2012 Plant Talk 15 Plants for Phytoremediation

Helianthus tuberosus Jerusalem ArtichokeGreetings plant lovers!

Life has finally started to slow down a bit for me and i am glad to introduce yet another totally new class to the Botany Every Day fold. Our world is increasingly subject to all sorts of pollution. Humans have introduced tens of thousands novel compounds into the environment just since WW II and very few of these have been tested for safety (McDonough & Braungart, 2002). It makes sense that even fewer plants have been tested in regards to dealing with toxins. All i could dig up in a semester of graduate school is below. Very humbling to delve into such a technical realm. i hope to dive in further at some point and greatly encourage anybody willing and able to join me. Would love to know more about the threat from foraging or community gardening in polluted urban environments in particular. Below is a quick summary of my recent botanical activities. Feel free to skip ahead if you want to get right to remediation.

Recent Events

i have just arrived back to beloved Appalachia. The leaves are gone here and the cold has begun to set in. That being said we have still had some beautiful clear 60 degree days lately and many Brassica greens as still growing. Since returning i have been in catch up mode with various projects including plant lists from Appalachian/Californian botanical surveying and Central America.

            Brew Report

Lots of brewing activity lately. Michael Gentry and i racked and bottled five gallons of Scuppernong wine while also racking Turtle´s birthday mead Goldenrod Ginger Blueberry (GRGBB) and starting a new batch of Blueberry Blackberry. Solo, i bottled the mead from my class at Jim Duke´s Green Farmacy Garden. Ingredients included Persimmon pulp, Yarrow leaf, Anise Hyssop, Spearmint, Peppermint, Tulsi and Spice Bush (Lindera benzoin) stems, four kinds of honey and Cote d´ Blanc culture. i also bottled the Celo Permaculture Gathering mead made on Lydiyah Sea´s birthday. This mead was crafted basically from left over Lamiaceae tea with a good bit of Tulsi and added honey. Coming up soon is the last trinumeral of our lifetime 12/12/12… Turtle will be having a big party at the Stonehouse in Nevada City, CA. For me, i will be brewing definitely but other activity is still unknown.

i also recently helped the Buchi folks package over 400 big flip top bottles of limited edition Holiday Kombucha that includes *Raw kombucha, *Apple juice, local cider from Hickory Nut Gap Farms, *Cinnamon, *Vanilla extract and *Clove where the  * equals certified organic. These folks make my favorite kombucha ever and have many other novel flavors and ingredients. Check the website for details www.drinkbuchi.com.

Upcoming Events

This weekend i will teach my last class of the year at Warren Wilson College. We will focus on the topic of fermentation and some items featured will include Kraut, Kimchee, Dosas, Water Kefir, Jun, Kvass, Yogurt Cheese, Seed Cheese, Fire Cider, Kombucha, Essene Bread, etc...

Next weekend Robert Eidus and the North Carolina Natural Products association are leading up an international Ginseng exposition coming to the Asheville area www.ncnaturalproducts.org .  i am grateful to both fill a roll as speaker on value added products and also facilitate the breakfast catering on Saturday. The breakfast menu is below just as a sample of how we roll.

Warren Wilson Farm and Farside Farm Egg Frittata with Beulah Farm Sausage, Yellow Branch Farm Cheddar Cheese, Chestnut School of Herbal Medicine and Warren Wilson College Brassica Greens. A vegetarian version minus sausage will be available as well. Fruit Salad Ambrosia with Big Pine Sorghum Molasses, Maple Pecan Dream Granola, Yogurt, Milks, Raisins, Haw Creek Wildflower Honey, Farm and Sparrow and West End Bakery Bread, and Imladris Farms Raspberry, Blackberry and Best Berry Jams!

Plants for Phytoremediation

            Phytoremediation entails the use of plants to mitigate the effects of some type of environmental toxin or damage. It may be used to remove contaminants from soil, toxins from air or simply re-vegetate and stabilize a disturbed area. In the process, phytoremediation may offer a suite of benefits familiar to those who work with plants including carbon sequestration, increased water quality, aesthetic value, food for wildlife, craft material etc. Below i treat a number of different areas regarding how plants have been employed for phytoremediation in Appalachia in particular in regards to coal. However, Much of this information can be extrapolated to other temperate areas where mining occurs. A study of plants that improve indoor air quality follows of which everyone can obviously benefit from.

