Human urinary occurrence of thiourea vulcanization accelerators and their human exposure

Thiourea vulcanization accelerators (TVAs) have been detected in various household dust samples, indicating their widespread human exposure. Until now, the occurrence of TVAs in human urine, a suitable matrix for assessing human exposure, has remained unknown. The present study comprehensively examined eight kinds of TVAs in urine samples (n = 277) from participants living in Taizhou, China. A total of eight TVAs were found in these human urine samples, exhibiting the detection frequencies ranging from 13% to 91%, highlighting widespread exposure among the general population. N, N'-ethylenethiourea (ETU; 1.7 ng mL^-1, min-max range, < limits of detection (LOD)-13 ng mL^-1) exhibited the highest mean human urinary concentration, followed by N, N'-diethylthiourea (DETU; 0.51 ng mL^-1, < LOD-3.1 ng mL^-1) and N, N'-diphenylthiourea (DPTU; 0.37 ng mL^-1, < LOD-0.69 ng mL^-1). Gender-specific analysis demonstrated no significant (p > 0.05) distinctions in urinary concentrations of ETU, DETU, and DPTU between males and females. Additionally, a significantly (p < 0.05) negative correlation was observed between urinary ETU levels and age, with younger individuals showing relatively higher urinary concentrations. Human daily exposure (DE) values of ETU, DETU, and DPTU were estimated, primarily using their determined urinary concentrations and the fraction of these TVAs that were excreted in human urine. The mean DE values of ETU, DETU, and DPTU were 99 ng/kg bw/day, 46 ng/kg bw/day, and 19 ng/kg bw/day, respectively. To our knowledge, the present study comprehensively characterized the human urinary occurrence of TVAs for the first time. These obtained data are important for advancing the knowledge on human exposure to these TVAs.