Regulation and Risk Assessment of 1,4-Dioxane - Environmental Investigation and Remediation - page 263

As described in Chapter 4, of the more than 10 million commercially available organic and inor-
ganic chemicals, only about a quarter million are subject to any form of regulation, far fewer are
routinely analyzed, and fewer still have been proi led and studied for health effects. Reviewing more
chemicals for addition to the list of regulated contaminants is essential to ensure public health pro-
tection. At the same time, some compounds on the list of regulated contaminants are being revisited
to determine whether to lower, raise, or eliminate their MCLs. For example, in California, revised
draft Public Health Goals for several chlorinated solvent compounds including methyl chloroform
and cis -1,2-dichloroethylene suggest that these compounds may not be as toxic as was i rst thought
when they were originally listed. Similarly, USEPA is reviewing whether to lower the toxicity
threshold used to establish the Preliminary Remediation Goal (PRG) for TCE. California has
established a Public Health Goal for perchloroethylene at 0.06 μg/L, whereas the MCL remains at
5 μg/L. Setting drinking water standards can be described as a l uid process that is by no means
smooth or certain. It is in this uncertain and sometimes controversial regulatory environment that
the evaluation of regulating 1,4-dioxane is being made.
The multiyear process of evaluating, listing, and approving additions to the list of regulated
contaminants includes many tiers of review and can be subjected to legal challenge and political
initiatives. For example, although methyl- tert butyl ether (MTBE) and perchlorate have been inves-
tigated and remediated for many years, the fact that these compounds are not yet regulated by a
federal MCL is due in part to a protracted review process. States may independently adopt and
implement regulation of drinking water contaminants on the basis of the prevalence and magnitude
of drinking water contaminants within their jurisdictions. To date, 1,4-dioxane and other solvent
stabilizer compounds are not regulated by USEPA, except for epichlorohydrin (formerly used to
stabilize TCE), which has an MCL goal of zero (USEPA, 2007b). In February 2008, 1,4-dioxane
was included in the third contaminant candidate list (CCL) (USEPA, 2008). 1,4-Dioxane has not yet
been included among the federal UCMR lists. Colorado became the i rst state to regulate 1,4-
dioxane in March 2005, as discussed further in Section 6.1.2.1 .
In 2004, USEPA's National Center for Environmental Assessment in the Ofi ce of Research and
Development began a review of the Integrated Risk Information System (IRIS) health assessment
for 1,4-dioxane (USEPA, 2004c). IRIS is a database of scientii c positions on potential adverse
human health effects that may result from chronic (or lifetime) exposure to chemicals in the envi-
ronment. IRIS contains chemical-specii c summaries of qualitative and quantitative health informa-
tion in support of dose-response evaluation. The IRIS database is used to support the development
of risk assessments, site-specii c environmental decisions, and rule making. USEPA's assessment of
the carcinogenic potential of 1,4-dioxane was added to the IRIS database in 1988.
The IRIS Program is preparing an assessment that will incorporate available health effects infor-
mation for 1,4-dioxane, as well as current risk-assessment methods. The assessment will present
reference values for the noncancer effects of 1,4-dioxane (the reference dose [RfD], and the refer-
ence concentration [RfC]), where supported by available data, and a cancer assessment. The
Toxicological Review and IRIS Summary will be subject to internal peer consultation, USEPA
review, and external scientii c peer review. The i nal product will rel ect the agency opinion on the
toxicity of 1,4-dioxane and is slated for completion by February 2009 (USEPA, 2007h).
This section proi les the existing regulations for 1,4-dioxane and compares the basis for
1,4-dioxane drinking water regulations and guidance adopted by three states.
6.1.1 F EDERAL
There is currently * no federal MCL or MCL Goal for 1,4-dioxane in drinking water. Several of the
USEPA regional ofi ces use an advisory guidance level of 6.1 parts per billion (ppb) for limiting
1,4-dioxane concentrations in drinking water. USEPA Region 9 covers the Pacii c southwest states
* As of early 2009.