Effects of exposure to low levels of environmental cadmium on renal biomarkers

We conducted a study among residents of a small community contaminated with heavy metals from a defunct zinc smelter and residents from a comparison community to determine whether biologic measures of cadmium exposure were associated with biomarkers of early kidney damage. Creatinine-adjusted urinary cadmium levels did not differ between the smelter and comparison communities; thus we combined individuals from both communities (n = 361) for further analyses. The overall mean urinary cadmium level was low, 0.26 microg/g creatinine, similar to reference values observed in the U.S. general population. For children ages 6-17 years, urinary concentration of N-acetyl-beta-D-glucosaminidase (NAG), alanine aminopeptidase (AAP), and albumin were positively associated with urinary cadmium, but these associations did not remain statistically significant after adjusting for urinary creatinine and other potential confounders. For adults ages 18 or older, urinary concentration of NAG, AAP, and albumin were positively associated with urinary cadmium. The associations with NAG and AAP but not with albumin remained statistically significant after adjusting for creatinine and other potential confounders. We found a positive dose-effect relationship between levels of creatinine-adjusted urinary cadmium and NAG and AAP activity, and statistically significant differences in mean activity for these two enzymes between the highest (> or =1.0 microg cadmium/g creatinine) and the lowest (< or =0.25 microg cadmium/g creatinine) exposure groups. The findings of this study indicate that biologic measures of cadmium exposure at levels below 2.0 microg/g creatinine may produce measurable changes in kidney biomarkers.