ENVIRONMENTAL

HEALTH 

PERSPECTIVES

ENVIRONMENTAL

HEALTH 

PERSPECTIVES

National Institutes of Health

U.S. Department of Health and Human Services 

Acute Pesticide Illnesses Associated with 

Off-Target Pesticide Drift from Agricultural 

Applications — 11 States, 1998–2006

Soo-Jeong Lee, Louise Mehler, John Beckman,

Brienne Diebolt-Brown, Joanne Prado,

Michelle Lackovic, Justin Waltz, Prakash Mulay, Abby Schwartz,

Yvette Mitchell, Stephanie Moraga-McHaley, Rita Gergely,

Geoffrey M Calvert

doi: 10.1289/ehp.1002843 (available at http://dx.doi.org/)

Online 6 June 2011

ehponline.org

ehp
1

Acute Pesticide Illnesses Associated with Off-Target Pesticide Drift from Agricultural 

Applications — 11 States, 1998–2006 

Soo-Jeong Lee1, Louise Mehler2, John Beckman3, Brienne Diebolt-Brown4, Joanne Prado5, 

Michelle Lackovic6, Justin Waltz7, Prakash Mulay8, Abby Schwartz9, Yvette Mitchell10, 

Stephanie Moraga-McHaley11, Rita Gergely12, Geoffrey M Calvert1

1Division of Surveillance, Hazard Evaluations, and Field Studies, National Institute for 

Occupational Safety and Health, Centers for Disease Control and Prevention, Cincinnati, Ohio 

2California Environmental Protection Agency, Sacramento, California 

3

Public Health Institute, Oakland, California 

4

Texas Department of State Health Services, Austin, Texas 

5Washington State Department of Health, Olympia, Washington 

6

Louisiana Department of Health and Hospitals, New Orleans, Louisiana 

7Oregon Health Authority, Portland, Oregon 

8

Florida Department of Health, Tallahassee, Florida 

9Michigan Department of Community Health, Lansing, Michigan 

10New York State Department of Health, Troy, New York 

11New Mexico Department of Health, Albuquerque, New Mexico 

12Iowa Department of Public Health, Des Moines, Iowa 

Corresponding author: Geoffrey Calvert, MD, MPH 

 NIOSH 

4676 Columbia Parkway, R-17 

Cincinnati, OH 45226 

Phone: 513-841-4448 

E-mail: jac6@cdc.gov 

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Running Title: Illnesses Associated with Agricultural Pesticide Drift 

Key Words: Agriculture, drift, pesticides, poisoning, surveillance 

Acknowledgements: Funding support was provided by NIOSH, EPA, and the state agencies that 

contributed data. The authors thank Walter Alarcon, Sangwoo Tak and Jia Li for assistance in 

conducting this study and Marie Sweeney, Michael O’Malley, Jennifer Sass, Misty Hein, and 

EPA for providing comments to improve this manuscript. 

Conflict of interest: The authors have no conflicts of interest to declare. Mr. Beckman is 

assigned to the California Department of Public Health by his employer (Public Health Institute 

[PHI]), and has never been involved in any advocacy activities of PHI. 

Disclaimer: The findings and conclusions in this report are those of the authors and do not 

necessarily represent the views of NIOSH or each author’s state agency. 

Abbreviations: 

CDC Centers for Disease Control and Prevention 

CDPR California Department of Pesticide Regulation 

CI Confidence Interval 

CIC Census Industry Codes 

EPA U.S. Environmental Protection Agency 

FIFRA Federal Insecticide, Fungicide, and Rodenticide Act 

NIOSH National Institute for Occupational Safety and Health 

OR Odds Ratio 

PISP Pesticide Illness Surveillance Program 

SENSOR Sentinel Event Notification System for Occupational Risks 

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Abstract 

Background: Pesticides are widely used in agriculture and off-target pesticide drift results in 

exposures to workers and the public. Objective: Estimate the incidence of acute illnesses from 

pesticide drift from outdoor agricultural applications, and describe drift exposure and illness 

characteristics. Methods: Data were obtained from the National Institute for Occupational Safety 

and Health’s Sentinel Event Notification System for Occupational Risks-Pesticides Program and 

the California Department of Pesticide Regulation. Drift included off-target movement of 

pesticide spray, volatiles, and contaminated dust. Acute illness cases were characterized by 

demographics, pesticide and application variables, health effects, and contributing factors. 

Results: During 1998–2006, 2,945 cases associated with agricultural pesticide drift were 

identified from 11 states. Forty-seven percent had exposures at work, 92% experienced low 

severity illness, and 14% were children (<15 years). The annual incidence ranged from 1.39 to 

5.32 per million persons over the 9-year period. The overall incidence (in million person-years) 

was 114.3 for agricultural workers, 0.79 for other workers, 1.56 for nonoccupational cases, and 

42.2 for residents in 5 agriculture-intensive counties in California. Soil applications with 

fumigants were responsible for the largest proportion (45%) of cases. Aerial applications 

accounted for 24% of cases. Common factors contributing to drift cases included weather 

conditions, improper seal of the fumigation site, and applicator carelessness near non-target 

areas. Conclusions: Agricultural workers and residents in agricultural regions were found to 

have the highest rate of pesticide poisoning from drift exposure, and soil fumigations were a 

major hazard causing large drift incidents. These findings highlight areas where interventions to 

reduce off-target drift could be focused. 

