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Re: silver toxicity
David Aiken wrote:
[snip]
> His "secret" was the use of
> a "stabilised hydrogen peroxide solution" called Hy-San at 5 ml per 10
> Litres of tank water, but said it was not possible to dose to that
> concentration in one dose - you had to build the dose over some hours or
> you ended up with over-oxygenation of the water and fish deaths.
[snip]
> My reservations about this technique at present are the colloidal silver
> and possible effect on biological filtration. I have no idea on toxicity
> effects for silver with fish or invertebrates. At the recommended dosing
> rate, the silver level would be less than 0.0000015 grams/litre or 0.0015
> mg/L by my calculation (I may have the maths wrong).
Hmmm. I calculate 0.015 mg/l, or 15 ug/l. That is 5 ml (.005 liters) of
product per 10 liters of water, or .0005 liters of product per liter of
water. At 0.03 grams colloidal silver (Ag) per liter of product, that is
a dose of 0.000015 grams/per liter, times a million to get 15 ug/l - same
as 0.015 milligrams/liter.
> Perhaps someone can comment on silver toxicity.
Ok. I'll quote from US EPA standards (45 F.R. 79318, Nov. 28, 1980):
"For freshwater aquatic life the concentration (in ug/L) of total
recoverable silver should not exceed the numerical value given by
e(1.72[ln(hardness)]-6.52) at any time. For example, at hardness of 50,
100, and 200 mg/L as CaCO3, the concentation of total recoverable silver
should not exceed 1.2, 4.1 and 13 ug/L, respectively, at any time. The
available data indicate that chronic toxicity to freshwater aquatic life
may occur at concentrations as low as 0.12 ug/l."
I've attended a few technical gatherings where members of a national
organization of silver users (like photographic film manufacturers and
developers) have disputed the toxicity of silver, mostly because there are
more complicating factors than the EPA assessment accounts for.
[snip]
> It doesn't seem to have had an effect on the
> fish but I don't know what the effect on the freshwater shrimp in my main
> tank would be and I have no intention of trying it out at this stage.
Probably a good idea. I think that crustaceans are generally more
sensitive to metals than are fish.
> I
> also don't know what the effect on biological filtration is but I suspect
> it can't be too bad.
I'm not sure about this one. Since the tank was planted it would be hard
to tell what you did to the bacterial population. I would worry, despite
the apparent success of fish in the bare test tanks.
Concidering all I've heard, I think silver should be regarded much like
copper; used at the right dosage and under favorable circumstances it
might have some beneficial effects, but we can't insure that those
conditions will be attained or maintained so we should probably just avoid
its use. The potential consequences could be disastrous for our aquaria.
Roger Miller
In Albuquerque where, gee, it sure is pretty outside. What am I doing in
here?