Environmental Engineering Reference
In-Depth Information
By using the cancer potency of 0.011 (mg/kg d) −1 from the same study (see footnote), the NL is
calculated as follows:
-
6
70
¥
10
NL
=
=
3.2
m
g/L
ª
3
m
g/L.
(6.6)
-
2
1.1
¥¥
10
2
6.1.2.3 Connecticut's Comparison Value for 1,4-Dioxane
The Connecticut Department of Public Health (CT DPH) derived an advisory comparison value of
20 ppb for 1,4-dioxane in drinking water. CT DPH notes that 1,4-dioxane can cause liver cancer at
and above 1000 mg per kilogram body weight per day (mg/[kg d]); 1,4-dioxane is somewhat toxic
to the liver and possibly carcinogenic at 100 mg/(kg d); and there is a slight suggestion of carcino-
genic response at 25 mg/(kg d) in rats. At 10 mg/(kg d), research studies note no tumors or toxicity
in the liver in rats. The chronic cancer NOAEL is therefore taken to be 10 mg/(kg d). CT DPH also
considers this NOAEL to be protective for other toxic effects, as it is 17,500 times greater than the
daily dose derived from drinking 2 L of water with a 1,4-dioxane concentration of 20 μg/L (Chute
and Ginsberg, 2004).
The Connecticut Comparison Value was derived by applying the NOAEL (10 mg/(kg d)) and a
UF of 3000 to obtain an RfD of 3.3 μg/(kg d). This dose is then calculated for a 70 kg person drink-
ing 2 L/day, which results in a threshold of 115 μg/L if 100% exposure is from drinking water. The
RSC of 20% exposure from drinking water is then applied, resulting in a comparison value of
23.1 ppb, which is rounded down to 20 ppb for simplicity (Chute and Ginsberg, 2004, 2005).
A 1,4-dioxane contamination case in Durham, Connecticut, led to a Health Consultation prepared
jointly by the Agency for Toxic Substances and Disease Registry (ATSDR) and CT DPH. The Health
Consultation focused on consequences of 1,4-dioxane in drinking water at concentrations of up to
27 ppb by up to 80 people obtaining drinking water from 20 private wells that were contaminated by
chlorinated solvents from nearby manufacturing businesses. The businesses produced metal boxes
and used methyl chloroform for vapor degreasing for 23 years; however, the duration of exposure to
1,4-dioxane in well water is unknown. The majority of 1,4-dioxane detections was below Connecticut's
20 ppb advisory comparison value. Because 1,4-dioxane concentrations were only slightly above the
20 ppb comparison value, and because the great majority of detections were below 20 ppb, CT DPH
does not think that these exposures are likely to cause adverse health effects (ATSDR, 2005c).
The 20 ppb comparison value provides a factor of safety ranging from 8000 to 40,000 depending
on assumptions of total exposure. Although past exposures in the Durham case could have been
higher than those measured recently, regulatory toxicologists estimate that the toxicity from expo-
sure to TCE, which is also present in well water and is now removed by carbon i lters, would likely
have posed a much greater health threat than exposure to 1,4-dioxane (ATSDR, 2005c). CT DPH
and ATSDR concluded that the 1,4-dioxane in well water does not pose a public health hazard
because exposure doses and risks are well below the threshold where adverse health effects caused
by exposure could reasonably be expected to occur. Nevertheless, as a precaution, CT DPH recom-
mended that residents use bottled water instead of treated well water, because the carbon treatment
did not remove 1,4-dioxane (ATSDR, 2005c). Table 6.2 summarizes the risk factors incorporated
into establishing regulatory guidance and statutes in California, Connecticut, and Colorado.
6.1.2.4 Michigan's Proposed Maximum Contaminant Level
Michigan pioneered the regulatory response to 1,4-dioxane contamination because of the large release
of 1,4-dioxane from the Pall Life Sciences/Gelman site near Ann Arbor (PLS/Gelman; see case his-
tory of this site in Chapter 8). When the contamination near Ann Arbor was i rst discovered in 1985,
Michigan's advisory generic residential cleanup criterion for 1,4-dioxane was 3 ppb for groundwater
and 60 ppb for soils. In June 1995, the state legislature amended Part 201 of the state code (the section
addressing environmental remediation), which resulted in an increase of the generic residential cleanup
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