NASA Technical Reports Server (NTRS) 20120003454: Phytoremediation of Indoor Air: NASA, Bill Wolverton, and the Development of an Industry

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by  NASA Technical Reports Server (NTRS)

Phytoremediation ofIndoor Air: NASA, Bill Wolverton, and the
Development ofan Industry
Gary W. Stutte, PhD. Space Life Science Laboratory, John F. Kennedy Space Center, Florida,
USAI
Indoor air pollutants are a source ofserious illnesses, includingasthma, cancer, reproductive and
neurological disorders. A 2002 World Health Organization Report attributes more than 1.6
million deaths ayear--3 deaths a minute--to complications resulting from indoorair pollution.
I
Volatile Organic Compounds (VOCs) are emitted from the materials used to construct the
buildings2, the floor and wall coverings used to protect the buildings3, the furnishings used to
decorate the interiors4, and the electronics and appliances that are used daill.
The problems associated with indoorairquality began to develop following the oil embargo of
the 1970's, and regulations to increase the energy efficiency ofbuildings were enacted. The
reduction in ventilation with outside air due to tighter seals, energy efficient glass, and lowerair
exchange rates resulted in the accumulation ofVOCs, microorganisms, and particulates. The
term "SickBuilding Syndrome" entered common usage.
In 1988, the U.S. Environmental Protection Agency (US EPA) conducted a survey ofair quality
in public buildings and identified more than 900 VOCs in office buildings, nursing homes,
hospitals and schools6. Ofthese VOCs, many were found in concentrations known to pose
serious acute and chronic health risks. These included such compounds as benzene,
ethylbenzene, xylene, styrene, trichlorethyhlene, decane, formaldehyde, 1,1,I-trichloroethane,
dichlorobenzene and ethyl toluene?
Solvents in glues, paints and varnishes commonlyused in the production ofcarpets, drywall and
pressed wood furniture, such as toluene and formaldehyde were omnipresent. Over40 VOCs
have been identified that come from modem appliances such as computers, monitors and
televisions8. The insidious effects ofindoor air pollutionhave been associated with a 74%
increase in asthmabetween 1980 and 1994 and children under the age of5 in the United States
have experienced an increase of160 percent9. Epidemiological studies suggest this increase is at
least partially attributable to reduced ventilation and increased energyefficiency in modem
buildings10. The problem is not limited to the United States. There has been a 5 fold increase in
Taiwan over20 years; and a 30 fold increase in asthma patients in medical facilities in Japan
over 30 years. Fifteen percentofthe population ofAustralia, New Zealand and the Pacific
Islands suffer from asthma as well. Indoorair pollution has been linked to increased prevalence
ofParkinson's disease, brain tumors, multiple chemical sensitivity and other nervous system
disorders.II
It was during this period ofthe early 1970's and 1980's when the issues associated with Sick
Building Syndromewere gaining attention that the United States National Aeronautics and Space
Administration (NASA) became an unlikely leader in identifying biological solutions to the
problem ofpoor indoor airquality. NASA had been supportingwork using biological systems
1Currentaddress: MarieCurie Research Fellow, Limerick InstituteofTechnology, Moylish Park, Limerick, Ireland
1
for atmospheric regeneration sincethe 1950's, with the emphasis on using photosynthetic
systems for the removal ofcarbon dioxide and regeneration ofoxygen as part ofa life support
system12. The then SovietUnion was conductingtests using algae systems in the BIO-1 program
(1964-1968) to regenerate the airatthe Siberian Branch ofthe Soviet AcademyofSciences in
Krasnoyarsk (Laterrenamed the Institute ofBiophysics). These tests were expandedto include
the use ofhigherplants in the BIOS-2 testing in the 1970's, and humans during BIO-3 in the
1980'SI3. Within NASA, large scaletesting ofbioregenerative life support systems was
conducted in the Biomass Production Chamber(BPC) at Kennedy Space Center, Floridaas part
ofthe ControlledEcological Life Support Systems (CELSS) Breadboardproject.14 However, the
use ofhigher plants for cleaning the airdid not evolve directly from these programs, butrather
from the unlikely source atNASA's Mississippi TestFacilityin Hancock County, Mississippi.
