Early-life exposure to persistent organic pollutants (OCPs, PBDEs, PCBs, PFASs) and attention-deficit/hyperactivity disorder: A multi-pollutant analysis of a Norwegian birth cohort

Environ Int. 2019 Apr:125:33-42. doi: 10.1016/j.envint.2019.01.020. Epub 2019 Jan 28.

Abstract

Background: Numerous ubiquitous environmental chemicals are established or suspected neurotoxicants, and infants are exposed to a mixture of these during the critical period of brain maturation. However, evidence for associations with the risk of attention-deficit/hyperactivity disorder (ADHD) is sparse. We investigated early-life chemical exposures in relation to ADHD.

Methods: We used a birth cohort of 2606 Norwegian mother-child pairs enrolled 2002-2009 (HUMIS), and studied a subset of 1199 pairs oversampled for child neurodevelopmental outcomes. Concentrations of 27 persistent organic pollutants (14 polychlorinated biphenyls, 5 organochlorine pesticides, 6 brominated flame retardants, and 2 perfluoroalkyl substances) were measured in breast milk, reflecting the child's early-life exposures. We estimated postnatal exposures in the first 2 years of life using a pharmacokinetic model. Fifty-five children had a clinical diagnosis of ADHD (hyperkinetic disorder) by 2016, at a median age of 13 years. We used elastic net penalized logistic regression models to identify associations while adjusting for co-exposure confounding, and subsequently used multivariable logistic regression models to obtain effect estimates for the selected exposures.

Results: Breast milk concentrations of perfluorooctane sulfonate (PFOS) and β‑hexachlorocyclohexane (β-HCH) were associated with increased odds of ADHD: odds ratio (OR) = 1.77, 95% confidence interval (CI): 1.16, 2.72 and OR = 1.75, 95% CI: 1.22, 2.53, per interquartile range increase in ln-transformed concentrations, respectively. Stronger associations were observed among girls than boys for PFOS (pinteraction = 0.025). p,p'‑Dichlorodiphenyltrichloroethane (p,p'-DDT) levels were associated with lower odds of ADHD (OR = 0.64, 95% CI: 0.42, 0.97). Hexachlorobenzene (HCB) had a non-linear association with ADHD, with increasing risk in the low-level exposure range that switched to a decreasing risk at concentrations above 8 ng/g lipid. Postnatal exposures showed similar results, whereas effect estimates for other chemicals were weaker and imprecise.

Conclusions: In a multi-pollutant analysis of four classes of chemicals, early-life exposure to β-HCH and PFOS was associated with increased risk of ADHD, with suggestion of sex-specific effects for PFOS. The unexpected inverse associations between p,p'-DDT and higher HCB levels and ADHD could be due to live birth bias; alternatively, results may be due to chance findings.

Keywords: Attention-deficit/hyperactivity disorder (ADHD); Contaminants; Endocrine disrupting chemicals (EDCs); Environmental chemicals; Hyperkinetic disorder; Neurodevelopment.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adolescent
  • Adult
  • Alkanesulfonic Acids / analysis*
  • Attention Deficit Disorder with Hyperactivity / epidemiology*
  • Child, Preschool
  • Environmental Exposure / analysis*
  • Environmental Pollutants / analysis*
  • Female
  • Flame Retardants / analysis*
  • Fluorocarbons / analysis*
  • Halogenated Diphenyl Ethers / analysis*
  • Humans
  • Hydrocarbons, Chlorinated / analysis*
  • Infant
  • Male
  • Milk, Human / chemistry*
  • Norway / epidemiology
  • Young Adult

Substances

  • Alkanesulfonic Acids
  • Environmental Pollutants
  • Flame Retardants
  • Fluorocarbons
  • Halogenated Diphenyl Ethers
  • Hydrocarbons, Chlorinated
  • perfluorooctane sulfonic acid