Motivated by the extensive damage that occurred as a result
of the April 1997 Red River flooding of Grand Forks, North
Dakota, scientists have developed a technology that can remove
recalcitrant fuel oil from solid building surfaces
contaminated by flood waters. Use of this microbial
remediation method could help homeowners avoid health effects
related to hydrocarbon exposures and limit the need for
expensive rebuilding or demolition. Eventually the technology
could be used to remove other hazardous compounds including
chemical warfare agents and explosives.
Environmental scientists monitor fuel oil
contamination of water and soil, but indoor exposure has only
recently come under investigation as a possible human health threat.
Fuel oil is a complex mixture containing hundreds of hydrocarbon
compounds such as benzene, toluene, and xylene. Inhaling or
contacting fuel oil components can cause a variety of health
problems, such as intoxication, headaches, hypertension, drowsiness,
skin irritation, and disorders of the immune and reproductive
systems. Such components occur in fuel oil in low concentrations of
0.5-5%, depending on the manufacturer. "But when you spill two
hundred gallons in a basement, that's a lot of toxic compounds,"
says David Tilotta, a chemistry professor at the University of North
Dakota in Grand Forks.
Tilotta set out to study indoor fuel oil contamination firsthand
when the Red River flooded Grand Forks in April 1997. After
documenting the problem, Tilotta teamed up with microbiologist
Evguenii Kozliak, also a professor at the University of North
Dakota, to probe why repeated cleanup procedures do not remove fuel
oil from building materials such as concrete and wood, and what
other cleanup possibilities there might be. What they've found may
someday result in a commercial product that could remove
hydrocarbons and other stubborn hazardous compounds such as chemical
warfare agents, explosives, and insecticides from solid materials.
Overflowing with Curiosity
When the Red River flooded Grand Forks, 11,000 homes and
businesses were swamped, and 50,000 of the town's 71,000 residents
were evacuated from their homes. After the torrential waters
subsided and the cleanup began, Tilotta noticed large amounts of
smelly fuel oil coating homes, fences, soil, and other structures.
One large trail of fuel oil was traced back to a school that had
filled its 3,000-gallon outdoor tank just before the flood struck.
In other cases, basements were contaminated when fuel oil leaked
from indoor storage tanks (which keep fuel from solidifying into a
gel form during the city's cold winters) or when fuel lines
ruptured. According to records kept by the Grand Forks fire
department, 1,200 homes reported problems with fuel oil spills
ranging from 50 to 260 gallons.
None of the residents of Grand Forks reported that their
postflood health symptoms were caused by fuel oil exposure. However,
this does not surprise Tilotta, because after a flood, stress and
anxiety levels run high, and people often blame symptoms on these
culprits. Plus, other exposures were occurring at the same
time--many people clean with bleach to kill mold, and local
hospitals reported health problems from people inhaling bleach
fumes. "It's hard to separate whether a rise in blood pressure, a
headache, or skin irritation is due to stress or inhaling bleach or
fuel oil [fumes]," says Tilotta.
Oil and water don't mix. Flooding can cause
structural damage to housing and heating systems, releasing
fuel oil into flood waters (above). In flooded basements,
oil-contaminated water can seep into walls and stairwells,
later releasing toxic hydrocarbons into indoor air (below).
image credits: David Tilotta
Many homeowners also try to mask flood-related odors with
perfumed air fresheners, which may contribute to health problems
similar to those caused by fuel oil vapors. Moreover, "like other
odors, after a while you become desensitized to fuel oil and stop
smelling it," says Wally Helland, environmental health supervisor at
the Grand Forks Public Health Department. However, the effects don't
disappear with the smell.
Tilotta, his curiosity piqued by the sight of the fuel-coated
structures and neighbors' reports of lingering fuel oil odors, set
out to investigate. He and Kozliak discovered that fuel oil
hydrocarbons become trapped deep inside structural materials. The
pressure of water is very high during a flood--the Red's flow rate
during the flood reached 140,000 cubic feet per second, compared to
the normal flow rate of 780 cubic feet per second--and it pushes
hydrocarbons deep into the microscopic pores of wood and concrete.
