Exposure to a supposedly safer alternative to traditional permanent chemicals during pregnancy and lactation causes lasting memory and learning deficits in adult rats. Animal studies suggest that early exposure to these synthetic compounds interferes with normal brain development. This study Frontiers of toxicology.
Perfluoroalkyl and polyfluoroalkyl substances, commonly known as PFAS, are highly stable synthetic chemicals characterized by very strong carbon-fluorine bonds. Manufacturers have been using them since the 1940s to make products resistant to heat, oil, and water. These functional properties make it very useful in nonstick cookware, food packaging, waterproof clothing, etc.
Because they break down very slowly, they accumulate in the environment and in the human body. Older versions of these chemicals typically consist of molecular chains featuring eight or more carbon atoms. Epidemiological studies have repeatedly linked prenatal exposure to these long-chain PFASs with adverse developmental outcomes such as cognitive and behavioral changes in children.
In response to health and environmental concerns, manufacturers have phased out these long-chain variants. They replaced them with shorter-chain varieties that supposedly have fewer carbon atoms and are eliminated from the human body more quickly. Two common chemical substitutes that fall into this category are GenX and perfluorobutanoic acid (commonly known as PFBA).
Despite the widespread adoption of short-chain PFAS, experimental data regarding their safety in the fetal and early stages remain very limited. Researchers from the University of Bologna and the Venice Institute of Animal Experimentation designed an animal experiment to test whether early exposure to GenX and PFBA affects the mammalian brain. Lead researchers Luca Lorenzini and Marzia Moretti sought to understand how exposure during pregnancy and breastfeeding alters brain structure and cognitive function into adulthood.
The researchers fed female rats food contaminated with either GenX or PFBA for 30 days before mating. The synthetic chemicals remained in the animals’ food supplies throughout gestation and until the newborn puppies were weaned. Doses are designed to be below the threshold where acute physical toxicity is typically observed and reflect the low but sustained exposure levels sometimes seen in human drinking water.
After weaning, the offspring ate a standard uncontaminated diet. This design reflects the way mammals transfer chemicals in the placenta and breast milk. The researchers waited until the offspring reached adulthood, approximately 12 weeks after weaning, to assess their neurocognitive abilities.
The researchers assessed several behavioral domains before testing learning and memory. They placed the animals in a new enclosed space and observed the animals’ natural movement patterns. While unexposed rats explored at a predictable pace, rats exposed to the lowest doses of PFBA showed abnormally high levels of activity and traveled much longer distances.
No such hyperactivity was seen in the highest dose group. This phenomenon, in which low and high doses produce very different biological responses, is a frequently observed feature of hormone-disrupting chemicals. The researchers also assessed the animals’ motor coordination by having them walk on a rotating pole. None of the exposed groups experienced problems with basic body balance.
To test learning and memory, researchers placed rats in large pools of opaque water. The animals needed to learn specific visual cues within the room to navigate toward a hidden underwater platform. This test assesses spatial learning and relies heavily on a brain region called the hippocampus.
Rats exposed to high doses of GenX and PFBA early in development struggled significantly with this task. They took longer than unexposed rats to learn the location of the hidden platform. When the researchers moved the platform to test cognitive flexibility, the exposed rats had great difficulty adjusting to the new location.
These memory problems occurred even though the chemicals were not present in the adult rats’ brains at the time of the experiment. Chemical analysis showed that GenX was completely withdrawn from the animal’s system. Although traces of PFBA remained in some organs, such as the liver, the brain was largely cleared of the chemicals, ruling out the possibility that acute biological toxicity could cause memory impairment.
Instead, the researchers investigated how early exposure disrupted the physical structure of the developing brain. To do so, they cultured brain cells taken from rat fetuses whose mothers had been exposed to PFBAs. The researchers watched these neurons under a microscope as they matured over three weeks in a laboratory dish.
When the researchers looked closely at the cultures after a week of maturation, the neurons in the exposed animals appeared to be strangely overgrown and sprouting discordant branches. By the third week, this early chaotic growth resulted in poorly developed structures. Neurons typically produce long, specialized extensions to communicate, eventually forming connection points called synapses. Cells exposed to PFBA produced fewer junctions and expressed lower levels of proteins essential for stable synapse formation.
The researchers also examined the actual brains of adult rats that underwent behavioral tests. They specifically focused on the dentate gyrus, the part of the hippocampus responsible for generating new brain cells. In healthy adult animals, this region constantly generates and matures new neurons that help form memories and learn.
Adult rats exposed to high levels of PFBA and GenX showed clear abnormalities in this central brain region. Researchers noted the increasing presence of biological markers associated with unspecialized stem cells. At the same time, markers of mature neurons sharply decreased in affected rats.
This pattern indicates a stall in the developmental process, where new cells are unable to transition into fully functional neurons. The researchers also analyzed gene activity within the hippocampus. They found obvious abnormalities in how the cells worked, particularly an increase in genes that cause cellular inflammation.
Inflammation in the brain can disrupt normal cell-to-cell communication and prevent the survival of new neurons. Male rats exposed to GenX showed significant elevations in multiple chemokines, which are immune signaling proteins. Female rats exposed to the chemical also showed similar but distinct signs of abnormal inflammation in their brain tissue.
Because hormones have a huge impact on brain development, the researchers also checked the animals’ circulating hormone levels. Male rats exposed to high doses of GenX or PFBA produced substantially lower levels of testosterone compared to unexposed animals. Female rats exposed to GenX experienced a similar decrease in progesterone.
These altered hormonal states persisted for months after exposure ended. Hormones such as testosterone play a major role in keeping newly formed neurons alive in the hippocampus. The lack of these hormones may have amplified the cognitive problems observed in affected rats.
Although the findings clearly demonstrate the neurotoxic potential of short-chain PFAS in rodent models, the researchers note that their study has certain limitations. The research team did not test hormone or chemical levels immediately after the rats finished nursing. This lack of data makes it difficult to distinguish between direct chemical toxicity on the infant’s brain and indirect effects of maternal distress.
This study investigated only two short-chain PFAS variants among thousands of similar synthetic compounds. The results obtained using GenX and PFBA may not apply to other members of the chemical family. Future experiments should examine a variety of short-chain compounds to determine whether these developmental problems are universal features of the entire class.
Translating these animal results directly to humans also requires patience. Humans eliminate these compounds from their bodies at a different rate than rodents. Assessing how low-dose chronic exposure affects human brain function will require targeted tracking of exposed populations over decades.
The study, “Short-chain PFAS exposure during pregnancy and lactation alters learning and memory in adulthood: Possible mechanisms relevant to brain development,” was authored by Luca Lorenzini, Marzia Moretti, Claudia Zanardello, Federica Gallocchio, Vito A. Baldassarro, Alessandra Moressa, Lorenzo Zanella, Michele Sannia, Greta Foiani, and Corinne Quadalti. Maura Cescatti, Valentina Brato, Margherita Sonchin, Marzia Mancin, Luciana Giardino, Franco Mutinelli, Marta Vasellari, Laura Calza. \
