Chlorpyrifos penetration

Correct for body weight by dividing the TDE by 70 kg (theoretical weight of adult). Correct for dermal absorption of 3% for chlorpyrifos penetration of the skin. 

Determine the percent penetration of chlorpyrifos through the outer layer of the torso section of the coverall (micrograms chlorpyrifos on t-shirt and briefs)/(micrograms chlorpyrifos on torso section). 

Sum the micrograms chlorpyrifos on the arms and legs and torso section of the coverall (outer whole-body dosimeter) and multiply by the percentage penetration of the chlorpyrifos through the coverall. 

Penetration of chlorpyrifos through the outer whole-body dosimeter to the inner-body dosimeter... 

In order to determine the dermal exposure of volunteers to chlorpyrifos, the penetration of chlorpyrifos through the outer whole-body dosimeter (coveralls) to the inner body dosimeter (t-shirt and briefs) was measured. The penetration factor was calculated for each volunteer in the study from the experimental data by dividing the amount of chlorpyrifos on the t-shirt and brief sample by the amount of chlorpyrifos on the torso section of the coveralls. This method of calculation assumes that the surface area of the torso section of the coveralls is nearly the same as the surface area of the t-shirt and briefs worn directly under the torso section of the coveralls. A mean penetration factor for each worker type was calculated by averaging all the worker volunteer... 

In our studies, the WBDs accumulated an average of 13,757 pg chlorpyrifos (n = 13), which would represent an administered dose of about 200 pg/kg. If the dermal absorption rate of chlorpyrifos is 9.6%/24 hr in humans (Thongsinthusak, personal communication), then the ADD would be 200 pg/kg x 0.096 = 19 pg/kg. If clothing penetration is taken into account, the estimated (daily) ADD resulting from the intensive 20-min contact period was about 2 pg/kg. 

The WBDs retained an average potential dermal exposure (PDE) of 13,757 pg chlorpyrifos. If clothing penetration is assumed to be 10% and dermal absorption 9.6% per 24 hr, then the absorbed dose would be 132 pg, and the absorbed dosage would be about 1.9 pg/kg. Biological monitoring of the 13 volunteers wearing cotton dosimeters indicated that the absorbed daily dose that penetrated the WBD and was absorbed was 2 pg chlorpyrifos equivalents/kg (Table 2). 

It will be noted that while the treatment imparted repellency to Dinoseb, chlorpyrifos and pentachlorophenol, it was relatively ineffective in the case of chlorpropham. However there is no indication from these data whether this means a chemical like chlorpropham, may penetrate the cloth, or whether what was being determined was merely a surface deposit. 

The quantity of suspended dust inhaled and the intake of pesticides adsorbed to it may be calculated rather exactly, and the intake of pesticides from deposited dust via oral pathways may at least be roughly estimated. But data supporting the amount of chemicals absorbed through dermal contact of contaminated house dust and through direct contact to contaminated surfaces are still lacking. Semivolatile pesticides like chlorpyrifos will accumulate not only in house dust but also on toys and on sorband surfaces [134]. Data from the NHEXAS of Arizona support the importance of dermal penetration of semivolatile pesticides like chlorpyrifos and diazinon as a route of residential human exposure [116]. 

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