Prenatal exposure to industrial chemicals has increased


A national study that enrolled a highly diverse group of pregnant women over 12 years found rising exposure to chemicals from plastics and pesticides that may be harmful to development.

Many of the chemicals that the women had been exposed to were replacement chemicals: new forms of chemicals that have been banned or phased out that may be just as harmful as the ones they replaced. The study also found many women had been exposed to neonicotinoids, a kind of pesticide that is toxic to bees.

Researchers measured 103 chemicals, mostly from pesticides, plastics, and replacement chemicals for BPA and phthalates, using a new method that captured dozens of chemicals or chemical traces from a single urine sample.

More than 80 percent of the chemicals were found in at least one of the women in the study, and more than a third of the chemicals were found in a majority of the participants. The study also found that some of these chemicals were present in higher amounts than seen in earlier studies.

“This is the first time we’ve been able to measure the amounts of chemicals in such a large and diverse group of pregnant women—not just identify chemicals,” said Tracey J. Woodruff, Ph.D., professor and director of the University of California, San Francisco (UCSF) Program on Reproductive Health and the Environment and co-director of the UCSF EaRTH Center, and the senior author of the study, appearing online May 10, 2022, in Environmental Science & Technology. “Our findings make clear that the number and scope of chemicals in pregnant women are increasing during a very vulnerable time of development for both the pregnant person and the fetus.”

Prenatal exposure to industrial chemicals can come from air, food, water, plastics, and other industrial and consumer products. Although these chemicals could be harmful to pregnancy and child development, few of these chemicals are routinely monitored in people.

The study included 171 women from California, Georgia, Illinois, New Hampshire, New York, and Puerto Rico who are part of the National Institutes of Health Environmental influences on Child Health Outcomes program. About one-third (34%) were white, 40% were Latina, 20% were Black, and the remaining 6% were from other or multiple groups.

The study found higher exposures for non-white women, those with lower educational attainment, or who were single or had been exposed to tobacco. But Latinas had especially high levels of parabens, which are used as preservatives, as well as phthalates and bisphenols, which are used in plastics.

“While pesticides and replacement chemicals were prevalent in all women, we were surprised to find that Latinas had substantially higher levels of parabens, phthalates and bisphenols,” said Jessie Buckley, Ph.D., associate professor of environmental health and engineering, as well as of epidemiology, at Johns Hopkins Bloomberg School of Public Health and first author of the study.

“This could be the result of higher exposures to products with chemicals, such as processed foods or personal care products,” Buckley said.

Executive functions are mental processes that form the basis of higher-level cognition, including problem-solving, planning, and reasoning [1]. The three core executive functions are inhibition, working memory, and cognitive flexibility [2]. Inhibition, the focus of the present study, is the ability to resist impulse and to focus one’s attention, behavior, and thoughts, despite external stimuli [1].

Although some executive function development begins at a young age, inhibition undergoes substantial evolution during adolescence. This evolution parallels structural and functional changes in the pre-frontal cortex, a part of the brain critical for most executive functions that occur in this age group [3].

Poor inhibition skills in childhood predict physical health problems and substance dependence, as well as lower socioeconomic position and income earned in adulthood [4]. In addition, altered inhibition is associated with a number of mental health disorders including anxiety, depression, and panic disorder [5]. Therefore, identifying modifiable risk factors associated with poorer inhibition skills may diminish the impact of such disorders.

Epidemiologic studies have provided evidence that prenatal exposures to environmental contaminants may be associated with cognitive impacts throughout the life course. The fetus is not well-protected from some environmental exposures as the placenta does not block the maternal transmission of pregnancy exposure to many environmental toxicants including organochlorines and some metals, which are ubiquitous in the environment [6,7,8,9]. In utero, the developing brain undergoes rapid neurological growth and is, therefore, highly sensitive to potential injury from toxic chemicals that may result in long-term neurotoxic impacts.

