Insecticide Residues on Hands: Assessment and Modeling with Video Observations of Determinants of ExposureA Study Among Subsistence Farmers in Nicaragua

This investigation quantitatively assessed hand residues of chlorpyrifos and methamidophos in a field setting and sought to explain the residues through application volume and determinants of exposure using application data for 28 subsistence farmers in the Pacific Region of Nicaragua. Hand residues were estimated by recovery of the pesticides by standardized wipe sampling for both hands, analyzed with solvent extraction and gas chromatography with electron capture detector. Application volumes were based on data on individual spraying rates and mixing volumes. Eleven determinants of exposure, related to work practices during mixing and spraying of the pesticides, were assessed for each subject from videotapes. Correlation and regression analyses estimated the associations between hand residues, application volume, pesticide type, and determinants of exposure. Correlations between residues for different hand parts were high (r 0.75-0.98). Total hand residue (sum of residues of parts of both hands) correlated with application volume (r 0.43, p 0.02), not washing hands (r 0.41, p 0.04), spraying nozzle forward (r 0.26, p 0.17), manipulation of hose (r 0.32, p .09), and insecticide type (chlorpyrifos vs. methamidophos; r 0.31, p 0.10). A model that explained total hand residue with these five variables yielded a multiple correlation coefficient of 0.67 (p 0.01). Unmeasured determinants and/or narrow range of the exposure situation probably account for the unexplained variance of the residues.