toxic copper levels

 olga at arts_ubc.ca  Wrote: <<<<<<<<<<<<<Subject: Copper & lime

Anyone have at their fingertips what a dangerous level of copper is?
If my tank measures copper at .15 ppm is this too high or about

Do you know what is the source of the copper? Tapwater or water
additives you use? Water hardness?

In aquaria books, copper levels of 0.5 mg/l are described as toxic
to fish. However, I would consider the fact that this information is
referred to acute exposures due to occasional use of Cu for a few
days as a medication. In toxicology, chronic exposures to certain
compounds may require much smaller doses to produce damage compared
to acute exposures.  The damage may take longer to become manifest,
and is not always very easy to detect. In addition, toxicity may be
dependent (besides the dose) on the physical and chemical conditions
of the environment, as well as on the host. Invertebrates are much
more sensitive to Cu than fish, and you could keep a few snails as
low-toxicity levels detectors . Some people on this list live in
areas with high tapwater copper levels with no or minor problems
with their tanks. 

If you are adding copper in some way (by using plant fertilizers for
example), I would try to reduce it. This line of thinking is why I
have chosen to use PMDD ingredients that stay within the limits of
the recipe originally provided on the list.
However, some other ingredients with high copper content have been
used by some people on this list  without apparent problems. Water
changes avoid excessive accumulation.  Anyway,  my personal,
untested, precautious opinion is that a  factor of at least 10X
should be adopted estimating unsafe chronic exposures from unsafe
acute exposures, in the absence of experimental data. 
In environmental medicine for example, the use of somewhat arbitrary
safety factors is a common practice in the estimation of acceptable
environmental levels of toxic pollutants for which no data on
chronic exposures exist. 
Is there anyone on this list that knows of what are the maximum
acceptable levels of copper in water for human consumption?

So, I would feel better maintaining levels below 0.05 mg/l, if this
can be achieved with reasonable efforts. If not, it would be very
reasonable to just keep the situation under careful observation,
reserving the use of water purification systems for situations where
problem are detectable.