Peak Spray Seasons Track With Worse Mood in Ecuadorian Adolescents and Young Adults
Agricultural pesticide exposure did not present as a distant environmental abstraction in this 2-year ecological momentary assessment study; it mapped onto day-to-day emotional and behavioral change. Across a floricultural region in Ecuador, peak spray seasons were associated with worse negative affect, greater behavioral dysregulation, and more fatigue and difficulty concentrating in adolescents and young adults. The pattern is clinically important because it suggests that seasonal pesticide use may coincide with short-term neurobehavioral shifts rather than only long-latency toxic effects.
The study followed 496 participants over 2.5 years and captured 14,332 mood assessments through one single assessment and nine 10-day bursts. That design matters because ecological momentary assessment reduces recall bias and catches fluctuations in real time, when irritability, anxiety, tiredness, and impulsivity are still embedded in daily life rather than flattened by memory. In regions where pesticide application rises and falls with the agricultural calendar, the brain and behavior may be responding on a similarly cyclical schedule.
Repeated Mood Sampling Revealed Seasonal Within-Person Changes
Investigators evaluated 10 peak and off-peak pesticide spray seasons and linked them to four mood domains. Negative affect included sadness, anxiety, stress, and anger; the mean score was 2.79 with a standard deviation of 1.32. Positive affect covered happiness and motivation, with a mean of 4.21 and standard deviation of 1.60. Behavioral dysregulation captured aggression and impulsivity, averaging 1.86 with a standard deviation of 1.29, while fatigue and concentration problems averaged 3.25 with a standard deviation of 1.34.
Generalized linear mixed models were used to estimate pooled, between-person, and within-person associations while adjusting for demographic and longitudinal factors. The strongest signal came from within-person change, which means participants tended to do worse during peak spray seasons than during their own off-peak periods. In environmental health research, within-person shifts are especially persuasive because they reduce confounding from fixed differences between people, such as baseline temperament, neighborhood conditions, or family background.
Peak spray seasons were associated with higher negative affect, with a beta of 0.11 and confidence limits of 0.06 to 0.16. Behavioral dysregulation also rose, with a beta of 0.10 and confidence limits of 0.05 to 0.15. Fatigue and difficulty concentrating increased as well, with a beta of 0.06 and confidence limits of 0.001 to 0.12. Positive affect did not materially change, with a beta of 0.01 and confidence limits of -0.05 to 0.07.
Positive mood held steady while irritability and dysregulation worsened.
Why Pesticide Cycles May Matter for the Developing Brain
The biological plausibility rests on how pesticide exposure may affect neural systems tied to emotion regulation, attention, and impulse control. Seasonal spray peaks can create repeated exposure pressure during critical developmental years, when the adolescent and young adult brain is still refining executive control and stress responsiveness. Even modest perturbations in these systems can surface first as poorer concentration, lowered frustration tolerance, heightened anger, or a sense of being mentally slowed.
In practical terms, the mood domains that shifted most are the ones adolescents and young adults need to navigate school, work, family responsibility, and social conflict. Fatigue and impaired concentration can disrupt classroom performance and daily functioning, while behavioral dysregulation can strain interpersonal relationships and increase risk in work environments already shaped by agricultural labor demands. The study does not claim a diagnosis or a clinical syndrome, but it does show a seasonal neurobehavioral signal that warrants attention.
Sex and Occupation Shaped the Pattern of Risk
The associations were not uniform across all participants. Sex modified the relationship with anger, and the increase in anger during peak spray seasons was stronger among males than females. Occupation also mattered: floricultural workers experienced greater behavioral dysregulation and lower positive affect than non-workers.
Those effect modifications point toward exposure intensity as a plausible driver. People working in floriculture are more likely to be in closer proximity to spraying activities, whether through direct work tasks, drift, contaminated surfaces, or repeated contact over time. Cohabitation with a floricultural worker was also assessed, reflecting another pathway for household exposure, although the abstract does not present a separate effect estimate for that factor.
The occupational signal is especially concerning because it moves the question beyond ambient community exposure and into the daily realities of work. When mood and impulse control worsen during spray peaks, the consequences can extend from individual distress to workplace safety, family interactions, and health-seeking behavior.
Ecological Momentary Assessment May Detect Subtle Neurobehavioral Harm
This study also argues for a measurement shift. Traditional questionnaires often miss short-lived changes that appear and fade with environmental conditions. EMA captures the lived texture of exposure by asking people how they feel across repeated time points, which makes it well suited to seasonal toxicology and occupational health research. In this setting, the method picked up changes that were tied to the agricultural calendar rather than to a single cross-sectional snapshot.
Because the analysis drew on repeated observations across 10 spray seasons, it offers a more dynamic view of pesticide-related risk than a one-time survey could provide. The finding that negative affect, dysregulation, and fatigue rose during peak spray periods suggests that environmental exposure may be reflected in daily functioning before it becomes obvious in formal psychiatric assessment. That is a useful signal for future studies that pair exposure biomarkers with repeated behavioral sampling.
What This Preprint Can and Cannot Establish
This is a preprint and has not undergone peer review, so the findings should be treated as provisional. The abstract does not provide exposure biomarker data, specific pesticide classes, or effect sizes translated into absolute clinical risk, and those omissions limit causal interpretation. Seasonal association is not the same as proof of toxicity, even when the timing is compelling and the within-person pattern is consistent.
Still, the study defines a credible concern: repeated peak pesticide spray seasons were linked to worse emotional and behavioral functioning in a young population living in an agricultural region. The next step is to determine which exposures drive the signal, whether biologic markers track alongside symptoms, and whether reducing spray-related exposure can blunt the seasonal rise in irritability, fatigue, and concentration problems.