California is the largest agricultural producer in the United States, and, as such, high volumes of pesticides are used throughout the state. Pesticides have a variety of health impacts, and public concerns have spurred mandates on the systematic collection and reporting of agricultural pesticide application data and the establishment of California's Pesticide Use Reporting (PUR) program.
Since its inception in 1990, the PUR has amassed millions of records on pesticide applications. While these data are comprehensive and highly detailed, many public health practitioners may not have the skills or knowledge needed to utilize this complex data set. The California Environmental Health Tracking Program (CEHTP) has played an important role in rendering this data set more actionable for public health research, communications, and policy.
Pesticide use and public health
Pesticides have well-documented impacts on human health, and researchers have noted associations with cancer, neurological disease, respiratory impacts, birth outcomes, and other adverse conditions in human populations.1 Children, in particular, are at greater risk for pesticide exposure and subsequent adverse health outcomes.2,3 Historically, pesticides research and regulatory efforts have focused on the prevention of acute health effects from pesticide poisonings and pesticide residues on foods, but more attention is being given to the deleterious chronic health effects resulting from low-level, ambient pesticide exposures.4
According to the California Department of Pesticide Regulation (DPR), “almost every pesticide application produces some amount of drift,” even when those applications are performed to regulatory standards.5 Likewise, low-level, ambient pesticide exposures are more likely when communities are in close proximity with pesticide use.6–8 This places many agricultural communities at increased risk for pesticide exposure and adverse health outcomes.
The disproportionate pesticide risks in agricultural communities raise considerations of environmental justice and civil rights. The most impacted communities are often majority Hispanic, may have low-English language capacity, and live in close proximity to pesticide applications and other environmental hazards. In 1999, the US Environmental Protection Agency received a title VI Complaint (Complaint 16R-99-R9) alleging that DPR discriminated against Hispanic schoolchildren because of disproportionate methyl bromide use near schools with a large proportion of Hispanic students.9 As a result, the US Environmental Protection Agency entered into an agreement with DPR in 2011 to expand DPR's air monitoring of methyl bromide and increase outreach and education to schools near areas of high methyl bromide use. However, higher pesticide exposures among children and in communities adjacent to agricultural fields remain a concern.10–12
Given the many public health and environmental justice impacts associated with the use of pesticides, comprehensive pesticide application data have been a high priority for environmental and health professionals, government agencies, and community groups throughout California.
Agricultural pesticide use data in California
California is the country's highest-producing agricultural state, and a large amount of pesticide applications support this production. Public health considerations of pesticide use began in California nearly 100 years ago when the Economic Poison Act of 1921 specified that pesticides detrimental to public health can be restricted. In the decades that followed, continued environmental and public health concerns led to greater regulatory oversight. After a series of high-profile pesticide illnesses from pesticide residues on foods, public concern dramatically increased in the 1980s. In response to these concerns and a need for better data, California's Food Safety Act of 1989 was passed.13,14 Among other environmental health advances, the legislation gave authority to DPR to require full pesticide use reporting.
The PUR program was launched in 1990 and is maintained by DPR.15 The PUR contains records on all agricultural pesticide applications by licensed pesticide applicators. Agricultural pesticide use is broadly defined and inclusive of all agricultural applications, as well as pesticide applications to parks, golf courses, cemeteries, rangelands, and along railroad/roadway rights-of-way. Applications in the home, institutional, and industrial settings are not reported in the PUR.
For each pesticide application, data reported include the chemical applied, the pounds of chemical applied, the acreage covered by the application, the time and date of application, and the agricultural commodity to which the pesticide was applied. Application data are publicly accessible via an online query and can be downloaded by county or by geographic units established by the Public Land Survey System (PLSS) of township, range, or section. The section level—roughly 1 square mile (or 640 acres) units with irregular shapes—is the finest geographic resolution available via the PUR.
The PUR data have been indispensable for monitoring pesticide use and trends in California over the past 2 decades. Although PUR data have been useful for public health research in largely academic settings, the large volume of highly detailed application records (about 80 million records from 1991 to 2014) and the complexity of queries needed to access its many variables can be a challenge even for these users.
As downloaded, the data cannot be easily deployed for some public health functions, such as mapping activities, community outreach, or health education. First, pesticide application data are disconnected from their location of use. The PUR data are downloaded in a tabular format, and the user must then join application data with PLSS geographies in their own mapping software. Second, the highest resolution data available are at the square mile section, hindering the ability for more refined geographic analyses, such as field or parcel-level analysis. Third, the application data are organized by individual chemical, limiting their relevance for public health practice in some instances. For example, a data user interested in carcinogenic pesticides would need to examine any chemical classified as a carcinogen individually or undertake a time-intensive process to manually identify and aggregate these compounds from PUR records.
