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Neonicotinoid Insecticides Adversely Affect Nervous System Health, According to Study

(Beyond Pesticides, January 19, 2023) Research published in Environmental Health Perspectives finds the presence of nine various neonicotinoids (neonics) and six neonic metabolites within human cerebrospinal fluid (CSF). CSF is an essential part of the central nervous system (CNS), especially for CNS development. Specific chemical biomarkers (measurable indicators of biological state), like pesticides, found in CSF are useful for diagnosing and evaluating numerous neurological diseases.

The nervous system is an integral part of the human body and includes the brain, spinal cord, a vast network of nerves and neurons, all of which are responsible for many of our bodily functions—from sensed to movement. However, mounting evidence over the past years shows that chronic exposure to sublethal (low) levels of pesticides can cause neurotoxic effects or exacerbate preexisting chemical damage to the nervous system. The impacts of pesticides on the nervous system, including the brain, are hazardous, especially for chronically exposed individuals (e.g., farmworkers) or during critical windows of vulnerability and development (e.g., childhood, pregnancy). Researchers identify the role agricultural chemicals play in CNS impacts causing neurological diseases, like amyotrophic lateral sclerosis (ALS) and Parkinson’s disease, dementia-like diseases such as Alzheimer’s, and other effects on cognitive function.

Over 300 environmental contaminants and their byproducts, including pesticides, are chemicals commonly present in human blood and urine samples and can increase neurotoxicity risk when crossing the brain barrier. Therefore, studies like this highlight the importance of understanding how chemical accumulation in the body can impact long-term health and disease prognosis.

The study explores whether the presence of neonics and their metabolites in CSF is an indicator of adverse CNS effects. From April 2019 to January 2021, researchers gathered 314 CSF samples from patients aged one month to 89 years in the First Affiliated Hospital of Shantou University, Shantou, China using a clinical lumbar puncture. Researchers collected CSF samples from patients experiencing similar symptoms with a different disease/clinical diagnosis (i.e., “mostly viral encephalitis, encephalitis other than viral encephalitis, leukemia, cerebral hemorrhage, cerebral laceration, urinary tract infection, respiratory failure, pulmonary tuberculosis, and posterior circulation ischemia”). To analyze the presence of neonics and their metabolites in CSF, researchers used acidification, solid phase extraction, and high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS). Ninety-nine percent of the 314 CSF samples contain at least one neonic. Of the 314 CSF samples, nine percent (28) have a single neonic compound, 84 percent (265) have between 2 and 6, and six percent (19) have between 7 and 10 neonic compounds. Nine of these neonics in CSF samples are nitenpyram (NIT), thiamethoxam, imidacloprid, acetamiprid (ACE), thiacloprid, clothianidin, flonicamid, imidaclothiz, and sulfoxaflor. Additionally, six neonic metabolites are present in CSF: N-desmethyl-thiamethoxam, olefin-imidacloprid, 5-hydroxy-imidacloprid, N-desmethyl-acetamiprid (N-dm-ACE), thiacloprid-amide, and 6-chloronicotinic acid.

Over the past 20 years, neonicotinoids served as an alternative for four major chemical classes of insecticides in the global market (organophosphates, carbamates, phenyl-pyrazoles, and pyrethroids). These systemic agricultural pesticides are highly toxic, resembling nicotine, and affect the central nervous system of insects, resulting in paralysis and death, even at low doses. Like other pesticides, neonics readily contaminate water and food resources as traditional water waste treatments typically fail to remove the chemical from tap water, and the systemic nature of neonics allows the chemical to accumulate within plant products. According to the Centers for Disease Control and Prevention (CDC), nearly half the U.S. population encounters at least one type of neonic daily, with children ages three to five having the highest exposure risk.

Health impacts of exposure to neonics can include neurotoxicity, reproductive anomalies, hepatic and renal damage, and an increase in gene expression linked to hormone-dependent breast cancer. Additionally, researchers identified that some neonicotinoids play a role in enzyme (aromatase) production that stimulates excess estrogen production, a known event in hormone-dependent cancer development.

Beyond its link to human health effects, neonicotinoids are infamous for their well-documented role in driving mass pollinator declines. However, pollinators are far from the only victims of ubiquitous neonicotinoid contamination. In a recent avian risk assessment, EPA scientists found that neonicotinoids levels in treated seeds exceed the agency’s threshold of concern for certain birds by as much as 200-fold. A 2017 study by researchers at the University of Saskatchewan confirmed that tiny amounts of neonicotinoids – the equivalent of just four treated canola seeds, for example – are enough to cause migrating songbirds to lose their sense of direction and become emaciated. Recent research uncovered the endocrine-disrupting health impacts of imidacloprid on white-tailed deer, adding to the concern of the same effect in humans.

This study adds to the growing research on pesticides and neurotoxic consequences. Although past studies on neonic toxicity focus on neurotoxicity among insects and aquatic invertebrates, emerging evidence demonstrates these compounds also adversely impact the nervous system of animals, including humans as well. Not only does research find exposure to sublethal doses of chemicals affect hormone receptors (endocrine disruption), but neural receptors, such as connections between nerves, the brain, enzymes, and DNA are affected as well. In addition to this research, several studies demonstrate autism, mood disorders (e.g., depression), and degenerative neurological conditions among aquatic and terrestrial animals, including humans, exposed to pesticides. Pesticides themselves, mixtures of chemicals such as the defoliant Agent Orange (2,4-D and 2,4,5-T) and its dioxin contaminants and therapeutic hormones in pharmaceutical products, possess the ability to disrupt neurological function. Furthermore, studies suggest that pesticides formulants (adjuvants) such as POEA (polyoxyethylene tallow amine) have both neurological and endocrine-disrupting activity. POEA is present in some glyphosate-based herbicides like Roundup and has higher nervous system toxicity than the active ingredient (glyphosate). Although the biological function and mechanism of neurotoxicity related to pesticide exposure is ambiguous, scientists note synchronized communication within and between cells that have a mechanism of action of “spamming” communication signals. The study concludes, “For continued global use of NEOs [neonics], mechanisms of toxicity, especially to the CNS in humans, need to be more rigorously investigated.”

The nervous system is integral to everyday human activities and the body’s ability to function normally. Pesticides themselves can possess the ability to disrupt neurological function. Pesticides’ impact on the nervous system, including the brain, are hazardous, especially for chronically exposed individuals or during critical windows of vulnerability and development. Therefore, studies related to pesticides and neurological disorders can help scientists understand the underlying mechanisms that cause neurodegenerative diseases. As captured by epidemiologic studies in Beyond Pesticides’ Pesticide-Induced Diseases Database (PIDD) and Daily News Blog, the adverse health effects of pesticides, exposure, and the aggregate risk of pesticides showcase a need for more precise research on pesticide exposure. Existing information, including this study, supports the clear need for a strategic shift away from pesticide dependency. For more information on the effects of pesticide exposure on neurological health, see Beyond Pesticides’ PIDD pages on brain and nervous system disorders, including dementia-like diseases, such as Alzheimer’s, and other impacts on cognitive function.

Beyond Pesticides advocates for organic land and agriculture management as precautionary approach to pest prevention and management. Buying, growing, and supporting organic can help eliminate the extensive use of pesticides in the environment and from your diet. For more information on why organic is the right choice for consumers and the farmworkers who grow our food, see Beyond Pesticides webpage, Health Benefits of Organic Agriculture.

All unattributed positions and opinions in this piece are those of Beyond Pesticides.

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