Aromatic Hydrocarbon Structure Index
What are polycyclic aromatic hydrocarbons?
Polycyclic aromatic hydrocarbons (PAHs) are a group of
over 100 different chemicals that are formed during the incomplete burning
of coal, oil and gas, garbage, or other organic substances like tobacco or
charbroiled meat. PAHs are usually found as a mixture containing two or more of
these compounds, such as soot.
Some PAHs are manufactured. These pure PAHs usually exist
as colorless, white, or pale yellow-green solids. PAHs are found in coal tar,
crude oil, creosote, and roofing tar, but a few are used in medicines or to make
dyes, plastics, and pesticides.
Activation by Polycyclic Aromatic Hydrocarbons: Evidence for the Involvement of
Stress-Activated Protein Kinases, Activator Protein-1, and Antioxidant Response
Characterization and Bioactivity of Polycyclic Aromatic Hydrocarbons from
Non-Oxidative Thermal Treatment of Pyrene-Contaminated Soil at 250-1,000°C
Polynuclear Aromatic Hydrocarbons (PNAs)
of Polynuclear Aromatic Hydrocarbons (PAHs)
The main chemicals of concern are polycyclic aromatic
hydrocarbons (PAHs) which are also known as polynuclear aromatic hydrocarbons (PNAs).
Possible health hazards associated with PAH exposure include cancer, skin
problems, immunodeficiency, and reproductive difficulties for both the exposed
and their offspring.
More than 100 different chemicals are compiled into the
general category of polycyclic aromatic hydrocarbons. Each of these chemicals
may affect the body in different ways. Therefore, identifying chemicals of
concern in CTPVs is important. These PAHs include benzo[a]pyrene and
dibenz[a]anthracene, which are known to cause cancer, and pyrene, acridine,
chrysine, phenanthrene, and anthracene.
Links to more
information about these chemicals.
TITLE: Chemical Contaminants in House Dust:
Occurrence and Sources AUTHOR(S) John W. Roberts1, William
T. Budd2, Jane Chuang3, and Robert G. Lewis4
PERFORMING ORGANIZATION NAME AND ADDRESS 3Battelle,
Columbus, OH 2Envirometrics, Inc. - Seattle, WA 1Engineering Plus, Inc., 1425 E.
Prospect #3, Seattle, WA 98112 and 4U.S. EPA, AREAL, RTP, NC 27711
SPONSORING AGENCY NAME AND ADDRESS U.S. Environmental
Protection Agency Atmospheric Research and Exposure Assessment Laboratory
Research Triangle Park, NC 27711
Pesticides, polynuclear aromatic hydrocarbons (PAHs),
lead (Pb), and other metals accumulate in home soil and house dust. Exposure of
infants and toddlers to Pb by dust may be greater than other pathways. Many
pollutants found in carpet dust are protected from degradation and accumulate
over time. Greater numbers of pesticides are found in house dust than in indoor
air. Pb and PAH concentrations appear to be magnified in house dust when
compared with midyard and walkway soil samples. Studies using methods developed
by the U.S. EPA show evidence of track-in and/or carry-in of Pb, PAHs and
pesticides on clothes. Preliminary results of an eight-home study report PAHs in
house dust at 1 to 100 ppm and suggest track-in as a major source of PAHs in
house dust. FOR ADDITIONAL INFORMATION, CONTACT GLORIA J. KOCH,
EPA, (919) 541-4109 OR FTS 629-4109
Introduction to Aromatic Hydrocarbons
When a double bond replaces one of the single
carbon-carbon bonds in cyclohexane, the double bond behaves just as a single
bond in hexene or any other alkene. Introduction of a second double bond on a
non-adjacent carbon gives cyclohexadiene; the two double bonds behave much like
double bonds when only one is present in the molecule. However, introduction of
a third double bond in the ring structure to give cyclohexatriene produces a
radical change in the electron distribution in the ring. Halogens and hydrogen
no longer are capable of adding to it easily, nor is it easily oxidized. All
carbon-carbon bonds are found to be identical in length and reactivity. All of
the carbon-hydrogen bonds are identical as well. The carbon atoms now lie in a
plane, where in cyclohexane and cyclohexene they do not. Thus the structural
representations appropriate for cyclohexatriene do not accurately describe the
nature of the cyclic C6H6 molecule.
As a consequence, the ring structure is called benzene
rather than cyclohexatriene and is often represented by a circle rather than
Benzene is the simplest of the aromatic
hydrocarbons, which are those hydrocarbons in which one or
more ring has aromatic character due to the rearrangement of the pi
bonding electrons in what would otherwise be alternating single and double
bonds. Aromatic character can arise whenever two equivalent canonical
structures involving alternate single and double bonds can be drawn for an
organic molecule, even if it is not a ring. The actual structure is sometimes
called a resonance hybrid of the two equivalent canonical structures. Rings with
aromatic character are remarkably stable to chemical attack.
Substituted benzenes can be formed by reagents such as
chlorine. Chlorine adds directly across the double bond of cyclohexene to give
1,2-dichlorohexane, but chlorine reacts only under more extreme conditions with
benzene and when it does so the products are chlorobenzene and hydrogen
While substituted benzenes can be named by the usual IUPAC
substitution method, many of them are commonly known by trivial names.
Methylbenzene, for example, is known as toluene, and the three possible
dimethylbenzenes are known as the xylenes.
The denoting of adjacent groups on a ring as ortho, those
of one carbon apart as meta, and those on opposite sides of the ring as para is
a common, though non-systematic, method of designating positions of substituent
groups on aromatic rings in more complex cyclic compounds. Other examples
of trivial names for substituted benzenes are phenol (hydroxybenzene), aniline (aminobenzene
or, more commonly, benzylamine), anisole (methoxybenzene), and phenetole (ethoxybenzene).
More complex cyclic hydrocarbons may involve many
rings, some aromatic and some non-aromatic or aliphatic. In most
cases the entire ring structure is given a particular non-systematic name. Two
of the simplest are the two-ring and three-ring aromatic structures,
which are called napthalene and anthracene. Multiple-ring structures are often
called polynuclear aromatic hydrocarbons.
Substitution upon polynuclear hydrocarbons whether aromatic
or aliphatic is described in the usual way, but the numbering of the carbons is
not obvious in complex structures. Reference works giving the ring structure and
indicating carbon number have been compiled and should be consulted in order to
name the structures.
1997 James R. Fromm (email@example.com)
1996 James A. Plambeck (Jim.Plambeck@ualberta.ca).