Relationship between environmental phthalate exposure and the intelligence of school-age children

Soo-Churl Cho, Soo-Young Bhang, Yun-Chul Hong, Min-Sup Shin, Boong-Nyun Kim, Jae-Won Kim, Hee-Jung Yoo, In Hee Cho, Hyo-Won Kim, Soo-Churl Cho, Soo-Young Bhang, Yun-Chul Hong, Min-Sup Shin, Boong-Nyun Kim, Jae-Won Kim, Hee-Jung Yoo, In Hee Cho, Hyo-Won Kim

Abstract

Background: Concern over phthalates has emerged because of their potential toxicity to humans.

Objective: We investigated the relationship between the urinary concentrations of phthalate metabolites and children's intellectual functioning.

Methods: This study enrolled 667 children at nine elementary schools in five South Korean cities. A cross-sectional examination of urine phthalate concentrations was performed, and scores on neuropsychological tests were obtained from both the children and their mothers.

Results: We measured mono-2-ethylhexyl phthalate (MEHP) and mono(2-ethyl-5-oxohexyl)phthalate (MEOHP), both metabolites of di(2-ethylhexyl)phthalate (DEHP), and mono-n-butyl phthalate (MBP), a metabolite of dibutyl phthalate (DBP), in urine samples. The geometric mean (ln) concentrations of MEHP, MEOHP, and MBP were 21.3 microg/L [geometric SD (GSD) = 2.2 microg/L; range, 0.5-445.4], 18.0 microg/L (GSD = 2.4; range, 0.07-291.1), and 48.9 microg/L (GSD = 2.2; range, 2.1-1645.5), respectively. After adjusting for demographic and developmental covariates, the Full Scale IQ and Verbal IQ scores were negatively associated with DEHP metabolites but not with DBP metabolites. We also found a significant negative relationship between the urine concentrations of the metabolites of DEHP and DBP and children's vocabulary subscores. After controlling for maternal IQ, a significant inverse relationship between DEHP metabolites and vocabulary subscale score remained. Among boys, we found a negative association between increasing MEHP phthalate concentrations and the sum of DEHP metabolite concentrations and Wechsler Intelligence Scale for Children vocabulary score; however, among girls, we found no significant association between these variables.

Conclusion: Controlling for maternal IQ and other covariates, the results show an inverse relationship between phthalate metabolites and IQ scores; however, given the limitations in cross-sectional epidemiology, prospective studies are needed to fully explore these associations.

Figures

Figure 1
Figure 1
Adjusted mean WISC Vocabulary score estimated by MEHP (A) and DEHP metabolites (B) quartiles of ln creatinine (Cr)-corrected urine concentrations. Adjusted means differed significantly between the second and fourth quartiles and between the third and fourth quartiles of ln creatinine-corrected MEHP and ln creatinine-corrected DEHP metabolites for boys (p < 0.05). Among girls, there were no significant associations between these variables. Estimated means are adjusted for age, sex, birth weight, history of breast-feeding, residential area, paternal education, SES, and maternal IQ. Error bars are SEs.

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