Environmental scientists monitor fueloil contamination of water and soil,but indoor exposure has only recently

come under investigation as a possiblehuman health threat. Fuel oil is a complexmixture containing hundreds of hydrocar-bon compounds such as benzene, toluene,and xylene. Inhaling or contacting fuel oilcomponents can cause a variety of healthproblems, such as intoxication, headaches,hypertension, drowsiness, skin irritation,and disorders of the immune and repro-ductive systems. Such components occurin fuel oil in low concentrations of0.5–5%, depending on the manufacturer.“But when you spill two hundred gallons

in a basement, that’s a lot of toxic com-pounds,” says David Tilotta, a chemistryprofessor at the University of NorthDakota in Grand Forks.

Tilotta set out to study indoor fuel oilcontamination firsthand when the Red Riverflooded Grand Forks in April 1997. Afterdocumenting the problem, Tilotta teamedup with microbiologist Evguenii Kozliak,also a professor at the University of NorthDakota, to probe why repeated cleanup pro-cedures do not remove fuel oil from build-ing materials such as concrete and wood,and what other cleanup possibilities theremight be. What they’ve found may somedayresult in a commercial product that could

remove hydrocarbons and other stubbornhazardous compounds such as chemical war-fare agents, explosives, and insecticides fromsolid materials.

Overflowing with CuriosityWhen the Red River flooded Grand Forks,11,000 homes and businesses wereswamped, and 50,000 of the town’s71,000 residents were evacuated from theirhomes. After the torrential waters subsidedand the cleanup began, Tilotta noticedlarge amounts of smelly fuel oil coatinghomes, fences, soil, and other structures.

One large trail of fuel oil was traced backto a school that had filled its 3,000-gallon

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outdoor tank just before the flood struck. Inother cases, basements were contaminatedwhen fuel oil leaked from indoor storagetanks (which keep fuel from solidifying intoa gel form during the city’s cold winters) orwhen fuel lines ruptured. According torecords kept by the Grand Forks fire depart-ment, 1,200 homes reported problems withfuel oil spills ranging from 50 to 260 gallons.

None of the residents of Grand Forksreported that their postflood health symp-toms were caused by fuel oil exposure.However, this does not surprise Tilotta,because after a flood, stress and anxiety lev-els run high, and people often blame symp-toms on these culprits. Plus, other exposures

were occurring at the same time—manypeople clean with bleach to kill mold, andlocal hospitals reported health problemsfrom people inhaling bleach fumes. “It’shard to separate whether a rise in bloodpressure, a headache, or skin irritation is dueto stress or inhaling bleach or fuel oil[fumes],” says Tilotta.

Many homeowners also try to maskflood-related odors with perfumed air fresh-eners, which may contribute to healthproblems similar to those caused by fuel oilvapors. Moreover, “like other odors, after awhile you become desensitized to fuel oiland stop smelling it,” says Wally Helland,environmental health supervisor at the

Grand Forks Public Health Department.However, the effects don’t disappear withthe smell.

Tilotta, his curiosity piqued by thesight of the fuel-coated structures andneighbors’ reports of lingering fuel oilodors, set out to investigate. He andKozliak discovered that fuel oil hydrocar-bons become trapped deep inside structuralmaterials. The pressure of water is veryhigh during a flood—the Red’s flow rateduring the flood reached 140,000 cubicfeet per second, compared to the normalflow rate of 780 cubic feet per second—andit pushes hydrocarbons deep into themicroscopic pores of wood and concrete.

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Grand Forks flood, 1997

The researchers quantified this effect bysimply weighing pieces of concrete beforeand after soaking them in water; in con-crete, 8–10% of the volume is accountedfor by pores. Then they applied variedamounts of hydrocarbons to 1-gram piecesof concrete. They found that if they appliedless than 2–2.5% hydrocarbon by volume,it was absorbed into the concrete rapidlyand irreversibly.

