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Re: depolluting plants - About that NASA Study

  • Subject: Re: depolluting plants - About that NASA Study
  • From: "Gareth Hambridge" <ghambridge@optusnet.com.au>
  • Date: Thu, 15 Dec 2011 11:09:41 +1100

Hello Genevieve, below are some links you should find interesting. I have 
only skimmed these articles but they seem to be much more accurate in their 
methods and results. Of particular interest is the research done by a team 
at the University of Technology, Sydney led by Prof. Margaret Burchett.
Also I point to remember is that the human body deals with pollutants 
everyday and the psychological effects of pretty green things growing in 
your office presumably have the knock on effect of improved health and 
therefore likely improved ability to deal with pollutants. The other links 
below have more detail.
cheers, Gareth.
----- Original Message ----- 
From: "Theodore Held" <oppenhauser2001@gmail.com>
To: "Discussion of aroids" <aroid-l@gizmoworks.com>
Sent: Wednesday, December 14, 2011 6:31 AM
Subject: Re: [Aroid-l] depolluting plants - About that NASA Study

> List,
> I seem to have misunderstood Genevieve's original inquiry. Based on
> subsequent postings it seems that the intent was to explore pollution
> abatement by houseplants involving the plants absorbing organic air
> pollutants.
> One notable reference is by a guy named B. C. Wolverton, who authored
> the study for NASA back in 1989. This document is available on the
> internet by way of an outfit called the National Foliage Foundation or
> the address provided by Sherry; or people can e-mail me and I'll send
> them the PDF file. To the credit of the National Foliage people, their
> welcoming page features a nice picture of a Peace Lily.
> I waded through the evidence described in Dr. Wolverton's paper and
> found the data to be questionable. My main objection, at least on
> first reading, is that they are testing air samples on an extremely
> complex system, involving plants or several types, soils of
> undisclosed compositions, sometimes with activated carbon and
> sometimes without, and air circulation equipment present. While they
> seem to have tested a few controls (the complex system without plants,
> for example), one is tempted to be skeptical since what they are
> trying to establish is rather subtle. The study bites off too much at
> once.
> Then there are the data. They describe injecting benzene into one of
> their test setups. They say they added 35 microliters of benzene,
> which comes out to be roughly 0.03 grams by weight. Then they drew
> samples and measured the amount of benzene that was not absorbed by
> the setup after 24 hours. The datum for Gerbera daisy, listed in their
> Table 2, page 10, is that this particular test absorbed a total of
> 107,653 micrograms of benzene, which translates to 0.108 grams by
> weight. When more material is removed than is added in the first place
> it makes one wonder. For benzene, the experiments withdrawing more
> than they put in comprise half of the data points. For
> trichloroethylene, two of their data points have this problem.
> We also have no idea of the reliability of the data points. It is
> customary in science to provide some indication of the "plus or minus"
> range (standard deviation). Here there is no information on this.
> Exactly 107,653? Not credible. Is that 107,653 micrograms a result of
> ten experiments, averaged? Or was it just a single experiment?
> The experimental plants range all over the map regarding the amount of
> leaf area exposed in a test. One plant type has a large leaf surface
> area while another has much less. How are we to compare the plant
> types? Maybe the amount of chemical removed is dependent on leaf area.
> But this does not come up in the discussion. They should at least have
> provided a calculation of the amount removed per a given leaf area
> standard. It makes it difficult to understand otherwise. The same
> criticism applies for listing the amount added as a volume and then
> report results as a weight.
> And why do we have varying amounts by weight of the three pollutants?
> While the amount by volume is said to be the same (35 microliters),
> the three pollutants have from low (benzene) to quite high
> (trichloroethylene) specific gravities. This means that the amount
> absorbed cannot be compared easily. If the amount removed is dependent
> on the initial loading then the data cannot be compared at all with
> any justification.
> And the three pollutants are quite different, chemically. Benzene is
> flammable, trichloroethylene is not. Benzene and trichloroethylene are
> both quite inert while formaldyhyde reacts with a wide variety of
