United States
Environmental Protection
Agency
Office of
Solid Waste and
Emergency Response
Publication 9230.0-05FSb
September 1992
Superfund Fact Sheet:
Exposure Pathways
Office of Emergency and Remedial Response
Hazardous Site Control Division (5203G)
Quick Reference Fact Sheet
Method Of Exposure A hazardous substance is a threat to human health only if people are exposed to it
Exposure happens only if the following three conditions are met. The substance must be:
• released from its containment;
• transported by some means (e.g., air, water, the food chain) from its source to human
beings; and
• taken into the human body by breathing, eating or drinking, or contact with the skin.
How a hazardous substance travels from safe containment to, and into, human beings is
its exposure pathway.
Containment and Safely stored, a hazardous substance presents no problem. To use a household example,
Releases mercury is a toxic metal. Securely contained in a glass thermometer, most of us keep it
in our medicine cabinets and confidently put it into our children's mouths.
By the same principle, hazardous substances properly stored at a site pose no problem to
the public. When there is a leak in the containment of a hazardous substance, a potential
problem develops. Such breakdowns in containment are generally referred to as "re-
leases" or "spills."
By the time EPA gets involved in a Superfund site or responds to an emergency, a
release usually has occurred. In addition to supervising the cleanup of the site, EPA must
investigate all potential exposure pathways, and collect information to assess the risk
posed by the release to people on and near the site.
In assessing risk, EPA investigators determine what chemicals have been released, in
what quantities, and over what period of time. Different chemicals pose different kinds
of risk; different chemicals persist in the environment for different lengths of time. The
nature of the chemical and the reactions it goes through after release give investigators
clues about which exposure pathways it may take to people.
Transport Unless people are working directly with a hazardous material, or come across an illegal
dumping ground, it is unlikely that they will be directly exposed to chemicals from a
hazardous release. Rather, the released chemicals will have to be transported through a
pathway—air, water, soil, or the food chain—from its source to where people live, work,
or play. More than one mode of transport may be involved for any release. By tracking
all possible pathways from the source to the population, EPA investigators can begin to
assess the risk associated with a release.
AIR pathways can begin with a release of a volatile chemical or by wind-blown
contaminated dust. This is a SOIL-AIR pathway. Carried by the wind, contaminants can
reach human beings directly or may reach animals to establish a potential AIR-FOOD
pathway. Airborne contaminants may also be deposited into surface water (for example,
ponds or rivers) to establish an AIR-SURFACE WATER pathway.
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SOIL pathways begin with a spill onto the ground or as a release from buried contami-
nants. Direct exposure can come from eating or touching contaminated soil. If the
contaminated soil supports edible plants, a potential SOIL-FOOD pathway may be estab-
lished. Or, as mentioned above, contaminated dust may establish a SOIL-AIR pathway.
Usually, liquid contaminants or contaminants washed from the soil by rainwater migrate
through the soil into ground water, where they potentially establish a SOIL-GROUND
WATER-DRINKING WATER pathway. Or, contaminated material may run off the soil into
lakes or rivers. There it may also potentially contaminate drinking water, or, if the water
is used for irrigation, watering animals, or fishing, a SOIL-WATER-FOOD pathway can
result A SOIL-WATER-AIR pathway can even be possible when contaminated drinking water is
turned to steam, as in a shower, and the possibility of inhaling the vapor is created.
Often the kind of chemical involved helps make clear what pathway the release will
take initially.
Volatile organic compounds and pesticides are most likely to evaporate and to be trans-
ported by air. Volatile organic compounds, or VOCs, are composed primarily of carbon
and hydrogen and often evaporate into the air from water or soil, although they can also
be found in ground water. Non-volatile organic compounds and toxic metals are more
likely to contaminate the soil than the air and either sink through the soil into ground
water or run off the soil into surface water.
Once in surface water, chemicals may behave differently. Some may re-evaporate into
the air, others, such as zinc or mercury, may sink into the mud, stones, and other
materials (also known as sediment) at the bottom of a stream or pond. The small animals
living in sediment that serve as food for fish and water-birds may all become contami-
nated, thus continuing the SEDIMENT-FOOD pathway.