NASAihad spectacularsuccess with the developmentofthe Mercury, Gemini andApollo
Programs that culminatedVinthe Moon landings. The Mississippi TestFacilityhad been crucial
in the developmentand testing ofthe rocket enginesthat propelledthe SaturnV rockets into
orbit. Wpen the Apollo program ended, and the endofproduction ofthe SaturnV rockets, there
was a dramatic decrease in funding to NASA andthe future ofthe Mississippi TestFacilitywas
in doubt. Jackson Balch, NASA CenterDirector, seizedthis periodofuncertainty, and
established an Applications EngineeringOffice to activelyoperate in a "marketplace" ofscience
and develop a synergism in research thatcould cross bureaucratic, governmental, and
disciplinary linesl5. DirectorBalch then set outto find people to implementthis strategy.
Bill Wolverton hadbecame known to Director Balchthreeyears earlierduring apresentation
Bill made at WinRock Farms, Arkansas on his finding thataquatic plants were capable of
absorbing AgentOrange (mixture of2,4,5-T,and2,4 D) and organophosphate insecticides, used
extensivelyduring the Vietnam warl6. DirectorBalchbelievedthatpractical application of
environmental science would be critical to the continuedoperation ofthe test facility, and he was
convinced Bill Wolverton's backgroundwas ideal for this new role.
Bill Wolverton was born in rural Mississippi in 1932 at the peakofthe GreatDepression, was
raised in Mississippi, graduatedhigh school and then servedin the United States Air Force
during the Korean Conflict. Afterleaving active service, he remained in the AirNational
Guard, andbegan his college education. He was awarded aBachelorofScience Degree in
Chemistry from Mississippi College in 1960, conducted graduate research onmultiple myeloma
andrheumatoid arthritis in the departmentofMicrobiologyarid Biochemistryat the University
ofMississippi Medical CenterinJackson, MS. He then,accepted aposition as a civilian scientist
at the Naval Weapons LaboratoryinDahlgren, VA as head ofthe Chemical/Biological Branch
Laboratorywhere he researched methods for protection ofmilitarypersonnel from chemical and
biologicalwarfare. "
In 1965 he was transferredabit closerto home at Eglin Air Force Base inthe panhandle of
Florida. There he continuedhis work onthe protection from and decontamination of, chemical
warfare agents, especially organophosphate agents, includingVX gas, Sarin and Mustard gas.
His and his research resulted in multiple patents.17,18,19 While working at Eglin Air Force Base,
he resumed graduate studies and focused on marine biologyatthe University ofWest Florida,
Pensacola, Florida. '
2
In 1971, DirectorBalch and Henry Auter, Director ofApplications Engineering, recruited Bill
Wolverton away from EglinAirForce Stationto head the Environmental Research Laboratory at
NASA's Mississippi TestFacility. Theprimary objectives ofthe Environmental Research
Laboratorywere to 1) Research the environment's natural abilities to cleanse itself; 2) Research
aclosed ecological life support system for long-term space habitation; and 3) Provide usable
Spin-offtechnologies to the American public.2o
I
Upon assuming the position as headofthe Environmental Research Lab, it became clearthat the
immediate need was to demonstrate the relevancy ofenvironmental research to NASA. Bill
Wolverton requested, and received, support from DirectorBalch to develop aconstructed
wetlands on the site in orderto remove the toxic wastes thatwere accumulating in the
environmentthough years oftestfiring ofrocket engines. This investmentpaid immediate
dividends, and the constructedwetlands are still functioning today. The value ofthis work to
NASA was summarized below:
"Before Wolverton beganhisresearch attheMTFin 1971, governmentandprivateentitiespaid
largesumsofmoneytrying to eradicate theplantil. Through theplantprogram, however, the
hyacinth becameusefulas anaturalresource, cleaningdomesticandlaboratorywaste waterwith its
large rootsystem resemblingoctopustentacles. Wolverton andMcDonaldusedtheplants, which
produce beautifullavenderblossomsto cleanallwastegeneratedattheNSTL, includinglaboratory
wastecontainingchemicalsandheavymetals.