Tilotta and Kozliak found that porevolume is even greater in wood. For wood,they let hydrocarbons applied on the sur-face diffuse through the piece of wood.Then they removed 5-centimeter chunks ofthe wood and analyzed them for the hydro-carbon. Within a matter of hours,hydrocarbons had penetrated a fewcentimeters into the wood.

Consequently, even rigoroussurface cleanings with pressurewashers, bleach, or other methodscannot penetrate enough to elimi-nate the fuel oil contaminants. “Ifit soaks into floor joists or otherporous material, fuel oil cannot beremoved with any cleaningmethod,” says Helland. In someGrand Forks homes, the damagewas limited to wooden structuressuch as basement staircases, whichwere removed and replaced. But inothers, the contamination was soextensive that the buildings had tobe demolished.

An Inside JobTilotta continued his inquiry bymeasuring concentrations of air-borne fuel oil components in threehomes about nine months after theflood, during the winter, when“the houses were shut up andfumes were distributed every-where,” he says. These homes wereselected because the owners reported stillsmelling fuel oil, even though they hadscoured the buildings with pressure washers,bleach, detergents, and other commoncleaning methods.

Tilotta used the best available technol-ogy at the time—portable chromatographymonitors that were set up in a home andrun overnight, much like a professionalradon test. According to Tilotta’s evalua-tion, volatile fuel oil components were stilldetectable. However, the portable moni-tors were intended to measure volatilehydrocarbons in gasoline, not the heavierhydrocarbons in fuel oil. So, although thevalues obtained showed that petroleumhydrocarbons were qualitatively present,Tilotta believes the quantitative readingswere inaccurate. (Because of this need for

better validation of fuel oil components inindoor air, Tilotta later received a grantfrom the U.S. Environmental ProtectionAgency [EPA] to find ways to better quan-titate hydrocarbons specific to fuel oil.)

Tilotta’s preliminary study promptedthe Grand Forks Public Health Departmentto request help from the EPA in investigat-ing further, in more homes, and in helpingto determine some kind of limits to advisepeople about safety and health problems. “Ihad never heard of indoor fuel oil con-tamination, and even the EPA didn’t haveany good background on it,” says Helland.

Experts from the EPA conducted astudy of 34 homes about one year after theflood occurred. Six homes still had mea-surable hydrocarbon vapors that were con-sidered a serious health problem; the

homeowners were advised to move orundergo major structural work to replacecontaminated structures.

Like most states, North Dakota did nothave a safety limit for indoor inhalationalexposure to volatile hydrocarbons in fuel oilbefore the devastating flood. Based onnumbers in the medical literature and look-ing at what a few other states had done,health experts in North Dakota in 1998 seta limit of 2.4 milligrams per cubic meter oftotal fuel oil in air for sensitive popula-tions—pregnant women, the elderly, andchildren—and 5 milligrams per cubic meterfor the general population.

Eating Away at ContaminationBecause Tilotta’s laboratory tracks environ-mental pollutants in water and soil, heknew that certain bacteria serve as biore-mediation agents. He drew on Kozliak’sexpertise to explore the use of microbes toclean up lingering fuel oil contaminationin concrete and wood. Researchers inKozliak’s laboratory isolated strains of thecommon and harmless soil and water bac-terium Pseudomonas aeruginosa, grew themin the laboratory, and then applied themicrobes to contaminated samples ofwood and concrete.

In the first experiment, building-gradeconcrete samples were saturated with naph-thalene or n-hexadecane, two representative

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Oil and water don’t mix. Flooding cancause structural damage to housing andheating systems, releasing fuel oil into floodwaters (above). In flooded basements, oil-contaminated water can seep into walls andstairwells, later releasing toxic hydrocarbonsinto indoor air (below).

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hydrocarbons found in fuel oil. The chemi-cals were radiolabeled with carbon-14 (14C)to monitor their movement out of the con-crete. From a local soil site contaminatedwith waste railroad engine oil, the researchersobtained strains of P. aeruginosa that con-sume either naphthalene or n-hexadecane,biodegrading the chemicals into measurablemetabolites such as carbon dioxide. P. aerug-inosa was applied to the samples in threeforms—as an aqueous solution, on filterpaper, or on agar (a gel).

