Pesticide Exposure with Disproportionate Effects Increases Risk of Asthma

(Beyond Pesticides, August 16, 2023) A study published in Environmental Science and Pollution Research further supports the indication that exposure to organophosphate insecticides (OPs) increases the risk of asthma among the U.S. general population. According to the Asthma and Allergy Foundation of America, “The burden of asthma in the United States falls disproportionately on people with low-income, senior adults, and Black, Hispanic and American Indian/Alaska Native people,” making these groups more susceptible to developing this chronic lung disease upon OP exposure.  

Organophosphorus pesticides have a wide range of biological uses—from insecticides to flame retardants—that make these chemicals ubiquitous, significantly contributing to ecosystem contamination. Furthermore, while organophosphates have less bioaccumulation potential, residues are consistently present in human and animal blood, urine, tissues, and milk. Although research demonstrates that OPs are highly toxic, there remains an inadequate understanding of how OP exposure impacts body systems like the repository system.

The respiratory system is essential to human survival, regulating gas exchange (oxygen-carbon dioxide) in the body to balance acid and base tissue cells for normal function. However, damage to the respiratory system can cause several issues—from asthma and bronchitis to oxidative stress that triggers the development of extra-respiratory manifestations like rheumatoid arthritis and cardiovascular disease. Therefore, the rise in respiratory illnesses and organophosphate use over the last three decades is highly concerning, especially as research fails to identify an exact cause for the increase in respiratory disease cases.

Focusing on non-institutionalized U.S. adults, researchers gathered representative information on health and nutritional well-being from the Centers for Disease Control and Prevention’s (CDC’s) National Health and Nutrition Examination Survey (NHANES). In total, 6,009 adults aged from 20 to 85 years old represented the 313.5 million adults in the non-institutionalized U.S. population. The study detected OP exposure using the urinary concentrations of six metabolites of dialkyl phosphates (DAPs), an indicator of OP concentration in the body. A survey-multivariable logistic regression (SMLR), a generalized weighted quantile sum (WQS) regression, and Bayesian kernel machine regression (BKMR) evaluated the link between OPs and asthma.

The study finds that of the 6,009 participants, 842 participants have asthma. Upon examining urine samples of the 842 patients, four out of the six DAPs were present—dimethyl phosphate (DMP), diethyl phosphate (DEP), dimethyl thiophosphate (DMTP), and dimethyl dithiophosphate (DMDTP)—demonstrating a positive association with asthma in adults. The strongest associations between asthma and OPs occur more strongly among females, non-Hispanic White populations, and individuals lacking physical activity. Thus, OP exposure can elevate asthma risk in the general population.

Working in close contact with pesticides throughout one’s lifetime increases the risk of asthma, Chronic Obstructive Pulmonary Disease (COPD), and other respiratory issues. Thus, the connection between pesticides and associated respiratory risks is nothing new, as many studies link pesticide use and residue to various respiratory illnesses. Studies find pesticide exposure can trigger asthma attacks and also causes asthma, as exposure to insecticides before the age of five can increase the risk of asthma diagnosis, with toddlers twice as likely to become asthmatic. Furthermore, Significant disparities in asthma morbidity and mortality disproportionately impact low-income populations, people of color, and children living in inner cities.

Chronic inhalation of agriculture-related dust (e.g., particulates from grains, feed, soils, and biological aerosols from plant and animal matter that may harbor synthetic pesticide and fertilizer residues) can increase airway inflammatory diseases, including asthma, chronic bronchitis, and COPD. The particulates in dust play a part in disease development, but so, too, do the various microbiota that may be part of a dusty agricultural environment. A disruption of the homeostasis of the human microbiome (known as dysbiosis) can increase the risk of asthma and other respiratory diseases. In addition, pesticide exposures can alter the gut microbiome, which mediates a significant portion of the human immune response.

