How Farmworkers Face Unequal Toxic Exposure
Integrating NHANES and ToxCast data reveals alarming disparities in pesticide exposure based on occupation and citizenship status
In the vast agricultural landscapes that produce America's food, an invisible threat persists—one that disproportionately affects the very people who put food on our tables.
Pesticide exposure represents a significant public health concern, particularly for agricultural workers who face regular contact with these chemicals through their work. Recent scientific advances have allowed researchers to uncover disturbing disparities in how these toxins affect different populations, revealing that citizenship status can dramatically influence one's toxic burden.
The integration of two powerful datasets—the National Health and Nutrition Examination Survey (NHANES) and the Environmental Protection Agency's Toxicity Forecaster (ToxCast)—has enabled scientists to paint a comprehensive picture of this public health challenge. This innovative approach not only measures pesticide levels in people's bodies but also determines whether these concentrations are sufficient to cause biological harm. The findings reveal a troubling story of environmental injustice and health disparities that demand our attention and action 1 3 .
Pesticides encompass a broad range of chemicals designed to control pests, including:
Historically, persistent pesticides like DDT and chlordane remained in the environment for years, accumulating in soil, water, and living organisms. While many of these were banned decades ago, their residues continue to pose health risks today 1 .
Human exposure occurs through multiple pathways:
For agricultural workers, exposure is particularly intense and frequent, occurring through mixing, applying, and harvesting treated crops. The take-home pathway further extends this risk, as workers can inadvertently carry pesticide residues on their clothing and equipment, exposing family members, including children 7 .
Research has linked pesticide exposure to a staggering array of health problems including endocrine disruption, various cancers, neurological conditions, respiratory issues, and immune system alterations. The World Health Organization estimates that pesticides are responsible for hundreds of thousands of deaths annually worldwide 1 7 .
The National Health and Nutrition Examination Survey (NHANES) is a remarkable ongoing research program conducted by the Centers for Disease Control and Prevention. Unlike typical health surveys, NHANES doesn't just ask questions—it includes comprehensive physical examinations and laboratory testing on a nationally representative sample of Americans.
Through sophisticated chemical analysis techniques like isotope dilution gas chromatography high-resolution mass spectrometry (GC/IDHRMS), NHANES researchers can detect astonishingly low levels of pesticide metabolites in urine and blood samples 1 4 .
While knowing pesticide concentrations in people is valuable, the critical question remains: are these levels high enough to cause harm? This is where the Toxicity Forecaster (ToxCast) program comes in.
Developed by the Environmental Protection Agency, ToxCast uses high-throughput screening technologies to test thousands of chemicals against hundreds of biological targets. The program establishes dose-response curves for each chemical and determines the Activity Concentration at Cutoff (ACC)—the minimum concentration at which a chemical produces a biologically significant effect 1 8 .
| Pesticide | Type | Detection Rate | Primary Exposure Routes |
|---|---|---|---|
| 2,4-dichlorophenoxyacetic acid | Herbicide | High | Agricultural application, food residues |
| β-hexachlorocyclohexane (BHC) | Insecticide | Moderate | Historical contamination, persistent in environment |
| p,p'-DDT | Insecticide | Moderate | Historical contamination, persistent in environment |
| p,p-DDE | DDT metabolite | High | Breakdown product of DDT |
| Malathion | Insecticide | Variable | Agricultural application, mosquito control |
By integrating NHANES biomarker data with ToxCast bioactivity thresholds, scientists can now determine not just who carries pesticides in their bodies, but whether their exposure levels are sufficient to cause biological harm. This innovative approach transforms public health research, moving from simply measuring exposure to understanding its functional implications 1 3 .
Researchers analyzed information from 23,592 non-farmworkers and 844 individuals with farmwork history drawn from NHANES surveys between 1999 and 2014. This substantial sample size provided the statistical power needed to detect even modest differences between groups 1 3 .
Participants were classified as farmworkers if they reported "Agriculture, Forestry and Fishing" as either their current or longest-held industry in the NHANES Occupation Survey. Citizenship status was determined through self-report, with individuals categorized as either U.S. citizens (by birth or naturalization) or non-citizens 1 4 .
The research team focused on twelve commonly detected pesticide biomarkers in NHANES participants. For each pesticide, researchers compared individual biomarker concentrations to established ACC values from ToxCast. If a participant's pesticide level equaled or exceeded the ACC threshold for any biological activity in ToxCast, their exposure was classified as "bioactive" 1 3 .