In thefinal analysis, theplantprogram savedthegovernmentmorethan $1 millionupfront, and
millionsmorefor operationsandmaintenancewillbesavedovertheyears. Wolverton gained
worldwiderecognitionfor the VascularAquaticPlantprogram. Newsmen,from Germany, England,
Japan, andmanyothercountries, visitedtheNSTL22 inorderto obtain theplantprogramstoryfor
theirviewers. Wolverton andthe aquaticplantprogram werealsofeaturedonmajorAmerican
television networks, such asNBCandCNN. In addition, Wolverton assistedwith designingand
installingsimilarwastetreatmentsystemsin CoralSprings, Disney World, Florida; Hercules, and
San Diego, California; andRioHondo, Texas. ,,23
AlthoughNASA's ApolloProgramhadended, NASA's interestinhumanspace flight hadnot. In the
early 1970'sNASAand the SovietUnionbegancooperatinginspace, and three manned SkyLab Space
stationmissions were conducted. Duringthe SkyLab 3mission, samples ofthe atmosphere were returned
for analysis, and they yieldedsurprisingresults. Therewere over300VOCs detectedin the SkyLab
samples and 107ofthose were identifiedin thecrew compartments duringmannedmissions. NASA
immediatelyrecognized thatselectionofmaterials lowinthe emissionoftoxicVOCs wouldbecriticalto
maintainingthe healthofthe crew. This recognitionresultedinextensive off-gassingtestsofany
material used inspaceflight. Extensive insituandpost-flightmonitoringofthespacecraftcontinues
withinNASA, and the range ofVOCs from themostrecent SpaceShuttleand International SpaceStation
Missions ispublicallyavailable.24
BillWolvertonhadcontinuedhis studies withwetlands atthe Institutefor AdvancedStudies, and
obtainedhis Doctoratedegree inenvironmentalengineeringin 1978. Followingthe SkyLabmissions,
Bill Wolvertonandcolleague, RebeccaMcDonald,turnedtheirattentionto theproblemofindoorair
quality. They askedthemselves whetherplantscouldremove toxic chemicalsfrom the air inthe same
mannerthataquatic plantswere removingtoxins fromtheenvironment.
3
-------------------------------------~----
Billapproached the CenterDirectorin 1980forfunding, and was providedamodestbudgetfrom the
CenterDirector'sDiscretionaryFundsto assess the abilityoffoliageplantstopurifythe airfrom energy
efficienthomes andfuture space stations. Theychoose to focus onformaldehyde, aVOCthat was
receivingconsiderable attentionas anindoorpollutantatthe time, due to its widespreaduse inpressed
wood, andinsulation usedin thehomeand inhouse trailers. A smalltestchamberwas built, andGolden
Pothos (Scindapsus aureus), nephthytis (Syngoniumpodophyllum) andsweetpotato(Ipomoea hatatas)
weretestedfor theirabilityto remove formaldehyde fromthe atmosphere. Itwas found thatthe
concentrationofVOC'scouldbereduced whencommonhouseplants were introducedinto the closed
environment. This was averyimportantfinding, and theybeganto furtherresearchplantremoval of
formaldehyde and otherVOCs from the air.
These initialexperimentswere veryencouraging, withallthreespecies showingdramatic reductions in
formaldehyde concentrations inthechambersovera 24hourcycle. Theseresults werefirst publishedas
25
an internal NASAtechnical memorandumin 1982. Additional testingwas performedandthe results of
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the NASAresearchwere publishedinthe JournalofEconomicBotanyin 1984 . Oneofthe conclusions
ofthe research was:
"Basedonthe Chlorophytum elatum var. vittatumdata, onespiderplant ina 3.8 I(l gal) potcan
effecttheremovalof31,220-62,440 JlgCH20/6hr. Tomeet the airpurificationneeds ofthe homejust
described, 8-15 spiderplants (3.8 Ipotsize) wouldbeneed to purifythe aircontinuously,,27.
