Diagnostic chelation challenge with DMSA: A biomarker of long-term mercuryexposure?

Chelation challenge testing has been used to assess the body burden of vari ous metals. The best-known example is EDTA challenge in lead-exposed indivi duals. This study assessed diagnostic chelation challenge with dimercaptosu ccinic acid (DMSA) as a measure of mercury body burden among mercury-expose d workers. Former employees at a chloralkali plant, for whom detailed expos ure histories were available (n = 119), and unexposed controls (n = 101) co mpleted 24-hr urine collections before and after the administration of two doses of DMSA, 10 mg/kg. The urinary response to DMSA was measured as both the absolute change and the relative change in mercury excretion. The avera ge 24-hr mercury excretion was 4.3 mug/24 hr before chelation, and 7.8 mug/ 24 hr after chelation. There was no association between past occupational m ercury exposure and the urinary excretion of mercury either before or after DMSA administration. There was also no association between urinary mercury excretion and the number of dental amalgam surfaces, in contrast to recent published results. We believe the most likely reason that DMSA chelation c hallenge failed to reflect past mercury exposure was the elapsed time (seve ral years) since the exposure had ended. These results provide normative va lues for urinary mercury excretion both before and after DMSA challenge, an d suggest that DMSA chelation challenge is not useful as a biomarker of pas t mercury exposure.