Estimation of biological half-life of urinary cadmium in inhabitants after cessation of environmental cadmium pollution using a mixed linear model

We investigated the biological half-life of urinary cadmium concentration (U-Cd) based on a 22-year follow-up study after cessation of environmental Cd pollution. Spot urine samples were obtained from the inhabitants (32 men and 36 women) in the target area in 1986, 1991, 1999, 2003 and 2008. These inhabitants were divided into higher or lower baseline U-Cd group by the cut-off of 5 mu gl(-1) or 5 mu gg(-1) creatinine. Biological half-life of U-Cd was estimated using a linear mixed model adjusted for the baseline age. In the higher baseline U-Cd groups, the estimated half-life and 95% confidence intervals were 12.4years (9.3-18.8years) and 11.4years (9.3-14.6years) for unadjusted U-Cd in men and women, respectively. For creatinine-adjusted U-Cd, they were 16.0years (13.0-20.7years) and 20.4years (16.6-26.2years) in men and women, respectively. In the lower baseline U-Cd groups, biological half-life for unadjusted U-Cd in men was solely significant (23.4years) and longer than the corresponding half-life in the higher baseline U-Cd group. The biological half-lives of U-Cd obtained in this study were identical with the values for U-Cd or total body burden determined by a different method.