NASApromotedthe release ofthese findings, and theresults were enthusiastically welcomed bythe
public. Dr. Wolvertoncontinuedthese studies, andexaminedthe abilityofplantsto remove combustion
.gases, whichare theprimaryindoorpollutantsformostofthe developingworld. Theseresults were
publishedinthe Journal oftheMississippi AcademyofSciences in 1985?8
Realizing the valueofthesefindings, the leadersofthe interiorplantscapeindustryapproachedDr.
Wolvertonaboutadditionalfunding forhisresearch. Asaresult ofthese discussions, The Associated
Landscape ContractorsofAmerica(ALCA, nowknownas theProfessionalLandcareNetwork)
approached the seniormanagementofthe newlyrenamedJohnC. Stennis SpaceCenter, aboutjointly
funding a twoyearstudyto evaluate theeffects ofthe mostcommonhouseplants inthe industryontheir
ability to rem~ve VOCs from the air.29,30 The research concentratedonthreeofthemostcommonVOCs:
formaldehyde, benzene andtrichloroethylene.
This workwas revealing, inthat itdemonstrated that there were significantdifferences inthe abilityof
differentplants toremove airborne contaminants. These findings were compiledandthefinal report
released. Based upon thepublic interestreceivedfrom the 1984articlepublishedinEconomicBotany,
Dr. Wolverton, the managementofNASAStennis Space Center, andthe ALCAwereanticipatingan
evenstrongerresponse fromthe public.
A strategywas developedwhereby the final report, entitled"InteriorLandscapePlants for IndoorAir
PollutionAbatement" wouldbereleasedduring apressconference attheNationalPress Club in
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WashingtonD.C. inconjunctionwith"Plantsfor CleanAirDay" onCapitolHill. A not-for-profit
organization, Plants for CleanAirCouncil,wasestablishedwithJanRoy as the director, to establisha
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nationalinformationcampaigntopromote the valueoflivingplants inthe home. The report was
subs~quentlypublishedinInteriorScapeMagazi~e.33
Followingthe release ofthe FinalReport in September, 1989,there was ahuge public interestinthe "Top
12PlantsforAirQuality". Dr. Wolvertonwas immediatelysoughtoutfor interviewsonmajorTV
networks, was interviewedbynumerous newspapersandmagazines, andpromotedthe value ofinterior
plants onairqualityatany opportunity. ThePlants for CleanAirCouncil, initiatedapublicrelations
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campaignas well, promotingthe workofNASAandDr. WolvertonatJohnC. Stennis SpaceCenter.
4
NASAfunded research inclosedenvironments for longdurationspace missionsfrom the late 1970's.The
BreadboardProjectoftheControlledEcologicalLife Support Systems (CELSS)programwas being
constructedatJohnF. Kennedy Space CenterinFloridato test thefeasibility Ofbioregenerative life
supportonaone personscale, large scalehumantestfacilities were beingdesignedat LyndonB. Johnson
Space CenterinTexas, andthe private enterprise SpaceV~ntureswas developingthe Biosphere2project
inOracle,Arizona. Theseprojects were focused onusingplantsfor life support. Theseexperiments
monitoredthe productionofVOC's35,36, butthe primaryresearch wasdirected towards the roleofplants
3
for life support ?
Incontrast,Dr. Wolverton, withthe supportofthe managementofStennis SpaceCenter, andbackingof
the ALCA, choseto scaleup theresearchat Stennisto demonstrate the beneficialrole ofplants inclosed
life supportsystemsto maintainahealthylivingenvironment. The resultwas theconstructionofthe
Biohome constructedofsynthetic materialsandengineeredfor maximumclosureofthe airexchangeand
energyefficiency. TheBiohomehad twospaces: a32m2livingareaanda27.5 m2bioregenerative area
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forreclamationofwaterand food .TheBiohome was constructedentirelyofsyntheticmaterials, highly
insulated(R-40), and tightlysealed. Uponenteringthe facility, there were highconcentrations ofVOCs
detected, andvisitorsexhibitedsymptomsoftoxicity, includingburningeyes, scratchythroat, trouble
breathingandotherclassicsymptomsofsickbuildingsyndrome.
