrations, and from 26 cadavers for cadmium, copper, and zinc concentrations. Total body burdens also were calculated and correlated against each other and age. The distributions for ash, copper, and zinc were close to normal, but those for lead and cadmium were closer to lognormal. Bone lead increased with age, whereas soft tissue lead did not. The calculated mean percentage of total body lead in the bones ranged from 78% at age 20 to 96% at age 80. Correlations of blood concentrations with total body burdens were negligible for cadmium and zinc. For copper the correlation coefficient was a poor 0.54. For lead in blood vs soft tissue burden it was a very poor 0.37, and vs total body lead it was negligible. Thus the use of blood samples as a convenient clinical measure of body burdens for these metals may be of limited value. These and other findings provide a useful bank of information for health studies.

Acute cadmium uptake by rabbit kidneys: mechanism and effects

Trapping of an arterial bolus in the kidney by 40 sec aortic occlusion permitted demonstration of diffusion-limited and Zn-sensitive renal uptake of nonfiltered but diffusible Cd from plasma; mercaptoethanol (ME) or 2,3-dimercaptopropanol (BAL) had been added to the bolus to prevent sequestration of the metals by plasma protein. Cadmium taken up by the kidney under these conditions, whether from blood or glomerular filtrate, unlike Zn, did not return to blood over a period of 2-3 min. Nor was Cd thus accumulated removed by EDTA; it had presumably been transferred into cells. The diffusion dependence of this internalization shows it to be a relatively slow process, as it is in jejunum. In contrast, uptake of Cd tightly bound in a lipid-soluble complex with diethyldithiocarbamate (DDTC) is rapid and flow dependent. Slow uptake in the presence of ME and its inhibition by Zn are therefore not likely to involve movement of undissociated ME complex across the cell membranes. Instead, it is suggested that (1) Cd-binding sites on the membrane possess a relatively high affinity for Cd and can compete for it with ME, and (2) it is the resulting Cd-membrane interaction which, as in jejunum, is depressed by Zn. During transient occlusion kidneys could be loaded with up to 25 micrograms Cd/g cortex without evidence of immediate malfunction. Inhibition of amino acid transport, as previously described, is seen only after an initiation period of 1-2 days following CdME injection, although cortical Cd levels at that time have decreased. The finding of a slowly developing inhibition of amino acid carrier systems suggests an indirect action of Cd; by implication, unique threshold concentrations should not be defined for Cd in renal cortex following subchronic exposures without reference to the duration of exposure.

Metallothionein production: similar responsiveness of avian liver and kidney to chronic cadmium administration

The accumulation of hepatic and renal Cd, Zn, Cu, and metallothionein (MT) was investigated in ringed turtle doves (Streptopelia risoria) chronically exposed to 3 different concentrations of dietary Cd. When only tissue-Cd was considered as an inducer of MT, kidney was found to be 35% as responsive as liver in producing MT. However, when all potentially relevant inducing metals (Cd + Zn + Cu) were taken into account, kidney was found to be 85% as responsive as liver. The greater production of MT/mol Cd in liver was accounted for mainly by a greater co-accumulation of Zn/mol Cd in liver than in kidney. We conclude that the apparent tissue specificity in expression of MT may be overestimated by failure to consider fluctuations in multiple inducers. Variability in tissue-MT concentrations after chronic dietary Cd administration is best accounted for by a consideration of tissue-Cd, -Zn, and -Cu, rather than tissue-Cd alone.

The concept of critical levels of toxic heavy metals in target tissues

The high reactivity of heavy metals with biological systems is well documented, although some disagreement remains on the precise dose-effect relationships involved. This represents a question of considerable importance, especially in attempts to assess the risks of exposure. The implicit assumption is usually made that a threshold concentration of specific metals exists in the most sensitive target organ, so that an increased frequency of functional lesions will be expected if this threshold is exceeded. The threshold for the metal defines its so-called critical level, and this review was written in order to examine the theoretical and practical difficulties in establishing such a level. Among these may be cited, for instance, the dependence of what constitutes the target tissue on the speciation of the metal, the changes in apparent critical level with rate and route of metal administration, the short half-life of some of the metals as well as their compartmentation in the tissues, and the considerable initiation delay frequently preceding the appearance of lesions. For these and other reasons a useful approximate value for a critical concentration has only been proposed so far for the total Cd concentration in the renal cortex of chronically exposed human adults.