California Environmental Health Tracking Program
The CEHTP was founded in 2002 as part of the Centers for Disease Control and Prevention National Environmental Public Health Tracking Program. The CEHTP's mission is to mobilize data for public health. Since its inception, the CEHTP has worked with data stewards to gather and disseminate environmental and public health data via its online data portal. Most data sets displayed by CEHTP are collected by external data stewards, such as DPR's PUR data. In addition to its public data portal, the CEHTP develops tools for data visualization and data linkage, enhances data analysis and research methods, and produces reports and other communication products on environmental health data and their uses in public health practice.
Ultimately, the goal of these efforts is to provide environmental health data in multiple formats that are accessible and understandable to a range of data users and relevant for public health research, communications, and policies.
Improving the Public Health Utility of PUR Data
Given the concerns regarding agricultural pesticide use in California, the CEHTP has taken multiple approaches to increase the utility and accessibility of pesticide use data for public health practice. This includes a Pesticide Linkage Service for highly skilled public health researchers, an online Pesticide Mapping Tool that targets a broader range of stakeholders, and in-depth analysis and reporting on pesticide use data to provide information relevant to public policy.
Pesticide Linkage Service
For public health researchers who are interested in the health impacts associated with agricultural pesticide use, the PUR is a rich information source of about 80 million records spanning more than 2 decades. However, working with these data can pose a challenge even to the most experienced analysts. Barriers include the need to join PUR data within a geographic information system (GIS), refine the geographic resolution of pesticide application records, and sort through more than a thousand chemical codes used to specify pesticide active ingredients.
The CEHTP sought to overcome these barriers to give public health researchers and other interested stakeholders a data resource that allowed for greater access, utility, and flexibility when using PUR data to summarize the proximity of individuals and groups to pesticide applications. In 2007, the CEHTP developed its Pesticide Linkage Service, a custom application operated by CEHTP staff to link populations of interest or individual research subjects with the PUR records based on geographic and temporal proximity.
The Pesticide Linkage Service allows geographic analysis of the full historical data set from PUR, which includes records from 1991 to 2014 for all agricultural pesticide applications (some data are available pre-1991, but full reporting requirements were not in effect). Key features of the linkage service include (1) geographic refinement of pesticide application records to better approximate agricultural field boundaries and (2) GIS intersection of PUR applications records with specific spatial-temporal windows for defined populations and for high volumes of data. Output can then be summarized by researchers depending on their specific study objectives.
Each pesticide application record in the PUR is listed with its PLSS section. While useful for the reporting of pesticide application data, PLSS geographies are limited in their use for public health analyses. Based on a method published by Rull and Ritz,16 each PUR record is matched with field boundaries drawn from land surveys conducted by the California Department of Water Resources based on PLSS and the type of crop specified in the record. In this way, each PUR record becomes associated with 1 or more agricultural fields described by the Department of Water Resources as shapefiles amenable to analysis using a GIS. In Figure 1, the intersection of user-supplied coordinates for linkage is represented by “+” surrounded by a buffer with radius “r.” Agricultural fields of interest, shown as cross-hatched figures, partially intersect with the selected buffer radius; the areas of the field that overlap, shown in black, are then included in pesticide use calculations using an area-weighted average. The white areas represent portions of the PLSS section that are excluded from the analysis, reducing exposure misclassification. The generation and intersection of buffered geographic coordinates described in Figure 1 can be automated by the linkage service, which requires approximately 10 seconds to process each record using current hardware, allowing for the analysis of high volumes of data.
Together, these features allow researchers to more efficiently and accurately estimate spatiotemporal relationships between pesticide use and health outcomes of interest. While these types of analyses can be programmed by advanced GIS users using publicly available PUR data, the Pesticide Linkage Service enables analysts to accomplish this without sizeable investments in software and hardware that might otherwise be prohibitive.
Pesticide Mapping Tool
The PUR data, as provided by DPR, are not intended for stakeholders who are interested in quickly exploring where pesticides are applied in California, the quantity of pesticides applied, or the trends in pesticide use from year to year. Many users—such as water systems managers, public health officials, community advocates, and media—still want information on where pesticides are applied but may not have the GIS resources, skills, or time to download and map PUR data.
