Development of a GIS-based indicator for environmental pesticide exposure and its application to a Belgian case-control study on bladder cancer.

We developed two indicators to assess the exposure of residents to agricultural pesticide use and applied it in a case-control study on bladder cancer in the province of Limburg, Belgium. The first indicator used a distance-weighted measure of crop area for specified crops (fruit trees, fruit bushes and vegetables). The second indicator used a distance-weighted measure of pesticide use. We used information at three scale levels: (a) information at individual's level, such as distance to crop fields; (b) information at the level of the municipality, such as time-series of crop area; and (c) regional information, such as pesticide use. Pesticide use data were available per group of pesticides (fungicides, herbicides, insecticides, growth regulators and group of other pesticides). Indicators were calculated for each individual in the case-control study. The indicators were calculated per year for a period of 20 years, taking into account address history. Variation of pesticide use and toxicity with time was addressed by a relative risk factor. A very strong correlation was found between the area of fruit trees and bushes and the use of fungicides as well as the use of "other pesticides", indicating that these groups of pesticides are predominantly used in fruit production. The indicator for fruit trees is highly skewed to the right, indicating a high number of subjects with low potential exposure to fruit trees. Pesticide pressure indicators are less skewed as they combine application to multiple crops; the highest skewness is found for fungicides corresponding with the distribution for fruit trees. Statistical analysis revealed no association between the indicators and the incidence of bladder cancer. The results show that, using GIS, it is possible to reconstruct potential environmental pesticide exposure accounting for changes in pesticide use, crop area and residence history. Validation of the method with measured exposure is considered essential in view of its future application in other studies.