In June 2010, EPA decided to put four of its ongoing IRIS assessments on hold pending a review of some of the underlying studies used in the assessments. The four assessments included: Methanol, MTBE (methyl tert butyl ether), ETBE (ethyl tert butyl ether) and Acrylonitrile.

EPA made this decision after receiving a report from the National Toxicology Program (NTP) that reviewed results of some research studies completed by the Ramazzini Institute (RI), a lab in Italy that conducts animal testing to evaluate the potential cancer-causing effects of chemicals. The report found differences of opinion between NTP and RI scientists in the diagnosis of certain cancers reported in a study on methanol.

• To follow up on these findings, EPA collaborated with the National Institute of Environmental Health Sciences (NIEHS) to jointly sponsor an independent group of scientists, the Pathology Working Group (PWG), to review a larger group of animal studies performed in the RI lab.
   
• The report pointed out some instances where the presence of respiratory infections in RI study animals made definitive diagnoses difficult, and that some RI diagnoses, primarily certain leukemias and lymphomas, were not considered to be malignant tumors. As a result, PWG scientists found fewer numbers of leukemias and lymphomas than had been originally reported by the RI.
   
• Because of the differences of opinion between the RI and PWG scientists in diagnosing leukemias and lymphomas, EPA has decided not to rely on data from the RI on lymphomas and leukemias in these IRIS assessments. This decision will impact the IRIS assessments for methanol, MTBE and ETBE. The draft assessment for acrylonitrile was not affected, as EPA relied on data from sources other than RI to complete this IRIS assessment.
   
• There was good agreement between the RI and PWG scientists in diagnosing solid tumors such as liver tumors from the RI study on vinyl chloride. EPA has therefore decided to continue to consider RI solid tumor data in IRIS assessments. RI solid tumor findings will be reviewed along with other data in determining the overall weight of evidence of carcinogenicity for substances on which EPA is conducting IRIS assessments.
   
• The PWG made recommendations for changes in RI's laboratory procedures and EPA hopes that RI will fully implement these recommendations to allow for the use of future RI data in IRIS assessments.

Previous Announcements

• EPA Places Four IRIS Assessments on Hold Pending Review, June 15, 2010
• EPA Announces Plan of Action to Address Four IRIS Assessments, April 11, 2011