Several studies have analyzed associations between prenatal environmental chemical exposures and inhibition. Prenatal exposures to organochlorines such as dichlorodiphenyldichloroethylene (DDE), hexachlorobenzene (HCB), and polychlorinated biphenyls (PCBs) have not been studied in relation to inhibition among adolescents specifically. However, among younger children in the Great Lakes region of the United States, two prospective cohort studies found evidence of an association between cord serum PCB levels and poor inhibition measured by psychometric tests of impulse control such as errors of commission on a Continuous Performance Test (CPT) and perseverative errors on the Wisconsin Card Sorting Test (WCST) [10,11,12].

In contrast, in the New Bedford Cohort (NBC), researchers did not find errors of commission on the Neurobehavioral Examination System 2 (NES2)-CPT to be adversely associated with cord serum DDE or PCB concentrations among 8-year-olds who had lower or similar exposure levels, respectively, to the two Great Lakes cohorts [13,14]. Of note, the NES2-CPT is less sensitive to errors of commission than some other CPT instruments [15].

Prenatal exposure to metals may also adversely impact childhood inhibition skills. Manganese (Mn) is an essential trace element necessary for proper brain functioning, though it can be neurotoxic at high levels [16]. The impact of prenatal exposure to Mn on inhibition has not been well-studied among adolescents, but in an exploratory study of younger children, deciduous tooth Mn levels were associated with multiple measures of behavioral disinhibition assessed with a forbidden toy task, a CPT, and a children’s Stroop Test at ages 36 and 54 months [17].

Finally, in a study of a high fish-eating population in the Seychelles, pre- and post-natal exposures to methylmercury (MeHg) measured in maternal and participant hair, respectively, were not found to be associated with inhibition, as measured by the Stroop Color–Word Test among 24-year-olds [18].

Exposure to chemical contaminants rarely occurs independently [19] and co-exposure to chemical mixtures may result in different, often worse, health effects than single chemical effects [20]. Only one study has assessed the association of a chemical mixture with inhibition. In a prospective cohort of children from Arctic Quebec, researchers found that the adverse association between current blood Pb and a child’s ability to inhibit a response in a Go/No-Go task was stronger in children with lower current MeHg and PCB exposures [21].

Other studies have assessed the relation of metal mixtures or metal-PCB mixtures with general executive function or other specific components of executive function, such as working memory. In a prospective cohort study based in Spain, prenatal co-exposure to a metal mixture (composed of cobalt, copper, As, cadmium, antimony, thallium, and Pb) measured in maternal urine during pregnancy was not associated with McCarthy Scales of Children’s Abilities (MSCA) executive function scores among 4-year-olds [22].

In a cross-sectional study of 8 to 11-year-old children from Bangladesh, researchers found that blood Mn was associated with lower Wechsler Intelligence Scale for Children (WISC-IV) working memory scores, but they did not observe a significant interaction between Mn and As [23]. Finally, in a birth cohort study based in the Faroe Islands, among participants with low cord blood levels of MeHg, high cord blood Pb concentrations were associated with lower Digit Span Backward scores, a measure of working memory, at age 14 [24].

In summary, many studies have linked prenatal exposures to organochlorines and metals with decrements in executive function among children. Few have focused on inhibition or on adolescence, when the impact of earlier exposures on executive function may become most readily apparent due to it being a time of substantial executive function development.

In addition, even though it has been well-established that the developing brain may be exposed to multiple pollutants simultaneously in utero, few studies have assessed the impact of prenatal exposure to mixtures of prevalent neurotoxic chemicals on executive function and only one has focused on inhibition. Therefore, the purpose of this study was to address this key gap in the literature by investigating the association of prenatal exposure to a prevalent chemical mixture of organochlorines (DDE, HCB, PCBs) and metals (Pb, Mn, MeHg, As) with detailed measures of inhibition among adolescents.

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More information: Environmental Science & Technology (2022). DOI: 10.1021/acs.est.1c08942


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