The Case of Coal in Appalachia

The main cause for phytoremediation in Appalachia is the effect of coal mining. Coal mining in Appalachia is a very controversial and complex issue. The effect of coal mining on society and the economy of Appalachia have been studied in depth (Eller, 1982; Erikson, 1976; Fisher, 1993; Shifflett, 1991). The effects on the environment are also present in the books mentioned above. However, a separate literature deals with the mitigation of environmental damage to areas once they have been mined.

Techniques in mining have evolved radically since the start of Appalachian coal extraction in the 1800’s. Initially mining consisted of digging tunnels and a lot of manual labor. Over time methods employing machines were developed for strip mining. Much of the Appalachian phytoremediation literature addresses the strip mining method. West Virginia was the first state to develop a strip mine reclamation law in 1939 (Mellinger, Glover, & Hill, 1966). Currently workers for coal companies practice mountain top removal (MTR). With this method the “overburden” covering the coal is exploded and then dumped into surrounding valleys often covering streams. In full disclosure i don’t agree with mountain top removal and wish it would stop. No amount of planting will bring buried streams back. Plants can however help prevent erosion, offer food for wildlife, and possibly mitigate toxic chemicals. Over 500 MTR sites have already been developed to date and need to me remediated in whatever ways possible (Voices, 2012).

Control of water sources, proper fertility, negation of acidic conditions sometimes caused by mine spoil and proper grading are all part of effective revegetation. Fly ash or fluidized coal residue from coal power plants and municipal sewage sludge have been researched as a means of raising pH and fertility (Joost, Olsen, & Jones, 1987; Taylor & Schuman, 1988; Topper & Sabey, 1986). Raising pH also tends to immobilize lead at a higher rate (Berti, Cunningham, & Cooper, 1998).

A relatively short list of plants has been developed for the task of phytoremediation. Typically revegetation uses a combination of woody species and grasses. Woody species have included Autumn Olive (Elaeagnus angustifolia), Scotch Pine (Pinus sylvestris), Red Pine (Pinus resinosa), White Pine (Pinus strobus), Black Locust (Robinia pseudoacacia), Virginia Pine (Pinus virginiana) and Short Leaf Pine (Pinus echinata). Pines tend to acidify soils which may increase mobility of heavy metals like cadmium and zinc if they are present (Bergkvist, Folkeson, & Berggren, 1989). Plants that have the ability to fix nitrogen and or low nutrient needs are at a distinct advantage. Plant tolerance to heavy metals which are often at mine sites is also helpful. Fast growth is ideal and part of the reason for selection of early succession species which typically exhibit such a pattern. Eventually, some areas may take on more diverse floras (Carter & Ungar, 2002).

Proper pH is even more important for herbaceous plants. Plants that have been employed and are useful in parts of Appalachia include: Alfalfa (Medicago sativa), Bird’s foot trefoil (Lotus corniculatus), Tall Fescue (Festuca arundinacea), Sericea Lespedeza (Lespedeza cuneata), Crown Vetch (Securigera varia) syn (Coronilla varia), Flat Pea (Lathyrus sylvestris) , Sweet Clover (Melilotus albus), Red Clover (Trifolium pratense), Red Top , switchgrass (Panicum virgatum), Big Blue Stem (Andropogon gerardii) , Little Blue Stem (Schizachyrium scoparius), Bermudagrass (Cynodon dactylon), Deer tongue, and Bahiagrass (Paspalum notatum) (Karlen, Lemunyon, & Singer, 2003). Many of these plants are introduced to the U.S. and some may become invasive. Proper care is required. Some of these plants are also used for hay and forage. One study has shown that hay may be more viable than pasture. However, hay also cost more to establish than trees (Baker, 2008). A bibliography that has been developed for the production of forages on reclaimed surface mine lands may offer more insight (G. C. Anderson & Schubert, 1981).

The role of phytoremediation for coal areas has a special significance for Appalachia. Native plants are preferred to exotics due to the potential for escape by introduced species. Prevalent phytoremediation families may be analyzed to provide a ready pool of possible detoxifying plants. John Todd (2008) has recently won a $100,000 grant from the Buckminster Fuller Institute for his proposal to remediate the damage from coal mining. His plan may lead to a more robust treatment of coal mine remediation than has historically been practiced.

Phytoremediation for Heavy Metals in Soil

Soil phytoremediation has only been developed in the last 30 years (Lasat). A prolific literature of phytoremediation in the soil has been developed in that time (Brooks, 1998a; McIntyre, 2003; Singh & Ward, 2004). Phytoremediation may be referred to as variously “phytorestoration”, “phytostabilization”, “agronomic stabilization” etc. The goal of soil focused phytoremediation often has to do with the presence of heavy metals such as nickel (Ni) lead (Pb), mercury (Hg), copper (Cu), zinc (Zn), chromium (Cr), aluminum (Al) cadmium (Cd)  and the metalloid arsenic (As) (McIntyre, 2003). The sources of these toxins include metal working, coal combustion, sewage sludge, pesticides, and fertilizers. Practitioners of phytoremediation have recently also turned to dealing with organic solvents such as Trichloroethylene, Polychlorinated Biphenyls, and various products of war.

