Internal exposure characteristics and health risk assessment of organophosphate esters in urban residents

The contents of 15 organophosphate ester （OPE） metabolites in the urine of 1 869 adults residing in urban areas were quantified using ultra performance liquid chromatography-tandem mass spectrometry （UPLC-MS/MS）. How gender， age， body mass index （BMI）， smoking status， exercise frequency， family income and dietary intake affected the contents of OPE metabolites in human urine were discussed. Furthermore， the daily intake （EDI） of OPEs was evaluated based on the contents of OPE metabolites in urine. The corresponding potential non-carcinogenic risks were calculated in combination with the non-carcinogenic risk reference dose （RfD）， with the health risks of individual OPE monomers and overall cumulative exposure expressed using the hazard quotient （HQ） and hazard index （HI）. Six OPE metabolites exhibited detection frequencies in excess of 60%， with bis（2-butoxyethyl） phosphate （BBOEP） and 1-hydroxy-2-propyl bis（1-chloro-2-propyl） phosphate （BCIPHIPP）， as the two main OPE metabolites， detected at levels of 0.56 and 0.36 ng/mL， respectively. Men exhibited higher urine contents of bis（1，3-dichloro-2-propyl） phosphate （BDCIPP）， BCIPHIPP， and BBOEP than women， whereas women exhibited higher urine contents of 4-hydroxyphenyl-phenylphosphate （4-HO-DPHP）. The levels of BCIPHIPP and diphenyl phosphate （DPHP） were found to correlate negatively with age， while the BCIPHIPP， and di-o-tolyl-phosphate （DoCP）/di-p-tolyl-phosphate （DpCP） levels correlated positively with family income. Higher exercise frequencies were found to be associated with significantly lower levels of BDCIPP and BCIPHIPP in urine. Furthermore， the frequency of nut consumption and the level of 4-HO-DPHP in urine were determined to be significantly negatively correlated. This study did not identify any significant associations between contents of urinary OPE metabolites and smoking or the intake of other foods， which suggests that smoking and dietary intake are not the primary OPE exposure pathways for the investigated population. Future research should have broader scope to elucidate the principal OPE exposure pathways. The overall OPE exposure levels for all participants in this study ranged between 5.60 and 2 800 ng/（kg⋅d） bw， with a median exposure level of 104 ng/（kg⋅d） bw. Among the four OPE monomers， Tris（2-butoxyethyl） phosphate （TBOEP） exhibited the highest exposure level， with a median value of 57.2 ng/（kg⋅d） bw （ranging between 1.11 and 1 330 ng/（kg⋅d） bw）， thereby contributing up to 55.6% of the total OPE exposure. Additionally， tri-n-butyl phosphate （TNBP） also exhibited significant exposure， with a median level of 32.4 ng/（kg⋅d） bw （ranging between 0.138 and 2 000 ng/（kg⋅d） bw）， which accounts for 31.5% of the total OPE exposure. Gender-based analysis revealed that men exhibited higher OPE exposure levels than women. Specifically， men exhibited a median exposure level of 112 ng/（kg⋅d） bw （ranging between 6.03 and 2 670 ng/（kg⋅d） bw） compared to the value of 89.9 ng/（kg⋅d） bw （ranging between 5.61 and 2 800 ng/（kg⋅d） bw） recorded for women. The vast majority of study participants exhibited HI values of less than one， indicative of no obvious non-carcinogenic risks. The OPEs exhibited HI values in the 0.000 2-1.03， with a median value of 0.06. The exposure risks associated with the four OPE monomers are ranked in following order： TBOEP （median HI=0.038， range： 0.000 7-0.883）， TNBP （median HI=0.013， range： 0.000 05-0.833）， tris（1，3-dichloro-2-propyl） phosphate （TDCIPP） （median HI=0.002， range： 0.000 8-0.288）， and triphenyl phosphate （TPHP） （median HI=0.001， range： 0.000 2-0.350）； these monomers contribute 68.9， 24.4， 4.2， and 2.5% to the overall HI value， respectively. Among all study participants， men exhibited a higher exposure risk （median HI=0.061， range： 0.002-1.03） than women （median HI=0.049， range： 0.002-0.840）. Notably， TBOEP was identified as the primary high-risk monomer for both genders， contributing 70.1% （median HI=0.042， range： 0.000 7-0.883） and 67.6% （median HI=0.035， range： 0.000 8-0.835） to the overall health risks of men and women， respectively. In conclusion， the study population was ubiquitously exposed to OPEs， with men exhibiting higher exposure levels and associated health risks， which suggests that OPE exposure levels are gender-dependent. This study revealed the exposure levels and profiles of OPEs of urban residents， and provides supporting data and a scientific foundation for subsequent studies and policy formulations.