Early Life Exposure to Common Plastic Chemical Linked to Increased Adult Anxiety in Rats

CHICAGO, IL – Male rats exposed to di-(2-ethylhexyl) phthalate (DEHP), a ubiquitous plasticizer found in numerous everyday products, during critical early developmental stages exhibited significantly higher levels of anxiety in adulthood. This groundbreaking research, presented at the Endocrine Society’s annual meeting, ENDO 2026, held in Chicago, Illinois, raises important concerns about the long-term behavioral consequences of endocrine-disrupting chemical (EDC) exposure in humans.

The study, conducted by researchers at the University of Buenos Aires School of Medicine in Buenos Aires, Argentina, provides compelling evidence that exposure to DEHP before and shortly after birth can lead to persistent alterations in behavior. "This research demonstrates that one of the most widely used plasticizers worldwide is capable of causing behavioral changes when the subject is exposed during the prenatal and immediate postnatal developmental stages, with this effect lasting over time," stated Osvaldo Juan Ponzo, M.D., Ph.D., a professor of physiology at the University of Buenos Aires School of Medicine and lead author of the study. The findings suggest a potential pathway through which environmental chemicals can shape neurodevelopment and influence mental health throughout an organism’s life.

The Pervasive Presence of DEHP

Di-(2-ethylhexyl) phthalate (DEHP) is a phthalate ester, a class of chemicals commonly added to plastics to enhance their flexibility, durability, and transparency. Its widespread use across various industries means that human exposure is nearly unavoidable, occurring through ingestion, inhalation, and dermal contact. DEHP is a key component in a vast array of consumer goods, including:

• Medical Devices: Intravenous (IV) bags, tubing, and catheters, where its flexibility is crucial for patient comfort and clinical application.
• Children’s Toys: Historically, DEHP was prevalent in soft plastic toys, though regulatory measures have reduced its use in this sector in many regions.
• Household Items: Shower curtains, vinyl flooring, wall coverings, and food packaging are common sources of DEHP.
• Personal Care Products: Some cosmetics and personal care items may also contain DEHP or related phthalates.

The chemical’s ability to leach from these products into the environment and subsequently into the human body has made it a subject of extensive scientific scrutiny. Previous research has consistently highlighted DEHP’s role as an endocrine disruptor, capable of interfering with the body’s hormonal systems. Studies have indicated that DEHP and its metabolites can affect multiple organ systems, with particular attention paid to its impact on reproductive development and function, as well as the nervous system. This current investigation builds upon this existing body of knowledge by specifically examining DEHP’s influence on anxiety-related behaviors.

Investigating the Neurobehavioral Impact of Early Life DEHP Exposure

The research team at the University of Buenos Aires aimed to elucidate the specific effects of early-life DEHP exposure on anxiety in adult male rats. A key focus of their investigation was to determine whether alterations in the levels or function of gamma-aminobutyric acid (GABA), a primary inhibitory neurotransmitter in the central nervous system, or testosterone, a critical sex hormone, played a mediating role in these behavioral changes.

The experimental design involved a carefully controlled timeline of DEHP administration and subsequent behavioral assessments. Pregnant female rats were administered daily oral doses of DEHP starting from the first day of gestation and continuing throughout the lactation period, ensuring that their offspring were exposed during crucial prenatal and early postnatal developmental windows. These periods are known to be particularly sensitive to environmental influences that can shape long-term neurodevelopmental trajectories.

Once the male offspring reached sexual maturity, at approximately 70 days of age, they were subjected to a standardized behavioral test designed to measure anxiety levels in rodents: the elevated plus maze (EPM). The EPM leverages the innate behavioral tendencies of rodents, which are naturally neophobic (fearful of novel stimuli) and have a strong aversion to open, elevated spaces due to predation risks. The maze consists of a central platform from which four arms extend: two arms are enclosed by walls, providing a sense of security, while the other two arms are open and elevated, representing a perceived threat.

Researchers meticulously recorded several key metrics during the EPM test:

• Arm Entry Frequency: The number of times each rat entered the open versus the enclosed arms.
• Time Spent in Arms: The duration each rat remained in the open versus the enclosed arms.
• Freezing Behavior: The amount of time rats spent immobile, a common indicator of fear and anxiety in rodents.

Rats exhibiting higher anxiety levels are expected to spend more time in the enclosed, safer arms of the maze and less time exploring the open arms. Increased freezing behavior is also a direct manifestation of heightened fear and stress.

Revealing the Anxiogenic Effects of DEHP

The results of the EPM test provided clear and significant findings. Male rats that had been exposed to DEHP during their early developmental stages displayed a marked increase in anxiety-related behaviors compared to control groups not exposed to the chemical. Specifically, these DEHP-exposed rats demonstrated:

• A reduced tendency to venture into the open arms of the maze.
• A significantly longer duration spent within the protective confines of the enclosed arms.
• An elevated amount of freezing time, indicating a heightened state of apprehension and stress.

These behavioral patterns strongly suggest that prenatal and early postnatal exposure to DEHP has a lasting anxiogenic (anxiety-producing) effect, altering the rats’ risk assessment and exploratory behaviors in adulthood. This is particularly concerning because the DEHP exposure ceased well before the adult testing began, highlighting the enduring nature of these developmental neurotoxic effects.

The Role of GABA and Testosterone in Mitigating Anxiety

A critical component of the study was to investigate potential neurobiological mechanisms underlying the observed behavioral changes and to explore whether these effects could be reversed. The researchers hypothesized that DEHP might disrupt the delicate balance of neurotransmitter systems, such as the GABAergic system, or hormonal pathways, like the testosterone axis, which are known to be crucial for regulating mood and anxiety.