The researchers quantified this effect by simply weighing pieces
of concrete before and after soaking them in water; in concrete,
8-10% of the volume is accounted for by pores. Then they applied
varied amounts of hydrocarbons to 1-gram pieces of concrete. They
found that if they applied less than 2-2.5% hydrocarbon by volume,
it was absorbed into the concrete rapidly and irreversibly.
Tilotta and Kozliak found that pore volume is even greater in
wood. For wood, they let hydrocarbons applied on the surface diffuse
through the piece of wood. Then they removed 5-centimeter chunks of
the wood and analyzed them for the hydrocarbon. Within a matter of
hours, hydrocarbons had penetrated a few centimeters into the wood.
Consequently, even rigorous surface cleanings with pressure
washers, bleach, or other methods cannot penetrate enough to
eliminate the fuel oil contaminants. "If it soaks into floor joists
or other porous material, fuel oil cannot be removed with any
cleaning method," says Helland. In some Grand Forks homes, the
damage was limited to wooden structures such as basement staircases,
which were removed and replaced. But in others, the contamination
was so extensive that the buildings had to be demolished.
An Inside Job
Tilotta continued his inquiry by measuring concentrations of
airborne fuel oil components in three homes about nine months after
the flood, during the winter, when "the houses were shut up and
fumes were distributed everywhere," he says. These homes were
selected because the owners reported still smelling fuel oil, even
though they had scoured the buildings with pressure washers, bleach,
detergents, and other common cleaning methods.
Tilotta used the best available technology at the time--portable
chromatography monitors that were set up in a home and run
overnight, much like a professional radon test. According to
Tilotta's evaluation, volatile fuel oil components were still
detectable. However, the portable monitors were intended to measure
volatile hydrocarbons in gasoline, not the heavier hydrocarbons in
fuel oil. So, although the values obtained showed that petroleum
hydrocarbons were qualitatively present, Tilotta believes the
quantitative readings were inaccurate. (Because of this need for
better validation of fuel oil components in indoor air, Tilotta
later received a grant from the U.S. Environmental Protection Agency
[EPA] to find ways to better quantitate hydrocarbons specific to
Tilotta's preliminary study prompted the Grand Forks Public
Health Department to request help from the EPA in investigating
further, in more homes, and in helping to determine some kind of
limits to advise people about safety and health problems. "I had
never heard of indoor fuel oil contamination, and even the EPA
didn't have any good background on it," says Helland.
Experts from the EPA conducted a study of 34 homes about one year
after the flood occurred. Six homes still had measurable hydrocarbon
vapors that were considered a serious health problem; the homeowners
were advised to move or undergo major structural work to replace
Like most states, North Dakota did not have a safety limit for
indoor inhalational exposure to volatile hydrocarbons in fuel oil
before the devastating flood. Based on numbers in the medical
literature and looking at what a few other states had done, health
experts in North Dakota in 1998 set a limit of 2.4 milligrams per
cubic meter of total fuel oil in air for sensitive
populations--pregnant women, the elderly, and children--and 5
milligrams per cubic meter for the general population.
Eating Away at Contamination
Because Tilotta's laboratory tracks environmental pollutants in
water and soil, he knew that certain bacteria serve as
bioremediation agents. He drew on Kozliak's expertise to explore the
use of microbes to clean up lingering fuel oil contamination in
concrete and wood. Researchers in Kozliak's laboratory isolated
strains of the common and harmless soil and water bacterium
Pseudomonas aeruginosa, grew them in the laboratory, and then
applied the microbes to contaminated samples of wood and concrete.
