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A study published in Environment International evaluates residues of individual and mixtures of endocrine-disrupting chemicals (EDCs), including pesticides, and finds an association between exposure and hyperactive behavior in children.
The researchers evaluated urine samples from over 800 preschoolers, identifying and statistically analyzing concentrations of 22 EDCs, and finding that nine of these chemicals are significantly associated with hyperactivity trajectories and EDC mixtures are positively associated with hyperactive behavior, noting the strongest association in girls.
“The current study indicates the adverse health effects of exposure to mixtures of EDCs among preschoolers, and suggests gender specificity in these effects,” the researchers stated.
They continued, “This highlights the importance of focusing on multi-pollutant exposure in early childhood.”
Study importance
“Attention-deficit/hyperactivity disorder (ADHD) is a common neurodevelopmental disorder in children, which has become one of the main factors leading to the burden of disease in children and adolescents worldwide.”
The authors continued: “Its core symptoms are high levels of inattention and/or hyperactivity/impulsivity during the preschool period. A meta-analysis showed that the overall prevalence of ADHD in children in China over the past 15 years was as high as 6.2%, and has been increasing over recent years.”
In comparison, according to the Centers for Disease Control and Prevention (CDC), data from 2022 suggest that in the U.S., an estimated 7 million (11.4%) children ages 3-17 years have ever been diagnosed with ADHD, based on a national survey of parents.
Beyond Pesticides has previously reported that children are susceptible and vulnerable to exposure to harmful contaminants, including EDCs and pesticides.
Children face much higher hazards than adults from exposure, with disproportionate risks due to their small size and developing organ systems, propensity to crawl and play near the ground, tendency for frequent hand-to-mouth motion and greater intake of air and food relative to body weight.
As shared in the “Children and Pesticides Don’t Mix” fact sheet, studies show children’s developing organs create “early windows of great vulnerability” during which exposure to pesticides can cause great damage.
With the ubiquitous use of chemicals in commonly used consumer products and throughout the environment in agriculture and land management, EDCs are encountered every day and contaminate the air, water, soil and food.
Endocrine disruptors function by:
- Mimicking the action of a naturally-produced hormone, such as estrogen or testosterone, thereby setting off similar chemical reactions in the body.
- Blocking hormone receptors in cells, thereby preventing the action of normal hormones.
- Affecting the synthesis, transport, metabolism and excretion of hormones, thus altering the concentrations of natural hormones.
Endocrine disruptors have been linked to ADHD, Parkinson’s and Alzheimer’s diseases, metabolic disorders, diabetes, cardiovascular disease, obesity, early puberty, infertility and other reproductive disorders, childhood and adult cancers, and other metabolic disorders. (See more at Pesticide-Induced Diseases: Endocrine Disruption.)
The Endocrine Society said:
“There are nearly 85,000 man-made chemicals in the world, many of which people come into contact with every day. Only about one percent of them have been studied for safety; however, 1,000 or more of these chemicals may be EDCs based on their probable endocrine-interfering properties.”
A wide body of scientific literature finds that many pesticide active ingredients act as EDCs.
As the current study shared, EDCs:
“are a group of chemicals that are widely used in industrial production, building materials, cosmetics, pesticides, and insecticides. By altering the production, release, transport, metabolism, and binding of endogenous hormones, EDCs increase the risk of diseases across the human life cycle.”
While there are various types of EDCs, the main chemicals assessed in this study include bisphenols, per- and polyfluoroalkyl substances (PFAS), which include pesticides, organophosphate flame retardants and parabens.
“At present, only a few studies have investigated the effect of EDC exposure on hyperactivity in preschoolers, and these studies have some limitations,” the researchers noted.
“For example, the effect of exposure to single types of EDC on hyperactivity in children is mostly investigated through cross-sectional design, which ignores the dynamic development of ADHD symptoms in children and the co-exposure of EDCs in children’s living environments.” (See here and here.)
Methodology
In collaboration with the Wuhu Maternal and Child Health and Family Planning Service Center, the researchers include 823 mother–child pairs from 13 urban and rural kindergartens across three districts and counties in Wuhu City, China.
The mothers collected morning urine samples from preschoolers (aged 3–6 years old) and completed behavioral surveys. The urine samples were tested for 24 EDCs, including eight bisphenols, six PFAS, five organophosphate flame retardants and five parabens.
The final analyses included 22 of the 24 EDCS due to low detection rates of bisphenols. The preschoolers’ hyperactive behaviors are evaluated using the hyperactivity index scale in Conners’ Parent Rating Scale-Revised (CPRS-48).
Data from the biomonitoring samples and surveys were used in statistical analyses to assess associations between hyperactive behavior and both single and mixture exposure to EDCs.
