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Zn analyses

> Many earlier
>analyses - including virtually all analyses included in our big public
>data bases - were collected with methods that may have allowed the samples
>to be contaminated with copper or zinc.

I'm having a hard time imagining this. What I do find easy to imagine is
that the "free" Zn and Cu was overestimated because the samples were
collected without ultrafiltration or high-speed centrifugation. Suspended
bacteria in "clear" water samples will be atomized in an atomic absorption
spectrophotometer, and one obtains a signal for the metals they contain. (I
had my students do this with some pond water this semester; turns out that
in some "clear" centrifuged samples, 80+% of the Fe can be removed by
filtration with a 0.2 micron filter, suggesting that it was incorporated
into bacteria, other living things or colloids to small to be centrifuged
out at moderate speeds.)

I do know that the known biological (non-pathological) roles of Zn have
greatly increased in number over the last 10 years or so.

Michael Schmidt
California State University, San Marcos
San Marcos, CA