12
Dec
Review Cites Memory and Learning Impairments; Children, Workers, and Nontarget Organisms at Risk
(Beyond Pesticides, December 12, 2024) A literature review of 161 articles in Discover Toxicology finds that pesticides with different mechanisms of action cause memory and learning impairments. These effects are noted in nontarget species including humans. Pesticide “[e]xposure during development, as well as chronic environmental and occupational exposure, can contribute to decreased cognitive performance,†the researchers say. With a focus on organophosphate pesticides, synthetic pyrethroids, and neonicotinoid insecticides, the authors highlight neurological impacts.
Both learning and memory are crucial for the survival of many species. “Considering the importance of learning and memory for human and non-human animal behavior and the growing association between pesticide exposure and cognitive impairment, the aim of this review was to describe the studies showing the impact of pesticide exposure on memory and learning abilities in nontarget species, providing evidence of the impact of pesticides in central nervous system function,†the researchers state.
The 161 articles included in the review were identified through database searches in PubMed/Medline and Scielo. The authors note, “Inclusion criteria for article selection included all articles published in English between 2015 and 2024 containing original studies in animals or humans with single or multiple pesticides exposure.â€
The articles consist of 132 preclinical studies involving animal models, most focusing on bees and rodents, and 29 human studies that assess occupational and environmental exposure. The researchers share that, “Regarding animal models, 58% of preclinical studies were conducted in rodents and 28% in bees, evidencing the lack of studies conducted in aquatic species, amphibians and other important animal models in ecotoxicological studies.†See related coverage on scientific deficiencies within Environmental Protection Agency (EPA) review processes here.
Preclinical Studies
Organophosphates
In the research, the majority of studies, related to organophosphates, assess the effects of exposure to chlorpyrifos, malathion, and diazinon and find that they cause damage to the learning and memory capacity in multiple species. The authors postulate that these effects of organophosphates on “[m]emory and learning deficits seem to involve mechanisms such as acetylcholinesterase and butyrylcholinesterase inhibition and oxidative stress.â€
Notable studies include:
- In bees, chlorpyrifos leads to slower olfactory learning and memory.
- Many studies find that chlorpyrifos impairs spatial and recognition memory in mice (see here, here, here, here, and here), as well as spatial learning and memory in rats (see here, here, and here).
- Short-term exposure to malathion causes damage to spatial memory in mice. The offspring of exposed mice also exhibit decreases in memory and behavior.
- Malathion exposure in rats induces spatial learning and memory deficits through mechanisms involving oxidative stress and synaptic damage.
- Rats subjected to diazinon show impaired reference memory and deficient attentional accuracy, in addition to decreased aversive memory (see here and here).
Pyrethroids
As the researchers report, “Studies have shown that exposure to pyrethroids caused learning and memory deficits in rats and mice and was associated with the disruption of dopaminergic pathways, oxidative stress and hippocampal damage.†Additional studies reveal effects on pollinator species.
Notable studies include:
- Flumethrin exposure during the larval stage in honeybees affects memory-related behaviors and decreases the expression of memory-related genes. Long-term exposure also impacts olfactory learning and memory and causes downregulation of memory-related genes.
- Deltamethrin impairs learning and memory formation in honeybees with short-term exposure to sublethal concentrations.
- Mice treated with deltamethrin show impairments in spatial memory and memory retention, as well as learning deficits, hippocampal endoplasmic reticulum stress, and impaired hippocampal neurogenesis (see here and here).
- Rats exposed to deltamethrin exhibit mitochondrial dysfunction in the hippocampus and striatum, and impaired learning and reference memory. Studies also show impaired learning and spatial/working memory (see here, here, here, and here).
- Bifenthrin exposure in mice presents memory retention deficits.
- Exposure to permethrin during the prenatal and postnatal periods in mice causes impairments in learning and memory in adulthood.
- Treatment with lambda-cyhalothrin in mice shows a decrease in retention and learning memories.
- Developmental exposure to cypermethrin impairs spatial learning in young rats.
- Cyfluthrin affects the pathways in the hippocampus, which alters learning and memory in the offspring of exposed rats.
Neonicotinoids
Most studies of neonicotinoid insecticides in the review report harm to various species of bees. The authors find that, “Olfactory, associative and aversive learning, as well as memory capacity were affected by the exposure to several neonicotinoid insecticides, particularly imidacloprid. These sublethal effects can affect the behavioral performance of bees and consequently their pollination activity, impacting pollinator-dependent agricultural systems, in addition to the maintenance of ecosystems.†See “What the Science Shows on Biodiversity†for additional studies regarding pollinators.