Using sophisticated statistical models, the research team calculated odds ratios to compare the likelihood of bioactive pesticide exposure between farmworkers and non-farmworkers, and between U.S. citizens and non-citizens. These models adjusted for potential confounding factors like age, education, and socioeconomic status 1 3 .
The study results revealed disturbing disparities. Farmworkers showed significantly higher levels of specific pesticides compared to non-farmworkers. Most notably, levels of 2,4-dichlorophenoxyacetic acid (a common herbicide) were 3.76 times higher in farmworkers, a statistically significant difference (p = 1.33×10⁻⁶) 1 3 .
Overall, farmworkers were 1.15 times more likely to have bioactive pesticide biomarker measurements compared to non-farmworkers. While this increased risk may seem modest, it represents a meaningful difference given the serious health implications of pesticide exposure and the cumulative nature of these chemicals' effects 1 .
Even more striking were the disparities based on citizenship status. Non-U.S. citizens were 1.39 times more likely to have bioactive pesticide biomarker concentrations compared to U.S. citizens (95% CI: 1.17, 1.64). This pattern held even after adjusting for potential confounding factors 1 3 .
When researchers examined specific pesticides, the disparities became even more pronounced. Non-citizens showed dramatically higher exposure to several persistent organic pollutants, highlighting how immigration status intersects with occupational exposure to create compounded health risks for migrant farmworkers 1 3 .
| Pesticide | Odds Ratio (Non-citizen vs. Citizen) | Statistical Significance |
|---|---|---|
| β-hexachlorocyclohexane (BHC) | 8.10 | p = 1.33×10⁻⁶ |
| p,p'-DDT | 7.75 | p = 0.01 |
| p,p-DDE | 2.60 | p = 0.02 |
| Population Group | Adjusted Odds Ratio | 95% Confidence Interval |
|---|---|---|
| Farmworkers vs. Non-farmworkers | 1.15 | 0.87, 1.51 |
| Non-citizens vs. U.S. citizens | 1.39 | 1.17, 1.64 |
| Non-citizen farmworkers vs. Citizen farmworkers | 1.31 | 0.75, 2.30 |
Perhaps most importantly, the study revealed that many farmworkers—particularly those without citizenship—are regularly exposed to pesticide concentrations that are biologically active according to ToxCast data. This means their exposure isn't just detectable; it's potentially causing harm at the cellular level, contributing to the health disparities observed between agricultural workers and the general population 3 7 .
The dramatic disparities in pesticide exposure based on citizenship status reflect broader social and economic realities. Non-citizen farmworkers, particularly migrant workers, face multiple barriers that increase their vulnerability:
The ToxCast data reveal that pesticides can interfere with biological systems through multiple mechanisms:
The health consequences of these disruptions are particularly concerning for agricultural workers, who may experience daily low-level exposure that accumulates over years or decades 7 .
Understanding how researchers study pesticide exposure requires familiarity with the tools and methods they employ. Below are some of the key components in the environmental health research toolkit:
| Tool/Reagent | Function | Application in Pesticide Research |
|---|---|---|
| Isotope Dilution Gas Chromatography High-Resolution Mass Spectrometry (GC/IDHRMS) | Precise chemical measurement | Quantifying pesticide biomarkers in biological samples at extremely low concentrations |
| ToxCast Database | Bioactivity screening reference | Providing thresholds for biologically significant pesticide concentrations |
| Urinary Creatinine Assay | Normalization metric | Adjusting for urine concentration variations in biomarker measurements |
| Blood Lipid Panel | Normalization metric | Accounting for lipid variations when measuring fat-soluble pesticides |
| Cell-based Bioassays | Mechanism screening | Identifying biological pathways affected by specific pesticides |
| Population Weighting Algorithms | Statistical adjustment | Ensuring representative estimates from complex survey data like NHANES |
The stark disparities revealed by this research demand policy responses. Potential approaches include:
While system-level changes are essential, individuals can also contribute to solutions:
The integration of NHANES and ToxCast data has revealed a troubling story of disparity—one where the people who produce our food face disproportionate exposure to harmful chemicals based on their occupation and citizenship status. These findings highlight the interconnections between environmental health and social justice, reminding us that pesticide exposure isn't just a chemical issue but a human rights issue.