Lead and Phthalate Concentrations Associated with Behavioral Outcomes in Children

Written by Angeline A. De Leon, Staff Writer. This study shows that although some indicators of child behavior were significantly associated with their urinary BPA and phthalate concentrations, the major chemical associated with adverse behavioral indicators was lead.

Early life exposure to environmental stressors like toxic chemicals is considered an important risk factor for the development of cognitive and behavioral problems in children ^1,2. Compared to adults, the developing brains of children are significantly more susceptible to the adverse effects of environmental stressors ³. Prenatal exposure to tobacco smoke, for example, has been consistently linked to childhood behavioral problems such as attention deficit hyperactivity disorder (ADHD) ⁴. Similarly, lead exposure has been argued to increase risk of hyperactivity and impulsivity symptoms ⁵. More recently, toxicology research has suggested that exposure to chemicals prevalent in everyday consumer products, such as bisphenol A (BPA, used to make plastics and resins) and phthalates (used to enhance flexibility of plastics), may also contribute to symptoms of ADHD ⁶. Urinary concentrations of BPA in children, for example, share a positive correlation with total problems score and a negative correlation with learning score on cognitive and behavioral tests ⁷. Both chemicals are considered endocrine disruptors, phthalates acting as anti-androgens and BPA mimicking estrogen, and may affect neurodevelopment through a number of different pathways ⁸. In a 2016 study ⁹ published in NeuroToxicology, researchers in Canada examined the role of environmental chemical exposure (BPA, phthalates, and lead) in the development of learning and behavioral problems in children.

Using a cross-sectional study design, researchers recruited a total of 1080 children (mean age = 8.58 years) from whom they collected mid-stream urine and whole blood samples for analysis of lead, BPA, cotinine, and various phthalate metabolites. The Strengths and Difficulties Questionnaire (SDQ) was administered to assess emotional symptoms, hyperactivity/inattention, and other behavioral problems (total difficulties score was computed, with borderline and abnormal scores grouped together and compared with normal scores of children in the same age group). Other outcomes of interest were parent-reported learning disability and/or a subset of learning disabilities reported as attention deficit disorder (ADD)/ADHD.

Parental reports indicated that the prevalence of a learning disability, ADD, and ADHD was 8.7%, 1.5%, and 2.8%, respectively. Based on SDQ scores, estimated prevalence of hyperactivity/inattention, emotional symptoms, and total difficulties was 16.9%, 15%, and 13%, respectively. Blood lead was found to be statistically associated with ADD/ADHD, with each one unit increase in blood lead increasing the odds of ADD/ADHD by 2.08 (95% Confidence Interval: 1.01 to 4.25, p = 0.047). Lead was also associated with total difficulties score, with a significant interaction (p = 0.029) between blood lead and prenatal smoking for total difficulties score (OR = 10.57 for prenatal smoking vs. OR = 1.98 for no prenatal smoking), and with hyperactivity/inattention SDQ outcome, with each one unit increase in blood lead associated with an OR of 2.75 (p = 0.005). For girls only, urinary mono-benzyl phthalate (MBzP) concentration was significantly associated with emotional symptoms score (OR = 1.38, 95% CI: 1.09 to 1.75, p = 0.046). No contaminants were found to be associated with learning disability.

Results of the study confirm the role of environmental chemical exposure in the etiology of behavioral disorders in young children. Lead was found to be the most significant factor, being associated with increased risk of ADD/ADHD, SDQ hyperactivity/inattention, and total difficulties score. Among phthalate metabolites, MBzP was shown to be linked to higher probability of emotional symptoms (based on the SDQ), though only true for girls. Consistent with previous research ⁴, prenatal exposure to tobacco also influenced behavioral outcomes in children (for each one-unit increase in lead levels, higher total difficulties score was greater if the mother smoked during pregnancy). The cross-sectional design of the study, which prevents the establishment of a direct causal relationship, should be noted, as well as the study’s inability to control for potential confounding variables, such as maternal nutrition and mental health. Additional studies are warranted to further investigate the sex differences observed in the association between chemical exposure and emotional outcomes. Given the absence of a significant association between BPA exposure and behavioral and emotional problems in the current study, a finding counter to previous research ⁷, the role of BPA exposure in ADD/ADHD and other behavioral outcomes in children deserves further investigation.

Source: Arbuckle TE, Davis K, Boylan K, et al. Bisphenol A, phthalates and lead and learning and behavioral problems in Canadian children 6-11 years of age: CHMS 2007-2009. NeuroToxicology. 2016; 54: 89-98. DOI: 10.1016/j.neuro.2016.03.014.

Crown Copyright ã 2016 Published by Elsevier Inc. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/)

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Posted October 14, 2019.

Angeline A. De Leon, MA, graduated from the University of Illinois at Urbana-Champaign in 2010, completing a bachelor’s degree in psychology, with a concentration in neuroscience. She received her master’s degree from The Ohio State University in 2013, where she studied clinical neuroscience within an integrative health program. Her specialized area of research involves the complementary use of neuroimaging and neuropsychology-based methodologies to examine how lifestyle factors, such as physical activity and meditation, can influence brain plasticity and enhance overall connectivity.

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