Characteristics of the site pro-
vide important clues to the
most likely exposure path-
ways released chemicals will
follow. Site characteristics
and questions such as the fol-
lowing may help to guide
EPA's investigation:
Access. If the site has not been
fenced or guarded, could
people have been directly ex-
posed to contamination or
have exposed others, by rais-
ing dust or carrying contami-
nated soil home on their shoes
or clothes?
Geology. Does the geology
beneath the surface soil of the
site offer a route for the chemi-
cal contaminants to reach
ground water?
Hydrology. If the spill could
have seeped into ground water
underneath the site, does that
Case Study: Canton, Mississippi
Southeastern Wood Preserving in downtown
Canton, Mississippi operated from 1928 until
early 1979, when its owners filed for bankruptcy
and abandoned the site. They left behind three
unlined, over-flowing ponds of creosote sludge
and water. EPA pumped 30,000 gallons from
the flooded areas of the site, but the untreated
sludge remained.
In December 1988, while surveying a creek that
borders the site, the Department of Agriculture's
Soil Conservation Service noticed an oily waste
leaching into the creek. Two exposure path-
ways—one potential, one actual—have been
identified in this case. The actual pathway—
SLUDGE-SOIL-SURFACE WATER-SKIN CONTACT—
leads to a swimming area in a state park a full
mile downstream from the site, where children
have complained of creosote burns. The poten-
tial pathway—SLUDGE-SOIL-GROUND WATER-
DRINKING WATER—leads to a municipal well 100
feet from the site. The well has been tested and
is not now contaminated.
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ground water feed drinking water sources? Does ground water seep into creeks or streams?
Soil. How dense is the soil? Is it sandy so that the spill could have seeped through it? Or is it
day-like, so that the spill would have remained on the surface or run off with rainwater?
Water. Does running water pass through the site? How fast is it moving? Where does it go?
Vegetation. Is there vegetation on the site that might have kept contaminated dust from
blowing? Or could the spill have contaminated a food supply for local animals, so that
their meat or milk would be dangerous for human consumption?
Wind, precipitation, temperature, and humidity may also be important to the
investigation. For example, if the chemical evaporates, the wind will have carried it off-
site. Investigators then must consider the prevailing wind or, perhaps, the exact wind
strength and direction for particular dates. Airborne particles, wherever the wind has
carried them, may be deposited in rain Rain can also wash surface contaminants down-
slope or leach chemicals through more porous soil. Again, investigators may look for
clues either in general rainfall statistics or in the records for specific dates.
Given their clues in the form of knowledge of the release, characteristics of the site, and
meteorological data, EPA investigators can formulate scenarios of what might have
happened. Hypotheses about the pathways that contaminants could have taken is only a
first step. Investigators must then confirm or disprove these hypotheses with evidence.
Where necessary, they will sample and analyze air (if possible), soils, surface water and
Surface Water
Contamination
EXPOSURE PATHWAYS
Air Contamination
csurface Water.
ntamlnatlon
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wells (for ground water), fish, and other creatures. Even when contaminants have passed
through soil or water on their way to other media, they leave behind traces of themselves,
thus making it possible to track the complete pathway and assign responsibility. Some-
times the investigation must work in the opposite direction. Contamination will be found
in a well or lake, and the pathway must be tracked back, from the evidence in the
environment to its source.
Protection at the
Exposure Point
On the other end of the exposure pathway, at the point where a hazardous substance
comes into contact with human beings (sometimes referred to as the exposure point),
protective measures are necessary.
To begin with ordinary household examples, hazardous products carry warnings that
advise their users of protective steps to take. If ingesn'on is a risk, for example, we are
advised to "keep out of the reach of childrea" If inhalation is a risk, we are advised to
"use only with adequate ventilatioa" If contact is a risk, we are advised to "wear
protective clothing."
On a larger scale, when EPA is responding to an emergency or to discovered contamina-
tion, protective measures also may be necessary. If the hazardous substance has made its
way into drinking water, an alternate source may have to be supplied. If the substance
has made its way into the food chain, the consumption of contaminated fish, animals, or
milk may have to be restricted. In extreme circumstances (generally, but not always,
involving a hazardous substance in the air), people may need to be evacuated and cleanup
workers may need to use gas masks and fully-protective clothing.