Results
“We identified two distinct hyperactivity classes (low and high) in line with previous studies,” the authors noted. “Previous studies have confirmed that children with ADHD show some symptomatic features during the preschool period, and these symptoms can persist for a long time.”
Based on the surveys, the study finds that boys are generally at a higher risk of following a high hyperactivity trajectory compared to girls.
The researchers provide a plausible explanation in saying:
“This disparity might be attributed to certain genes located on the Y chromosome, such as those involved in dopamine receptor function, which have been associated with an increased risk of developing hyperactive symptoms in males.
“Moreover, increased testosterone levels in boys may enhance dopamine system activity, contributing to heightened impulsivity and externalizing behaviors.
“Furthermore, this disparity may also be influenced by factors such as differences in the manifestation of hyperactivity symptoms between boys and girls, as well as diagnostic biases, including clinician-related prejudices and social expectations.”
The mixture exposure modeling from the urine samples, however, reveals gender stratification with significant positive relations to hyperactivity trajectories only in girls.
“The Q-gcomp model found that the EDCs mixture was significantly associated with hyperactivity trajectories in both boys and girls, but the effect was more pronounced in girls,” the authors explained.
They continued:
“This may be influenced by sex hormones. EDCs can mimic estrogen, bind to estrogen receptors, interfere with the hypothalamic-pituitary–gonadal axis, and affect normal hormone regulation, which may result in symptoms such as attention deficit and hyperactivity.
“Furthermore, Frederiksen et al. (2020) demonstrated that estrogen levels in prepubescent girls are significantly higher than those in boys. Therefore, the effect of exposure to the EDCs mixture may be greater in girls.”
Previous research
Similar research, covered in the previous Daily News, published in Environment International, finds that young children who exhibit higher levels of pesticide metabolites in their urine show more pronounced neurobehavioral problems at the age of 10.
Researchers in China document how exposure during early childhood, especially during the sensitive window before age 2, is linked to hyperactivity/inattention problems such as ADHD.
While adding to the body of science connecting pesticide exposure to learning and developmental disorders, this study offers a “novel perspective on characterizing the fluctuation in repeated measurements of multiple environmental chemicals and identifying the potential critical windows,” the authors shared.
Additional scientific literature, cited within the current study, shows:
- Exposure to EDCs is associated with ADHD in children, with some compounds showing a dose-response relationship.
- In analyzing the relationship between 27 EDCs in breast milk and ADHD in children, one study finds “that the concentrations of perfluorooctane sulfonate (PFOS) and β‑hexachlorocyclohexane (β-HCH) in breast milk were positively correlated with the risk of ADHD in children.” The study also shows that “early exposure to β-hexachlorocyclohexane (β-HCH) and perfluorooctane sulfonate (PFOS) may increase the risk of ADHD in children, and the effect of PFOS is stronger in girls.”
- A study of the relationship between urinary EDCs and hyperactivity in children shows that phthalate exposure is associated with impulsivity in children with ADHD.
- “Maternal exposure to organophosphates during pregnancy or during childhood may disrupt neuronal migration, synapse formation, and myelination, thereby impacting brain development and resulting in long-term cognitive and behavioral deficits.” (See studies here and here.)
- An analysis of urinary bisphenol exposure in 619 children ages 4-8 years reveals that these compounds are associated with ADHD in children at the age of 6 years. One bisphenol compound is positively correlated with hyperactivity scores in girls at the age of 6 years, but not in boys.
- Urinary propylparaben residue is positively associated with attention problems in adolescents.
- Exposure to phthalate mixtures is “related to ADHD symptoms in preschoolers, especially hyperactivity and impulsivity.”
- Exposure to “PFAS mixtures at age 2 years was significantly associated with an increased risk of ADHD symptoms at age 8 years.”
- Since PFAS can “cross the blood–brain barrier, accumulate in the brain, and induce neurotoxicity,” these compounds can alter brain structure and lead to hyperactive behavior.
The organic alternative
Chemical exposure at an early age increases the body burden of harmful toxicants, many of which can stay in the body for a lifetime, and escalates the risk for certain diseases such as cancer and Parkinson’s disease.
With multiple routes of exposure to EDCs, reducing children’s exposure to harmful chemicals is critical. By adopting organic land management strategies, the exposure to endocrine-disrupting pesticides can be mitigated.
Beyond Pesticides promotes healthy environments for learning and recreation for children. Alternatives are available for schools and for creating sustainable parks that do not unnecessarily put children’s health at risk.
Make The Safer Choice to avoid hazardous home, garden, community and food use pesticides to protect children as they grow and develop.
Originally published by Beyond Pesticides.
