Re: [CPEO-MEF] Air Force challenges draft TCE assessment

[Lenny Siegel <lsiegel@cpeo.org>]

In response to my posting on the dispute between the state of Colorado
and the Air Force over the use of standards based on EPA's draft
toxicity assessment for trichloroethylene (TCE), I indirectly received a
series of documents on the subject from Denver-based EPA Region 8.
Region 8 apparently agrees with the Air Force position.

I have pasted below two of those documents. The other two are more
technical. I believe the unit "_g/m3" in the second document below
represents micrograms per cubic meter.

The discussion, in the second document, of "background" levels of TCE in
air is particularly significant. We've been confronting this issue at
one of the military housing areas here at Moffett Field. The reported
ambient presence of TCE at concentrations that pose health concerns
might lead to an easing of requirements at TCE remediation sites,
because the contamination appears to be everywhere, beyond control. 

But it is by no means re-assuring.  Unlike other background contaminants
- such as arsenic and manganese - TCE does not occur naturally in the
environment. TCE supposedly breaks down fairly rapidly in the
atmosphere. If it turns out that many of us are breathing unhealthy
levels of TCE around the clock, that represents a failure of the
risk-based system of response to toxic substance exposure. At Moffett,
it appears that reports of high ambient regional concentrations were
exaggerated, but we residents of Mountain View are awaiting the results
of more widespread sampling before we breathe easy.

Lenny

***

Trichloroethylene Briefing Package
[U.S. EPA Region 8]

March 25, 2003

Purpose of Briefing

The purpose of this briefing is to provide information for Superfund and
RCRA management on the scientific issues relating to the hazard
assessment of trichloroethylene (TCE) and its implications for the
Region.  More detailed information is in the attachments. 

History of TCE Hazard Assessment

TCE is a chlorinated solvent which has been widely used in the
industrial degreasing of fabricated metal parts; it is also commonly
used as a chemical intermediate in the production of vinyl chloride. 
TCE is a common air and water pollutant, and it is frequently identified
in the groundwater at Superfund and RCRA sites. Long-term exposure to
TCE may be associated with liver and kidney toxicity, neurotoxicity,
developmental toxicity, immunotoxicity, and several forms of cancer.

EPA conducted hazard assessments for TCE in 1985 and 1987.  Based on the
findings of cancer in laboratory animals, EPA classified TCE as a
Probable Human Carcinogen (Group B2).  EPA derived an oral Cancer Slope
Factor of 0.011 per mg/kg-day and an Inhalation Unit Risk of 0.0000017
per µg/cubic meter.  These values were formally loaded on EPA's
Integrated Risk Information System (IRIS).  Because of the continuing
dispute with EPA's Science Advisory Board over the cancer
classification, EPA withdrew these assessment from IRIS in July 1989. 
However, EPA has continued to endorse the use of these risk values.

In August 2001, EPA's National Center for Environmental Assessment
(NCEA) completed a preliminary Draft Assessment of the health risks
posed by TCE (USEPA, 2001).  The Draft Assessment proposed a provisional
oral reference dose (RfD) of 0.0003 mg/kg(d and a provisional inhalation
reference concentration (RfC) of 0.04 mg/m3.   Several provisional
cancer slope factors (CSFs) were developed, with most between 0.02 and
0.4 per mg/kg(d.  These new risk values dramatically increased the
calculated risk at the same exposure.  These values have not been loaded
on IRIS.  The Superfund Technical Support Center and several Regions are
using these values. 

The public comment period for the Draft Assessment closed in January,
2002.  Approximately one thousand pages of comments were submitted.  In
June, 2002, the EPA Science Advisory Board (SAB), Environmental Health
Committee, convened a panel of TCE experts to provide an external peer
review of the Draft Assessment.  The SAB panel's review was released in
September (SAB, 2002).  Our interpretation of the SAB panel's review of
the Draft Assessment indicates that several man-years of effort are
required to adequately respond to the issues raised by the SAB panel.

Recommendation of Region 8 Toxicologists

EPA Region 8 Toxicologists do not recommend using the provisional hazard
assessment for the following reasons:   

1) methods used to reconstruct TCE exposures in the epidemiological
studies employed in the development of the provisional values are
inappropriate; and  

2) comments provided by EPA's Science Advisory Board TCE Review Panel
indicate numerous critical scientific issues in the Draft Assessment of
TCE requiring significant improvement; and

3)  risk-based concentrations (RBCs) based on the provisional CSFs fall
below typical indoor air background levels.

EPA Region 8 Toxicologists recommend using the old hazard assessment and
quantitative values until the IRIS consensus review process has finished
and a new file is loaded on IRIS.  

***

EPA REGION 8 POSITION PAPER

Provisional Trichloroethylene Cancer Slope Factors:
Impact on Evaluation of Background Trichloroethylene Concentrations in
Indoor Air

March 25, 2003


Purpose
The purpose of this position paper is to provide a brief discussion
regarding the impact of the new provisional TCE Cancer Slope Factors
(CSFs) on evaluation of TCE concentrations in indoor air.

Summary

Implementation of the new provisional values in the derivation of RBCs
for TCE in indoor air will drive acceptable levels below those typically
encountered as background from the use of consumer products and
lifestyle.  For example, using the high end of the provisional CSF range
proposed in the TCE Draft Assessment, 0.4 (mg/kg(d)-1, the RBC for TCE
in ambient air at a cancer risk level of one in one million (1.0 x 10-6)
is 0.016 _g/m3 (EPA Region 3 Risk-Based Concentration Table, October
2002).  Average background concentrations in indoor air have been
reported in the literature as ranging between 0.15 and 5.0 _g/m3 (Foster
et al. 2002; Kurtz and Folkes 2002; MADEP 1998).  Comparison of the RBC
with background range illustrates that the RBC is approximately 10 - 300
times lower than the range of average indoor air concentrations.  The
result in terms of risk management will be an increased number of sites
at which TCE is identified as a risk driver, as well as a significant
increase in costs associated with remediation at those sites.  


References

Foster SJ, Kurtz JP, Woodland AK (2002) Background indoor air risks at
selected residence in Denver, Colorado. Proceedings: Indoor Air 2002,
9th International Conference on Indoor Air Quality and Climate,
Monterey, CA, June 30-July 5, 2002; pp. 932-937.  

Kurtz JP, Folkes DJ (2002) Background concentrations of selected
chlorinated hydrocarbons in residential indoor air. Proceedings: Indoor
Air 2002, 9th International Conference on Indoor Air Quality and
Climate, Monterey, CA, June 30-July 5, 2002; pp. 920-925.  

Massachusetts Department of Environmental Protection (MADEP) (1998)
Indoor Air Sampling and Evaluation Guide. Draft. September.

USEPA (2002) Region 3 Risk-Based Concentration Table (October).  http://www.epa.gov/reg3hwmd/risk/index.htm.

USEPA (2001) External Review Draft: Trichloroethylene Health Risk
Assessment: Synthesis and Characterization. Office of Research and
Development, Washington, DC. EPA/600/P-01/002A; http://cfpub1.epa.gov/ncea/cfm/nceahome.cfm.


-- 


Lenny Siegel
Director, Center for Public Environmental Oversight
c/o PSC, 278-A Hope St., Mountain View, CA 94041
Voice: 650/961-8918 or 650/969-1545
Fax: 650/961-8918
<lsiegel@cpeo.org>
http://www.cpeo.org

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