Summary Determining how people
may be exposed to chemical
contaminants from a Super-
fund site or an accidental re-
lease is complicated. The
air, soil, ground water, and
surface water are all poten-
tial pathways for contami-
nants to travel once they are
no longer safely stored.
EPA investigators are skilled
at tracing the paths chemi-
cals take once they are
spilled or released from
storage. The Superfund Pro-
gram has established proce
dures to protect people from
exposure to hazardous sub-
stances. In this way, Super-
fund is able to meet its Con-
gressional mandate to protect
human health and the envi-
ronment from the effects of
uncontrolled releases of haz-
ardous materials.
Case Study: Cherokee
County, Kansas
Cherokee County, Kansas, has been a lead and
zinc mining center for over a century. Piles of
waste from mining processes (mine tailings) cover
the surface, and old mine shafts and pits honey-
comb the subsurface for thousands of acres. The
nature of the mining operations, the extent of the
site, and the impossibility of closing off the area
create a very high number of potential exposure
pathways.
Radon gas releases create a potential AIR path-
way. Stirred up dust from tailings makes a po-
tential SOIL-AIR PATHWAY for toxic metals. Chemi-
cals from the tailings and mine shafts that seep
into ground water create a SOIL-GROUND WATER-
DRINKING WATER pathway, and many wells are
contaminated with lead, zinc, cadmium, selenium,
and chromium. Runoff from the tailings into sur-
face water has contaminated fish, creating a po-
tential SOIL-SURFACE WATER-FOOD pathway.
Water treatment systems and temporary alterna-
tive water supplies have been provided while the
cleanup continues.
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EPA is developing the Superfund Accelerated Cleanup Model (SACM) to make hazardous waste
cleanups more timely and efficient. This will be accomplished through more focus on the front end
of the process and better integration of all Superfund program components. The approach involves:
• A continuous process for assessing site-specific conditions and the need for action.
• Cross-program coordination of response planning.
• Prompt risk reduction through early action (removal or remedial).
• Appropriate cleanup of long-term environmental problems.
SACM will operate within the existing statutory and regulatory structure. As SACM develops, there
may be modification of certain policies noted in this fact sheet. However, overall priorities will
remain the same: deal with the worst problems first; aggressively pursue enforcement opportunities;
and involve the public in every phase of the process.
Regional Superfund Community Relations Offices
Region 1
Superfund Community Relations
Office of Public Affairs
EPA Region 1 (RPA-74)
#1 Congress Street
Boston. MA 02203
(617) 565-3425
Region 2
Community Relations Branch
External Programs Division
EPA Region 2 (2-EPD)
26 Federal Plaza
New York, NY 10278
(212) 264-7054
Region 3
Superfund Community Relations
Office of External Affairs
EPA Region 3 (3EA21)
841 Chestnut Street
Philadelphia, PA 19107
(215) 597-9905
Region 4
Superfund Community Relations
Waste Management Division
EPA Region 4
345 Courtland Street, N.E.
Atlanta, GA 30365
(404) 347-2643
Region 5
Superfund Community Relations
Office of Public Affairs
EPA Region 5
Metcalfe Federal Bldg.
77 West Jackson Blvd.
Chicago, IL 60604
(312)353-2073
Region 6
Superfund Community Relations
Hazardous Waste Mgmt. Division
EPA Region 6 (6H-SS)
1445 Ross Avenue
12th Floor, Suite 1200
Dallas, TX 75270
(214) 655-2240
Region 7
Community Relations
Office of Public Affairs
EPA Region 7
726 Minnesota Avenue
Kansas City, KS 66101
(913) 551-7003
Region 8
Community Relations Branch
Office of External Affairs
EPA Region 8 (80EA)
1 Denver Place
999 18th Street, Suite 1300
Denver, CO 80202
(303)294-1144
Region 9
Superfund Community Relations
Hazardous Waste Mgmt. Division
EPA Region 9 (T-1-3)
75 Hawthorne Street
San Francisco, CA 94105
(415) 744-2178
Region 10
Community Relations Section
Hazardous Waste Division
EPA Region 10 (HW117)
1200 6th Avenue
Seattle, WA 98101
(206) 553-6901
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