Notable studies include:
- Bumblebees exposed to imidacloprid during brood or early adult development exhibit learning deficits in adulthood. Imidacloprid also causes impaired olfactory, associative, aversive, and motor learning in many bee species (see here, here, here, here, here, and here).
- Sublethal concentrations of imidacloprid also negatively affect learning and short-term memory in paper wasps.
- Imidacloprid causes a spatial memory disorder in Hipposideros terasensis bats (see here and here).
- Chronic exposure to clothianidin affects olfactory learning in honeybees and bumblebees, while acute exposure compromises short-term to mid-term memory and memory recovery in honeybees (see here and here).
- Thiamethoxam exposure in honeybees and bumblebees impairs visual and olfactory learning and presents learning delays and memory deficits.
- Rats exposed to thiacloprid display short-term working memory impairment, oxidative stress, and neuroinflammation.
Human Studies
Neurological effects in children and adults following pesticide exposure are heavily documented. Both chronic and acute exposure, even at low doses, can cause permanent damage to the brain, especially during critical periods of development. As the researchers report, “Learning and memory problems are not the only outcomes associated with early exposure to chemicals: intellectual disability, autism spectrum disorder, motor delays, attention problems, and others can have far-reaching effects on children’s educational success, socioemotional development, and quality of life.†See more on brain and nervous system disorders here.
While children are more susceptible to negative health effects from pesticide exposure due to their developing system and more limited ability to detoxify compounds, adults also experience many neurological impacts. Particularly affected are those who are subjected to pesticides during occupational activity including farmers and farmworkers. This disproportionate risk is associated with poorer memory and learning performance.
“Epidemiological studies have mostly reported the exposure of agricultural workers to organophosphate and carbamate pesticides, in addition to other pesticides used on crops. Long-term exposure to pesticides has been suggested to have long-lasting toxic effects on the central nervous system, and studies have recognized that chronic exposure is a possible risk factor for dementia and Alzheimer’s disease,†the authors say. (See studies here and here.) They continue, “In addition to cognitive deficits and neurodegenerative diseases, studies suggest a positive association between pesticide exposure and psychiatric conditions, such as depression, anxiety and suicide.â€
Notable studies include:
- In 10-year-old children from a birth cohort in California, mothers living close to intensive applications of organophosphate and carbamate pesticides exhibit decreased cognitive function, such as in working memory.
- Children in Costa Rica living near banana plantations show neurodevelopment impairment. Specifically, children exposed to mancozeb have poorer verbal learning abilities, while exposure to chlorpyrifos is associated with poorer working memory.
- A study of Ecuadorian children observed an association between residential proximity to greenhouse agriculture and impaired cognitive performance.
- School-age children in rural areas of Colombia who experience environmental exposure to organophosphates, pyrethroids, and fungicides show decreased working memory index. Home usage of pesticides is also associated with a lower processing speed index.
- Organophosphate and carbamate pesticide exposure in Chile decreases cholinesterase activity and affects memory function in people living near plantations (see here and here).
- In Uganda, a cross-sectional study shows that overall pesticide exposure in farmers, specifically to glyphosate, is associated with impaired visual memory.
- Costa Rican farmers exposed to multiple pesticides with higher concentrations of insecticide biomarkers, including metabolites from chlorpyrifos and pyrethroids, display reduced prefrontal cortex activity during working memory tasks.
- After decades of occupational exposure, veterans show problems with concentration and memory as symptoms of Gulf War Illness (see studies here, here, and here as well as additional coverage on veterans here).
Organic as a Solution
The dependence on petrochemical pesticides and synthetic fertilizers leads to an increase in human exposure to toxic chemical compounds. Contamination of the environment, as well as residues in food and water, subjects nontarget organisms to chemicals that result in deleterious health effects. These pesticides also play a critical role in the current existential crises of public health, biodiversity, and climate change (see more here and here).
As an alternative, organic land management offers a path forward that mitigates these negative effects and promotes the health of all organisms and the environment. Learn more about the environmental and health benefits of organic, as well as how to buy organic products and grow your own organic food. Stay up to date with Daily News and sign up to receive Action of the Week and Weekly News Updates delivered straight to your inbox.
All unattributed positions and opinions in this piece are those of Beyond Pesticides.
Source:
Honatel, K.F. et al. (2024) An update of the impact of pesticide exposure on memory and learning, Discover Toxicology. Available at: https://link.springer.com/article/10.1007/s44339-024-00011-9.
