Abstract
We analyzed 300 urine samples (24h voids) from the German Environmental Specimen Bank, for specific diisononylcyclohexane-1,2-dicarboxylate (DINCH) metabolites ranging from the simple monoester to several oxidized monoesters. Urine samples were collected in the years 1999, 2003, 2006, 2009 and 2012, 60 samples per year, from 30 male and 30 female volunteers (age: 21-29 years). The design of this retrospective study was chosen to investigate the time trend of DINCH exposure due to the market introduction of DINCH in 2002 and increasing production volumes ever since (to approx. 200,000 metric tons in 2012). The samples were analyzed by on-line HPLC-MS/MS with isotope dilution quantification. The LOQs for the oxidized DINCH metabolites are 0.05 µg/l and 0.1 µg/l for the monoester. All samples were blinded before analysis. We detected no DINCH metabolites in the 1999 and 2003 samples. From 2006 on the percentage of samples with DINCH metabolites above the LOQ increased significantly over the years (7% in 2006, 43% in 2009 and 98% in 2012). As expected, the hydroxyl monoester (OH-MINCH) was predominant followed by the carboxyl monoester (cx-MINCH) and the oxo monoester (oxo-MINCH). The median (and 95th percentile) of the OH-MINCH concentrations (in µg/L) increased from <LOQ (0.08) in 2006, to <LOQ (1.02) and 0.39 (2.09) in 2012. Similar trends, albeit at lower concentrations were observed for the other metabolites. All oxidized DINCH metabolites correlated strongly among each other over all concentrations spanning 4 orders of magnitude (rho>0.75, p>0.001). The median (95th percentile) DINCH intake in 2012 was calculated to be 0.14 (1.07) µg/kg body weight/day. Our results impressively show the advent and development of the exposure of the German population to DINCH since its market introduction in 2002. Daily intakes are still lower compared to the phthalates it is used for as a substitute; future measurements will enable us to monitor the development of exposure.
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