In the first experiment, building-grade concrete samples were
saturated with naphthalene or n-hexadecane, two representative
hydrocarbons found in fuel oil. The chemicals were radiolabeled with
carbon-14 (14C) to monitor their movement out of the
concrete. From a local soil site contaminated with waste railroad
engine oil, the researchers obtained strains of P. aeruginosa
that consume either naphthalene or n-hexadecane, biodegrading the
chemicals into measurable metabolites such as carbon dioxide. P.
aeruginosa was applied to the samples in three forms--as an
aqueous solution, on filter paper, or on agar (a gel).
The bacteria soon went to work "eating" the radiolabeled
contaminants. Kozliak explains that by feeding on hydrocarbons on
the surface, bacteria create a gradient that allows hydrocarbons
deep inside pores to migrate to the surface more quickly than they
would naturally. This helps to accelerate the diffusion of
hydrocarbons trapped inside. Once they make it to the surface, these
hydrocarbons either are degraded by the bacteria or evaporate,
diffusing into the air at safe concentrations.
The aqueous solution of bacteria proved the poorest way to
eliminate hydrocarbons from the concrete chips. After seven days of
incubation, just 19% of the n-hexadecane and 35% of the naphthalene
was removed. Other researchers have reported that water hinders the
diffusion of volatile organic compounds in concrete and soil, which
parallels Kozliak's finding that aqueous solutions of bacteria
inefficiently degraded hydrocarbons. "When pores fill with water,
volatile organic compounds cannot volatilize and escape," explains
In contrast, applying bacteria on filter paper or agar removed
80% of n-hexadecane and 55% of naphthalene. The results of this
study will be published in a future issue of the journal Acta
In the second experiment, pieces of Southern yellow pine, a
common wood for home construction, were soaked with
14C-labeled naphthalene. Strains of P. aeruginosa
that consume naphthalene were applied either as an aqueous solution,
on filter paper, or on agar. Once again, the filter paper and agar
proved superior to solutions of bacteria. Between 90% and 98% of the
naphthalene was removed in two days with either filter paper or agar
treatments, compared to just 82% removed by a solution of bacteria
after seven days of treatment. This information was presented at the
Sixth International Symposium for Environmental Biotechnology, held
in Veracruz, Mexico, in June 2002, and is being prepared for journal
The researchers also saturated a piece of wood with fuel oil
(rather than just two of its components), treated it with P.
aeruginosa, and monitored the changes in 200 hydrocarbon
components of the fuel oil by chromatographic techniques. All 200
compounds were reduced to varying degrees over a three-week
treatment period, says Kozliak. So far, he's analyzed only
straight-chain hydrocarbons with 10-20 carbons (such as dodecane).
These compounds were reduced by an average of 75%.
These preliminary proof-of-concept experiments are the first step
toward a commercial product that could rid solid materials of
hydrocarbons and other hazardous compounds including chemical
warfare agents, explosives, and insecticides. Kozliak foresees
bacteria being applied to contaminated surfaces in a gel or pellet
form, methods that mimic the laboratory application by agar or
filter paper. Patent applications on the technology have been filed
by the University of North Dakota.
This research on contaminated concrete and wood is "very relevant
to the conditions in regions with floods," says Sergio Revah, a
chemical engineer who works with microbial degradation of
recalcitrant compounds at Universidad Autonoma Metropolitana in
Iztapalapa, Mexico. Although many details remain to be worked out,
such as the best types of microorganisms and how to apply them, the
approach "may lead to interesting bioremediation technologies,"
Beklemishev MK, Kozliak EI. In press. Bioremediation of
concrete contaminated with n-hexadecane and naphthalene. Acta
Juhasz AL, Naidu R. 2000. Bioremediation of high molecular
weight polycyclic aromatic hydrocarbons: a review of the microbial
degradation of benzo[a]pyrene. Int Biodeterior
Wilhelm RW, Bouchard RJ. 1989. Assessment and remediation of
residential properties contaminated with home heating oil. In:
Kostecki PT, Calabrese EJ, eds. Petroleum Contaminated Soils:
Remediation Techniques, Environmental Fate, and Risk Assessment.
Chelsea, MI:Lewis Publishers, 329-346.