 The selection of phytoremediation techniques depends on site; size, location, history, soil characteristics, type and physical state of contaminants, degree of pollution, desired final land use, technical and financial means available, and environmental, legal, and social issues (Vangronsveld & Cunningham, 1998). Other methods for remediation include excavation, soil washing, thermal treatment, electro-reclamation, chemical, and other biological techniques. However, all of these tend to be more expensive than phytoremediation.

Heavy metals may take several forms. Methyl mercury is the most dangerous form of Hg and is typically created in an anaerobic environment such as the bottom of water bodies. It may then enter the food chain and bioaccumulate through fish. Lead is one of the most worrisome metals and it can be ingested through inhalation or ingestion. Lead can cause a vast array of neurological disorders especially in children. However, Zinc and Cadmium tend to be more bioavailable in soil than lead (Lasat, n.d.).

         Soil additives such as synthetic chelates are sometimes used in concert with plants to enhance uptake of Pb in particular (Henry, 2000). Some additives are used to simply complex and stabilize pollutants in place. Plants that exhibit tolerance for metal contaminated soils may then be used for soil stabilization instead of phytoextraction (Schat & Verkleij, 1998). Additives include agents that change pH such as liming agents or acidifiers. Phosphates, aluminosilicates and steel shots are also used to affect soil chemistry (Vangronsveld & Cunningham, 1998).

         A hyperacculmulator is a plant species capable of accumulating 100 times more metal than a typical plant (Henry, 2000). Typically hyperaccumulators will take up greater than 1% of their mass in metals (Vangronsveld & Cunningham, 1998). Most hyperaccumulators that have been identified take up Ni while some have been shown to accumulate Pb, Cd, Co, Cu, Se, and Zn. Hyperaccumulators for Hg have not yet been found (Henry, 2000). Alyssum is a common plant that has been shown to be a hyperaccumulator of Ni (Schat & Verkleij, 1998)

         Plant family trends may elucidate patterns in hyperaccumulation. Research shows that the mustard (Brassicaceae) and carnation (Caryophyllaceae) families contain many obligate metallophytes but are usually nonmycorrhizal (Colpaert, 1998). Poinsettia (Euphorbiaceae) and Snapdragon (Scrophulariaceae) families have also been shown to accumulate metals (Henry, 2000). Metallophytes in the subtropical and tropical parts of the world often belong to Bean (Fabaceae), Mint (Lamiaceae), Sunflower (Asteraceae) and Grass (Poaceae) families (Colpaert, 1998).

         Most plants that hyperaccumulate metals have been identified for other areas than the U.S.A.  (Brooks, 1998b) Relevant genera to the U.S.A. and Appalachia include Penny cress (Thlaspi spp.), Alyssum (Alyssum spp.), and Astragalus (Astragalus spp). Ultramafic soils of which Appalachia has some, represent one place on which such plants are typically found.  Therefore, potential may exist to discover some indigenous Appalachian hyperaccumulators. Such soils are rare in Appalachia and the plants represented from such places would need to be bred and propagated in order to be applied for use.

            Plant breeding has been pursued to increase the efficacy of phytoremediation. The total flora of plants adapted to metalliferous soils in western and central Europe is no more than fifty higher plant species and many of these are not fit for the work of phytoremediation (Schat & Verkleij, 1998).  Traditional breeding of plants has shown promise in providing faster growth and greater tolerance to a larger range of metals (Schat & Verkleij, 1998). Some plants that are metal tolerant may not provide effective ground cover or have unknown cultural needs (Vangronsveld & Cunningham, 1998). Research has also been conducted on using transgenic plants for removal of mercury (Henry, 2000; Lasat, n.d.).

            Some plants are naturally tolerant to metalliferous soils. Within these species intra-specific tolerance can vary greatly. Plants also vary in their transport of metals from root to shoot which may be an issue with grazing animals. Paper birch (Betula papyrifera) has been shown to accumulate twice as much copper as many other trees while only translocating 20% of the Cu into its foliage versus 60% for the other trees studied (Lepp & Dickinson, 1998). Plants that deposit metals in their foliage can act as a vector of toxic exposure for wildlife and even ultimately people. Soil additives can help decrease the level of translocation from the soil into foliage (Vangronsveld & Cunningham, 1998). Certain mycorrhizal relationships may also serve to sequester metals in the root zone rather than the foliage (Colpaert, 1998). Recently, the role of fungal relations in overall phytoremediation has been recently championed even further (Stamets, 2005).