A comparison of the effects of dietary cadmium on heart and kidney antioxidant enzymes: evidence for the greater vulnerability of the heart to cadmium toxicity

This study demonstrates the greater susceptibility of the heart as compared to the kidney to cadmium in the presence of high dietary selenium. Male weanling rats were fed an adequate-copper low-selenium feed supplemented with 0, 10 or 50 ppm copper with or without 50 ppm dietary cadmium for 7 weeks. All rats received 0.5 ppm selenium in their drinking water. Cadmium treatment resulted in histopathological lesions in the heart, but not in the kidney. Although cadmium treatment resulted in more extensive effects on glutathione peroxidase and superoxide dismutase in the heart as compared to the kidney, no increase in peroxidation was noted in either organ, suggesting that cadmium cardiotoxicity can be dissociated from tissue peroxidation. Mean cadmium concentrations in the heart ranged from 0.55 to 1.22 micrograms cadmium g-1 tissue, wet weight, and in the kidney from 11.53 to 21.04 micrograms cadmium g-1 tissue, wet weight. In both tissues examined, cadmium levels were influenced by dietary copper and heart cadmium concentrations did not correlate with either the biochemical or histological lesions observed. Thus, tissue cadmium levels alone may not be adequate for predicting cadmium toxicity.

Age dependent changes in metallothionein and accumulation of cadmium in horses

1. Analysis of livers and kidneys from 28 horses for cadmium, zinc and metallothionein showed low cadmium content in liver. There was a gradual increase in cadmium content in kidney with age. 2. Metallothionein values varied with zinc content in the liver and with cadmium content in the kidney; copper values did not vary in either tissue. 3. Metallothionein was localized mainly in the cytoplasms in liver and kidney of horses by immunohistochemistry.

Biological monitoring, by in vivo XRF measurements, of occupational exposure to lead, cadmium, and mercury

In vivo X-ray fluorescence (XRF) techniques were used for biological monitoring of lead, cadmium, and mercury. Lead accumulates in bone, the level of which may thus be used for monitoring of exposure. However, there was no close association between lead levels in bone and exposure time, partly because of differences in exposure patterns and partly, probably, because of variations in the toxicokinetics of lead. There are at least two separate bone lead compartments. The average over-all half-time is probably 5-10 yr. The finger bone level may be an index of the lead status of the total skeleton. In lead workers, the mobilization of bone lead causes an "internal" lead exposure and affects the blood lead level considerably. In cadmium workers, in vivo XRF is a sensitive and risk-free method for assessment of accumulation in kidney cortex, the critical tissue as to toxic effects; workers displayed increased levels. However, there was no clear association with duration and intensity of exposure, cadmium levels in urine, or microglobulinuria. Determinations of kidney cadmium may add important information on the state of accumulation and, thus, risk of kidney damage. Workers exposed to elemental mercury vapor, as well as fishermen exposed to methyl mercury, had mercury levels in bone below the detection limit of the XRF method.

Cadmium concentrations in human kidneys from the UK

The concentration of cadmium in the cortex and medulla of nearly 1000 kidneys obtained at autopsy was determined by atomic absorption spectrophotometry. Particular care was taken over the analytical procedures to ensure the accuracy and precision of the results; intrakidney variability was examined and found to be small. The frequency distributions of cadmium concentrations were approximately lognormal. There was much variability in cadmium concentrations between individuals, with geometric coefficients of variation for both cortex and medulla of around 100%. Cadmium concentrations varied with age and smoking habits, but not sex. Values were successively higher than those in the previous age-group up to 50-59 years (geometric mean 19 micrograms/g), after which they were successively lower; on average, heavy smokers had cadmium concentrations some 15-20% higher than those in light smokers who in turn had values some 15-20% higher than those in non-smokers. No definite conclusions could be reached on the variation of cadmium concentrations with either cause of death or location, or over time. The present study, the first of its kind in the UK, has provided benchmark data; its results are broadly in line with those from previous but smaller studies in other countries.

