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Fact Sheet on the Draft IRIS Toxicological Review of Libby Amphibole Asbestos for Interagency S cience Consultation May 13 , 2011

Background: In Libby, M ontana , the mining and milling of vermiculite, which was contaminated with amphibole asbestos, exposed workers and the residents to asbestos fiber s. Several million homes in the United States and Canada may have vermiculite attic insulation from the Libby mine. For the purposes of this document, the material from the mine near Libby, M T will be ca lled Libby Amphibole asbestos

. Amphiboles are a complex group of minerals.

INHALATION REFERENCE CONCENTRATION (RfC ):

Version Principal Study / Critical Effect POD (fibers

- yr/cc) UFs RfC (fibers/cc)

Current RfC
on IRIS N/A N/A N/A N/A

Inter a gency Science Consultation Draft (Ma y 2011) Marysville, OH worker cohort

exposure to Libby Amphibole asbestos ( Lockey et al., 1984; Rohs et al., 2008).

Sub

- cohort (n= 119 ) of total worker population (n=434)

, e xposure data based on analytical

measurements (post

- 1972) and recent follow

- up was selected due to limitations in exposure estimates (no measurement pre

1972), and preference for use of radiographic data from the 2002

- 2005 update.

Critical effect selected is localized pleural thickening as identified by radiographic analysis. BMC L 10 = 0.076 100

10

– intra species
10

– database
uncertainties 1 x 10 - 5

*See footnote
for details



### * The POD is based on cumulative exposure. To obtain the RfC, the POD is divided by 60 years (lifetime of 70 years minus 10 years to account for lagged exposures) and then divided by the UF of 100.

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CANCER ASSESSMENT:

Version Cancer

Descriptor Study used for Q uantitation Extrapolation
Method Inhalation

Unit Risk (fibers

yr /cc) Oral Slope

Factor (mg/kg

- day) - 1

Current assessment on IRIS 1 N/A N/A N/A N/A N/A

Inter a gency Science Consultation Draft ( May 2011) “Carcinogenic

to human.”

Based on strong human evidence of an association between exposure to Libby Amphibole asbestos and the

occurrence of mesothelioma and lung cancer in the workplace and a finding of mesothelioma risk among

non

occupationally exposed residents of Libby, MT. Libby worker cohort:

s tudied by NIOSH researchers with several updates (Amandus and Wheeler, 1987; Amandus et al., 1987a; Sullivan

, 2007).

NIOSH conducted two epidemiologic investigations, resulting in several publications (listed above). EPA collaborated with NIOSH to update the mortality data through 2006. It is this update which has been modeled by EPA to derive the IUR.

Workers were employed at the Libby, MT vermiculite mine, mill and processing plant. Sub

cohort (n=880) , hired after 1959 or later, of total worker population (n=1871) selected for derivation of IUR due to limitations in earlier exposure estimates, and resulting issues with exposure

- response modeling of full cohort data. Linear extrapolation from PODs determined by lifetable analysis. 0.17 None established

1 Although there is currently no health assessment specific to Libby Amphibole asbestos, there is a previous inhalation health assessment for asbestos in general that EPA has previously used in assessing risks from L ibby Amphibole asbestos . That assessment (U.S. EPA, 1988) determined that asbestos is a human carcinogen (Class A) based on an synthesis of 14 human studies (including chrysotile, amosite and asbestos mixtures) demonstration lung cancer and/or mesothelioma following exposure to various forms of asbestos (AAHUA, 1986). That assessment derived an IUR of 0.23 fibers/cc.