The bacteria soon went to work “eat-ing” the radiolabeled contaminants. Kozliakexplains that by feeding on hydrocarbonson the surface, bacteria create a gradientthat allows hydrocarbons deep inside poresto migrate to the surface more quickly thanthey would naturally. This helps to acceler-ate the diffusion of hydrocarbons trappedinside. Once they make it to the surface,these hydrocarbons either are degraded bythe bacteria or evaporate, diffusing into theair at safe concentrations.

The aqueous solution of bacteria provedthe poorest way to eliminate hydrocarbonsfrom the concrete chips. After seven days ofincubation, just 19% of the n-hexadecaneand 35% of the naphthalene was removed.Other researchers have reported that waterhinders the diffusion of volatile organiccompounds in concrete and soil, which par-allels Kozliak’s finding that aqueous solu-tions of bacteria inefficiently degradedhydrocarbons. “When pores fill with water,volatile organic compounds cannotvolatilize and escape,” explains Kozliak.

In contrast, applying bacteria on filterpaper or agar removed 80% of n-hexadecaneand 55% of naphthalene. The results of thisstudy will be published in a future issue ofthe journal Acta Biotechnologica.

In the second experiment, pieces ofSouthern yellow pine, a common woodfor home construction, were soaked with14C-labeled naphthalene. Strains of P.aeruginosa that consume naphthalene wereapplied either as an aqueous solution, onfilter paper, or on agar. Once again, the

filter paper and agar proved superior tosolutions of bacteria. Between 90% and98% of the naphthalene was removed intwo days with either filter paper or agartreatments, compared to just 82%removed by a solution of bacteria afterseven days of treatment. This informationwas presented at the Sixth InternationalSymposium for EnvironmentalBiotechnology, held in Veracruz, Mexico,in June 2002, and is being prepared forjournal publication.

The researchers also saturated a piece ofwood with fuel oil (rather than just two ofits components), treated it with P. aerugi-nosa, and monitored the changes in 200hydrocarbon components of the fuel oil bychromatographic techniques. All 200 com-pounds were reduced to varying degreesover a three-week treatment period, saysKozliak. So far, he’s analyzed only straight-chain hydrocarbons with 10–20 carbons(such as dodecane). These compounds werereduced by an average of 75%.

These preliminary proof-of-conceptexperiments are the first step toward acommercial product that could rid solidmaterials of hydrocarbons and other haz-ardous compounds including chemicalwarfare agents, explosives, and insecticides.Kozliak foresees bacteria being applied tocontaminated surfaces in a gel or pelletform, methods that mimic the laboratoryapplication by agar or filter paper. Patentapplications on the technology have beenfiled by the University of North Dakota.

This research on contaminated concreteand wood is “very relevant to the conditionsin regions with floods,” says Sergio Revah, achemical engineer who works with micro-bial degradation of recalcitrant compoundsat Universidad Autonoma Metropolitana inIztapalapa, Mexico. Although many detailsremain to be worked out, such as the besttypes of microorganisms and how to applythem, the approach “may lead to interestingbioremediation technologies,” Revah says.

Carol Potera

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Sugge s t ed Read ingBeklemishev MK, Kozliak EI. In press. Bioremediation of concrete contaminated with

n-hexadecane and naphthalene. Acta Biotechnol.

Juhasz AL, Naidu R. 2000. Bioremediation of high molecular weight polycyclic aromat-ic hydrocarbons: a review of the microbial degradation of benzo[a]pyrene. IntBiodeterior Biodegradation 45:57–88.

Wilhelm RW, Bouchard RJ. 1989. Assessment and remediation of residential propertiescontaminated with home heating oil. In: Kostecki PT, Calabrese EJ, eds. PetroleumContaminated Soils: Remediation Techniques, Environmental Fate, and RiskAssessment. Chelsea, MI:Lewis Publishers, 329–346.

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