To fill this need, CEHTP developed the Pesticide Mapping Tool, a publicly available and interactive online mapping tool that utilizes the Google Maps interface for users to visualize and explore agricultural pesticide data.17 Summaries of PUR application data by year serve as the underlying data for the Pesticide Mapping Tool. The data are simplified by the categorization of more than a thousand compounds contained in the PUR into categories of public health relevance, such as carcinogens, endocrine disruptors, fumigants, and reproductive and developmental toxicants. A simple point-and-click query coupled with the familiar Google Maps interface greatly increases the accessibility and utility of PUR data.
Users can select an individual pesticide or pesticide category, the year, and/or the crop of interest to dynamically query pesticide application data, resulting in a choropleth map (Figure 2). The Pesticide Mapping Tool displays the results at the county, township, or square mile section for the entire state. The user can pan and zoom to explore areas of interest and click on the map to view different metrics of use (summed pounds, treated acres, and pounds per acre) and to view trends in pesticide use over time (in both table and chart formats).
Improving data relevant to public policy: pesticide use near schools
The use of agricultural pesticides near schools has remained a concern for many years following the title VI complaint regarding disproportionate use near Hispanic schoolchildren.18 In response to stakeholder needs for better information, the CEHTP tailored data and research methods to provide high-resolution estimates of pesticide use near public schools in California.19 To do so, the CEHTP had to improve school location data, enhance the geographic resolution of pesticide application records, and intersect the improved geospatial data with PUR application records using the Pesticide Linkage Service.
First, data on 2511 public school addresses in the top quartile of counties by pesticide use (15 counties, accounting for 85% of pesticide use in 2010) were obtained from the California Department of Education. School addresses were geocoded, and school locations were verified and overlaid with parcel data to identify school boundaries. Second, agricultural field boundary data were obtained from 13 of the 15 counties assessed, allowing for improved spatial resolution of pesticide application records. Finally, a one-fourth mile buffer was placed around school boundary polygons. Using the Pesticide Linkage Service, the one-fourth mile buffers were intersected with PUR records and improved field location data to estimate pounds of pesticides applied near each school.
More than 80% of pesticide applications near schools—nearly 61 000 applications—were matched to the field on which they were applied. Fewer than 1% of pesticide applications were matched to the PLSS square mile section, the highest spatial resolution available via the PUR; 19% were matched to Department of Water Resources land-use polygons. This process generated the most comprehensive and highest resolution estimates of pesticide use near schools to date in California.
Of 2511 schools included in the study, most (64%, n = 1612) had no pesticide use within one-fourth mile in 2010, while 36% of schools (n = 899) had some pesticide use nearby. Of the top 5% of schools with any use nearby (45 schools and more than 35 000 students), pesticide use ranged from 2635 to 28 979 lb. Across the 15 counties assessed, 3 fumigants were the most heavily used pesticides within one-fourth mile of schools: chloropicrin, 1,3-dichloropropene, and methyl bromide. Nine of the 10 most commonly used pesticides near schools have a chemical persistence in the range of days to months; 6 of 10 remain chemically active for 50 days or longer (Table).
The data also highlighted pesticide use as a persistent environmental justice issue. Hispanic children represent 54% of the students in the 2511 schools assessed; however, in the top quartile of schools by pesticide use, 68% were Hispanic. Overall, Hispanic children were 91% more likely than non-Hispanic white children to attend a school near the highest agricultural pesticide use. Although this finding is not surprising—92% of farmworkers in California identify as Hispanic and many agricultural counties are primarily Hispanic20—it underscores the entrenched disproportionate hazards and continued needs of environmental justice communities.
The results of this analysis were summarized and published in CEHTP's 2014 report, titled Agricultural Pesticide Use Near Public Schools in California.
Impact on Public Health Practice
Public health research and analyses
The Pesticide Linkage Service has been used to examine the relationship between agricultural pesticide use and autism,21,22 hypospadias,23,24 neural tube defects and other birth defects,25,26 gastroschisis,27 and congenital heart defects,28 expanding the scientific body of knowledge on pesticides and health.
The Pesticide Mapping Tool has also been used to support public health research. For example, the CEHTP used the tool to identify communities with historically high pesticide use for potential participation in a pesticide biomonitoring study. The tool served a screening function that allowed researchers to plan visits with identified communities to assess suitability and interest in participation.