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Introduction 

Pesticide drift, which is the off-target movement of pesticides, is recognized as a major 

cause of pesticide exposure affecting people as well as wildlife and the environment. In the 

United States in 2004, more than 1,700 investigations were conducted in 40 states due to drift 

complaints and 71% of the incidents confirmed that drift arose from pesticide applications to 

agricultural crops (Association of American Pesticide Control Officials, 2005). Pesticide drift 

has been reported to account for 37-68% of pesticide illnesses among U.S. agricultural workers 

(California Department of Pesticide Regulation [CDPR] 2008; Calvert et al. 2008). Community 

residents, particularly in agricultural areas, are also at risk of exposure to pesticide drift from 

nearby fields. Agricultural pesticides are often detected in rural homes (Harnly et al. 2009; 

Quandt et al. 2004). Alarcon et al. (2005) reported that 31% of acute pesticide illnesses that 

occurred at U.S. schools were attributed to drift exposure. 

The occurrence and extent of pesticide drift is affected by many factors such as the nature 

of the pesticide (e.g., fumigants are highly volatile, increasing their propensity for off-site 

movement [U.S. Environmental Protection Agency (EPA), 2010]), equipment and application 

techniques (e.g., size and height of the spray nozzles), the amount of pesticides applied, weather 

(e.g., wind speed, temperature inversion), and operator care (Hofman and Solseng 2001). 

Pesticide applicators are required to use necessary preventive measures and comply with label 

requirements to minimize pesticide drift. Pesticide regulations such as the Federal Insecticide, 

Fungicide, and Rodenticide Act (FIFRA) and the Worker Protection Standard, an amendment to 

FIFRA, require safety measures for minimizing the risk of pesticide exposure, and many states 

have additional regulations for drift mitigation (Feitshans 1999). 

Better understanding about the magnitude, trend, and characteristics of pesticide 

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poisoning from drift exposure of agricultural pesticides would assist regulatory authorities with 

regulatory, enforcement, and education efforts. The purpose of this study was to estimate the 

magnitude and incidence of acute pesticide poisoning associated with pesticide drift from 

outdoor agricultural applications in the U.S. during 1998–2006 and describe the exposure and 

illness characteristics of pesticide poisoning cases arising from off-target drift. Factors associated 

with illness severity and large events were also examined. 

Materials and Methods 

Data on acute pesticide poisoning cases were obtained from the National Institute for 

Occupational Safety and Health (NIOSH)’s Sentinel Event Notification System for Occupational 

Risks (SENSOR)-Pesticides program and CDPR’s Pesticide Illness Surveillance Program 

(PISP). The SENSOR-Pesticides program has collected pesticide poisoning surveillance data 

from 12 states, using standardized definitions and variables available since 1998 (Calvert et al. 

2010). This study included data from 11 states for the following years: Arizona (1998–2000), 

California (1998–2006), Florida (1998–2006), Iowa (2006), Louisiana (2000–2006), Michigan 

(2000–2006), New Mexico (2005–2006), New York (1998–2006), Oregon (1998–2006), Texas 

(1998–2006), and Washington (2001–2006). North Carolina, which joined SENSOR-Pesticides 

in 2007, was not included. Because each state removes personal identifiers from the data prior to 

submission to the Centers for Disease Control and Prevention (CDC), this study was exempt 

from consideration by the federal Human Subjects Review Board. 

Participating surveillance programs identify cases from multiple sources including health 

care providers, poison control centers, workers’ compensation claims, and state or local 

government agencies. They collect information on the pesticide exposure incident through 

investigation, interview, and/or medical record review. On some occasions such as large drift 

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events, active surveillance is undertaken for further case finding by interviewing individuals 

living or working within the vicinity affected by the off-target drift (Barry et al. 2010). Although 

SENSOR-Pesticides focuses primarily on occupational pesticide poisoning surveillance, all of 

the SENSOR-Pesticides state programs except California collect data on both occupational and 

nonoccupational cases. In California, PISP captures both occupational and nonoccupational 

cases. SENSOR-Pesticides and PISP classify cases based on the strength of evidence for 

pesticide exposure, health effects, and the known toxicology of the pesticide, and use slightly 

different criteria for case classification categories (Calvert et al. 2010). This study restricted the 

analyses to cases classified as definite, probable, possible, or suspicious by SENSOR-Pesticides 

and definite, probable, or possible by PISP. Analyses restricted to definite and probable cases 

only were also performed. Because these findings were similar to those that included all four 

classification categories (i.e., definite, probable, possible, or suspicious), only the findings that 

used the four classification categories were reported. 

In this study, a drift case was defined as acute health effects in a person exposed to 

pesticide drift from an outdoor agricultural application. Drift exposure included any of the 

following pesticide exposures outside their intended area of application: 1) spray, mist, fumes, or 

odor during application; 2) volatilization, odor from a previously treated field, or migration of 

contaminated dust; and 3) residue left by offsite movement. It should be noted that our drift 

definition is broader than EPA’s “spray or dust drift” definition, which excludes post-application 

drift caused by erosion, migration, volatility, or windblown soil particles (EPA 2001). A drift 

event was defined as an incident where one or more drift cases experienced drift exposure from a 

particular source. Both occupational and nonoccupational cases were included. An occupational 

case was defined as an individual exposed while at work. Among occupational cases, 

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agricultural workers were identified using 1990 and 2002 Census Industry Codes (CIC): (1990 

CIC = 010, 011, 030; 2002 CIC = 0170, 0180, 0290) (U.S. Census Bureau 1992, 2005). 

