Re: Aquatic Plants Digest V1 #134

>From: huntley at ix_netcom.com (Wright Huntley )

>Zeb, I think you may be mistaken about the toxicity of lead to humans (and
>plants or fish). I don't know where you got your information, but it keeps
>cropping up, and I would like to find out where it's coming from.

It looks like a little "wake-up call" is in order here.  Wright, I don't
know where you get *your* information about lead, but you're cutting some
serious corners here.  A good reference on lead exposure routes and
toxicity is

        Toxicology: the Basic Science of Poisones, by Casarett and Doull's

This is THE basic textbook in toxicology, used by graduate students all
over the country.  I'll answer some of the points you are raising, based on
information from the textbook, OK?

>Lead is very inert in water that isn't fairly acid. Sure, a child (or
>painter) eating a *lot* of lead-oxide paint can slowly develop some
>heavy-metal poisoning symptoms, but that's not the same thing, at all. This
>paint problem has lead ( :-) ) to a hysterical press reaction comparable only
>to the asbestos scare, and a regulatory zeal that provides jobs for a huge
>number of government employees, certified lead-removal contractors, etc.

Lead is toxic at *any* dose.  While some of the effects are subtle
neurological changes, they are detectable and have been replicated in many
laboratory experiment.  As the intruments and tests have gotten more
precise, effects have been found at lower and lower doses.
As for the exposure, lead dissolves in water, albeit slowly, and then lands
in the gastro-intestinal tract and/or the bloodstream (through
respiration).  The major danger of lead is not its acute toxicity, but its
extremely long half-life inside the body (approx. 20 years), where over
time it accumulates to toxic levels and impairs several neurological
processes.  Tap water, which is often alkaline, still dissolves lead in
small doses.  It ends up in the drinking water and gets ingested that way.
Between 10 and 20% of the lead exposure to humans is through water (most of
the rest is through inhalation).

>If someone out there can document the toxicity of metallic lead, not
>dissolved by gastric acids, I would like to know of it. Then I can shut up
>about this little piece of urban folklore. Until that happens, I'll happily
>use lead anchors when I need them (which is almost never). I'll also repond
>whenever anyone uses that emotion-laden press word, "toxic," without
>justifying the use of such a scare word.

Metallic lead is indeed not toxic as such, but it gets metabolized by a
variety of routes, not just gastric acids.  I agree that the lead weights
are not a big problem, unless you're keeping super-valuable and/or rare
plants and fish in your tank, and plan on breeding them for many
generations.  And yes, I also use lead weights in my tank (I wished there
was an alternative, though).

Is lead toxic? YOU BET!

Jean Opsomer

                               | Jean D. Opsomer                           |
                               | Department of Statistics                  |
                               | Snedecor Hall                             |
                               | Iowa State University                     |
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                               | tel: (515)294-8196                        |