A numberoflow-lighttolerantfoliage plants were placedintothe'Biohome' and the facility allowed to
equilibrate for several days. The strikingresult was that the symptoms ofrunny eyeswere no longer
exhibited, and GC/MS analysis confirmedthe reductionofVOCs inthe atmosphere. Inorderto develop
acasestudyforhabitation, agraduate studentlived in thechamberfor the summer, withno negative
healtheffects observed. An important finding in the studyrevealedthatplants are mosteffectivein
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removingVOCs in non-ventilated, energy-efficientbuildings .
Upon thecompletionofitsresearch role, the"BioHome"was movedfrom the EnvironmentalResearch
Laboratoryto the StennisVisitorCenterandrenamed"OneMainstreetMars", whereitcontinuedto serve
aneducationalrole onthe valueofinteriorplants. Thefacility was destroyed in2005 whenHurricane
Katrinamade landfallalongthe Mississippi coastline40•
I
In 1990, following the release ofthefinal report ofthe researchoninteriorplants,Dr. Wolvertonretired
fromNASAandstartedasmallresearchcompany, WolvertonEnvironmental Services, withhis wife,
Yvonne, andson,John. Priortohis retirement, Dr. Wolvertonreceivedmanyawards from NASA,
includinginductionintothe U.S. SpaceFoundationsHallofFame in 1988. He was also invitedto open
the 1989AaslmeerFlowertrade ExhibitionintheNetherlands, the first Americantobeawarded that
honor.
Wolverton~nvironmentalServices concentratedon obtainingadditional dataonthe use of
phytoremediationto address wastewaterand indoorairpollutionproblems. To further demonstrate how
interiorplants couldbe used to purifyandrevitalize indoorair while treatingrawsewage, he hadsucha
systeminstalled inasunroomat his home inPicayune, Mississippi, This systemworkedsuccessfullyfor
seventeenyears before he converteditbackto aregularhydroculture plantgrowthsystemwithoutraw
sewage as the nutrients41•
Since leavingNASA, Dr. Wolvertonhas continuedto conductresearch, supportedthe interiorplant
industry, lecturedalloverthe worldandpublishedthree books. His firstbook,Eco-Friendly
Houseplants was publishedinthe UnitedKingdomin 1996,thenreleasedthe followingyearinthe United
Statesunderthe title How to GrowFreshAir. This bookhas nowbeentranslatedinto 15 languages and
provides the basic information for usingplants to improveairquality the worldover.
5
Dr. Wolvertonservedas the scientificspokespersonfor the 'Plants for CleanAirCouncil,participatingin
campaigns to educatethepublicabout the abilityofinteriorplantsto improve indoorairquality andto
promotetheirhealthbenefits. He has participatedinpublicitytours ofmostmajorcities, and isa
frequent guestontelevisionandradioshowsand is regularly interviewedbynewspapers andmagazines.
Dr. Wolvertonhasprovidedhundreds oflecturesatprofessionalassociationssuchas the American
Institute ofArchitects, landscapearchitectgfoups, universities,andlocalinteriorscape associations.
Dr. Wolvertonhas helpedshapepublicpolicybyprovidingtestimonybeforetheUnited StatesHouseof
Representatives; Subcommittee onAgriculturalDevelopment,FoodandDrugAdministrationandRelated
ServicesUnited States Senate; Committee onEnvironment andPublic Works; Subcommittee onToxic
Substances, EnvironmentalOversight,ResearchandDevelopment.