The process of case selection is presented in Figure 1. We selected cases if exposed to 

pesticides applied for agricultural use including farm, nursery, or animal production, and 

excluded cases exposed by ingestion, direct spray, spill, or other direct exposure. We then 

manually reviewed all case reports and excluded persons exposed to pesticides used for indoor 

applications (e.g., greenhouses, produce packing facilities), persons exposed within a treated area 

(e.g., pesticide applicators exposed by pesticides blown back by wind, workers working within 

or passing through the field being treated), and persons exposed to pesticides being mixed, 

loaded, or transported. Drift cases therefore represented the remaining 9% and 27% of all 

pesticide illness cases identified by the SENSOR-Pesticides and PISP, respectively. We also 

searched for duplicates from the two programs identifying California cases. Since personal 

identifiers were unavailable, date of exposure, age, sex, active ingredients, and county were used 

for comparison. A total of 60 events and 171 cases were identified by both California programs. 

These were counted only once and were included in the PISP total only. 

Drift events and cases were analyzed by the following variables: state, year and month of 

exposure, age, gender, location of exposure, health effects, illness severity, pesticide 

functional/chemical class, active ingredient, target of application, application equipment, 

detection of violations, and factors contributing to the drift incident. EPA toxicity categories 

ranging from toxicity I (the most toxic) to IV (the least toxic) were assigned to each product 

(EPA 2007). Cases exposed to multiple products were assigned to the toxicity category of the 

most toxic pesticide they were exposed to. Illness severity was categorized into low, moderate, 

and high using criteria developed by the SENSOR-Pesticides program (Calvert et al. 2010). Low 

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severity refers to mild illnesses that generally resolve without treatment. Moderate severity refers 

to illnesses that are usually systemic and require medical treatment. High severity refers to lifethreatening or serious health effects that may result in permanent impairment or disability. 

Contributing factors were retrospectively coded with available narrative descriptions. One 

NIOSH researcher (SJL) initially coded contributing factors for all cases. Next, for SENSORPesticides cases, state health department staff reviewed the codes and edited as necessary. Any 

discrepancies were resolved by a second NIOSH researcher (GMC). For PISP cases, relatively 

detailed narrative descriptions were available for all incidents. These narratives summarize 

investigation reports provided by county agriculture commissioners, who investigate all 

suspected pesticide poisoning cases reported in their county. After initial coding, two NIOSH 

researchers discussed those narratives that lacked clarity to reach consensus. 

Data Analysis 

Data analysis was performed with SAS v 9.1. Descriptive statistics were used to 

characterize drift events and cases. Incidence rates were calculated by geographic region, year, 

sex, and age group. The numerator represented the total number of respective cases in 1998–

2006. Denominators were generated using the Current Population Survey microdata files for the 

relevant years (U.S. Census Bureau 2009). For total and nonoccupational rates, the denominators 

were calculated by summing the annual average population estimates. A nonoccupational rate for 

agriculture-intensive areas was calculated by selecting the five counties in California where the 

largest amount of pesticides were applied in 2008 (Fresno, Kern, Madera, Monterey, and Tulare) 

(CDPR 2010). For occupational rates, the denominators were calculated by summing the annual 

employment estimates including both “employed at work” and “employed but absent.” The 

denominator for agricultural workers was obtained using the same 1990/2002 CIC codes used to 

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define agricultural worker cases (U.S. Census Bureau 1992, 2005). Moreover, in California

where data on pesticide usage are available, incidence was calculated per number of agricultural 

applications and amount of pesticide active ingredient applied (CDPR 2009). Incidence trend 

over time was examined by fitting a Poisson regression model of rate on year and deriving the 

regression coefficient and its 95% confidence intervals (CIs). 

Drift events were dichotomized by the size of events into small events involving < 5 

cases and large events involving ≥ 5 cases. This cut point was based on one of the criteria used 

by CDPR to prioritize event investigations (CDPR 2001). Illness severity was dichotomized into 

low and moderate/high. Simple and multivariable logistic regressions were performed. Odds 

ratios (OR) and 95% CIs were calculated. 

Results

Number and Incidence of Drift Events and Cases 

From 1998 through 2006, we identified 643 events and 2,945 illness cases associated 

with pesticide drift from agricultural applications (Figure 1). Of these, 382 events (59%) and 791 

cases (27%) were identified by SENSOR-Pesticides (excluding 60 events and 171 cases also 

identified by PISP), and 261 events (41%) and 2,154 cases (73%) were identified by PISP. Drift 

cases consisted of 53 definite (1.8%), 2,019 probable (68.6%), 823 possible (27.9%), and 50 

suspicious (1.7%) cases. Among drift cases, 1,565 (53%) were nonoccupational and 1,380 (47%) 

were occupational. Agricultural workers accounted for 73% (n=1,010) of the occupational cases. 

A total of 340 events (53%) occurred between May and August and these involved 1,407 cases 

(48%). 

The overall incidence rate of drift-related pesticide poisoning was 2.93/million personyears (Table 1). The rates of nonoccupational and occupational drift-related pesticide poisoning 

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were 1.56 and 2.89, respectively. Among occupational cases, the rate was 114.3 for agricultural 

workers and 0.79 for all other workers. Among nonoccupational cases identified in California, 

the rate was 42.2 for residents in the 5 agriculture-intensive counties and 0.61 for residents of all 

other California counties (data not shown). The rate was highest in the western states for both 

nonoccupational and occupational cases (Table 1). In California, per 100,000 agricultural 

applications, 1.6 drift events and 11.8 cases were identified; per 10 million pounds applied, 1.9 

events and 14.4 cases were identified (data not shown). 

The total annual incidence rate ranged from 1.39 to 5.32 per million persons over the 9-

year time period (Table 1). Over time, the rate of drift cases involved in large events showed the 

same pattern as the rate of all drift cases, showing a spike every three years (Figure 2). The rate 

of drift cases involved in small events varied within a narrow range from 0.49 to 1.11 and there

was no significant rate change over this time period; however, for the 5 states that provided data 

for all 9 years, a significant decrease in the rate was found (i.e., an estimated 9% decrease per 

year, 95% CI 3–15%, p = 0.004). 