           Mycorrhizal relationships also play an important role in the tolerance of plants for metals and the potential for remediation. It may be possible to identify certain fungal organisms that may make tree establishment easier on metal contaminated soils (Lepp & Dickinson, 1998). Arbuscular mycorrhizal (AM) fungi in particular seem to colonize a number of different metalophyte plants across a range of plant families (Colpaert, 1998). Crown vetch (Coronilla varia) plants that were colonizing anthracite wastelands in Pennsylvania were heavily colonized with AM fungi (Colpaert, 1998). Actinorhizal plants such as Alder (Alnus spp.), Sea Buckthorn (Hippophae spp.), Bog Myrtle (Myrica spp.), and She Oak (Casuarinas spp.) may also have a role to play in phytoremediation due to their tolerance of marginal environments.

           Some plants show tolerances to several different heavy metal types while others are more specific. Plants that can tolerate and remediate metallic soils may be different than plants used to clean up organic compounds (Vangronsveld & Cunningham, 1998). Canada has set up a database called PHYTOREM that covers the phytoremediating ability of vascular plants, fungi, bryophytes, lichen, algae and bacteria (McIntyre, 2003). Within the database 775 species in 76 families are included.

           Most plants show accumulation, tolerance or hyperaccumulation of only one metal. Water plants show the largest ability to accumulate multiple metals. These include Hydrilla (Hydrilla verticillata), Duckweed (Lemna minor), Water .Lettuce (Pistia stratiotes) Water Fern (Salvinia molesta) Giant Duckweed (Spirodela polyrhiza), Water Hyacinth (Eichhornia crassipes) Water Hyssop (Bacopa monnieri) Water Fern (Azolla filiculoides) and Tape Grass (Vallisneria americana) (McIntyre, 2003). Most of these are exotic to North America with the exception of Duckweed and Tape Grass. Many have escaped cultivation and are now terrible problems all over the world. Several edible plants have been shown to accumulate metals. Water Hyacinth is edible however care should be taken not to consume it when metal contamination is a concern (Couplan, 1998). Some common edible terrestrial plants also have been shown to accumulate multiple metals including Indian mustard (Brassica juncea), Sunflower (Helianthus annuus) Bent Grass (Agrostis castellana) and Alpine Penny Cress (Thlaspi caerulescens) (McIntyre, 2003).

          Several limitations to the application of phytoremediation have been identified. Phytoremediation is limited to areas with low concentrations of toxins. This technique only tends to remove toxins relatively close to the surface. The resulting plant material from phytoremediation may have to be classified as hazardous waste. The site soil type and climatic conditions can also limit the efficacy of phytoremediation.

          Benefits from phytoremediation abound. Phytoremediation is economical. It reduces waste going to the landfill by up to 95%. Soil disturbance is reduced lowering chance of cross contamination. It is easy to implement, environmentally friendly, and aesthetically pleasing (Henry, 2000). Overall the techniques of phytoremediation may offer an additional tool in the suite of techniques used to mitigate toxic elements in the environment.

Overview of Air Quality issues and the Role of Phytoremediation

          Many toxins that occur in the home environment need to be removed to facilitate good human health. Various plant species have been shown to remove indoor air pollutants (IAPs) (Kent Kobayashi, Kaufman, Griffis, & McConnell, 2007; B. C. Wolverton & Wolverton, 1993; B. C. Wolverton, 1997). Some of The IAP substances that researchers have removed with plants include Formaldehyde, Xylene, Toulene, and Benzene.


Sources of some major common indoor air pollutants


Gasoline, marker pens, photocopiers, printers, adhesives, joint compounds, floor coverings, solvents, dyes, kerosene smoke,


Synthetic carpet, wood floor finishes, cigarette smoke, printers, photocopiers, solvents, adhesives, wallpaper, joint compound, vinyl flooring, caulking compound, paint, kerosene smoke


Cigarette smoke, glues, resins, carpets, curtains, facial tissues, floor coverings, gas stoves, grocery bags, paints, paper towels, particle board, permanent press clothing, plywood, stains, varnishes, foam insulation,


Solvents, tobacco smoke, paints, finishes, caulk,

Sources: (E. L. Anderson & Albert, 1999; Godish, 2001; Murphy, 2006; Warde, 1997; B. C. Wolverton, 1997)

              Several of the plants that remove indoor toxins are relatively easy to propagate (Bryant, 2006). Propagation is the process by which a plant is reproduced. However, some of the plants that remove toxins from the air are themselves also toxic. The toxicity of plants is mostly concern in the case of accidental ingestion by young children (Alber & Alber, 1993) Therefore, house plant owners must be as aware of plant toxicity as they are of air toxicity. When possible poisoning by children is a factor less toxic plants could be chosen.

