Re: Biology Question on Trees and Polution
Subject: Re: Biology Question on Trees and Polution
From: email@example.com (Jim Cook)
Date: 21 Mar 1995 06:57:28 GMT
Article: 22137 of sci.bio
Newsgroups: sci.environment, sci.bio
References: <firstname.lastname@example.org> <eeeD5Dx4u.DMv@netcom.com> <email@example.com>
Xref: bigblue.oit.unc.edu sci.environment:54435 sci.bio:22137
In article <firstname.lastname@example.org>, email@example.com says:
>In article <firstname.lastname@example.org>, <email@example.com> writes:
>> Simonich and Hites (1994) estimated that most of the atmosphere to soil
>> flux of polycyclic aromatic hydrocarbons (PAHs) occurs via absorption
>> to plants. They suggested that this may also be the case for other low
>> vapor pressure and hydrophobic atmospheric pollutants -- such as
>> polychlorinated dibenzo-p-dioxins, dibenzofurans and biphenyls.
>> It's true that trees and other plants release hydrocarbons to the
>> atmosphere, and that these hydrocarbons contribute to the formation
>> of smog and haze. However, the rate limiting reactant in this
>> photochemical reaction is NOx, which is largely anthropogenic in most
>> urban areas.
>> ....Simonich, S.L. and Hites, R.A. (1994) Importance of Vegetation
>> in Removing Polycyclic Aromatic Hydrocarbons from the Atmosphere.
>> Nature, 370, 49-51.
>Thanks for the citation...always a help.
>I'm not in this field, but it seems to me what you are saying is that, as
>part of the process of transpiration, trees and other plants will carry
>hydrocarbons disolved in the ground water into the tree, and then it will
>blow off in to the air.
>Is it therefore correct to say that trees are only responsible for moving
>the hydrocarbons from the soil to the air? That is, they do not *create*
>any of these things?
I guess I wasn't clear enough. Trees and other plants make and release
a variety of hydrocarbons -- terpenes -- that are responsible for many
plant odors. Generally speaking, plant roots don't absorb hydrocarbons
in the soil very efficiently.
>If so, then the question really is, how did the hydrocarbons such as
>dioxins get into the ground?
PAHs, PCBs and dioxins get into the soil from the atmosphere -- except
for point source contamination. And, for the most part, they get into
the air from human sources. There's also some "recycling" of old
contaminants from soil and water reserviors.
>I'm sure Mr. Reagan would blame the ground-hogs. and that Mr Thorson
>would believe him.
Actually, Reagan was correct that "trees pollute," at least in a way.
However, as I noted, the rate limiting factor is [NOx], which mostly
comes from human sources.
That brings up an interesting point. EPA could have attempted to
control either hydrocarbons or NOx to reduce smog and haze, and they
decided to regulate hydrocarbon emissions -- because it was less
expensive. However, they found that less anthropogenic hydrocarbons
didn't necessarily mean less snog/haze -- given the background from
trees and other plants. It turned out they need to reduce NOx
emissions as well. So it goes.