Regulation and Risk Assessment of 1,4-Dioxane - Environmental Investigation and Remediation - page 305

by-product from the production of ethoxylated surfactants. Nevertheless, many more people may
experience nonoccupational exposure to low concentrations in shower air containing 1,4-dioxane
from contaminated water or from shampoos, soaps, lotions, cosmetics, and related products. Even so,
the low concentrations of 1,4-dioxane likely to result from showering and using soaps and shampoos
are well below the inhalation slope factor used in California, 0.027 (mg/kg d) −1 , and the California
chronic inhalation Reference Exposure Level for 1,4-dioxane, 3000 μg/m 3 (Cal EPA, 1999, 2007c).
Inhalation exposure from 1,4-dioxane in contaminated shower water is proi led in the following
section; this section reviews incidental low-level exposure that could result from the presence of
residual 1,4-dioxane in soaps and shampoos. If it is assumed that shampoo contains the 1980s levels
of 1,4-dioxane (50 ppm), an average inhalation exposure per event is calculated at 13 μg/m 3 , and the
yearly average is then projected to be 0.0576 μg/m 3 . These values yield an internal dose of 0.02 μg
1,4-dioxane per kilogram body weight per day. Assumed parameter values used to calculate esti-
mates of inhalation exposure to 1,4-dioxane at levels measured in the 1980s in shampoos, baby
lotions, and dish-washing soaps are proi led in Table 6.22 (ECB, 2002).
Japanese domestic wastewater was evaluated for 1,4-dioxane content derived from shampoos and
soaps; the potential exposure was determined to be approximately 0.25 mg/person/day (Abe, 1999).
The highest cumulative worst-case uptake in the ECB 2002 risk assessment would amount to only
4% of the total mass of 1,4-dioxane ascribed to soaps and sundries in Japan. The majority of
1,4-dioxane that may have been, or continues to be, present in shampoos and sundries ends up in the
sewer. Inhalation exposure to 1,4-dioxane from shampoos, baby lotions, and dish-washing soaps is
four to i ve orders of magnitude lower than the NOAEL. The concentrations one might breathe while
shampooing, coupled with dermal exposure, are inconsequential and do not constitute a health risk
(ECB, 2002).
6.5.5.1 Lactational Transfer Following Occupational Exposure
Infants nursed by mothers breathing elevated levels of 1,4-dioxane in the workplace may be exposed
to 1,4-dioxane through breast milk. A PBPK * modeling study simulated maternal exposure to 1,4-
dioxane at the 25 ppm TLV established for workplace safety regulation. The PBPK model used
estimated blood/air and milk/air partitioning coefi cients to calculate blood/milk partitioning. The
model predicted that perchloroethylene, bromochloroethane, and 1,4-dioxane would be present in
breast milk at concentrations exceeding the USEPA noncancer ingestion rates for children. The
PBPK simulation of lactational transfer is not well developed for volatile organic compounds; the
study necessarily applies assumptions regarding the kinetics and properties of lactational transfer,
but nonetheless suggests that this route of exposure could be signii cant for infants nursed by moth-
ers exposed to 1,4-dioxane by breathing vapors in the workplace (Fisher et al., 1997). Analysis of
breast milk has shown that the inhalation-lactational transfer route of exposure was completed in a
woman who visited her husband at his dry cleaning establishment for the lunch hour each day. Her
breast milk contained elevated levels of perchloroethylene because daily exposure saturated her
body's ability to eliminate the chemical (Bagnell and Ellenberger, 1977). Methyl chloroform, carbon
tetrachloride, dichloromethane, TCE, and perchloroethylene have all been detected in breast milk
(Pellizzari et al., 1982; Labrèche and Goldberg, 1997; Solomon and Weiss, 2002).
6.5.5.2 Inhalation Risk from Showering in 1,4-Dioxane Contaminated
Water
Showering in water contaminated with 1,4-dioxane will cause inhalation exposure. Although 1,4-
dioxane is hydrophilic and less susceptible to partitioning from the liquid to vapor phase, the rate of
volatilization is increased when water contaminated with 1,4-dioxane is heated. The total surface
area available for mass transfer is a key determinant of the rate of volatilization. Shower nozzles
break up the water stream into i ne droplets, maximizing the opportunity for volatilization and
* PBPK = physiologically based pharmacokinetic model; see Chapter 5.