         The study described here focused on learning the techniques to propagate plants that help alleviate the issues of indoor air pollution. The presence of plants in the indoor environment also helps alleviate a host of other societal ills. For instance, plants in the work environment can increase happiness and worker productivity (Kent Kobayashi et al., 2007). Working with plants can also help provide a connection with nature that many people in our society desperately lack (Louv, 2005; Nabhan & Trimble, 1994).

          Future sustainability depends on the combination of the old and the new. Much of the natural world has been discounted in the relentless pursuit of sophisticated modern technological solutions. Sometimes these solutions cause problems that are just as bad as what they are trying to remedy (Carson, 2002). The natural world often can offer solutions to problems without deleterious side effects (Bradley & Barbara, 1997).

          The model of Appropriate Technology (AT) serves to underpin the initiative espoused in this class. AT seeks simple solutions that use inexpensive locally attainable ideally indigenous materials (Schumacher, 1973). A resource explaining AT in an Appalachian context has also recently been published (Fritsch & Gallimore, 2007). Plant propagation is an ancient practice used by the Romans and even societies before them. Many air detoxifying plants are readily available to the everyday building dweller. In fact several species of detoxifying plants already commonly occur within the built environment. The propagation of some of these plants is known due to its extreme ease and utility. Yet, how many people still go to some big box store to purchase plants from afar that could be propagated for free from local stock? It stands to reason that the planting of these particular useful plants would increase were the knowledge of the air detoxifying power known more widely. Propagation lowers the barrier of accessibility for people whom plants can sometimes be too costly to buy. FEMA trailer residents and others in manufactured housing are examples of  populations that might benefit from such knowledge. Manufactured housing in general tends to have the highest residential levels of formaldehyde (Godish, 2001). This type of housing is also prevalent for low income people in Appalachia as well. The provision of plants that detoxify the air for such situations may help avoid excessive exposure. The prevalence of high exposure levels to toxic chemicals by disadvantaged groups represents a social justice issue (Murphy, 2006). Propagation of plants can also serve as a form of income for these people and others.

          Humans have developed many methods for propagating plants. The right technique/s for each type of plant is necessary to ensure success. The physical product of some of my research was the propagation of four different species of air cleaning houseplants. The plants for this project were propagated using offsets, cuttings and divisions. Other species and other propagating methods were also explored to give the reader a fuller sense of the technological potential. Many of the most effective de-polluting plants are more difficult to propagate and or harder to acquire.

          The plants included were Air Plant (Chlorophytum comosum), English Ivy (Hedera helix), Golden Pothos (Epiprenum aureum) Mother in law’s tongue (Sansevieria trifasciata) Aloe (Aloe barbandensis) and Rubber Plant (Ficus elastica syn F. robusta). These plant types represent air cleaning species that were the easiest to obtain cheaply while also seeming easy to propagate according to the literature.

Literature Review for Houseplant Phytoremediation of Poor Air Quality

          The main purpose of the current review is to unify the disparate literatures of house plants, air quality phytoremediation, plant propagation and plant toxicity within the framework of plant family trends. Writings on plant propagation are numerous and have a long history. Phytoremediation on the other hand as has been stated already is a rather new science. Work on the detoxifying properties of house plants in particular rests largely on the shoulders of the researcher B.C. Wolverton (B. C. Wolverton, Johnson, & Bounds, 1989; 1996; B. C. Wolverton, 1997, n.d.; B. Wolverton, Mcdonald, & Watkins, 1984). Experiments by Wolverton and others were carried out on behalf of the National Aviation and Space Administration (NASA) as a means of preserving air quality in space. Wolverton ultimately ranked 50 plants on their ability to clean the air, ease of cultivation, susceptibility to insect infestation, and transpiration rate (B. C. Wolverton, 1997). Wolverton also demonstrated that soil microorganisms play a significant role in the detoxification of air along with the plants in his studies.

