Background: Few population studies have reported on the long-term changes in the internal cadmium dose and simultaneously occurring mortality.
Objective: We monitored blood cadmium (BCd), 24-hr urinary cadmium (UCd), and mortality in an environmentally exposed population.
Methods: Starting from 1985, we followed BCd (until 2003), UCd (until 1996), and mortality (until 2007) among 476 and 480 subjects, randomly recruited from low- exposure areas (LEA) and high-exposure areas (HEA). The last cadmium-producing plant in the HEA closed in 2002.
Results: From 1985-1989 to 1991-1996, BCd decreased by 40.3% and 18.9% in the LEA and HEA, respectively (p < 0.0001 for between-area difference). From 1991-1996 until 2001-2003, BCd remained unchanged in the HEA (+ 1.8%) and increased by 19.7% in the LEA (p < 0.0001). Over the entire follow-up period, the annual decrease in BCd averaged 2.7% in the LEA (n = 258) and 1.8% in the HEA (n = 203). From 1985-1989 to 1991-1996, UCd fell by 12.9% in the LEA and by 16.6% in the HEA (p = 0.22), with mean annual decreases of 2.7% (n = 366) and 3.4% (n = 364). Over 20.3 years (median), 206 deaths (21.5%) occurred. At baseline, BCd (14.6 vs. 10.2 nmol/L) and UCd (14.1 vs. 8.6 nmol/24-hr) were higher in deaths than in survivors. The risks (p < or = 0.04) associated with a doubling of baseline UCd were 20% and 44% for total and noncardiovascular mortality, and 25% and 33% for a doubling of BCd.
Conclusions: Even if zinc-cadmium smelters close, historical environmental contamination remains a persistent source of exposure. Environmental exposure to cadmium increases total and noncardiovascular mortality in a continuous fashion without threshold.
Keywords: cadmium; environmental exposure; mortality.