cheers, Gareth.
----- Original Message -----
From: "Theodore Held"
To: "Discussion of aroids"
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 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
>> _______________________________________________
>> Aroid-L mailing list
>> Aroid-L@www.gizmoworks.com
>> http://www.gizmoworks.com/mailman/listinfo/aroid-l
>>
>>
>> _______________________________________________
>> Aroid-L mailing list
>> Aroid-L@www.gizmoworks.com
>> http://www.gizmoworks.com/mailman/listinfo/aroid-l
>>
> _______________________________________________
> Aroid-L mailing list
> Aroid-L@www.gizmoworks.com
> http://www.gizmoworks.com/mailman/listinfo/aroid-l
>
_______________________________________________
Aroid-L mailing list
Aroid-L@www.gizmoworks.com
http://www.gizmoworks.com/mailman/listinfo/aroid-l
|
IAS on Facebook
IAS on Instagram