> materials almost instantly (removing it, in a sense, from the system).
> Besides that, formaldehyde converts to a polymeric form upon
> evaporation. That means it is not dispersed into the system as a vapor
> as they describe.
> Maybe I've missed some things. If so, please let me know.
> Absent from the Wolverton paper is an answer to the question, "Where
> does the pollutant go?" Back in 1989 it was probably difficult to
> answer that question. With today's techniques it should be possible to
> answer it. Is the pollutant merely absorbed, being retained in the
> tissues? Is it metabolized or otherwise destroyed? If it is
> metabolized and destroyed that would be good. If it's just sitting
> around somewhere, like in plant tissues, that's not so good.
> Dr. Wolverton is careful to state that the levels of his experimental
> pollutants are far in excess of what might be expected in the average
> office or home. How good are plants with the removal of vastly smaller
> trace quantities? This is outside the scope of the NASA testing, so we
> don't really know. Since what we want to know is how good plants are
> at removing these normal amounts, the answer is important. If they are
> effective on normal (probably non-hazardous) levels it is something to
> boast about (regardless of whether there is an actual health threat).
> On the other hand, it is quite feasible that plants can do well in the
> artificial test conditions, but are useless for normal levels.
> Maybe plants can act as efficient pollutant scrubbers in ways that are
> not merely suicidal (meaning they adsorb material, probably to the
> detriment of the plant). But I am worried about a study that implies
> that living plant tissue is as effective or more effective that
> activated carbon in the removal of benzene, formaldehyde and
> trichlorethylene when the gold standard for the removal of such gases
> from the air is, in fact, activated carbon.
> On that note, one other thing is the use of their little combination
> device with activated carbon. Nice, so far as it seems. But notice
> that they did not run a control with these experiments. The graphs
> look nice: The pollutants go down in a regular fashion. But one would
> expect that with activated carbon alone. Why bother with the plant?
> There is no comparable graph showing actibvated carbon alone. Why not?
> Finally, there is some discussion about microorganisms in the soil,
> etc. While the implication here is that these organisms are
> contributing to a kind of bioremediation, this is not explored. The
> reader is left to use her imagination about what the work is meant to
> show. As a matter of personal experience, I know for certain that the
> degree of actual bioremediation of organic pollutants is quite a bit
> lower than that implied by Dr. Wolverton. In fact, to suggest that it
> happens on any measurable scale in their setup within 24 hours is a
> sleight of hand trick at the least. My own work has shown that even
> for rather readily biodegraded materials (like corn oil) in ideal
> situations preliminary degradation (defined as any portion of the
> original molecule having been nibbled off) is only on the order of
> about half the original material in a month's time. For more
> recalcitrant materials (and benzene and trichloroethylene would fit
> that description) the rate is far, far lower.
> There is more to say, but this entry has probably put most people to
> sleep by now. Just be advised that not everything you read is correct.
> That applies even when the work is touted to have been done for NASA.
> Maybe plants can do something like what we'd all like to believe. But
> this paper does not show it.
> Ted Held.
> On Thu, Dec 8, 2011 at 6:17 PM, Sherry Gates <TheTropix@msn.com> wrote:
>> Hi everyone,
>> I remember NASA doing a study about this very thing. Here's a link to a
>> little info about it. I'm sure y'all can find other information as well.
>> I wish every one of y'all and your loved ones the Happiest and Merriest
>> Christmas ever!
>> Sherry
>> http://en.wikipedia.org/wiki/List_of_air-filtering_soil_and_plants
>> ----- Original Message -----
>> From: Geneviève Ferry
>> To: Discussion of aroids
>> Sent: Monday, December 05, 2011 11:24 AM
>> Subject: [Aroid-l] depolluting plants
>> Dear aroiders ,
>> I want your opinion on depolluting plants because the aroids family is
>> often present (Anthurium, Pothos, Philodendron and especially
>> Spathyphillum). There are scientific studies about aroids? If so, which?
>> Or that is only a means for commercial sale?
>> I 'm very interested.
>> All the best ,
>> Geneviève Ferry
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