The relationships between pesticide metabolites and neurobehavioral test performance in the third National Health and Nutrition Examination Survey

Association between 2,4-dichlorophenoxyacetic acid and cognitive impairment in older adults: a cross-sectional study from NHANES 2001-2002 and 2011-2014

BACKGROUND

2,4-Dichlorophenoxyacetic acid (2,4-D) is reported to be the most widely used herbicide in home and garden environments, rendering it commonly encountered in daily life. Despite being ubiquitous, there is a scarcity of studies that have comprehensively assessed the relationship between 2,4-D exposure and cognition using multiple models.

OBJECTIVE

To explore the association between 2,4-D exposure and cognition among older American people.

METHODS

This was a cross-sectional study that included 3 cycles of data from the National Health and Nutrition Examination Survey. Generalized linear models (GLMs), restricted cubic spline (RCS) regression, and generalized additive models (GAMs) were used to assess the relationship between exposure to 2,4-D and cognitive performance by the Consortium to Establish a Registry for Alzheimer's Disease (CERAD) word learning sub-test, Digit Symbol Substitution Test (DSST), and Animal Fluency Test (AFT).

RESULTS

A total of 1364 older U.S. adults (60+ years) were included in the study. The GLMs revealed a negative association between median high levels (0.315-0.566 μg/L) of 2,4-D and cognitive impairment on the DSST and AFT, with multivariate-adjusted ORs of 0.403 (95% CI: 0.208-0.781, P = 0.009) and 0.396 (95% CI: 0.159-0.986, P = 0.047); the RCS regression and GAMs revealed a "U" shaped curve, the left part of which is consistent with the result of the GLMs.

IMPACT STATEMENT

There is a U-shaped relationship between human urinary 2,4-D concentrations and cognitive impairment in older U.S. adults, especially in males, so controlling 2,4-D exposure within an appropriate range is particularly important for cognitive function.

Urinary Glyphosate, 2,4-D and DEET Biomarkers in Relation to Neurobehavioral Performance in Ecuadorian Adolescents in the ESPINA Cohort

BACKGROUND

Herbicides are the most used class of pesticides worldwide, and insect repellents are widely used globally. Yet, there is a dearth of studies characterizing the associations between these chemical groups and human neurobehavior. Experimental studies suggest that glyphosate and 2,4-dichlorophenoxyacetic acid (2,4-D) herbicides can affect neurobehavior and the cholinergic and glutamatergic pathways in the brain. We aim to assess whether herbicides and insect repellents are associated with neurobehavioral performance in adolescents.

METHODS

We assessed 519 participants (11-17 years of age) living in agricultural communities in Ecuador. We quantified urinary concentrations of glyphosate, 2,4-D, and two N,N-diethyl-meta-toluamide (DEET) insect repellent metabolites [3-(diethylcarbamoyl)benzoic acid (DCBA) and 3-(ethylcarbamoyl)benzoic acid (ECBA)] using isotope-dilution mass spectrometry. We assessed neurobehavioral performance using 9 subtests across 5 domains (attention/inhibitory control, memory/learning, language, visuospatial processing, and social perception). We characterized the associations using generalized estimating equations and multiple imputation for metabolites below detection limits. Models were adjusted for demographic and anthropometric characteristics, urinary creatinine, and sexual maturation. Mediation by salivary cortisol, dehydroepiandrosterone, 17 β -estradiol , and testosterone was assessed using structural equation modeling.

RESULTS

The mean of each neurobehavioral domain score was between 7.0 and 8.7 [standard deviation (SD) range: 2.0-2.3]. Glyphosate was detected in 98.3% of participants, 2,4-D in 66.2%, DCBA in 63.3%, and ECBA in 33.4%. 2,4-D was negatively associated with all neurobehavioral domains, but statistically significant associations were observed with attention/inhibition [score difference per 50% higher metabolite concentration ( β ) = - 0.19 95% confidence interval (CI): - 0.31 , - 0.07 ], language [β = - 0.12 (95% CI: - 0.23 , - 0.01 )], and memory/learning [β = - 0.11 (95% CI: - 0.22 , 0.01)]. Glyphosate had a statistically significant negative association only with social perception [β = - 0.08 (95% CI: - 0.14 , - 0.01 )]. DEET metabolites were not associated with neurobehavioral performance. Mediation by gender and adrenal hormones was not observed.

CONCLUSION

This study describes worse neurobehavioral performance associated with herbicide exposures in adolescents, particularly with 2,4-D. Replication of these findings among other pediatric and adult populations is needed. https://doi.org/10.1289/EHP11383.

