Enclosure (1) TO COMDTINST 16478.12
the original mercury remained, nearly all of it in elemental form. It was
shown to be tightly "bonded" to the zinc plate and carbon electrode, thus
unlikely to dissolve or volatilize. They conjectured that the missing mercury
was vaporized by the chemical reactions that produce electricity. A small
amount of ionic mercury, was also present in the spent battery. If any of the
ionic mercury were released in the water, it would quickly dissipate and avoid
detection. No organometallic mercury was found.
Analysis of aquatically submerged discarded batteries confirmed
the earlier
results. These batteries contained less than 5 percent of their
original
mercury content, nearly all in elemental form. Some mercury was
also found in
broken batteries, apparently surviving for at least 25 years of
exposure in an
open marine environment (Morel and Mason, 1994).
To evaluate the possible effects of the released mercury on water quality,
Morel and Mason also studied the rate of mercury dissolution in the
laboratory. They immersed new and decaying battery cells in salt water tanks
and measured the increase of mercury concentration in the water. Very low
levels of elemental mercury were released. The researchers concluded that the
elemental mercury bonds tightly to the zinc plates (especially when the
battery is spent) and to the carbon in the electrodes (Mason and Morel
1993).At most, only microgram quantities of Hg(0) were released per day. When
the submersion method was used, mercury concentrations were measured before
and after submersion. For an intact battery cell (containing approximately 8 g
of mercury) placed in a plastic drum containing 10 L of 0.5 M of salt water,
with stirring, the increase in mercury concentration in water over 36 hours
was <0.02 g/L (reactive Hg was measured), and the dissolution rate was <10(-7)
g/L per day. Analysis of an intact battery with the top removed revealed a
dissolution rate of 17 g/L per day - higher than an intact battery.
Based on these results, the researchers concluded that batteries disposed of
in sea water should retain half of their remaining mercury for at least 300
years. Because the analysis od salvaged batteries suggests a 20-year half
life, an additional mercury release mechanism is involved. Drs. Morel and
Mason did not speculate on this mechanism, but suggested further research.
Magnitude of Release
Morel and Mason also offer an environmental impact assessment of mercury
from batteries. A generous estimate of all the mercury contained in all
the primary AtoN batteries ever used by the Coast Guard would be:
(5 g per battery)x(200 batteries per AtoN)x(12000 AtoNs) =13.25 tons
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