National Toxicology Program

National Toxicology Program

NTP PACs Research

Man working on asphalt roadway

Polycyclic Aromatic Compounds are widespread environmental contaminants. There are many different types of PACs, and this large group of chemicals includes polycyclic aromatic hydrocarbons. PACs may occur in complex mixtures or be synthesized as individual chemicals.

PACs are found naturally in fossil fuels (petroleum and coal) and are created and released into the environment through burning of organic material (e.g., fuels, garbage, wood). Polycyclic aromatic hydrocarbons were of particular concern following the Deepwater Horizon oil spill (see NIEHS Gulf Oil Spill Response Efforts). Some PACs stay in the environment for a long time and do not break down easily.

How People are Exposed to PACs

People are usually not exposed to single PACs, but to complex mixtures of PACs that differ depending on the source of the exposure and other factors (e.g., sunlight, weathering of contaminated materials). Environmental releases of PACs can occur through natural events (e.g., volcanic eruptions, forest fires). People can be exposed to PACs by eating certain foods (e.g., chargrilled meat, smoked fish), breathing contaminated air, drinking contaminated water, or through the skin by handling tainted soil. People can be exposed at workplaces that use petroleum or coal, or burn organic material like wood, oil, garbage, and vegetation. For example, workers at plants that produce tar or asphalt may be exposed to PACs, as well as workers that use materials with PACs like roofers and pavers.

Health Concerns Associated With Exposure to PACs

Some PACs are known carcinogens, and studies in experimental animals have shown that certain PACs can cause toxicity to the immune and reproductive systems. The vast majority of PACs have not been evaluated for potential effects on health, and research is needed to understand the combined effects of multiple PACs. NTP is currently studying PACs to learn more about the toxicity of individual PACs and PAC mixtures.

Polycyclic Aromatic Hydrocarbons are Polyclyclic Aromatic Compounds

PACs is a broad categorical term that describes a large group of chemicals. PACs include chemicals like PAHs and other related polycyclic compounds.

PAHs are made up of only carbon and hydrogen atoms within the ring structure. PAH ring structures may have other atoms attached to the rings, such as alkyl-PAHs, nitro-PAHs, and oxy-PAHs.

PACs that are not PAHs contain other atoms besides just carbon and hydrogen, such as nitrogen, oxygen, or sulfur within the ring structure.

NTP is studying PAHs and other PACs, so the broader term, PACs, is used to describe the range of compounds that are part of NTP's research effort.

NTP is located at the National Institute of Environmental Health Sciences, part of the National Institutes of Health.