EPA Research Provides Important Information on Health Effects of Perchlorate Exposure
Published October 15, 2024
Perchlorate is a naturally occurring contaminant in dry regions of the Southwest United States or can be manufactured and used as an industrial chemical that, if ingested via drinking water, may cause thyroid disruptions that are particularly critical to a developing fetus. It may lead to low levels of thyroid hormones in the blood, negatively impacting various systems in the body, such as the developing brain.
It’s been detected at varying levels in drinking water, groundwater, surface water, food, soil, and sediment across the U.S., introduced into the environment most often by human activity through fireworks, matches, signal flares, munitions, airbag initiators for vehicles, and solid rocket propellants.
Based on the available information, the health risks posed by perchlorate exposure are highest during pregnancy, when insufficient thyroid hormones can disrupt the development of the brain. For example, inadequate levels of thyroid hormones during gestation can lead to learning impairments in children. The risk is greater under conditions of maternal dietary iodine insufficiency. To further our understanding of the effect of perchlorate exposure on the developing brain, there is a need for studies of perchlorate exposure and developmental neurotoxicity health outcomes.
EPA scientist Dr. Mary Gilbert published several papers reporting on her animal toxicity studies in rodents that demonstrate how maternal perchlorate ingestion can alter the fetal thyroid system and the developing brain. This research found that a cluster of neurons failed to migrate to their appropriate destination, creating a structural malformation in the brain of exposed offspring. This malformation was the result of perchlorate’s action on the maternal and the fetal thyroid gland. Perchlorate reduced the amount of maternal thyroid hormone available for transfer to the developing fetus. Perchlorate also directly crossed the placenta reducing thyroid hormone synthesis in the fetal thyroid gland.
In Gilbert’s study, this cluster of neurons that failed to migrate can lead to both anatomical and functional problems in the connections between cortical neurons and the formation of neural circuits. These malformations disrupt the transfer of information between neurons and pose a risk for neurodevelopmental disorders including epilepsy and autism in humans. This finding shows that pregnant rodents and their fetuses have high health risks associated with perchlorate exposure and suggests that pregnant women and their fetuses may be similarly sensitive.
Gilbert’s work also found that the thyroid hormone levels returned to normal in late gestation; however, lingering effects on the brain’s signaling pathways persisted and brain malformations were permanent. The EPA research team found that these structural malformations in the offspring worsened when perchlorate was paired with dietary iodine deficiency.
Gilbert’s team uses changing scientific approaches to research modeling. Gilbert’s recent studies show successful applications of adverse outcome pathways (AOP), demonstrating how a series of linked events at different levels of biological organization can impact one another. Gilbert and her team used an in vivo model, which is an essential element to validating the utility of New Approach Methods (NAMs) in developmental neurotoxicology.
EPA researchers used the AOP method to identify adverse health outcomes that are relevant to risk assessment or regulatory decision making in response to these real-world environmental risk factors.
Considerable efforts have been made within and outside of EPA to design cellular tools that test chemicals for thyroid disrupting effects, and these cellular studies can be used to model potential long-term health consequences on many communities.
The knowledge gained by Gilbert and her team provide important health effects information that has been used to inform assessments at EPA and other health agencies like the European Food Safety Association.
“Our research fills existing knowledge gaps of perchlorate impacts and furthers the understanding of real-world risks posed by these environmental contaminants,” Gilbert said.
The research conducted by Gilbert and her team expands the awareness of the harm perchlorate exposure can have on the development of children’s brains, furthers the knowledge of toxicant health impacts, and offers a roadmap for future research following AOPs. This research can help inform decision making and help protect communities.
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