Enclosure (1) TO COMDTINST 16478.12
an insignificantly small fraction of the total mercury pool in the freshwater
or marine system.
Mercury which is deposited in the sediments close to the batteries can
potentially be available for ingestion in or exposure to aquatic organisms.
The quantity of mercury in the sediments close to batteries slowly decreases
over time through (1) transformations followed by dissolution into the water
column, (2) resuspension and transport of the sediment particles and the
associated mercury, (3) burial and preservation in the sediments, or (4)
ingestion by biota. Ingestion by biota is the pathwat which can potentially
result in exposure and hazard to human health and the enviroment. The other
possible destinies of the mercury associated with sediments in the immediate
AtoN area could pose a hazard, but the degree of hazard is only a fraction of
that from ingestion and exposure by sediment dwelling organism in the
proximity of the AtoN. If this pathway shpws no or minimal hazard, there is
no concern about entry of the mercury in the other pathways.
As described in detail in Section 1, mercury in the aquatic environment
undergoes multiple and complex chemical transformations. The transformation
of greatest concern is the formation of the organic or methyl form.
Methylmercury is more soluble than the elemental form and also much more toxic
and available for ingestion by organisms. The factors affecting and rates of
methylization are not completely known but the process is complex and dynamic.
Methylmercury in the sediments of aquatic systems generally represents only a
small fraction of the total (about 1 percent or less) unless there is a source
of methylmercury or conditions in the environment, such as flooded wetland
soild, accelerate the rate of methylization.
Without exception, all of the prototype and laboratory investigations of AtoN
batteries found that methylization rates in systems studied were low,
batteries were not a source of methylmercury, and methylization rates adjacent
to batteries were no different than in the general area. Laboratory studies
directly measured methylmercury in AtoN batteries and found low
concentrations. Similarly, the portion of mercury occurring in the methyl
form (and thus an indication of methylization rate) was within the range of
unaffected sites reported in the literature and generally at the extreme low
end of the range. At no location was the percentage of methylmercury higher
near batteries or in areas with a high concentration of batteries. The final
fact substantiating the lack of effect from batteries on the bio availability
of mercury were the low concentrations found in organisms. In areas with high
methylmercury concentrations, organisms accumulate mercury in the tissue
directly from water and sediments and also through the food chain. The levels
of mercury in tissue at all the lighted AtoNs investigated was within the
range seen in areas not affected by batteries.
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