For over a decade Dr. Wolverton has also served as a consultant to Takenaka Garden Afforestation, the
largest interiorscape company in Tokyo, where 'Ecology Gardens' are designed in hospitals to improve
the psychological and physiological health of both patients and employees. The interior gardens are
designed to complementthe mind/body healingbyincludingplants to improve airquality ina garden that
is designedto improvehealingand recovery.42
Research by WolvertonEnvironmental Services has found thatincreasingthe flow ofairthrough the root
systemincreasesthe removal ofVOCs significantlymore thanaSIngle traditionalpotted plant. This
43
discovery waspatented ,and he has teamed withaJapanesecompany, ActreeCorporation, to develop
what the Japanesefirm is marketingas the EcoPlanter. Usinghigh-efficiencycarbonfilters andaroot
levelcirculationsystem, the potallows theplantto remove approximately200times more VOCs thana
singletraditionally-pottedplantcanremove. In the U.S., asimilarproductis manufacturedby U.S. Health
44
EquipmentCompanyunderthe trade.name, PlantAirPurifier. '
Dr. Wolverton's mostrecentbook Plants: Why You Can'tLive Without Them written withKozaburo
Takenakawaspublishedin2010, andprovides an overviewofthe developmentofthe industry, from
smallchamberstudiesatNASA'sMississippiTestFacility(nowNASAJohnC. Stennis SpaceCenter) to.
the designofbuildings encompassingliving walls, atriums and interiorlandscaping. This bookclearly
shows the impactthatNASA, Dr. Wolverton, and industry-backing, have made to the lives ofmillions
aroundthe world.
Dr. Wolverton'spioneeringresearchatNASA's JohnC. Stennis SpaceCenterhas increasedthe public's
45
awareness ofthe criticalrole ofplants intheenvironment ,stimulated debate onthe role ofinterior
plantsfor improvingindoorairqualitl6,47,48, expandedresearchontherole ofmanyplants to improve air
qualitl9,5o,51,52 andprovidedthe foundation for arobust andexpandingindustryto incorporate living
53
plants intobuildingswherewelive and work ,54.
Acknowledgements: Theauthorwishes to extendasincere appreciationto Dr. BillWolvertonfor his
friendship, openness, andinsights inpreparingthis manuscript. Without his input, it wouldnothave
,beenpossible. Theauthoralso acknowledgesNASAfortheirrecognition, andpublicpromotion, ofthe
forreaching impacts ofDr. Wolverton's research.
1WHO, ed.TheWorld Health Report 2002 :ReducingRisks, PromotingHealthyLife. Geneva,World Health
Organization,2002.
2USEnvironmenta'i ProtectionAgencyReporttoCongress:. IndoorAirQuality: ExecutiveSummaryand
Recommendations. 1989.EPA/400/1-89/001A
3Ibid.
4Ibid.
6
J
\
5Wensing, M, Determinationoforganicchemical emissionsfrom electronicdevices'.InG.Raw,C.Aizlewood and
th
O.Warren (eds). Proc.8 Intern.Conf.on IndoorAirandClimate. Edinburg, UK. 1999,5:87-92.
6USEnvironmental ProtectionAgencyReporttoCongress:. IndoorAirQualityin PublicBuildings Vol Iand II
EPA/00/6-88/009ab
7
1bid
8Wesington, M. 1999.Determinationoforganicchemical emissionsfrom electronicsources, in RawetaL (eds),
Proc. 8th InternConfon IndoorAirandClimate. Edinburg, UK Vol 5:87-92
9ClaudioL2011. PlantingHealthierIndoorAir. Environ Health Perspect119:a426-a427:
http://dx.doi.org/10.1289/ehp.119-a426
10Heinrich,J. Influenceofindoorfactors indwellingsonthe developmentofchildhood asthma. Ind.J. HygEnvir
Health. 2011. Jan: 214: 1-25
11Wolverton, B.C. and KozaburoTakenaka. 2010. Plants: Why You Can'tLiveWithoutThem. Roli Books: New
Delhiand referencestherein
bioregener~tive
12WheeleretaL, 1996 NASA'sbiomassproductionchamber: Atestbed for lifesupportstudies
AdvancesinSpaceResearch Vol 18,Issues4-5,1996, Pages215-224.
13Gitelson et.aL 1989.Long-termexperimentson man'sstayin biological life-supportsystem
Advancesin SpaceResearch, vol 9(8):65-71.
14WheeleretaL,1996 NASA'sbiomassproductionchamber:Atestbedfor bioregenerative lifesupportstudies
AdvancesinSpace Research Vol 18,Issues4-5,1996, Pages215-224. )
15Herring, WayStationtoSpace:AHistoryoftheJohnC. StennisSpaceCenter. NASASP-4310. 1997.
