A team from Inserm and theUniversité Grenoble Alpes, in collaboration with the CNRS, the Grenoble Alpes University Hospital, and the University of Granada (Spain), investigated the impact of perinatal exposure to these substances on children’s intelligence quotient (IQ), as assessed at age three. Based on a cohort study involving 380 mothers and their children, and a modeling approach incorporating prior knowledge on the subject, the researchers observed associations between exposure to certain phthalates and bisphenol A during the third trimester of pregnancy and the children’s IQ scores. These results are published in Environmental Health Perspectives.

Characterizing the health effects of chemical pollutants is a major public health issue. Because these chemicals are present in our environment, our food, and the objects around us, we are exposed to numerous chemical substances on a daily basis. Among them, phthalates and phenols are two major families of chemicals used as additives in certain plastics, as well as preservatives and formulation agents.

Phthalates and phenols have been detected in nearly the entire population, and some of them are endocrine disruptors capable of affecting the endocrine system.

In a study, a team of researchers from Inserm at the Institute for the Advancement of Biosciences (IAB—UGA/CNRS/Inserm) provides new data on the associations between exposure to certain of these substances and children’s cognitive development.

Scientists were able to measure exposure markers for 26 phthalates and phenols—including bisphenols and parabens—using repeated urine samples collected from a cohort of pregnant women and their infants. This repeated collection of biological samples is one of the study’s methodological advances. It allows for a more precise assessment of exposure to these substances—whose levels in the body fluctuate rapidly—than in previous studies, where often only a single urine sample per woman was available. In total, 380 mothers and their children were included in the analysis.

The children’s IQ at age 3 was assessed by a neuropsychologist using a standardized test. The researchers also collected data on other factors that influence a child’s IQ, such as the parents’ level of education and the duration of breastfeeding.

From a statistical standpoint, the researchers supplemented their analyses with data from previous studies—conducted in animals or humans—that provided insights into the links between the substances under study and cognitive development. “The results published prior to our study made it possible to identify, among all the substances measured in the cohort, those with the highest level of evidence for an effect on cognitive development. In this case, the substances identified by previous studies as the most harmful were bisphenols A and S, and certain phthalates, including DEHP, DEP, DnBP, and DiBP. We considered these to be priorities in our study.”, explains Vicente Mustieles, the study’s lead author and a researcher at the University of Granada.

“Prioritizing these substances based on existing knowledge helped guide our statistical models and their interpretation. The negative associations with IQ scores were more pronounced for these prioritized substances. This literature review—which takes toxicological studies into account—also provided insights into the biological plausibility of the observed associations.”, adds Rémy Slama, Inserm research director and author of the study.

An association was observed between exposure to the mixture of the six priority substances during the third trimester of pregnancy and children’s IQ scores at age 3. On average, IQ scores decreased by 2.86 points as exposure to all substances in the mixture increased by one level.

“A few IQ points lower may not seem like much for a single child, but on a population-wide scale, it translates into more children facing difficulties. This has consequences for education, health, and the economy—especially when we keep in mind that we haven’t considered all potentially neurotoxic chemicals.”, explains Claire Philippat, an Inserm researcher and the study’s last author.

Also in the third trimester of pregnancy, the concentrations of four of the six priority substances, when considered individually, were also associated with lower IQ scores.

“The substances studied here do not persist long in the body,” Claire Philippat points out. “This makes them good targets for prevention. If we can eliminate sources of exposure from our environment, internal exposure levels could decrease rapidly. There are several steps individuals can take: for example, using fewer cosmetics or limiting the consumption of food packaged in plastic, especially when it is heated. Nevertheless, regulating and restricting substances proven to be harmful is the most effective measure for reaching the entire population.”", she concluded.