          Of the plants in this study English Ivy (Hedera helix) has been shown by to remove formaldehyde the most followed by Spider Plant (Chlorophytum comosum), Snake Plant (Sansevieria trifasciata) and Aloe (Aloe barbadenis). However Spider plant removes the most Xylene followed by Snake Plant and English Ivy (B. C. Wolverton & Wolverton, 1993).  In another study Golden Pothos (Epiprenum aureum) was also shown to remove comparable amounts of formaldehyde to English Ivy (B. C. Wolverton et al., 1989). In the same study English Ivy was the best at removing benzene and Golden Pothos was third. Many of the studies by Wolverton use varying techniques and plant materials so a standardized comparison is hard to do. Nonetheless, the overall summation is that these plants mentioned above are some of the most effective at detoxifying while also factoring in ease of propagation.

          Many other plants were shown by Wolverton to be better at detoxifying than the ones in this study. However, most of these plants are either more expensive to acquire, harder to propagate, or harder to take care of. Monkey grass (Liriope spicata) is another potential good detoxifying plant but not included in this study. It is second overall to the plants studied in formaldehyde and xylene removal as well as a strong remover of ammonia (B. C. Wolverton & Wolverton, 1993). Florist’s mum (Chrysanthemum morifolium) is another potentially readily available good detoxifier of formaldehyde, xylene and ammonia. Typically ferns, members of the Ficus genus, and members of the Peace Lily (Araceae) Palm (Arecaceae) and Agave (Agavaceae) families have been shown to be the best at detoxifying in general for formaldehyde, xylene, ammonia, and benzene (B. C. Wolverton et al., 1989; B. C. Wolverton & Wolverton, 1993; B. C. Wolverton, 1997). A few of the most effective detoxifying plants may significantly increase the air quality of the average enclosed office (B. C. Wolverton & Wolverton, 1993).

Health Effects of Indoor Air Pollution

          This section also offers a brief overview of the health effects from various chemicals. Our society is becoming increasingly saturated with synthetic substances. The more these substances can be removed from the environment the healthier society will be.

          The modern age construction uses air tight building envelopes that encourage energy efficiency. These impermeable barriers can sometimes lead to the trapping of deleterious substances inside the buildings. “Sick building syndrome” is evidence of the unwanted effect that comes from such tight insulation. Maladies such as asthma, allergies, and chemical sensitivities can be traced to this modern building phenomenon but are hard to prove (May, 2006; Murphy, 2006). Different people may react differently to the same level of chemical exposure. Animal testing normally involves acute dosages and cannot be directly correlated to humans. Very little study has looked at low level chronic exposure (E. L. Anderson & Albert, 1999). The methodology of Indoor Air Quality (IAQ) risk assessment is very diverse and many studies do not correlate well in general. There is a general lack of proven connection between Volatile Organic Compounds (VOCs) and sick building syndrome. However, this may be due to the lack of adequate testing protocols amongst other variables.

          The Environmental Protection Agency (EPA) initially spent much more time regulating outside air quality than inside (E. L. Anderson & Albert, 1999). However, the indoor air environment may be up to ten times more polluted than the outdoors (B. C. Wolverton, 1997). Today people spend as much as 90% of their time indoors (E. L. Anderson & Albert, 1999). With statistics like these it is not hard to see why an increase in illness related to IAQ might be occurring.

          Modern society is filled with novel toxins that did not exist until the industrial revolution (McDonough & Braungart, 2002). The catch phrase “better living through modern chemistry” has been shown to have significant deleterious side effects (Carson, 2002).  Many potential toxins exist in the indoor environment. Mold, radon, asbestos, tobacco smoke, particulates from combustion, carbon monoxide, various microscopic insects, etc all represent potentially toxic elements in the indoor environment (Spengler, Samet, & McCarthy, 2001). Airborne toxins such as formaldehyde, benzene, toluene, xylene, are the current focus. Nonetheless, plants have been shown to remove some microbial contaminants as well (B. C. Wolverton & Wolverton, 1996).

         Aldehydes such as formaldehyde are irritants to the mucous membranes of the eyes and upper respiratory tract (Godish, 2001). Formaldehyde is one of the most toxic of this group of chemicals. It may cause neurological symptoms and evidence points to the fact that formaldehyde may aggravate asthmatic problems as well. Significant deleterious effects have been shown to occur at concentrations as low as 1 part per million (ppm) after just 90 minutes (Godish, 2001).  Formaldehyde has also been found to be carcinogenic (E. L. Anderson & Albert, 1999; Moeller, 2005). The level of .20 - .40 parts per million (ppm) allowable by the U.S. Department of Housing and Urban Development for mobile homes is well above the threshold of .05 – 2 ppm under which the above mentioned symptoms may occur (Warde, 1997).

