Notice of Intended Changes—Cadmium, Methyl Isobutyl Ketone, and Trichloroethylene

Health risk assessment of long-term exposure to non-genotoxic chemicals: application of biological indices

For chemical pollutants, health risk assessment of long-term exposure is usually best realized through an epidemiologic approach which attempts to link cumulative levels of exposure to the potential for occurrence of early adverse effects. For some chemicals, however, the frequency of peak exposures may be more relevant for assessing the health risk than the integrated dose. In very few circumstances, biological exposure indices directly reflect the cumulative dose (e.g. PCB in blood). More frequently they are indicators of short-term interval dose but provided they have been measured with a sufficient frequency, their integration over the duration of exposure may represent a valid surrogate of the cumulative dose. This has been clearly demonstrated for lead or cadmium in blood. The selection of the appropriate biological effect markers for the study of the dose-effect/dose-response relationships is frequently a controversial issue when information on the mechanism of action of the pollutant is insufficient. In this case, the study of the health significance of the observed biological changes may be required for assessing a meaningful no-adverse-effect level. For example, in adult male workers moderate exposure to lead may affect the synthesis of vasodilatory prostaglandins in the kidney but presently there is no indication that this effect should be taken into account to define the acceptable occupational exposure level to lead because it is not associated with an impairment of the hemodynamic response of the kidney to an acute protein load. On the contrary, a low-molecular-weight proteinuria induced by cadmium may be predictive of an increased age-related decline of the glomerular filtration rate. Although the use of early biological effect markers for the study of the dose-effect or dose-response relationships in humans is probably less affected by selection biases than morbidity data, the possibility of such an interference cannot be excluded. For example, in the general population, the tubulotoxic effects of cadmium may occur at a lower body burden of the metal than in adult male workers. Whatever the adverse biological effect considered, the application of an uncertainty factor remains justified when extrapolating a no-effect level from adult male workers to the general population.

Markers of early renal changes induced by industrial pollutants. III. Application to workers exposed to cadmium

Cadmium (Cd) was the third heavy metal investigated in the European collaborative research project on the development and validation of new markers of nephrotoxicity. Fifty workers exposed to Cd and 50 control workers were examined. After application of selection criteria 37 workers (mean age 43) exposed to Cd for an average of 11.3 years; and 43 age matched referents were retained for final analysis. The average concentrations of Cd in blood (Cd-B) and urine (Cd-U) of exposed workers were 5.5 micrograms Cd/l and 5.4 micrograms Cd/g creatinine respectively. By contrast with lead and mercury, Cd had a broad spectrum of effects on the kidney, producing significant alterations in amounts of almost all potential indicators of nephrotoxicity that were measured in urine--namely, low and high molecular weight proteins, kidney derived antigens or enzymes, prostanoids, and various other biochemical indices such as glycosaminoglycans and sialic acid. An increase in beta 2-microglobulin and a decrease of sialic acid concentration were found in serum. Dose-effect/response relations could be established between most of these markers and Cd-U or Cd-B. The thresholds of Cd-U associated with a significantly higher probability of change in these indicators were estimated by logistic regression analysis. Three main groups of thresholds could be identified: one around 2 micrograms Cd/g creatinine mainly associated with biochemical alterations, a second around 4 micrograms Cd/g creatinine for high molecular weight proteins and some tubular antigens or enzymes, and a third one around 10 micrograms Cd/g creatinine for low molecular weight proteins and other indicators. The recent recommendation by the American Conference of Governmental Industrial Hygienists (ACGIH) of 5 micrograms Cd/g creatinine in urine as the biological exposure limit for occupational exposure to Cd appears thus justified, although for most of the effects occurring around this threshold the link with the subsequent development of overt Cd nephropathy is not established. In that respect, the very early interference with production of some prostanoids (threshold 2 micrograms Cd/g creatinine) deserves further investigation; although this effect might contribute to protect the filtration capacity of the kidneys, it might also play a part in the toxicity of Cd on bone.