Polycyclic aromatic compounds (PACs) are widespread environmental contaminants. There are many different types of PACs, including polycyclic aromatic hydrocarbons (PAHs), which are discussed below. PACs can occur in complex mixtures or be synthesized as individual chemicals.

PACs are found naturally in fossil fuels (petroleum and coal). The release of PACs can occur through natural events such as volcanic eruptions and forest fires. They are also created and released into the environment by burning organic material such as fuels, garbage, and wood. Some PACs stay in the environment for a long time and do not break down easily. Polycyclic aromatic hydrocarbons were a particular concern following the Deepwater Horizon oil spill (see NIEHS Gulf Oil Spill Response Efforts).

How People are Exposed to PACs

People are rarely exposed to a single PAC. They are more often exposed to complex mixtures of PACs. The mixture depends on the source of the exposure, as well as other factors such as sunlight or weathering of contaminated materials.

People can be exposed to PACs in various ways, including:

• Eating certain foods such as chargrilled meat or smoked fish
• Breathing contaminated air
• Drinking contaminated water
• Absorbing PACs through the skin from tainted soil
• Exposure in workplaces which use petroleum or coal
• Exposure in workplaces that burn organic material such as wood, oil, garbage, or plants

For example, workers who produce tar or asphalt, or use these substances in roofing and paving, may be exposed to PACs.

Health Concerns Associated with Exposure to PACs

Some PACs are known carcinogens. Animal experiments have shown that certain PACs can cause damage to the immune and reproductive systems. However, the majority of PACs have not been evaluated for potential health effects, and research is needed to understand the combined effects of multiple PACs. NTP is currently studying PACs to learn more about the effects of individual PACs and PAC mixtures.

About Polycyclic Aromatic Hydrocarbons

PAC is a broad term which describes a large group of chemicals, including PAHs. PAHs are made up of only carbon and hydrogen atoms within their ring structure. PAH ring structures may have other atoms attached to the rings, creating alkyl-PAHs, nitro-PAHs, and oxy-PAHs.

Heterocyclic PACs contain other atoms besides carbon and hydrogen, such as nitrogen, oxygen, or sulfur within the ring structure. NTP is studying both PAHs and other PACs, so the broader term PACs is used to describe the range of compounds which are part of our research effort.

One of NTP's study efforts is the Polycyclic Aromatic Compounds Mixtures Assessment Program (PAC-MAP). This program aims to increase our understanding of the toxicity of PACs and PAC mixtures. In December 2012, NTP presented the research concept for PAC-MAP to the NTP Board of Scientific Counselors. In 2012, NTP Board members gave the approval for NTP research.

Under this program, NTP will use a wide range of tests in cells and rodents to assess the toxicity of individual PACs and PAC mixtures, and to identify potential health hazards.

See the table for a list of the studies and their descriptions.

PACs Tested in Rat Immunotoxicity Study

Below is a list of PACs tested in the rat immunotoxicity (28-day) study:

Cookstove Activities

The burning of solid fuels such as wood, charcoal, and dung results in a significant global health burden with over four million premature deaths per year attributed to indoor air pollution from inefficient use of solid fuels.

NTP is involved in studies to analyze the release of PACs associated with cookstove activities. Indoor air pollution caused by biomass burning is one of the five focus areas of environmental health concern for the Collaborating Centre for Environmental Health Sciences of World Health Organization (WHO), of which NIEHS is a partner. This formal partnership provides new opportunities for translating research findings into effective global public health interventions.

As an initial step, NTP held the Symposium on Assessing Exposures and Health Effects Related to Indoor Biomass Fuel Burning at NIEHS, Research Triangle Park, NC. This symposium brought together researchers to discuss policies and the way forward.

The 2012-2017 NIEHS strategic plan also identified Global Environmental Health as a priority research area with a focus on cookstoves and indoor air pollution.

Other NTP Evaluations

NTP has published a variety of technical reports, toxicity reports, immunotoxicological studies, and developmental toxicity abstracts for PACs and/or mixtures that contain PACs.

• NTP Technical Reports for PACs or Mixtures that Contain PACs
• NTP Toxicity Reports for PACs or Mixtures that Contain PACs
• Immunotoxicology Studies on 1,2:5,6-Dibenzanthracene
• Developmental Toxicity Abstract Studies on Naphthalene
• Report on Carcinogens (RoC) PAH Studies
• PAH Studies on Inflammation and Atherosclerosis

NTP Future Research

In the future, NTP will design experiments to see if we can predict the toxicity of PAC mixtures using our understanding of individual PACs. Data will also be gathered on environmental mixtures that contain PACs and used to predict the toxicity of untested mixtures.

Results from PAC-MAP will help address knowledge gaps identified in the 2011 NIEHS workshop Advancing Research on Mixtures: New Perspectives and Approaches for Predicting Adverse Human Health Effects.

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