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>Date: Fri, 4 Apr 1997 13:05:19 -0500 (EST)
>From: "Roger S. Miller" <rgrmill at mack_rt66.com>
>To: Aquatic-Plants at actwin_com
>Subject: alkalinity and copper
While I am not generally an "advocate" for adding copper, I thought I would
add a few comments to this nice summary and offer some reasons why an
aquatic gardener "might" want to intentionally add copper.
>I was surprised the find that anyone would intentionally add copper to a
>plant fertilizer. The following is taken from "Quality criteria for
>water, 1986" EPA 440/5-86-001.
>"Acute toxicity data [for copper] are available for species in 41 genera
>of freshwater animals. At a hardness of 50 mg/L the genera range in
>sensitivity from 17.74 ug/L for _Ptychocheilus_ to 10,240 ug/L for
>_Acroneuria_. Data for eight species indicate that acute toxicity
>decreases as hardness increases. Additional data for several species
>indicate that toxicity also decreases with increases in alkalinity and
>total organic carbon."
>"Chronic values are available for 15 freshwater species and range from
>3.873 ug/L for brook trout to 60.36 ug/L for northern pike.
I note for the arithmetically challenged, that the values above convert to
.003-.06 ppm. I can't remember the safe values for drinking water (e.g. tap
water), but I think they are much higher than .003ppm. So many of us
probably add water with more than this level.
>invertebrate species seem to be about equally sensitive to the chronic
>toxicity of copper."
This statement applies to a range of concentrations affecting all of the
tested species. It is my understanding that the toxicity tests include ones
of particular interest -- like food fishes and native fishes. So the first
point is that it does not necessarily apply to the range of sensitivity of
all fish and invertibrates. Secondly, it is worth noting that all species
are not equally sensitive. I would suspect that many (or even most) fish are
much much more tolerant than the values quoted. In fact, the 96-hr LC 50
values for Bluegills is 0.2ppm , for goldfish (0.4 ppm, but in hard water)
and for green sunfish,it is 0.9ppm.
>"Toxicity tests have been conducted on copper with a wide range of
>freshwater plants and the sensitivities are similar to those of animals."
This really bothers me. I suspect that it may apply to a particular group of
plants (including Vallisneria and other native plants that appear to be
particularly sensitive to copper). I seriously doubt that the tests included
any tropical plants. Not to say that tropical plants are insensitive to
copper or less sensitive than temperature plants....just that the particular
plants tested is important to know. I would also want to know if the tests
were done in hard or soft water and if the plants are native to hard or soft
>So how does anyone get by with adding copper to an aquarium plant
>fertilizer? Much of the copper in solution combines with hydroxide, with
>bicarbonate or with complex organic compounds that appear to be less toxic
>(see, for instance Bioaccumulation and toxicity of copper as affected by
>interactions between humic acid and water hardness by Robert Winner in
>Water Resources, v. 19, 1985). The actual toxicity of copper in your tank
>will depend on the stability of the original chelate (assuming that it is
>chelated), on the pH and alkalinity of your aquarium, and on the presence
>of other organic compounds in the water. And of course, on the
>sensitivity of the plants and animals you keep. These are all factors
>that vary from tank to tank, so copper levels that are relatively safe in
>one tank could potentially destroy another. The worst case would probably
>be when the water is comprised mostly of RO product, it is changed
>frequently and few if any hardening chemicals added, where the pH is
>maintained below 7 and nutrients are added through regular addition of a
>copper-containing trace element mix.
This is probably why soil (or other organic matter) can be so helpful in an
aquarium. I speculated earlier that they may be why Karen who has Cu levels
as high as .25ppm in the water and perhaps substantial accumulation in the
substate needs soil to grow some plants like Hygrophila polysperma.
>Why take the chance?
First, because experience teaches us that small copper concentrations are
NOT harmful in the aquarium, except if you are keeping trout and other
sensitive fishes. Among the most sensitive are some cyprinids (especially
zebra danios), corys, other catfishes, loaches and livebearers.
Ceratophyllum and Val are two of the more sensitive plants. If hornwort
thrives, the copper is not too high.
Second, with soil or other OM, copper will be much less toxic. Ditto for
hard water. Third, some plants are intolerant to copper and may even benefit
from it at more than the mere trace levels. These include the crypts. It has
been reported in the aquarium literature (as early as 1970) that 0.5ppm Cu
stimulates crypts. I have also observed this and have written about it
myself. Finally, many species of algae are very sensitive to copper, so
small amounts of copper (certainly greater than .003ppm) are beneficial to
keeping some types of algae down. Unfortunately, I cannot and won't
recommend a safe Cu level. Except for the most sensitive species, however, I
would not worry about chronic exposure to levels of 0.01 or even
higher(assuming we could make such evaluations at home <g>), unless of
course it was in RO type water and without OM (as Roger also points out).
Neil Frank Aquatic Gardeners Association Raleigh, NC
The Aquatic Gardener - journal of the AGA - now in its seventh year!!