Men comprised 53% of all cases (Table 1). The rate by gender was similar among 

nonoccupational cases. For occupational cases, the rate was 1.25 times higher in male workers 

than female workers, but 2.89 times higher in female agricultural workers than male agricultural 

workers. Among nonoccupational cases, children aged < 15 years accounted for 33% of cases 

with known age and showed the highest rate (1.88/million person-years) (Table 1). 

Responsible Pesticides, Application Targets, and Application Equipment 

In 430 (67%) of 643 drift events, exposure was to pesticides from a single functional 

class (Table 2). Insecticides were the most commonly identified (31% of events), accounting for 

23% (n=678) of all cases. Fumigants were involved in only 8% of drift events but accounted for 

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45% (n=1,330) of all cases. Organophosphorous compounds were the most common pesticide 

chemical class involved in drift events (28%). Most cases (66%) were exposed to toxicity I (high 

toxicity) pesticides. 

For the intended application targets, 71% of events involved applications to fruit, 

grain/fiber/grass, or vegetable crops (Table 2). Soil applications accounted for 9% of drift events 

and 45% of all cases. For application equipment, aerial applications (e.g., by airplane) were 

responsible for 39% of drift events, accounting for 24% of all cases. Chemigation (i.e., 

application via an irrigation system) or soil injectors were used in 7% of drift events and 

accounted for 44% of cases. All soil injector events and 95% of chemigation events involved the 

use of fumigants applied to soil (data not shown). 

Location of Exposure and Health Effects 

Common exposure locations were private residences (44%) and farms/nurseries (37%) 

(Table 3). More than half of cases experienced ocular (58%) or neurological (53%) 

symptoms/signs and illness severity was low for most cases (92%) (Table 3). Moderate/high 

severity illness was significantly associated with female sex, older age groups, and exposure to 

multiple active ingredients, before and after controlling for other case and pesticide 

characteristics (p < 0.05) (Table 4). Compared to fumigants, exposures to herbicides, 

insecticides, or multiple classes were significantly associated with moderate/high severity illness. 

Table 5 provides the list of 15 active ingredients most commonly found among drift cases and 

their distribution according to illness severity. 

Size of Drift Events 

Most drift events involved a single case (n=387, 60%). For multi-person events, 168 

events (26% of the total) involved 2–4 cases, 78 events (12%) involved 5–29 cases, and 10 

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events (1.5%) involved ≥ 30 cases. Table 6 provides details on the 10 largest events. Detailed 

investigation reports of some of these events are available elsewhere (Barry et al. 2010; CDC 

2004; O'Malley et al. 2005). The occurrence of large versus small events (events with ≥5 cases 

compared with <5 cases) was significantly associated with the use of fumigants (compared to 

insecticides), and applications to soil, small fruit crops, or leafy vegetable crops (compared to 

other targets) (p < 0.05) (Table 7). 

Contributing Factors to Drift Incidents 

Of 299 drift events with information on violations of pesticide regulations, 220 (74%) 

had one or more violations and accounted for 2,093 cases (89% of cases with violation 

information) (Table 8). However, not all of the observed violations may have directly

contributed to the drift exposure. Factors contributing to the drift exposure were identified in 164 

events accounting for 1,544 (52%) cases. Common contributing factors identified for drift events 

included applicators’ carelessness near/over non-target sites (e.g., flew over a house, did not turn 

off a nozzle at the end of the row), unfavorable weather conditions (e.g., high wind speed, 

temperature inversion), and poor communication between applicators/growers and others. 

Improper seal of the fumigation site (e.g., tarp tear, early removal of seal), identified in 9 events, 

accounted for the largest proportion (60%) of cases with contributing factors identified. 

The distance between the application and exposure site was identified in 1,428 (48%) 

cases (Table 8). Occupational cases accounted for 68% of cases exposed within 0.25 miles of the 

application site, and nonoccupational cases accounted for 73% of cases exposed over 0.25 miles 

away. 

Discussion 

To our knowledge, this is the first comprehensive report of drift-related pesticide 

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poisoning in the US. We identified 643 events involving 2,945 illness cases associated with 

pesticide drift from outdoor agricultural applications during 1998–2006. Pesticide drift included 

pesticide spray, mist, fume, contaminated dust, volatiles and odor that moved away from the 

application site during or after the application. While the incidence for cases involved in small 

drift events (<5 cases) tended to decrease over time, the overall incidence maintained a 

consistent pattern chiefly driven by large drift events. Large drift events were commonly 

associated with soil fumigations. 

Occupational Exposure 

Occupational pesticide poisoning is estimated at 12–21/million U.S. workers per year 

(Calvert et al. 2004; Council of State and Territorial Epidemiologists n.d.). Compared to those 

estimates, our estimated incidence of 2.89/million worker-years suggests that 14–24% of 

occupational pesticide poisoning may be attributed to off-target drift from agricultural 

applications. It should be noted that our study included pesticide drift from outdoor applications 

only and excluded workers exposed within the application area. Our findings show that the risk 

of illness resulting from drift exposure is largely borne by agricultural workers, and the incidence 

(114.3/million worker-years) was 145 times greater than that for all other workers. Current 

regulations require agricultural employers to protect workers from exposure to agricultural 

pesticides, and pesticide product labels instruct applicators to avoid contacting humans directly 

or through drift (EPA 2009). 