To test this hypothesis, a subset of the DEHP-exposed rats received specific treatments shortly before undergoing the EPM test. These treatments included:

• GABA Agonists: Molecules designed to mimic the action of GABA by binding to and activating GABA receptors. GABA is the principal inhibitory neurotransmitter in the brain, and its activation generally leads to a calming or anxiolytic effect.
• Testosterone Administration: Male rats were treated with testosterone every 48 hours for 14 days leading up to the anxiety testing. Testosterone has been implicated in modulating anxiety and stress responses in male mammals.

The results of these therapeutic interventions were striking. In DEHP-exposed rats that received either GABA agonists or testosterone treatment, the previously observed signs of increased anxiety were significantly attenuated. These animals exhibited behavioral patterns that more closely resembled those of non-exposed control rats. They spent more time exploring the open arms, less time in the enclosed arms, and showed reduced freezing behavior.

This reversal of anxiety-like behaviors strongly indicates that the anxiogenic effects of early DEHP exposure are, at least in part, mediated by alterations in GABAergic neurotransmission and/or the testosterone signaling pathway. The ability of these treatments to counteract the effects suggests that the underlying neuroendocrine changes are not irreversible and may be amenable to therapeutic intervention, although such interventions would need extensive further research and validation in humans.

Broader Implications and Expert Commentary

The findings presented at ENDO 2026 have significant implications for public health and environmental policy. While the study was conducted in rodents, the biological pathways involved in neurodevelopment and anxiety are conserved across mammalian species, including humans. This suggests that similar long-term behavioral consequences could arise in humans exposed to DEHP during critical developmental windows.

"This work demonstrates that contact with DEHP in the early stages of life could modify behavior with regard to anxiety, even in the absence of DEHP exposure in adulthood," Dr. Ponzo emphasized. "These neuroendocrine changes can be reversed by treating with GABA agonists or testosterone."

The research underscores the vulnerability of the developing brain to environmental insults. Exposure to endocrine-disrupting chemicals during prenatal and early postnatal life, a period characterized by rapid neural proliferation, migration, and differentiation, can have profound and lasting effects on brain structure and function. This can manifest not only as behavioral alterations but potentially as an increased susceptibility to various neurological and psychiatric disorders later in life.

Timeline of Research and Event Context

The research leading to the presentation at ENDO 2026 represents a culmination of ongoing scientific efforts to understand the impact of environmental chemicals on health.

• Historical Context of Phthalates: Concerns about phthalates like DEHP began to emerge in the late 20th century as their widespread use became apparent and preliminary studies indicated potential health risks.
• Pre-2020s: Numerous studies identified DEHP as an endocrine disruptor, linking it to reproductive abnormalities in animal models and raising concerns about human health impacts, particularly in vulnerable populations like pregnant women and children.
• Recent Research Focus: In the past decade, research has increasingly focused on the neurodevelopmental effects of EDCs, including phthalates, exploring their potential to disrupt brain development and contribute to conditions such as ADHD, autism spectrum disorder, and mood disorders.
• ENDO 2026 Presentation: The presentation at ENDO 2026 in Chicago marks a significant milestone in this ongoing research, offering specific data on DEHP’s impact on anxiety and the potential role of GABA and testosterone. The annual meeting of the Endocrine Society serves as a critical platform for scientists and clinicians to share cutting-edge research and discuss emerging health challenges related to the endocrine system.

Potential Regulatory and Public Health Responses

The findings from the University of Buenos Aires study are likely to fuel ongoing discussions and calls for stricter regulation of DEHP and other phthalates. Regulatory bodies worldwide, such as the U.S. Environmental Protection Agency (EPA) and the European Chemicals Agency (ECHA), continuously evaluate the safety of chemicals. Evidence of long-term behavioral impacts, especially on neurodevelopment, can trigger:

• Re-evaluation of Existing Regulations: Existing limits on DEHP in consumer products, particularly those intended for children or medical applications, may be revisited and potentially lowered.
• Increased Restrictions on Use: Further restrictions or outright bans on DEHP in certain product categories could be considered.
• Public Health Advisories: Health organizations may issue advisories to pregnant women and families about minimizing exposure to DEHP-containing products.
• Promotion of Safer Alternatives: The research could accelerate the development and adoption of safer chemical alternatives for plasticizers.

While DEHP’s use has been restricted in some applications, such as children’s toys in many regions, its continued presence in medical devices and other consumer goods means that human exposure remains a significant concern. The longevity of the observed behavioral effects in the rat study highlights the importance of addressing chemical exposures that occur during critical developmental windows.

Future Directions and Research Needs

The study by Ponzo and colleagues opens several avenues for future research:

• Human Cohort Studies: Longitudinal studies in human populations are crucial to confirm whether similar associations between early-life DEHP exposure and adult anxiety exist. These studies would need to carefully control for other confounding factors.
• Mechanistic Studies: Further investigation into the precise molecular and cellular mechanisms by which DEHP disrupts GABAergic and androgenic signaling during neurodevelopment is warranted. This could involve more detailed genetic and epigenetic analyses.
• Developmental Timing: Exploring the specific critical windows of vulnerability during development for DEHP’s neurobehavioral effects would refine our understanding of risk.
• Intervention Strategies: While GABA agonists and testosterone showed promise in reversing effects in rats, research into potential human interventions for managing the long-term consequences of EDC exposure would be invaluable.

The presentation at ENDO 2026 serves as a potent reminder of the intricate interplay between environmental exposures and human health. As science continues to unravel the complex pathways through which chemicals like DEHP can shape our biology and behavior, robust scientific evidence will be critical in guiding policy decisions and protecting public health for current and future generations.