Time-response necessary in validation for extraction of pesticides from cloth patches used in field exposure studies.

Environmental exposure in field studies is generally monitored by the cloth patch technique. Many investigators question the accuracy of the technique, in part due to lack of validation. The objective was to examine extraction of chemicals from cloth patches for potential technique validation. Chemicals studied were glyphosate, atrazine, malathion, alachlor and 2,4-dichlorophenoxy acetic acid (2,4-D), a selection of hydrophilic (glyphosate) and varying lipophilic compounds. The 14C-radiolabeled chemical was applied to a cotton patch (two types used) and solvent extracted over a 48-h time period. The chemical was soluble in the application solvent and in the extraction solvent. Extraction was near 100% at time 0 h, but statistically (P < 0.05 or greater) decreased to levels of 20-50% by 48 h. The missing chemical was detected in cloth residue and accountability was always excellent. The chemicals exhibited a time-response by incorporating into the cotton patch and not being available for extraction. Thus, validation of the cloth patch technique must include the time-period from the start of a field trial until laboratory analysis, a process which can take several days. This may account in part for differences noted between cloth patch technique and biological monitoring. It was subsequently shown that sonication loosens chemicals incorporated in the cloth patch, making the chemicals available for extraction. That sonication dislodged the chemicals suggests that the chemicals were not chemically bonded within the fabric but were probably sequestered within the fabric away from the solvent.