Estimates of pesticide use near schools generated for CEHTP's 2014 report were used by US Environmental Protection Agency Region IX to help select schools for a pilot project that attempted to develop a screening tool for detecting pesticide residues on outdoor surfaces (P. Tenbrook, PhD, e-mail communication, January 4, 2017). In addition, the data were used to inform DPR's statewide pesticide air monitoring efforts: of 5 additional monitors to be added, 3 are proposed to be located at impacted schools, and 6 additional pesticides identified in the report will be included in the air-monitoring program.29
Increased public awareness of pesticides and health
Stakeholders have used the Pesticide Mapping Tool to fit a variety of communication needs since its launch in 2009. The tool has given journalists a more easily accessible way to view and assess pesticide use data and has been used in news reporting.30 The tool is also integral to the CDPH Occupational Health Branch's strategy to target outreach efforts to workplaces surrounded by agricultural fields. Many of these businesses have staff working outside, placing them at increased risk for exposure when pesticides are used nearby. The Pesticide Mapping Tool will allow Occupational Health Branch's staff to more efficiently target limited resources to those workers at greatest risk for pesticide exposure (J. Weinberg, MSEHS, CIH, e-mail communication, January 4, 2017).
The CEHTP's research on pesticide use near schools generated substantial media on data and information related to pesticides, public health, and public policy issues. The report, Agricultural Pesticide Use Near Public Schools in California, was highlighted in major newspapers across the state and informed policy conversations on pesticide use near schools.31,32 Data were used in a long-form news investigation on pesticide use in the strawberry industry; this news story even inspired a play (in both English and Spanish) by a Pulitzer Prize–nominated playwright.33,34 This widespread media exposed many individuals to scientific information they may not have otherwise seen and, along with the many mobilization efforts of community health advocates, spurred communities to engage in the policy discussions.
Policy change to protect public health
Findings from the pesticide and schools report led to a variety of policy changes at the state and county levels. Proposed regulations have included restrictions on pesticide use near schools and the codification of communications between pesticide applicators and schools. In Monterey County, following the report's release, a program was launched to notify 3 highly impacted schools—cited in CEHTP's schools data—5 days in advance of any fumigant application within one-fourth mile.35
At the state level, citing the CEHTP report as part of its rationale, DPR began a process to update and standardize regulations on pesticide use near schools.36,37 The regulations were shaped through a series of community workshops, and the drafted regulations propose limiting pesticide use within one-fourth mile of schools during the school day and annual notifications to schools of expected pesticide applications. Final public comments were received in December of 2016, and the proposed regulations are scheduled to begin in January 2018.38 The final enacted regulations will be the first uniform statewide standards regulating pesticide use near schools in California.
The CEHTP has worked to further the utility and accessibility of pesticide use data. For more than a decade, this work has successfully mobilized data that impacts public health research, engages with diverse stakeholders, and informs public health policies in California. In the coming years, there are opportunities to advance pesticide data that elevate these conversations further and generate public health gains through reduced pesticide exposures and improved health outcomes.
The utility of PUR data would be improved with the routine and standardized collection, digitization, and reporting of agricultural field locations. The technology exists to collect these data, and high-quality data are already available for some counties.39 Improvements to the visualization of PUR data, such as incorporating sensitive land uses into the Pesticide Mapping Tool—including schools, nursing homes, and hospitals—could make the tool more meaningful for communities, planners, and environmental health professionals.
In addition to improvements in pesticide use data, there is a need to improve our understanding and reporting of pesticide illnesses. For many years, the primary focus of public health surveillance has been on acute pesticide illnesses; yet, these acute outcomes are likely undercounted. Pesticide illness reports are often made only when the exposure is reported by the victim, the outcome is very serious and/or requires hospitalization, and it is recognized as such by the attending medical provider.40,41 Furthermore, less policy attention has been paid to chronic health outcomes associated with pesticide exposures. With increasing knowledge about pesticides' impacts on cancer, diabetes, lung function, neurodegenerative disorders, intelligence quotient, birth defects, and reproductive impacts, it will be important for public health research and surveillance efforts to improve the ability to identify and monitor chronic health impacts related to pesticide exposure.42–46
Implications for Policy & Practice
- CEHTP has identified ways to make PUR data more accessible, understandable, and useful to a range of data users.
- As a result, these efforts—the Pesticide Linkage Service, the Pesticide Mapping Tool, and in-depth data improvements to estimate pesticide use near schools—have led to diverse public health actions at the state and local level, informing pesticide research and analyses, community outreach and education, and policy change.
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