Association Between Polycyclic Aromatic Hydrocarbons Internal Exposure With Puberty Timing In Children:a Cohort Study

Objective: To establish a prospective cohort in order to explore the association between polycyclic aromatic hydrocarbons(PAHs)internal exposure and puberty timing in both boys and girls.Methods: By using purposive sampling,four representative urban primary schools in Jiulongpo District,Chongqing were selected,and all students were enrolled with written informed consent.The baseline survey of girls was conducted in December 2014,so as it in boys in December 2015.Questionnaire survey of the general information,physical examination of growth and pubertal development were conducted.Four PAHs metabolites in urine,including 1-hydroxypyrene(1-OHPyr),2-hydroxynathalene(2-OHNap),2-hydroxyfluorene(2-OHFlu)and 9-hydroxyphenanthrene(9-OHPhe)were detected.Urinary specific gravity(SG)was used for the correction of the concentration of 4 PAHs metabolites.After excluding students who have entered into puberty at the baseline survey,the other students wereincluded in our cohort study.The median level of PAHs metabolites was used as the cutoff point between exposed group(higher level PAHs exposure)and control group(lower level PAHs exposure).Testicular development,first spermatorrhea,breast development and menarche were the outcome measures of the cohort study with frequency of once every six months.Results: The detection result showed that the detection rate of 4urinary PAHs metabolites in boys and girls were all 100%.In 735 girls,the urinary concentration were highest for 9-OHPhe(median 3.27 ng/ml,or 3.74 ng/ml SG corrected),followed by 2-OHNap(median 2.72 ng/ml,or 3.17 ng/ml SG corrected),2-OHFlu(median 1.32 ng/ml,or 1.48 ng/ml SG corrected),and 1-OHPyr(median 0.40 ng/ml,or 0.48 ng/ml SG corrected).In 675 boys,the urinary concentration were highest for9-OHPhe(median 3.40 ng/ml,or 3.69 ng/ml SG corrected),followed by2-OHNap(median 3.06 ng/ml,or 3.21 ng/ml SG corrected),2-OHFlu(median 1.09 ng/ml,or 1.14 ng/ml SG corrected),and 1-OHPyr(median0.22 ng/ml,or 0.25 ng/ml SG corrected).Cox regression showed that,by controlling age and BMI,it took more time for girls with higher level of2-OHNap to enter into breast development(RR=0.763,95%CI:0.637~0.913)and experience menarche(RR=0.779,95%CI:0.625~0.972).There was no significant difference in testicular development and first spermatorrhea between higher level and lowerlevel PAHs exposure boys(p>0.05).Conclusion: The levels of PAHs internal exposure in this study were higher than that in other areas,especially 9-OHPhe exposure.The association between PAHs internal exposure and puberty timing was observed in girls.It took more time for girls with high level 2-OHNap to enter into breast development and occur menarche.However,the association between PAHs internal exposure and puberty timing in boys is still not clear,and further follow-ups are needed to confirm the association.