          Formaldehyde, toluene and xylene represent are all types of Volatile Organic Compounds (VOCs). Hundreds of VOCs have been identified in indoor air of which about 50 are common (Kostiainen, 1995; Warde, 1997). Formaldehyde has been studied more than the other VOCs. Toulene is considered as a possible cause of anemia and a sensitizer that lowers dosages of other VOCs that are required to produce symptoms (Warde, 1997). Xylene is an eye and respiratory irritant and central nervous system depressant. Xylene may also cause liver, kidney, and heart damage (Warde, 1997).

Other Mitigation Techniques for Indoor Air Toxins

            Detoxifying plants represent just one method of relieving the problem of Indoor Air Pollution (IAP). A mixture of techniques is most prudent to avoid the effects of VOCs. Formaldehyde emissions naturally decrease significantly over time (Godish, 2001). Proper air circulation can help remove these gases. Air circulation in combination with carbon filtration and/or plants also increases the efficacy of plants in detoxification (Leviton, 2001; B. C. Wolverton, 1997). Heat and moisture increase off gassing and may be used to speed up the release of gases prior to habitation. Using products that are low in VOCs will also decrease the total load. People who employ methods of decreasing toxins typically follow a certain pattern. First research is done to see if a substance might be eliminated or substituted. Next, the process involving the substance is possibly altered or equipment is changed. Isolating the substance follows and finally personal protective equipment is employed. The field of Industrial Ecology (IE) deals with such design processes (Ayres & Ayres, 2002; Kleindorfer, 2002; Manahan, 1999). Ultimately, more stringent regulations are necessary to stimulate such research especially if mitigation techniques may cost manufacturing businesses more money. However, it has been shown that significant savings by increased productivity may be had for businesses that are willing to mitigate the effects of poor indoor air quality on their workforce (Fisk, 2001).

          Testing for VOCs varies for each compound. Many techniques have been developed to determine the level of toxins in the air (American Society for Testing and Materials, 1999) For formaldehyde diffusion tube testers and DNPH devices are the most common. The DNPH devices are considered to be the most accurate (Warde, 1997). In either case the testers must be sent off for analysis. However, only a few prominent VOC’s even have developed tests.

Methods of propagation

          Many techniques are available to the potential propagator. These actions can be simple and mundane such as cutting a piece of plant and putting it in soil or water until it roots. However, complex laboratory techniques that need special equipment and absolute sterility are necessary for some plants. The techniques for the plants in this study were all simple and are variations of taking cuttings.

          Most propagation books describe a multitude of ways to propagate plants. Some of these books do a better job than others. Visual imagery and step by step instructions can greatly assist the understanding of how certain plants are propagated (Smith, 2007; Toogood, 1999) As might be understood, older references may not provide as many visual aids or refer to modern innovations (Kains, 1942). Very few of the propagation books refer to the uses of the plants whether for improved environmental quality or aesthetic beauty. Toxicity is also rarely mentioned except in a specialized literature dealing with that subject alone.

Houseplant Toxicity and Plant Family Trends

          The toxicity of certain houseplants is well known. Plants that both clean the air and contain inherent toxicity tend to come from the families Araceae, Araliaceae, and Euphorbiaceae (Frohne & Pfander, 2005). Knowledge of which plants are toxic and which ones aren’t would help alleviate the phenomenon of unintentional poisonings that occur every year across the world. What follows is a chart of the plants from the current study with their related toxicity.

Toxic elements of selected air detoxifying plants

Scientific Name

Common Name

Plant Family


Hedera helix

English Ivy



Chlorophytum comosum

Spider plant/Air plant



Sansevieria tritrifasciata

Mother in law's tongue


Saponins when consumed in very high doses

Aloe barbandensis



Barbaloin is a purgative

Epiprenum aureum

Golden Pothos


Rahphides of calcium oxalate

Ficus elastica

Rubber plant



Source: (Alber & Alber, 1993; Frohne & Pfander, 2005; Turner & Szczawinski, 1995)

Analysis of plants at the family level may also allow the discovery of other potential air purifying plants. Out of the 50 plants discussed by Wolverton (1997) only about 20 families are represented.

