Technical Factsheet on: POLYCYCLIC AROMATIC HYDROCARBONS (PAHs)
List of Contaminants
As part of the Drinking Water and Health pages, this fact sheet is part of a larger publication:
National Primary Drinking Water Regulations
Drinking Water Standards
MCLG: zero mg/L
Mcl: 0.0002 mg/L
HAL(child): none
Health Effects Summary
Acute: EPA has found polycyclic aromatic hydrocarbons (PAHs)
similar to benzo(a)pyrene to potentially cause the following
health effects from acute exposures at levels above the MCL: red
blood cell damage, leading to anemia; suppressed immune system.
Drinking water levels which are considered "safe" for short-term
exposures have not been established at this time.
Chronic: Benzo(a)pyrene has the potential to cause the
following health effects from long-term exposures at levels above
the MCL: developmental and reproductive effects.
Cancer: There is some evidence that benzo(a)pyrene has the
potential to cause cancer from a lifetime exposure at levels
above the MCL.
Usage Patterns
Benzo(a)pyrene is one of a group of compounds called polycyclic
aromatic hydrocarbons (PAHs), or polynuclear aromatic
hydrocarbons (PNAs). They are not produced or used commercially
but are ubiquitous in that they are formed as a result of
incomplete combustion of organic materials.
Release Patterns
PAHs are found in exhaust from motor vehicles and other gasoline
and diesel engines, emission from coal-, oil-, and wood-burning
stoves and furnaces, cigarette smoke; general soot and smoke of
industrial, municipal, and domestic origin, and cooked foods,
especially charcoal-broiled; in incinerators, coke ovens, and
asphalt processing and use.
There are two major sources of PAHs in drinking water: 1)
contamination of raw water supplies from natural and man-made
sources, and 2) leachate from coal tar and asphalt linings in
water storage tanks and distribution lines. PAHs in raw water
will tend to adsorb to any particulate matter and be removed by
filtration before reaching the tap.
PAHs in tap water will mainly be due to the presence of
PAH-containing materials in water storage and distribution
systems. Though few data are available for estimating the
potential for PAH release to water from these materials, there
are reports that levels can reach 0.01 mg/L with optimum leaching
conditions.
Environmental Fate
Released benzo(a)pyrene is largely associated with particulate
matter, soils, and sediments. Although environmental
concentrations are highest near sources, its presence in places
distant from primary sources indicates that it is reasonably
stable in the atmosphere and capable of long distance transport.
When released to air it may be subject to direct photolysis,
although adsorption to particulates apparently can retard this
process. It may also be removed by reaction with ozone (half-life
37 min) and NO2 (half-life 7 days), and an estimated half-life
for reaction with photochemically produced hydroxyl radicals is
21.49 hr.
If released to water, it will be expected to adsorb very strongly
to sediments and particulate matter. It will not hydrolyze. It
has been shown to be susceptible to significant metabolism by
microorganisms in some natural waters without use as carbon or
energy source, but in most waters and in sediments it is stable
towards biodegradation. BaP will be expected to undergo
significant photodegradation near the surface of waters.
Evaporation may be significant with a predicted half-life of 43
days. However, adsorption to sediments and particulates may
significantly retard biodegradation, photodegradation, and
evaporation.
If released to soil it will be expected to adsorb very strongly
and will not be expected to leach to the groundwater. However,
its presence in some groundwater samples indicates that it can be
transported there by some mechanism. It will not hydrolyze, and
evaporation from soils and surfaces is not expected to be
significant. Biodegradation tests in soils have resulted in a
wide range of reported half-lives: 2 days to 1.9 yr. Based on
these values and the apparent lack of a significant competing
fate process, biodegradation may be an important process in
soils.
Benzo(a)pyrene is expected to bioconcentrate in aquatic organisms
that can not metabolize it. Reported BCFs include: Oysters, 3000;
Rainbow trout, 920; Bluegills, 2,657; zooplankton, 1000 to
13,000. The presence of humic acid in solution has been shown to
decrease bioconcentration. Those organisms which lack a metabolic
detoxification enzyme system, tend to accumulate polycyclic
aromatic hydrocarbons. For example, BCFs have been found to be
very low (<1) for mudsuckers, sculpins and sand dabs.
Human exposure will be from inhalation of contaminated air and
consumption of contaminated food and water. Especially high
exposure will occur through the smoking of cigarettes and the
ingestion of certain foods (eg smoked and charcoal broiled meats
and fish).
Chemical/ Physical Properties
CAS Number: 50-32-8
Color/ Form/Odor: Pale yellow needlelike crystals, faintly
aromatic
M.P.: 179-179.3 C B.P.: >360 C
Vapor Pressure: >1 mm Hg at 20 C
Density/Spec. Grav.: 1.35 at 15 C
Octanol/Water Partition (Kow): Log Kow = 6.04
Solubility: 0.0038 mg/L of water at 25 C; very low solubility
in water
Soil sorption coefficient: Log Koc =6.6 to 6.8; very low mobility
in soil
Odor/Taste Thresholds: N/A
Bioconcentration Factor: BCFs range from <1 to 2675 in fish;
expected to bioconcentrate in aquatic organisms which are unable
to metabolize it.
Henry's Law Coefficient: N/A; volatilization not significant
Trade Names/Synonyms: 3,4-Benz(a)pyrene; BaP; BP
Other Regulatory Information
Monitoring For Ground/Surface Water Sources:
- Initial Frequency- 4 quarterly samples every 3 years
- Repeat Frequency- If no detections during initial round:
- 2 quarterly per year if serving >3300 persons;
- 1 sample per 3 years for smaller systems
- Triggers - Return to Initial Freq. if detect at > 0.00002 mg/L
Analysis:
| Reference Source |
Method Numbers |
| EPA 600/4-88-039 |
525.1; 550; 550.1 |
Treatment- Best Available Technologies:
Granular Activated Charcoal
For Additional Information:
EPA can provide further regulatory and other general information:
EPA Safe Drinking Water Hotline - 800/426-4791
Other sources of toxicological and environmental fate data include:
Toxic Substance Control Act Information Line - 202/554-1404
Toxics Release Inventory, National Library of Medicine - 301/496-6531
Agency for Toxic Substances and Disease Registry - 404/639-6000
List of Contaminants
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