Our study found that the incidence of drift-related pesticide poisoning was higher among 

female and younger agricultural workers and in western states. These groups were previously 

found to have a higher incidence of pesticide poisoning (Calvert et al. 2008). It is not known why 

the incidence is higher among female and younger agricultural workers, but hypotheses include 

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that these groups are at greater risk of exposure, that they are more susceptible to pesticide 

toxicity, or that they are more likely to report exposure/illness or seek medical attention. 

However, consistent patterns were not observed among workers in other occupations, requiring 

further research to identify the explanation. The higher incidence in the western states may 

suggest that workers in this region are at higher risk of drift exposure; however, it may also have 

resulted from better case identification in California and Washington states through their higherstaffed surveillance programs, extensive utilization of workers’ compensation reports in these 

states, and use of active surveillance for some large drift events in California. 

Nonoccupational Exposure 

This study found that more than half of drift-related pesticide poisoning cases resulted 

from nonoccupational exposures and 61% of those were exposed to fumigants. California data 

suggest that residents in agriculture-intensive regions have a 69 times higher risk of pesticide 

poisoning from drift exposure compared to other regions. This may reflect California’s use of 

active surveillance for some large drift events. Children were found to have the greatest risk 

among nonoccupational cases. The reasons are not known but may be because children have

higher pesticide exposures, greater susceptibility to pesticide toxicity or greater medical attention 

seeking by concerned parents. Recently several organizations submitted a petition to the U.S. 

EPA asking the agency to evaluate children’s exposure to pesticide drift and adopt interim 

prohibitions on the use of drift-prone pesticides near homes, schools, and parks (Goldman et al. 

2009). 

Contributing Factors 

Soil fumigation was a major cause of large drift events, accounting for the largest 

proportion of cases. Due to the high volatility of fumigants, specific measures are required to 

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prevent emissions after completion of the application. Given the unique drift risks posed by

fumigants, EPA regulates the drift of fumigants separately from non-fumigant pesticides. EPA 

recently adopted new safety requirements for soil fumigants which took effect in early 2011, and 

include comprehensive measures designed to reduce the potential for direct fumigant exposures, 

reduce fumigant emissions, improve planning, training, and communications, and promote early

detection and appropriate responses to possible future incidents (EPA 2010). Requirements for 

buffer zones are also strengthened. For example, fumigants that generally require a > 300 foot 

buffer zone are prohibited within 0.25 miles (1,320 feet) of “difficult-to-evacuate” sites (e.g., 

schools, daycare centers, hospitals). We found that, of 738 fumigant-related cases with 

information on distance, 606 (82%) occurred > 0.25 miles from the application site, which 

suggests that the new buffer zone requirements, independent of other measures to increase 

safety, may not be sufficient to prevent drift exposure. 

This study also showed the need to reinforce compliance with weather-related 

requirements and drift monitoring activities. Moreover, applicators should be alert and careful, 

especially when close to non-target areas such as adjacent fields, houses, and roads. Applicator 

carelessness contributed to 79 events (48% of 164 events where contributing factors were 

identified), of which 56 events involved aerial applicators. Aerial application was the most 

frequent application method found in drift events, accounting for 249 events (39%). Drift 

hazards from aerial applications have been well documented (CDC 2008; Weppner et al. 2006). 

Applicators should use all available drift management measures and equipment to reduce drift 

exposure, including new validated drift reduction technologies as they become available. 

Limitations

This study requires cautious interpretation especially for variables with missing data on 

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many cases (e.g., age, violation, contributing factors, distance). This study also has several 

limitations. First, our findings likely underestimate the actual magnitude of drift events and cases 

because case identification principally relies on passive surveillance systems. Such underreporting might have allowed the totals to be appreciably influenced by a handful of California 

episodes in which active case-finding located relatively large numbers of affected people. 

Pesticide-related illnesses are underreported due to individuals not seeking medical attention 

(because of limited access to health care or mild illness), misdiagnosis, and health care provider 

failure to report cases to public health authorities (Calvert et al. 2008). Data from the National 

Agricultural Workers Survey suggests that the pesticide poisoning rates for agricultural workers 

may be an order of magnitude higher than those identified by the SENSOR-Pesticides and PISP 

programs (Calvert et al. 2008). Second, the incidence of drift cases from agricultural 

applications may have been underestimated by using crude denominators of total population and 

employment estimates which may also include those who are not at risk. On the other hand, the 

incidence for agricultural workers may have been overestimated if the denominator data 

undercounted undocumented workers. Third, the data may include false-positive cases because 

clinical findings of pesticide poisoning are nonspecific and diagnostic tests are not available or 

rarely performed. Fourth, when data from SENSOR-Pesticides and PISP were combined, some 

duplication of cases and misclassification of variables may have occurred although steps were 

taken to identify and resolve discrepancies. Also there may be differences in case detection 

sensitivity between SENSOR-Pesticides and PISP since the two programs use slightly different 

case definitions. Lastly, contributing factor information was not available for 48% of cases, 

either because an in-depth investigation did not occur, or sufficiently detailed findings were not 

entered into the database. The retrospective coding of contributing factors was often based on 

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limited data and may have produced some misclassification. 

Conclusion 

The study findings suggest that the incidence of acute illness from off-target pesticide 

drift exposure was relatively low during 1998–2006 and most cases presented with low-severity 

illness. However, the rate of poisoning from pesticide drift was 69 times higher for residents in 5 

agriculture-intensive California counties compared with other counties, and the rate of 

occupationally exposed cases was145 times greater in agricultural workers than in nonagricultural workers. These poisonings may largely be preventable through proper prevention 

measures and compliance with pesticide regulations. Aerial applications were the most frequent 

method associated with drift events, and soil fumigations were a major cause of large drift 

events. These findings highlight areas where interventions to reduce pesticide drift could be 

focused. 

