ABSTRACT OF THE DISSERTATION 


Pesticide Drift and the Hazards of Place 
in San Joaquin County, California 
by JOHN PAUL TIEFENBACHER 
Dissertation Director 


Professor Susan L. Cutter 


This dissertation examines the distribution of airborne 
drift from agricultural pesticide applications to determine 
the potential for non-agricultural residential exposure at the 
rural-urban fringe. Three questions are posed: (1) What is 
the extent and distribution of drift events from agricultural 


applications? (2) How does the process of suburbanization 
affect the risk of drift exposure to residential populations? 


(3) What socioeconomic factors, if any, determine which 
neighboring residents are exposed to drift? 


San Joaquin County, California, was studied based on 
three parameters: rapid population growth, strong 
agricultural presence, and data availability. Pesticide 
application records for 1986 were acquired fromthe California 
Department of Food and Agriculture. The Bache, Lawson, and 
Uk model simulated downwind transport of airborne pesticides 
based on four variables: wind speed, release height, surface 
roughness length, and droplet sedimentation velocity. Of the 
almost 8,000 treatments with complete data, about 66 percent 
had drifted beyond 800 meters. Release height did not 
contribute substantially to propensity to drift. Drift was 
inversely related to the density of the pesticide. Wind speed 


contributed to drift potential, but most drift events occurred 
when wind was within safety guidelines. 


The spatial distribution of drift events shows areas of rapid residential development at the urban fringe to be less likely to receive drift from agricultural operations. A land conversion dynamic creates a buffer of idled land that separates high-value residential property from agricultural operations. The areas with the greatest number of drift events in the non-developing fringe, including French Camp and northeast Lodi, are places where the population is not growing quickly, are of lower land value, and have higher percentages of poor and minority residents. 

Using a hazards of place approach, the analysis explores 
physical, technological, and social factors to explain the 
distribution of the drift hazard. Suburbanization may act to 
reduce the likelihood of residential exposure by creating a 
buffer between development and agriculture. But in areas of 
lower land value, residential areas abut farmland directly. 
The residents of these areas are not likely to have the 
social, economic, or political power to reduce pesticide use. 


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