We used California's Pesticide Use Report (PUR) and land-use survey data to conduct a simulation study evaluating the potential consequences of misclassifying residential exposure from proximity to agricultural pesticide application in health effect studies.
One way to increase the spatial resolution of the PUR beyond the square-mile PLSS section is by using land-use survey data available from the California Department of Water Resources (CDWR 2002; Miller et al.
In the present analysis, we used California's unique PUR and land-use survey databases to conduct a simulation study relying on actual data of historical pesticide use and crop cover in an agricultural region (Western Kern County).
We used the land-use survey closest in time, conducted in 1990, to map the most likely land use during 1988.
To make the PUR compatible with land-use survey data, we collapsed all nonpermanent field crops, including cotton, tomatoes, potatoes, grains, and alfalfa, into a single class of "field crops."
We used a three-tiered approach to link the PUR information to our reclassified land-use survey data.
Third, if we found a PUR for a given PLSS section, but according to the land-use survey no field, vineyard, or orchard crops were present in the section, we assumed that any area within the entire section could have been treated.
As a result, we restricted the parcels in this simulation to those located in rural western Kern County by selecting those whose geometric centroids were within the area of the available land-use survey for 1990 and within or adjacent to a PLSS section containing an agricultural land-use polygon.
With the help of the land-use survey, we identified the locations of the orchard crops on which the agent was predominantly applied, calculated proximity of residences to these orchard crops, and then compared the exposure status derived only from land-use surveys to that derived from the gold standard.
We estimated the annual percentage of specific crop acres treated by a specific pesticide by dividing the total crop acres treated (PUR data) by the total acreage of the crop (land-use survey data).
For parathion, we created another exposure definition based only on land-use survey data (Table 6).
This may occur, for example, if the PUR reports a treatment on carrots in a section, but the land-use survey instead reports tomatoes and potatoes.