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application of metam-sodium, Arvin, California, July 2002. J Agromedicine 10(4):27-42. 

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and residential pesticides in wipe samples from farmworker family residences in North 

Carolina and Virginia. Environ Health Perspect 112(3):382-387. 

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November 2008]. 

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spray drift study: children's exposure to methamidophos in an agricultural community 

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Page 21 of 32
Table 1. Number and incidence ratea of off-target drift events and pesticide poisoning cases by year, region, sex, and age, 11 S

Drift Cases 

Drift Events Occupational Case

All Cases Nonoccupational Cases Ag Worker Casesd Other 

 Variable Count % Count 

Population 

estimateb Rate Count Ratec Count Employment estimateb,d Rate Count E

Total 643 100 2,945 1004.1 2.93 1,565 1.56 1,010 8.83 114.33 370 Year of exposure (# of states included) 

1998 (6) 60 9.3 130 93.6 1.39 46 0.49 45 1.11 40.46 39 

1999 (6) 82 12.8 407 95.0 4.28 273 2.87 72 1.12 64.22 62 2000 (8) 64 10.0 193 110.3 1.75 76 0.69 93 1.24 74.94 24 2001 (8) 88 13.7 177 112.6 1.57 98 0.87 43 1.12 38.47 36 2002 (8) 81 12.6 580 113.7 5.10 271 2.38 281 1.11 252.33 28 2003 (8) 75 11.7 348 116.4 2.99 265 2.28 43 0.79 54.64 40 2004 (8) 47 7.3 232 117.4 1.98 43 0.37 177 0.75 235.33 12 2005 (9) 70 10.9 642 120.6 5.32 409 3.39 168 0.75 224.77 65 2006 (10) 76 11.8 236 124.5 1.90 84 0.67 88 0.84 104.53 64 

Region 

Weste 433 67.3 2,484 397.9 6.24 1,240 3.12 933 4.44 210.20 311 

Southf 193 30.0 426 365.6 1.17 311 0.85 59 3.25 18.17 56 East/Centralg 17 2.6 35 240.6 0.15 14 0.06 18 1.15 15.68 3 

Sex n/a 

Male 1560 491.6 3.17 742 1.51 554 6.90 80.27 264 Female 1360 512.5 2.65 807 1.57 448 1.93 231.90 105 Unknown 25 -- -- 16 -- 8 -- -- 1 

Age n/a 

< 15 418 221.2 1.89 415 1.88 3 -- -- 0 

15–24 398 142.0 2.80 182 1.28 182 1.44 126.39 34 25–34 453 140.0 3.24 140 1.00 240 1.81 132.53 73 35–44 458 156.7 2.92 181 1.16 187 2.08 89.89 90 45–54 306 136.1 2.25 172 1.26 78 1.59 49.00 56 

55–64 164 90.9 1.80 103 1.13 37 1.10 33.61 24 65+ 92 117.2 0.78 80 0.68 9 0.81 11.11 3 Unknown 656 -- -- 292 -- 274 -- -- 90 

a. Per 1,000,000 persons. b. Numbers (in million) were estimated using the Current Population Survey data. Participating years vary by state. Only years of participation were included.c. Denominators were population estimates. d. Cases and employment estimates of agricultural workers were defined with 1990/2002 Census Industry Codes (010, 011, 030; 0170, 0180, 0290). e. Arizona, California, New Mexico, Oregon, Washington f. Florida, Louisiana, Texas g. Iowa, Michigan, New York
23

Table 2. Off-target drift events and pesticide poisoning cases by pesticide and application 

characteristics, 11 states, 1998-2006 

 Drift Cases Drift Events 

(n=643) Total 

(n=2,945) 

Occupational 

(n=1,380) 

Nonoccupational 

(n=1,565) 

