Regulation and Risk Assessment of 1,4-Dioxane - Environmental Investigation and Remediation - page 297

cause, qualii ed by probability of occurrence and uncertainty associated with the estimates (Cohrssen
and Covello, 1989).
Table 6.18 summarizes the information needed to estimate the total dose by all routes of expo-
sure to 1,4-dioxane in residential water.
6.5.2 E XPOSURE P ATHWAYS AND R OUTES
Risk assessments typically proi le 1,4-dioxane toxicity data by exposure route. The primary expo-
sure routes for 1,4-dioxane are oral, inhalation, and dermal. European risk assessments generally
rely upon the NOAEL or UF approach, whereas current U.S. risk assessments use a slope factor
based on linear low-dose extrapolation. In the United States, inhalation toxicity thresholds are
developed by the ATSDR, not by USEPA.
6.5.3 1,4-D IOXANE T OXICITY D ATA U SED IN R ISK A SSESSMENTS
A key decision in preparing a risk assessment is the selection of suitable toxicity data for a given route
of exposure. Risk assessments review available toxicological studies and evaluate the relevance of the
derived toxicity values to the exposure framework under examination. For example, exposure to 1,4-
dioxane vapors can cause toxicity to the liver through inhalation exposure. ATSDR (2004) calculated
an acute-duration inhalation minimal risk level (MRL) of 2.0 ppm and a chronic-duration inhalation
MRL of 1.0 ppm for 1,4-dioxane. The chronic-duration inhalation MRL was also adopted as the
intermediate-duration inhalation MRL. ATSDR used the LOAEL of 50 ppm from the study by
TABLE 6.18
Data Requirements for Estimating Total Dose by Different
Routes of Exposure to 1,4-Dioxane in Water
Direct ingestion of 1,4-dioxane through drinking:
Quantity water consumed (2 L for adults; 1 L for a 10 kg child)
Fraction of ingested 1,4-dioxane absorbed through gastrointestinal tract
Inhalation of 1,4-dioxane:
Air concentrations from showering, bathing, swimming, etc.
Duration of activities and amount of contaminated air breathed
Fraction of inhaled 1,4-dioxane absorbed through lungs
Skin absorption of 1,4-dioxane in water:
Period of time spent bathing or swimming
1,4-Dioxane content of cosmetics, shampoos, lotions
Quantity of residual shampoo, lotion applied, or cosmetic applied
Area of skin to which dioxane-containing sundries and cosmetics applied
Fraction of 1,4-dioxane absorbed through skin during bathing or swimming
Ingestion of 1,4-dioxane in food and drugs:
Concentration of 1,4-dioxane in food or drugs
Quantity of food and drugs consumed daily
Fraction of 1,4-dioxane absorbed through gastrointestinal tract
Source: Cohrssen, J.J. and Covello, V.T., 1989, Risk analysis: A guide to prin-
ciples and methods for analyzing health and environmental risks.
Washington, DC: Council on Environmental Quality.
Note: Average body weight is needed for all routes of exposure.