Adapted from (B. C. Wolverton, 1997)

          The Araceae family alone accounts for 24% of the total while the Palm family (Arecaceae) and the Agave family (Agavaceae) account for another 10% each. For many families only one individual species has been identified. Typically many members of a family will exhibit similar characteristics such as uses for food, medicine, poisonous properties (Elpel, 2004). This phenomenon might be extended to detoxifying abilities. All the plants included from the Araceae family are toxic (Alber & Alber, 1993; Frohne & Pfander, 2005). Exploration in the benefits of other species within underrepresented relatively non-toxic families such as the Sunflower (Asteraceae), Begonia (Begoniaceae), Prayer plant (Marantaceae) and Fig (Moraceae) might be a good direction for further research. New non-toxic families of houseplants that could be explored include the Mint (Lamiaceae) and Geranium (Geraniaceae) Different species of the same genus often act similarly as is demonstrated by Wolverton’s inclusion of four Philodendron spp., four Draceanea spp. and three Ficus spp. in his treatment of the fifty plants (B. C. Wolverton, 1997) However, Removal rates were shown to vary by species

Data Analysis of an Experiment on Propagation of Air Detoxifying Plants

          An analysis of the data leads to the idea that English Ivy (Hedera helix) is by far the best prospect. It is an exotic invasive that can be readily found for free in the environment. It is easy to propagate, and it is one of the most effective detoxifiers. However, English Ivy is also toxic and should not be planted outdoors due to its invasiveness. Snake Plant (Sansevieria trifasciata) is easy to propagate by division but hard to propagate by cuttings. Spider Plant (Chlorophytum comosum), Aloe (Aloe barbadensis) and Pothos (Epiprenum aureum) are easy to propagate but not as good at toxin removal.

          Many house plants grow slowly or are hard to propagate and it might be difficult to reproduce a plant that one might find in the store economically. English Ivy (Hedera helix), Spider Plant (Chlorophytum comosum), and Pothos (Epiprenum aureum) are notable exceptions.

          Propagation of air detoxifying plants offers a beneficial economics angle. People that need jobs might make a living by propagating and selling plants to institutions like businesses, schools, hospitals and churches. This concept goes far beyond just plants that may be used for air purification. Disadvantaged people can have the cost of plants subsidized or they may be encouraged to do work trade, or come to a workshop and create their own. English ivy (Hedera helix), Spider Plant (Chlorophytum comosum), and Pothos (Epiprenum aureum) can be propagated easily and often found already growing in many people’s houses. Monkey grass (Liriope sp.) and florist Mums (Chrysanthemum sp.) may also be easy to propagate. Members of the Palm family (Arecaceae) may be worth purchasing and eventually dividing due to their superior abilities to detoxify the air.


            Most work on soil phytoremediation has been done outside the country. Development of knowledge for appropriate plants indigenous to Appalachia for phytoremediation of metals contaminants in particular offers an excellent opportunity for further study. Plant that are used for phytorestoration of denuded coal areas mainly come from the Grass (Poaceae) and Bean (Poaceae) families. These plants may be grown for wildlife, pasture, or hay. Some plants that have been employed for such purposes are exotic invasives whose use might be questioned and discontinued.

         A combination of propagating plants that are easy to reproduce and very effective at cleaning the air coupled with purchasing plants that offer the most detoxification for the lowest price is probably the most effective strategy.

            Study at the plant family level clearly shows trends in the ability of certain groups to help detoxify the environment. Similarly many plants that detoxify the environment can in fact be toxic themselves. Focusing at the plant family level may be helpful in introducing people to such concepts and provide directions for further study in a simplified manner.

Potential New Families for further Air Detoxification Use



Scientific name

Common Name








Dianthus, Carnation



Fittonia vershaffeltii

Mosaic plant

Not known


Potential New Genera for further Air Detoxification Study



Scientific name

Common Name



Colocasia esculenta

Elephant's ear



Cordyline terminalis

Ti plant



Cosmos bipinnatus




Dizygotheca elegantissima

False aralia

Not known


Fatsia japonica


Not known


Gyanura aurantiaca

Velvet plant


For the next class we will cover plants of Desert, Aquatic and Alpine environments and it will be posted around December 15th

Below are items to think about/comment on. Please write me directly at marc@botanyeveryday.com or leave information in the commentary under this class.


- Decide to make a plant craft for the holidays and share with us your choice

- Look up some of the families mentioned in this post in Botany in a Day and

   share some information about them   with the group. Or provide info from

    your personal experience

- Read one article on Phytoremediation and do your part to add to our collective knowledge  on this important topic

- Post any clear photos of question plants to Facebook or send in an email.

Praises to all that have donated to the cause!!! i encourage everyone reading this to donate as they are able financially, commentarialy, or energetically... Your contributions greatly help me continue this crucial work of ethnobotanical research and education. Please let me know your thoughts in general and any way i can help this class serve you best.

Thanks, marc





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