The diabetogenic effects of pesticides: Evidence based on epidemiological and toxicological studies

While the use of pesticides has improved grain productivity and controlled vector-borne diseases, the widespread use of pesticides has resulted in ubiquitous environmental residues that pose health risks to humans. A number of studies have linked pesticide exposure to diabetes and glucose dyshomeostasis. This article reviews the occurrence of pesticides in the environment and human exposure, the associations between pesticide exposures and diabetes based on epidemiological investigations, as well as the diabetogenic effects of pesticides based on the data from in vivo and in vitro studies. The potential mechanisms by which pesticides disrupt glucose homeostasis include induction of lipotoxicity, oxidative stress, inflammation, acetylcholine accumulation, and gut microbiota dysbiosis. The gaps between laboratory toxicology research and epidemiological studies lead to an urgent research need on the diabetogenic effects of herbicides and current-use insecticides, low-dose pesticide exposure research, the diabetogenic effects of pesticides in children, and assessment of toxicity and risks of combined exposure to multiple pesticides with other chemicals.

Neurobehavioral Effects of Low-Dose Chronic Exposure to Insecticides: A Review

The modes of action of insecticides frequently involve a neurotoxic effect; therefore, the study of neurotoxic effects caused by long-term and low-dose insecticide exposure is of particular interest. This study looks at whether or not new studies conducted after 2009 and up to 2021 have provided new evidence for a better understanding of the actual neurobehavioral risk associated with long-term insecticide exposure. We selected and reviewed studies carried out on the neurobehavioral effects of neurotoxic insecticides (organophosphates and/or carbamates, pyrethroids, multiple or undefined insecticides, and organochlorines) considering occupational and non-occupational exposures. The articles were also scored and ranked based on seven parameters. Eighty-six studies were chosen for a final review process from among the 950 scientific papers identified. Twenty-six addressed occupational exposure and six environmental exposure. Among the latter group of studies, 17 focused on rural residents, to be assumed exposed because of living in rural areas, and 43 on the general population. Pending doubts have not been resolved in the last ten years due to the presence of contradictory and hardly comparable results and the fact that in most of the studies showing an evident neurobehavioral impairment the frequent presence of a previous episode of poisoning and hospitalization, with severe brain hypoxia, impaired the possibility of confirming the presence of a causal association with insecticide exposure. Interestingly, the most severely exposed groups, such as applicators who did not wear personal protective equipment, performed worse on neurobehavioral tests. As for residential exposure, there is sufficient evidence to suggest that prenatal OP exposure may increase the risk of ADHD in children.

Neurotoxicity of pesticides in the context of CNS chronic diseases

Following the introduction and application of pesticides in human life, they have always been along with health concerns both in acute poisoning and chronic toxicities. Neurotoxicity of pesticides in chronic exposures has been known as one of the most important human health problems, as most of these chemicals act through interacting with some elements of nervous system. Pesticide-induced neurotoxicity can be defined in different categories of neurological disorders including neurodegenerative (Alzheimer, Parkinson, amyotrophic lateral sclerosis, multiple sclerosis), neurodevelopmental (attention deficit hyperactivity disorder, autism spectrum disorders, developmental delay, and intellectual disability), neurobehavioral and neuropsychiatric (depression/suicide attempt, anxiety/insomnia, and cognitive impairment) disorders some of which are among the most debilitating human health problems. In this review, neurotoxicity of pesticides in the mentioned categories and sub-categories of neurological diseases have been systematically presented in relation to different route of exposures including general, occupational, environmental, prenatal, postnatal, and paternal.

Relationship between urinary dichlorophenols and cognitive function among people over 60 years old from NHANES

Studies have shown that exposure to dichlorophenols (DCPs) and their precursors might have potential neurotoxicity, which may be related to low cognitive function, but there are few large-scale, representative population data to explore the association between DCP exposure and cognitive function. We aimed to examine the relationship between urinary DCPs and cognitive function in the US older people. A total of 952 participants ≥ 60 years old from the National Health and Nutrition Examination Survey (NHANES) in two cycles (2011-2014) were enrolled. The Consortium to Establish a Registry for Alzheimer's disease Word Learning subtest (CERAD W-L), the Animal Fluency test (AFT), and the Digit Symbol Substitution test (DSST) were used to assess cognition. Multivariate logistic regression and restricted cubic spline (RCS) were used to evaluate the relationship between DCP exposure and cognitive function. A positive association between 2,5-DCP and the risk of bad performance of DSST was observed (P for trend = 0.024) after adjusting for the covariates. Compared to the lowest quartile, OR of DSST for the highest quartile of 2,5-DCP was 1.72 (95%CI:1.03-2.87, P = 0.039). There were no significant associations between DCPs and the other tests. The RCS plot showed an inverted J-shaped relationship between 2,5-DCP, 2,4-DCP, and the DSST score. The inflection points for the curves were found at 1.531 μg/L and 0.230 μg/L, respectively. On the right side of the inflection points, the DSST score dropped sharply. In subgroup analysis, those under 70 years old, smokers, and alcohol drinkers had a higher risk of bad performance in DSST when exposed to 2,5-DCP. The higher concentration of urinary DCPs is associated with a lower score of DSST in the US older people.