 Variable N % N % % %

Pesticide functional class 

Insecticide only 198 30.8 678 23.0 32.9 14.3 

Herbicide only 108 16.8 195 6.6 4.0 8.9 

Fungicide only 29 4.5 64 2.2 3.7 0.8 

Fumigant only 52 8.1 1,330 45.2 27.0 61.2 

Other, single 43 6.7 87 3.0 2.8 3.1 

Multiple 207 32.2 585 19.9 29.4 11.4 

Unknown 6 0.9 6 0.2 0.2 0.2 

Common pesticide chemical classa 

Organophosphorous compound 181 28.1 660 22.4 36.7 9.8 

Inorganic compound 87 13.5 231 7.8 11.1 5.0 

Pyrethroid 52 8.1 207 7.0 9.6 4.7 

Dithiocarbamatesb 47 7.3 726 24.7 22.5 26.5 

N-methyl carbamates 33 5.1 71 2.4 4.1 1.0 

Chlorophenoxy compound 26 4.0 47 1.6 0.9 2.2 

Triazines 11 1.7 34 1.2 1.1 1.2 

Maximum toxicity category 

I 203 31.6 1,944 66.0 59.9 71.4 

II 167 26.0 468 15.9 21.2 11.2 

III 154 24.0 327 11.1 13.6 8.9 

Unknown 119 18.5 206 7.0 5.2 8.6 

Application target 

Fruit crops 189 29.4 588 20.0 27.6 13.2 

Grain/fiber/grass crops 185 28.8 411 14.0 12.8 15.0 

Vegetable crops 85 13.2 374 12.7 22.9 3.7 

Soil 55 8.6 1,337 45.4 27.5 61.2 

Landscape/forest 32 5.0 64 2.2 2.8 1.7 

Undesired plants 29 4.5 44 1.5 0.9 2.0 

Other (e.g., misc. crops, seed, livestock farm) 27 4.2 66 2.2 2.0 2.5 

Unknown 41 6.4 61 2.1 3.6 0.8 

Application equipment 

Aerial applicator 249 38.7 695 23.6 32.0 16.2 

Handheld or backpack sprayer 24 3.7 63 2.1 3.8 0.6 

Chemigation 22 3.4 752 25.5 16.4 33.5 

Soil injector 20 3.1 558 18.9 10.0 26.8 

Other ground applicator 254 39.5 747 25.4 32.6 19.0 

Multiple 8 1.2 41 1.4 0.2 2.4 

Unknown 66 10.3 89 3.0 4.9 1.4 

a. Categories with the largest numbers of cases. Events/Cases can be exposed to multiple categories. 

b. Mostly from single products. 

Page 23 of 32
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Table 3. Location of exposure, health effects, and illness severity of drift cases (n=2,945) 

Variable % 

Location of exposure 

Private residence 44.5 

Farm/Nursery 36.7 

Road/Right-of-way 5.6 

School 3.6 

Agricultural processing facility 2.4 

Other/Unknown 7.2 

Health effecta 

Eye (e.g., pain/irritation/inflammation, lacrimation) 58.2 

Neurological (e.g., headache, paresthesia, dizziness) 52.8 

Respiratory (e.g., dyspnea, respiratory tract pain/irritation, cough) 47.8 

Gastrointestinal (e.g., vomiting, nausea, diarrhea, abdominal pain) 41.5 

Skin (e.g., pruritus, pain/irritation, rash) 14.7 

Cardiovascular (e.g., chest pain) 5.1 

Other (e.g., fatigue, fever) 11.4 

Illness severity 

Low 92.2 

Moderate 7.3 

High 0.5 

a. Cases can be included in multiple categories. 

 

Page 24 of 32
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Table 4. Illness severity by case and pesticide characteristics 

 

High/Moderate 

Severity (n=230) 

Low severity 

(n=2,715) High/Moderate severity (versus Low) 

Variable N % N % OR 95% CI aORb

 95% CI 

Sexa 

Female 126 54.8 1,234 45.5 1.43 (1.09,1.87) 1.53 (1.15,2.04) 

Male 104 45.2 1,456 53.6 Ref Ref 

Age 

< 15 16 7.0 402 14.8 Ref Ref 

15-24 28 12.2 370 13.6 1.90 (1.01,3.57) 1.34 (0.68,2.62) 

25-34 48 20.9 405 14.9 2.98 (1.66,5.33) 1.95 (1.02,3.71) 

35-44 48 20.9 410 15.1 2.94 (1.64,5.27) 1.91 (1.02,3.58) 

45-54 38 16.5 268 9.9 3.56 (1.95,6.52) 2.34 (1.24,4.41) 

55-64 21 9.1 143 5.3 3.69 (1.87,7.27) 2.42 (1.20,4.91) 

65+ 16 7.0 76 2.8 5.29 (2.54,11.03) 3.67 (1.72,7.86) 

Unknown 15 6.5 641 23.6 0.59 (0.29,1.20) 0.63 (0.30,1.33) 

Work-related 

Yes 126 54.8 1,254 46.2 1.41 (1.08,1.85) 0.99 (0.70,1.40) 

No/Unknown 104 45.2 1,461 53.8 Ref Ref 

No. of active ingredients 

One 90 39.1 1,719 63.3 Ref Ref 

More than one 140 60.9 996 36.7 2.72 (2.07,3.58) 1.42 (1.02,1.99) 

Pesticide functional class 

Fumigant 35 15.2 1,295 47.7 Ref Ref 

Herbicides 33 14.3 162 6.0 7.54 (4.56,12.46) 4.10 (2.34,7.19) 

Insecticide 79 34.3 599 22.1 4.88 (3.24,7.35) 3.34 (2.10,5.32) 

Fungicides 2 0.9 62 2.3 1.19 (0.28,5.08) 0.77 (0.18,3.37) 

Multiple 71 30.9 514 18.9 5.11 (3.37,7.76) 3.09 (1.85,5.16) 

Other/Unknown 10 4.3 83 3.1 4.46 (2.13,9.32) 2.82 (1.29,6.15) 

a. Excluded unknown cases.

b. Adjusted for all other variables. 

Page 25 of 32
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Table 5. Fifteen most common active ingredients for drift cases and percentage of high/moderate severity 

Cases exposed to single active ingredient 

Active ingredient Functional class Chemical class 

Casesa 

(N=2,945) Total 

(n=1,809) 

% of High/Moderate 

Severity (n=90)b

Metam-sodium Fumigant Dithicarbamate 664 664 3 

Chloropicrin Fumigant Trichloronitromethane 637 532 1 

Chlorpyrifos Insecticide Organophosphate 240 49 10 

Sulfur Insecticide/Fungicide Inorganic compound 147 32 25 

Mancozeb Fungicide Dithicarbamate 144 4 0 

Methamidophos Insecticide Organophosphate 133 0 0 

Malathion Insecticide Organophosphate 122 96 11 

Spinosad Insecticide Spinosyn 107 1 0 

Methyl-bromide Fumigant Alkyl bromide 84 11 27 

Dimethoate Insecticide Organophosphate 68 10 20 

Cyfluthrin Insecticide Pyrethroid 59 2 0 

Methomyl Insecticide N-methyl carbamate 56 13 15 

Atrazine Herbicide Triazine 54 8 0 

lambda-Cyhalothrin Insecticide Pyrethroid 52 39 3 

Propargite Acaricide/miticide Sulfite ester 52 10 30 

a. Can be exposed to other active ingredients also.

