Regulation and Risk Assessment of 1,4-Dioxane - Environmental Investigation and Remediation - page 307

production of aerosols. The relatively coni ned space of a shower in a bathroom will exacerbate the
potential for exposure to chemical contaminants in shower water.
Numerous risk assessments have been developed to estimate shower exposure. Shower exposure
models account for the factors that contribute to volatilization, the exposure duration, and attributes
of the exposed population. The groundwater concentration of 1,4-dioxane exceeding the risk of one
excess cancer in 1 million exposed was calculated as 3 μg/L by staff at the Massachusetts Department
of Environmental Protection (MADEP spreadsheet model for inhalation exposures from shower-
ing—based on Foster & Chrostowski shower model by Paul W. Locke and Rafael McDonald,
Massachusetts Department of Environmental Protection, personal communication, 2006). The
MADEP calculation used a chronic-inhalation RfC of 0.12 mg/m 3 (USEPA, 1992b) and the IRIS
oral CSF of 0.011 (mg/kg d) −1 The MADEP model calculates an internal dose that is compared
to the oral slope factor. Table 6.23 lists the model parameters considered in the MADEP shower
model. The assumption of a single value for many of these parameters is a simplii cation to avoid

TABLE 6.23
Model Parameters Used for Shower Model of 1,4-Dioxane Inhalation Exposure
Value

Physical Considerations
Receptor: Young child, 1-8 years old

16.8 kg

Receptor: Older child, 8-15 years old 39.7 kg

Receptor: Adult, 15-30 years old 54.2 kg

Shower water temperature 318 K

Ventilation rate 15 L/min

Shower droplet diameter 1 mm

Shower droplet time 2 s

Universal gas constant 8.205 × 10 -5 (m 3 atm)/(mol K)

Gas-i lm mass transfer coefi cient, water 3000 cm/h

Liquid-i lm mass transfer coefi cient 20 cm/h

Calibration water temperature for air mass transfer 293 K

Water viscosity at mass transfer temperature 1.002 centipoise

Water viscosity at shower temperature 0.596 centipoise

Shower duration 15 min

Shower room volume 6 m 3

1,4-Dioxane Attributes
Henry's law constant

4.91 × 10 -6 (atm m 3 )/mol

Molecular weight 88 g/mol

Gas-i lm mass transfer coefi cient 1356.8 (kg cm)/h

Liquid-i lm mass transfer coefi cient 14.14 (kg cm)/h

Overall mass transfer coefi cient 14.14 cm/h

Adjusted mass transfer coefi cient 19.1 cm/h

Concentration leaving water droplet 0.47 μg/L

Indoor-air generation rate 0.79 μg/(m 3 min)

Exposure factor—noncancer

0.0965 (μg/m 3 )/(μg/L)

Exposure factor—cancer risk

0.0414 (μg/m 3 )/(μg/L)

Noncancer risk 200 μg/L

Cancer risk 3 μg/L

Source: European Chemicals Bureau (ECB), 2002, European Union risk assessment report: 1,4-Dioxane.
Institute for Health and Consumer Protection, European Union.