Endocrine disruptors also function as nervous disruptors and can be renamed endocrine and nervous disruptors (ENDs)

Endocrine disruption (ED) and endocrine disruptors (EDs) emerged as scientific concepts in 1995, after numerous chemical pollutants were found to be responsible for reproductive dysfunction. The World Health Organization established in the United Nations Environment Programme a list of materials, plasticizers, pesticides, and various pollutants synthesized from petrochemistry that impact not only reproduction, but also hormonal functions, directly or indirectly. Cells communicate via either chemical or electrical signals transmitted within the endocrine or nervous systems. To investigate whether hormone disruptors may also interfere directly or indirectly with the development or functioning of the nervous system through either a neuroendocrine or a more general mechanism, we examined the scientific literature to ascertain the effects of EDs on the nervous system, specifically in the categories of neurotoxicity, cognition, and behaviour. To date, we demonstrated that all of the 177 EDs identified internationally by WHO are known to have an impact on the nervous system. Furthermore, the precise mechanisms underlying this neurodisruption have also been established. It was previously believed that EDs primarily function via the thyroid. However, this study presents substantial evidence that approximately 80 % of EDs operate via other mechanisms. It thus outlines a novel concept: EDs are also neurodisruptors (NDs) and can be collectively termed endocrine and nervous disruptors (ENDs). Most of ENDs are derived from petroleum residues, and their various mechanisms of action are similar to those of "spam" in electronic communications technologies. Therefore, ENDs can be considered as an instance of spam in a biological context.

Neurotoxicity in Preclinical Models of Occupational Exposure to Organophosphorus Compounds

Organophosphorus (OPs) compounds are widely used as insecticides, plasticizers, and fuel additives. These compounds potently inhibit acetylcholinesterase (AChE), the enzyme that inactivates acetylcholine at neuronal synapses, and acute exposure to high OP levels can cause cholinergic crisis in humans and animals. Evidence further suggests that repeated exposure to lower OP levels insufficient to cause cholinergic crisis, frequently encountered in the occupational setting, also pose serious risks to people. For example, multiple epidemiological studies have identified associations between occupational OP exposure and neurodegenerative disease, psychiatric illness, and sensorimotor deficits. Rigorous scientific investigation of the basic science mechanisms underlying these epidemiological findings requires valid preclinical models in which tightly-regulated exposure paradigms can be correlated with neurotoxicity. Here, we review the experimental models of occupational OP exposure currently used in the field. We found that animal studies simulating occupational OP exposures do indeed show evidence of neurotoxicity, and that utilization of these models is helping illuminate the mechanisms underlying OP-induced neurological sequelae. Still, further work is necessary to evaluate exposure levels, protection methods, and treatment strategies, which taken together could serve to modify guidelines for improving workplace conditions globally.

Learning Ability as a Function of Practice: Does It Apply to Farmworkers?

OBJECTIVE

Farmworkers experience significant work-related health risks including pesticide-associated cognitive impairment. Practice effect is a surrogate for learning ability. This study examined differences in cognitive function and learning capacity in Latino farmworkers and nonfarmworkers.

METHODS

Tasks of learning and short-term memory, executive function and working memory, perceptual coding, and psychomotor function were assessed at baseline and 3-month follow-up in 136 farmworkers and 116 nonfarmworkers.

RESULTS

Farmworkers had better performance on visuospatial learning and short-term memory at baseline (P < 0.05). Nevertheless, nonfarmworkers showed more practice effects, or improvement on cognitive performance, at 3-month follow-up relative to farmworkers. Furthermore, the amount of improvement on visuospatial learning ability, short-term visuospatial memory, and perceptual coding ability was significantly higher in nonfarmworkers than in farmworkers.

CONCLUSIONS

Practice effects may serve as an additional cognitive readout to differentiate healthy individuals from those with cognitive impairment.

Effects of exposure to mixed volatile organic compounds on the neurobehavioral test performance in a cross-sectional study of US adults

While the environmental exposure to multiple volatile organic compounds (VOCs) is ubiquitous, its neurobehavioral effects are not well understood. We assessed the associations between short-term exposure to VOC mixtures and neurobehavioral test performances on 497 participants in the Third National Health and Nutrition Examination Survey, using quantile and ordinary least squares regression models. We grouped 10 blood VOCs into 3 mixtures based on the principal component analysis, where Mix1 included benzene, toluene, ethylbenzene, m-/p-xylene, o-xylene, and styrene; Mix2 included chloroform and tetrachloroethene; and Mix3 included 1,1,1-trichloroethane and 1,4-dichlorobenzene. We found a general lack of significant adverse effects with exceptions limited to those with the worst performance (i.e. the top 10 percent) in the simple reaction time test, suggesting that these people were potentially more susceptible to impacts of VOC mixtures. However, further research is needed to clarify the neurobehavioral effects of chronic low-level exposure to VOC mixtures among the general population.