NTP Posts Concept Papers on Chemicals Under Review for Report on Carcinogens

The National Toxicology Program has posted concept papers describing its planned approaches to evaluate five chemicals for possible or updated listing in the Report on Carcinogens.

The papers describe NTP's rationale for considering a chemical, medicinal, biological, radiological, or other substance.

They also describe in general terms the types of information, such as human or laboratory animal studies, that will be available for the review, the proposed approach for getting public and expert comment, key scientific questions at issue, what types of information the agency already has received from the public, and what NTP's approach was to identify scientific studies about the compound it will review.

The concept papers do not include proposed or final conclusions about the carcinogenicity of any of the chemicals being reviewed.

The five chemicals are 1-bromopropane (Chemical Abstracts Service No. 106-94-5), cumene (CAS No. 98-82-8), pentachlorophenol (PCP; CAS No. 87-65-5), ortho-toluidine (CAS No. 95-53-4), and trichloroethylene (CAS No. 79-01-6).

The concept papers along with public comments received to date were recently posted on NTP's website.

Concerns Raised About Worker Exposure.

NTP cites concerns about worker exposure as a key rationale for several of the reviews.

For example, “occupational exposure to workers is the major source of exposure to 1-bromopropane,” a solvent used in industrial and commercial applications and made in volumes between 1 million and 10 million pounds, NTP said.

The only enforceable occupational standard regulating 1-bromopropane in the United States is a California Occupational Safety and Health Administration permissible exposure limit of five parts per million (ppm), it said.

However, dry-cleaning workers are reported to be exposed to levels up to 54 ppm, while employees working in an adhesive spray facility with no ventilation were exposed to concentrations up to 247 ppm, NTP said.

“There is neither an OSHA Permissible Exposure Limit (PEL), nor a National Institute for Occupational Safety and Health Recommended Exposure Limit,” it said.

New scientific studies along with concerns about exposures to the general public are a key reason for the review of trichloroethylene, which is classified as a reasonably anticipated human carcinogens in the Report on Carcinogens, NTP said.

By Pat Rizzuto  

NTP's website, which provides links to each concept paper as well as public comments received to date, is at http://ntp.niehs.nih.gov/?objectid=94FDE852-AE35-3731-AFC44FA6BC15CD5D.