[Leica] Mercury (Hg) Batteries and Minamata

["William Gower" <wgower@eco-tec.com>]

With regards to the recent postings on Hg, batteries and Minamata:

> From: "Raimo Korhonen" <raimo.korhonen@pp2.inet.fi>

> Metallic mercury is not particularly harmful - but some organic compounds
> that contain mercury are lethal and thatīs what caused Minamata, not
> mercury batteries.

Partly true: Metallic (elemental Hg) is not "harmless" per se, but the rate
of absorption into the bloodstream via the skin slow. Slow enough, that you
would have to be in direct contact for long periods  of time for any
significant symptoms to manifest themselves. Not that it wouldn't or
couldn't happen, mind you - it's just that the likelihood is small.

Remember handling the stuff as a kid when you broke a thermometer or old
thermostat ? How about good old dental fillings (amalgams of Mercury and
Tin). Although I wouldn't recommend it, accidental swallowing some Hg is
generally considered harmless (save for a tummy ache).

My point - exposure by handling or occasional ingestion of elemental Hg (the
good old silver liquid) is, for all intensive purposes, benign. The skin is
a pretty good barrier to uptake of Hg.

However, increase the rate of absorption of Hg into the bloodstream, and
trouble begins.

How to you increase the absorption ? Via the respiratory tract is one.
Exposure to Hg dust (mining of sulphide ores rich in cinnabar) or vapour
(heating Hg in the presence of oxygen, forming HgO) are the two most common
and toxic occupational exposure routes.

Dimethyl Mercury (CH3)2Hg is the real bugger in the environment. This is an
organic mercury compound that is readily absorbed into the bloodstream. In
nature, certain aquatic organisms will break down elemental Mercury into
this organic form. If the level of Mercury in natural waters is high, the
concentration of of Dimethyl Mercury will be high as well. This translates
into accumulation of Hg in marine life (i.e. fish).

Minamata is a prime example. It was the high concentrations of Hg in the bay
from industrial processes that caused an elevated level of Dimethyl Hg in
the aquatic life. This, combined with a diet rich in seafood that caused the
high incidence of Hg poisoning in the areas surrounding Minamata Bay, Japan.

There have been other cases of widespread Hg poisoning due to eating
contaminated grains that had been treated with organic Mercury pesticides. I
believe it was in somewhere in the middle east (Iraq or ?)

No, I'm no "expert", but I took enough toxicology and biochemistry courses
to know that Hg is bad news. And yes, I have a Rollei 35s that needs to be
recalibrated to the '625 alkaline cells.

Kind regards

William Gower