Removal of Diethylhexyl Phthalate from Hands by Handwashing: Evidence from Experimental N-of-1 and Crossover Designs

Abstract

Phthalate exposure through skin is often neglected due to the small quantity and limited dermal absorption rate. However, free phthalate can be ingested by hand-to-mouth action or by contact with food. To evaluate the effectiveness in removing phthalate exposure on hand, we compare here the removal efficiency of di-(2-ethylhexyl)phthalate (DEHP) on hands by handwashing with soap-and-water versus water-only. In two three-day N-of-1 trials, residual DEHP was measured in a single female adult who washed exposed hands with soap-and-water or water-only. Subsequently, a crossover study was performed by randomly assigning another 28 subjects equally to wash with soap-and-water or with water-only, and then each one received the other treatment 24 hrs later. In the N-of-1 trials, mean DEHP removal rates range from 95.9% (SD = 0.1%) to 97.0% (SD = 2.5%) for soap-and-water handwashes, and 1.8% (SD = 0.1%) to 7.0% (SD = 0.3%) (n = 3) for water-only. In the crossover study, mean removal rate was 94.6% (SD = 6.5%) for handwashing with soap-and-water (n = 28) and 8.7% (SD = 5.7%) for water-only (n = 28). We concluded that handwashing with soap-and-water removes 80% more DEHP than handwashing with water alone, and may be a cost-effective way of removing other endocrine disruptors from hands.

Figure 1

Box-Whisker plot showing the removal rate of dermal DEHP exposure of both hands in each study. (a) Average of the two N-of-1 trials on one female subject; (b) The crossover study on 28 study subjects.

Figure 2

Removal rate of dermal DEHP exposure over both hands in each individual. (a) N-of-1 trials on one female subject; (b) The crossover study on 28 study subjects. The removal rate accomplished by handwashing with soap and water (black) or water only (gray) for each individual whose hands were exposed to 0.5 mL of 1000 μg/mL standard DEHP solution.

Figure 3

Flowchart of the different study designs. (a) First experimental episode of the N-of-1 on one female subject; (b) Second experimental episode of the N-of-1 on one female subject (c) Crossover study on 28 subjects. The interventional studies included prewash with water rinsing (cross), then direct dispersing of 0.5 mL of 1000 μg/mL standard DEHP solution evenly over both hands (arrow), handwashing with soap and water (circle) or water only (square), and additional water rinsing (triangle). A washout period of 60 min was implemented between each handwashing intervention, and repeats of the intervention pairs were separated by 24 hrs.