EPA Analysis Finds Combustion Chemical, Coal Tar Constituent Carcinogenic to Humans

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By Pat Rizzuto  


The Environmental Protection Agency on Aug. 21 released a draft toxicological review of benzo[a]pyrene that found the combustion byproduct and coal tar constituent is carcinogenic to humans and harmful to developing organs and systems.

“There is no known commercial use for benzo[a]pyrene,” which is part of a family of air pollutants produced unintentionally by combustion, EPA said.

Benzo[a]pyrene (CAS No. 50-32-8) is ubiquitous in the environment from forest fires, motor vehicle exhaust, coal-burning furnaces, and other combustion sources, EPA said.

The chemical also is a constituent of coal tar, which is used for roofing and asphalt from which it drains into watersheds, EPA said. Coal tars are complex combinations of polycyclic aromatic hydrocarbons (PAHs), phenols, heterocyclic oxygen, sulfur, and nitrogen compounds. The tars are among the by-products of coal coking and gasification.

Information in the toxicological review may be useful for cumulative risk assessments that examine the combined effect of multiple agents acting on the same organs or biological systems, the document said.

EPA said workers involved in the production of aluminum, coke, graphite, and silicon carbide along with ones dealing with coal tar may be exposed to benzo[a]pyrene and other PAHs.

Next Steps Outlined

The analysis, conducted as part of EPA's Integrated Risk Information System program, is subject to public comment through Oct. 21. They should be marked Docket ID No. EPA-HQ-ORD-2011-0391 and submitted to http://www.regulations.gov.

The analysis, which will be peer-reviewed, will be discussed at a public meeting Oct. 23-24, EPA said in an Aug. 21 notice (78 Fed. Reg. 51,719).

When final, the analysis' information about the health problems benzo[a]pyrene can cause and dose levels that could trigger those effects would be considered by agency, state, and other decisionmakers when they consider the human health risks of particular situations involving exposure to benzo[a]pyrene and determine whether regulations or other forms of risk management are needed.

In April, Vincent Cogliano, acting director of IRIS, said the benzo[a]pyrene assessment would be illustrative of changes the IRIS program is making in response to recommendations by the National Academies and other advisory groups (37 CRR 405, 4/8/13).

The draft toxicological review was organized to provide varying levels of information, from a summary of key findings to details on the scientific literature identified and criteria used to select studies for analysis.

New Organizational Structure Included

The document included a new organizational structure that separates hazard information from data about various doses that could trigger divergent hazards.

The document included dozens of tables and graphical depictions to communicate information and better explain how EPA reached its conclusions.

The draft analysis included the agency's first-ever dermal slope factor, which risk assessors could use to predict cancers that may result after skin exposure to benzo[a]pyrene.

Finally, the draft analysis included more information about how benzo[a]pyrene can affect different organs and biological systems, such as the immune system, than EPA often is able to provide for other chemicals.

EPA's draft analysis concluded benzo[a]pyrene is carcinogenic to humans based on “strong and consistent evidence in [laboratory] animals and humans.”

The conclusion would change EPA's classification of the chemical, which the agency currently considers to be a probable human carcinogen.

The proposed classification is consistent with conclusions reached in 2010 by the International Agency for Research on Cancer and California's Environmental Protection Agency, according to supplemental information accompanying the draft toxicological review.

Early life exposures to benzo[a]pyrene would increase the chemical's potential to cause cancer later in life, EPA's draft toxicological review said.

The draft analysis provided potency information and age-dependent adjustment factors to help risk assessors modify their analyses based on the situations and ages of the populations they are analyzing.

Concerns About Development

EPA's analysis also would provide the agency's first numerical values that risk assessors could use to determine exposure levels that should not result in benzo[a]pyrene causing health problems other than cancer.

When EPA examined non-cancer effects in 1987, scientific data were not available to provide these risk values, called reference doses (RfDs) for ingested compounds and reference concentrations (RfCs) for inhaled substances.

Scientific studies conducted since then raised a variety of concerns other than cancer. EPA chose to focus on potential harm benzo[a]pyrene could cause to human development because studies found those problems could occur at lower doses than other problems.

In response to previous suggestions by scientific advisers, state agencies, and other parties that would like to fine-tune their risk assessments to specific situations and populations, EPA's draft analysis proposes a variety of RfDs and RfCs.

The reference values provide information about organ and systemic effects studies have shown the chemical to have.

Cumulative Risk Assessments

“These reference values may be useful for cumulative risk assessments that consider the combined effect of multiple agents acting on the same biological system,” EPA's toxicological review said.

EPA also provided what it called an overall RfD and RfC to designate the lowest dose levels that EPA estimates people, including vulnerable populations, could experience over their lifetimes without harm.

To prevent harm to the developing nervous system, EPA proposed an overall RfD of 0.0003 milligrams benzo[a]pyrene per kilogram of bodyweight per day (mg/kg-d) or 3 x 10-4 mg/kg-d.

Based on fetal deaths that occurred in laboratory rats, EPA derived an overall RfC of 0.000002 milligrams benzo[a]pyrene per cubic meter of air (mg/m3) or 2 x 10 -6 mg/m3.


EPA's draft toxicological review of benzo[a]pyrene and related information are available at http://cfpub.epa.gov/ncea/iris_drafts/recordisplay.cfm?deid=66193.

Information about the Oct. 23-24 meeting and registration is available at http://www.epa.gov/iris/publicmeeting/iris_bimonthly-oct2013/index.htm.

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