b. High (n=7), Moderate (n=83) 

Page 26 of 32
Table 6. 10 largest drift events, 1998-2006 

Cases Pesticide application 

State Year Total (n=1,293) Occupational (n=452) Non-occupational (n=841) Target Equipment California 1999 170 6 164 Soil Chemigation California 2000 33 33 0 Almonds Aerial application California 2002 250 72 178 Soil Soil injector California 2002 123 123 0 Soil Chemigation California 2003 161 10 151 Soil Soil injector California 2004 122 122 0 Potatoes Aerial application California 2005 324 1 323 Soil Chemigation California 2005 42 42 0 Soil Chemigation California 2005 34 34 0 Oranges Ground sprayer Texas 2005 34 9 25 Cotton Ground sprayer 

Page 27 of 32
Table 7. Factors associated with large drift events (≥5 cases) 

Small Event (n=555) Large Event (n=88) Large Event (versus Small) 

N % N % OR (95% CI) 

Pesticide functional class 

Insecticide 172 31.0 26 29.5 Ref Fumigant 29 5.2 23 26.1 5.25 (2.64,10.41) Multiple combination 178 32.1 29 33.0 1.08 (0.61,1.91) Other single pesticide class or unknown 176 31.7 10 11.4 0.38 (0.18,0.80) 

Application target 

Soil 31 5.6 24 27.3 8.50 (4.57,15.79) 

Small fruit cropsa 38 6.8 14 15.9 4.04 (2.03,8.06) Leafy vegetable cropsb 25 4.5 8 9.1 3.51 (1.49,8.27) 

Otherc 461 83.1 42 47.7 Ref 

Application method 

Aerial application 223 40.2 26 29.5 0.91 (0.54,1.53) 

Chemigation 20 3.6 22 25.0 8.58 (4.31,17.09) Otherd 312 56.2 40 45.5 Ref 

a. e.g., berries, grapes, currant. b. e.g., beets, celery, broccoli, lettuce, spinach c. Includes tall fruit or other vegetable crops, other crop categories, landscape/forest, undesired plants, livestock farms, unknown. 

d. Includes other ground application equipment, multiple, and unknown. 
29

Table 8. Violation in and contributing factors to occurrence of drift incidents/exposures 

 Drift Cases Drift Events 

(n=643) Occupational 

(n=1,380) 

Nonoccupational 

(n=1,565) 

Variable N % N % N % 

Violation of federal/state pesticide regulation 

Yes 220a 73.6 971 85.6 1122 93.2 

No 79 26.4 164 14.4 82 6.8 

Unknown/Pending 344 245 361 

 

At least one contributing factor identifiedb 164 (100) 486 (100) 1,058 (100) 

Applicator carelessness near non-target sitesc 79 (48.2) 49 (10.1) 98 (9.3) 

By aerial applicator 56 (34.1) 21 (4.3) 66 (6.2) 

Weather (wind, temperature inversion) 75 (45.7) 309 (63.6) 593 (56.0) 

Poor/ineffective communication 19 (11.6) 102 (21.0) 11 (1.0) 

Improper seal of fumigation sited 9 (5.5) 94 (19.3) 837 (79.1) 

Inappropriate monitoringe 7 (4.3) 118 (24.3) 199 (18.8) 

Applicator not properly trained or supervised 5 (3.0) 45 (9.3) 0 (0.0) 

Excessive application 4 (2.4) 20 (4.1) 6 (0.6) 

Use of inadequate equipmentf 2 (1.2) 125 (25.7) 2 (0.2) 

Otherg 8 (4.9) 28 (5.8) 206 (19.5) 

 

Distance from application site n/a 700 (100) 728 (100) 

≤ 50 feet 66 (9.4) 54 (7.4) 

> 50–100 feet 77 (11.0) 29 (4.0) 

> 100–300 feet 113 (16.1) 69 (9.5) 

> 300 feet–0.25 mile 267 (38.1) 93 (12.8) 

> 0.25–0.5 mile 175 (25.0) 256 (35.2) 

> 0.5–1 mileh 0 (0.0) 116 (15.9) 

> 1 milei 2 (0.3) 111 (15.2) 

Note: Percentages in parentheses were calculated only among cases with available data 

a. 159 (72%) were identified by the California Department of Pesticide Regulation 

b. Cases can be included in multiple categories. 

c. e.g., the applicator didn't turn off a nozzle at the end of the row, the crop duster flew overhead. 

d. e.g., leakage from torn tarp, early removal of seal, use of contaminated water 

e. e.g., did not measure wind speed, did not monitor drift from the application site 

f. e.g., used longer spray boom than specified on the label, used sprinklers without required calibration device. 

g. e.g., treated additional rows without permission, permeable soil type, aerial application with very low height, building/vehicle 

ventilator system sucking outside air in 

h. Cases are from three events in California, Louisiana, and Washington. 

i. Cases are from two events in California. 

Page 29 of 32
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Figure 1. Eligible pesticide drift events and cases, 11 States, 1998-2006 

Figure 2. Incidence rate of pesticide poisoning associated with off-target drift 

exposure over time, 11 states, 1998-2006 

Page 30 of 32
 

Figure 1. Eligible pesticide drift events and cases, 11 States, 1998-2006 

190x142mm (300 x 300 DPI) 

Page 31 of 32
 

Figure 2. Incidence rate of pesticide poisoning associated with off-target drift exposure over time, 

11 states, 1998-2006 

50x13mm (300 x 300 DPI) 

Page 32 of 32