Wolv~rton,
16 Bill personalcommunication .
17USPatent3,634,278,January, 1972
18US Patent3,714,349,January, 1973
19US Patent3,725,269,April, 1973
20BillWolverton, personalcommunication.
21 CommonWaterHyacinth(Eichhorniacrassipes) isnativetorapidlygrowingaquaticplantnativetotheAmazon
region ofSouthAmerica. Uponintroductiontothe United States, itnaturalizedand hasdeveloped intoan
aggressive invasivespecies.
22 NASA'sNationalSpaceTechnology LaboratoryatJohnC.StennisSpaceCenter, Mississippi.
23 Herring, M.R. 1997. WayStationtoSpace:AHistoryoftheJohn C.StennisSpaceCenter. NASASP-4310. Chapter
12
24http://www.nasa.gov/centers/iohnson/slsd/about/divisions/hefd/facilities/toxicology-saa.html(accessed 10
October, 2011)
25Wolverton, B¥C. and Rebecca C. McDonald. 1982. Foliageplantsforremovingformaldehydefrom
contaminatedairinsideenergy-efficienthomesandfuturespacestations. NASATechnical MemorandumTM
84674. 1-13pp.
c.,
26Wolverton, B. Rebecca C. McDonald, and E. A. Watkins,Jr. 1984. Foliageplantsfor removingindoorair
pollutantsfrom energy-efficienthomes. EconomicBotany. 38(2):224-228.
27Ibid.
c.,
28Wolverton, B. R. C. McDonald,and HayneH. Mesick. 1985. Foliageplantsfor indoorremoval oftheprimary
combustion gasescarbon monoxideand nitrogen. JMSAcadSci.30:1-8.
29B. Wolverton, personal communication
30Wolverton, B. C. and KozaburoTakenaka. 2010. Plants: Why You Can'tLiveWithoutThem. Roli Books: New
Delhiand referencestherein. )
c.,
31Wolverton, B. AnnJohnsonand Keith Bounds. 1989. Interiorlandscapeplantsforindoorairpollution
abatementFinal Report-September, 1989,NASAJohn C.StennisSpaceCenter
32B. Wolverton, Personal communication,and detailed inWolverton, B.C.and KozaburoTakenaka. 2010. Plants:
WhyYou Can'tLiveWithoutThem. Roli Books: NewDelhiand referencestherein.
c.,
33Wolverton, B. AnnJohnsonand Keith Bounds. 1989. Interiorlandscapeplantsforindoorairpollution
abatement. Interiorscape 8(6):37-63.
34NASASpinoff, 1989, CleanerAirforHomeandOffice, pg72-78.
7
J
.
~
35Stutte,G.W. and R.M. Wheeler. 1997. Accumulation andeffectofvolatileorganiccompoundsinclosed life
~ystems.
support Adv. inSpace Res. 20: 1913-1922.
36Larrat, E.P.,G.W.Stutte,and R.M. Wheeler. 2005. Potential effectsofbiogeniccompound productionon human
healthinclosed lifesupportsystems.SAETech. Paper2005-01-2772
37Wheeler, R.M.,G.W.Stutte, e.L. Mackowiak, N.e.Yorio,J.e.SagerandW.M. Knott. 2008. GasExchange Ratesof
PotatoStandsfor Bioregenerative LifeSupport. AdvSpace Res. 41: 798-806
38Wolve'rton, B.e.and KozaburoTakenaka. 2010. Plants: WhyYouCan'tLiveWithoutThem. Roli Books: New
Delhi and referencestherein.
39B.Wolverton, personal communication
40Ibid.
41 Ibid.
42http://www.takenakateien.co.jpL(accessed 10October, 2011)"
43 .
U.S. Patent5,433,923
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49Darlington,Aetal. 1998. Theuseofbiofilterstoimproveindoorairquality: the removal oftoluene,TCEand
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50Darlington,A. etaI., 2000. TheBiofiltrationofIndoorAir: ImplicationsforAirQuality. IndoorAir10:36-36
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52Yang DS, etal.Screeningindoorplantsforvolatileorganicpollutantremoval efficiency. HortScience44(5):1377
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