Researchers in Europe have shown that up to 54% of pregnant women in Sweden were exposed to complex mixtures of endocrine-disrupting chemicals disruptive to brain development.
While current risk assessment tackles chemicals and their allowable exposures on an individual basis, these findings show the need to take mixtures into account for future risk assessment approaches. The study was published in Science.
A growing body of evidence has shown that industrially produced chemicals have endocrine disrupting properties and can thus be dangerous to human and animal health and development. A huge number of new compounds is released every year into the environment during the production of plastic derivatives and other goods.
While exposures for individual chemicals falls below thresholds, exposure to the same chemicals in complex mixtures can still impact human health. However, all current exposure thresholds, are based on chemicals being examined individually. Therefore, an alternative strategy needed to be tested, in which the actual mixtures measured in real life exposures could be tested as such in both the epidemiological and experimental setting. The EDC-MixRisk project set out to tackle this unmet need.
“The uniqueness of this comprehensive project is that we have linked population data with experimental studies, and then used this information to develop new methods for risk assessment of chemical mixtures,” said Carl-Gustaf Bornehag, professor at Karlstad University, Project Manager of the SELMA study.
The study was conducted in three steps:
- A mixture of chemicals in the blood and urine of pregnant women was identified in the Swedish pregnancy cohort SELMA, associated with delayed language development in children at 30 months. This critical mixture included a number of phthalates, bisphenol A, and perfluorinated chemicals.
- Experimental studies uncovered the molecular targets through which human-relevant levels of this mixture disrupted the regulation of endocrine circuits and of genes involved in autism and intellectual disability.
- The findings from the experimental studies were used to develop new principles for risk assessment of this mixture.
“It is striking that the findings in the experimental systems well reflected what we found in the epidemiological part, and that the effects could be demonstrated at normal exposure levels for humans,” said Joëlle Rüegg, professor of environmental toxicology at Uppsala University.
“Human brain organoids (advanced in vitro cultures that reproduce salient aspects of human brain development) afforded, for the first time, the opportunity to directly probe the molecular effects of this mixture on human brain tissue at stages matching those measured during pregnancy. Alongside other experimental systems and computational methods, we found that the mixture disrupts the regulation of genes linked to autism (one of whose hallmarks is language impairment), hinders the differentiation of neurons and alters thyroid hormone function in neural tissue,” said Giuseppe Testa, principal investigator of the EDC-MixRisk responsible for the human experimental modelling.
“One of the key hormonal pathways affected was thyroid hormone. Optimal levels of maternal thyroid hormone are needed in early pregnancy for brain growth and development, so it’s not surprising that there is an association with language delay as a function of prenatal exposure,” said Barbara Demeneix, professor of physiology and endocrinology at the Natural History Museum in Paris.
By combining these techniques, the researchers were able to show that 54% of children included in the SELMA study were at risk of delayed language development (at age 30 months) as they were prenatally exposed to a mixture of chemicals at levels that were above the levels predicted to impact neurodevelopment. Yet this risk fell below the exposure limits for individual chemicals.
Source: EURION Cluster