Cadmium in kidney cortex of inhabitants of North-West Germany: its relationship to age, sex, smoking and environmental pollution by cadmium

The cadmium concentration in kidney cortex (CdKc) was determined in 388 deceased persons, who at the time of death had lived in the cities of Düsseldorf and Duisburg, Federal Republic of Germany (FRG), and surrounding areas. The average CdKc concentration was found to be 17.1 micrograms/g wet weight. Individual values range from less than 0.4 to 94.3 micrograms/g wet weight. The CdKc levels rapidly increase during the first decades of life. At the age of about 40 years, a plateau phase is reached. At high ages (greater than 70 years), the CdKc levels tend to decrease. Cigarette smokers have significantly higher CdKc concentrations than non-smokers. The increase of CdKc depends on the number of cigarettes smoked. Cigar and pipe smokers have slightly increased CdKc levels compared to non-smokers. Non-smokers who had spent the major part of their life in the area of Duisburg, a cadmium-polluted area, have, on the average, significantly higher CdKc levels than non-smokers from the less-polluted surrounding areas. In smokers the residential factor is masked by the effect of cigarette smoking.

The critical level of cadmium in renal cortex: the concept and its limitations

Because renal cortex is a primary target organ of Cd the seriousness of human exposure is commonly assessed in terms of the extent to which it permits renal cortical Cd concentrations to approach a critical value. The critical value has been defined in terms of PCC-10, the population critical concentration at which 10% of exposed individuals may be expected to show abnormal renal function. In chronically exposed human populations, PCC-10 appears to lie in the range of 180 to 220 μg Cd/gram fresh weight of cortex. However, Cd accumulated in the kidney under these conditions is distributed between more than one compartment, in all likelihood differing greatly in their toxicological characteristics. For instance, a major fraction of this Cd is bound to metallothionein, and may as such be relatively inert. Compartmentation of tissue Cd, in turn, is strongly influenced by the nature of exposure, and the PCC-10 value of 200 μg/g may therefore have limited general significance. The problem of risk assessment is further complicated by the high variability of Cd absorption. Nevertheless, human renal Cd levels commonly reach values as high as 1/3 to 1/6 of the chronic PCC-10, and further increases in Cd intake should therefore be avoided.

Metallothionein and cadmium in human kidney cortex: influence of smoking

Post-mortem specimens of human kidney cortex of 47 individuals classified according to their smoking habits were analysed for tissue cadmium and cadmium bound to metallothionein. The cadmium content in the kidney cortex of all individuals was 5-99 micrograms/g wet wt. In smokers consuming more than 20 cigarettes/day the mean content of renal cortex cadmium was twice that of non-smokers and amounted to 33.3 +/- 12.5 micrograms/g wet wt. The amount of cadmium bound to metallothionein of all individuals was 0.3-66 micrograms/g wet wt. directly correlating with the cadmium content of the kidney cortex (r = 0.932). More than 50% of renal cortex cadmium was associated with the metallothionein fractions. Due to constant values of zinc and copper in metallothionein the relative amount of zinc and copper to cadmium in metallothionein decreased with increasing tissue cadmium. Together with the elevated binding of cadmium to renal cortex metallothionein, cadmium increasingly was bound to non-metallothionein ligands. These results suggest that, in the renal cortex of smokers with elevated cadmium, a major portion of cadmium is bound to metallothionein. However, it is unclear yet whether the binding of cadmium to metallothionein with subsequent liberation of the metal during degradation of the protein, the impairment of metallothionein functions by the binding of cadmium or the increased binding to non-metallothionein ligands contribute to the toxicity of cadmium in highly exposed individuals.

Cadmium body burden of an occupationally non burdened population in southern Bavaria (FRG)

The cadmium body burden of the occupationally non-burdened population in the southern Bavarian area was estimated from the cadmium concentrations in liver and renal cortex, determined by ET-AAS of 263 autopsy cases. A mean value of 17.9 mg cadmium was calculated for all cases and 21.9 mg cadmium for all adults. The body burdens found do not depend on sex but greatly on smoking habits. Mean values for non-smokers are 13.5 mg, for moderate smokers 22.5 mg and for heavy smokers 33.2 mg. The dependence on age is similar to that of the cadmium concentration in the kidney cortex: an increase up to an age of approximately 50 years and a decrease at higher ages. Between the average value we found and the critical body burden calculated by Roels et al. (1983) is a safety factor of 8 to 10, but in some of our cases of middle-aged, heavy smokers this safety factor drops to a value lower than 1. It is concluded that it seems to be imperative to control the further trend of the cadmium body burden in occupationally non-burdened populations.