Many researchers, including those in this study, suggest an increase in environmental pollutants like pesticides may be responsible for the influx of respiratory diseases. Regarding this study, OPs have a significant influence on respiratory pathology. This chemical class has a similar mode of action as cholinesterase inhibitors, which means they bind to receptor sites for the enzyme acetylcholinesterase, or AChE, essential to normal nerve impulse transmission. In binding to these receptor sites, cholinesterase inhibitors inactivate AChE and prevent the clearing of acetylcholine. The buildup of acetylcholine can lead to acute impacts, such as uncontrolled, rapid twitching of some muscles, paralyzed breathing, convulsions, and, in extreme cases, death. The compromise of neural transmission can have broad systemic impacts on the function of multiple body systems, including the respiratory system.

This study also adds to the growing body of research demonstrating disproportionate risk to certain population groups from chemical exposure. The stronger association between asthma, OPs, and women highlights sex-specific disparities characterized by chemical metabolization (breakdown) and elimination in the body. OPs exhibit endocrine-disrupting properties that may alter estrogen or testosterone activity and receptors, resulting in differences in the clearance rate and toxicity of OPs. For instance, a 2018 study finds female rats manifest airway hyperactivity—a characteristic asthma symptom—at lower OP doses than males. Additionally, CDC data establishes women as having a higher prevalence of asthma incidence compared to men. Low-income populations, people of color, and children living in inner cities also experience disproportionately high morbidity and mortality due to asthma. For instance, African Americans are at least three times more likely than whites to die from asthma. Therefore, any time policies allow regulators to permit the use of pesticides with known asthma effects, a disproportionate impact is felt among these communities. 

Despite the difference in methods, the study emphasizes that the data results remain consistent. “Though with different study designs, objectives, and populations, our study found plenty of evidence that is consistent with previous similar studies which explore the complicated associations of OPI metabolites with asthma.” The study concludes, “Our findings suggest that more urinary OPIs exposure may be associated with an increased risk of asthma in the general US adults. Meanwhile, further prospective studies are needed to confirm the causality between OPIs exposure and asthma and explore the potential harm of low-dose but chronic exposure to OPIs in the development of asthma.”

In the U.S., over 25 million people live with asthma. The increasing rate of respiratory pathology since the 1980s demonstrates a need for better environmental policies and protocols surrounding contaminants like pesticides. Considering respiratory diseases represent a significant health issue for agricultural workers—who often experience pesticide exposure at higher rates due to occupation—it is essential to understand the association between pesticide exposure and respiratory pathology or the study of causes and effects of respiratory diseases. Furthermore, with a new report finding an association between air pollution and higher death rates (9%) related to SARS-CoV-2 (COVID-19), global leaders must eliminate excessive pesticide use to mitigate respiratory diseases’ impacts on human health. Policies should enforce stricter pesticide regulations and increase research on the long-term impacts of pesticide exposure. Beyond Pesticides tracks the most recent studies related to pesticide exposure through our Pesticide Induced Diseases Database (PIDD). This database supports the clear need for strategic action to shift away from pesticide dependency. For more information on the multiple harms of pesticides, see PIDD pages on asthma/respiratory effects and other diseases. Learn more about how inadequate pesticide use regulations, including organophosphates, can adversely affect human and environmental health; see Beyond Pesticides’ Pesticides and You article “Highly Destructive Pesticide Effects Unregulated.”

Beyond Pesticides advocates a precautionary approach to pest management in land management and agriculture by transiting to organic. Buying, growing, and supporting organic can help eliminate the extensive use of pesticides in the environment and from your diet. For more information on how organic is the right choice for consumers and the farmworkers who grow our food, see the Beyond Pesticides webpage, Health Benefits of Organic Agriculture. Removing pesticides from parks that disproportionately affect people of color in the community and as landscapers. Help convert your parks, playing fields, and schoolyards to organic land management through Beyond Pesticides’ Parks for a Sustainable Future program. 

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

Source: Environmental Science and Pollution Research