Enclosure (1) TO COMDTINST 16478.12
assessments concluded there was no difference in mercury concentrations close
to batteries compared to locations up to 30 meters away. Similar tests also
concluded no difference between samples from lighted and unlighted AtoNs.
In Tampa Bay conditions varied considerably from those observed at the other
prototype investigations. There were over 200 batteries found at some AtoNs
and it was not unusual to have over 50 primary batteries per AtoN. Also, a
high percentage of the batteries were broken, either when they were discarded
or subsequently as the cases deteriorated. As a result of these conditions,
the findings of the Tampa Bay prototype investigation indicate that mercury
was released from the batteries and some accumulated in the sediments.
The distribution of mercury sediment concentration around the eight lighted
AtoNs investigated in Tampa Bay showed a very similar pattern. The average
concentration of samples taken 10 meters or more from the AtoN (where
batteries were only rarely found) was comparable to concentrations at
unlighted AtoN and the background concentration reported in the literature
(about 0.06 mg/kg). Within 10 meters of lighted AtoNs where most batteries
were found, the average concentration of mercury (about 0.20 mg/kg) was about
four times background concentration. The average of samples collected
adjacent to batteries, the concentration measured was even higher (0.25
mg/kg).
Potential Environmental Hazard from Discarded AtoN Batteries
AtoN batteries generally do not pose a hazard to organisms in freshwater or
marine ecosystems through direct exposure to sediment or water column dwelling
organisms or through bioaccumulation in the tissue of organsims. However,
under certain combinations of environmental and AtoN conditions there may be
hazard to sediment dwelling organisms in the immediate vicinity or batteries
(i.e. less than 10 meters). The hazard is expected to be low and over a very
small area and thus even in extreme cases there does not appear to be any
hazard at the community level.
Hazard to aquatic ecosystems was investigated by examining both sediments
(because as described above they are the most likely pathway of exposure) and
tissue concentrations of sediment dwelling organisms (because they are the
most likely and direct receptors). The investigation of sediment focused on
the total and methylmercury concentrations in sediments around AtoNs.
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