Air Quality Criteria for Lead Volume II of II - (NEPIS)(EPA) - US ...

AbdAllah and Moustafa (2002) studied the Pb storage capability of organs in the marine
snail Nerita saxtilis. Enlarged electron-dense vesicles and many granules were observed in
digestive cells of these snails and are suggested to be the site of storage of detoxified metals.
N. saxtilis were found to be capable of concentrating Pb up to 50 times that of surrounding
marine water without exhibiting signs of histopathologic changes. This ability has been
attributed to chelation with various biochemical compounds, such as thionine (forming
metallothionine) (Rainbow, 1996), or complexation with carbonate, forming lipofuchsin
(AbdAllah and Moustafa, 2002). Granules observed in lysosomal residual bodies were presumed
to be the result of Pb accumulation. The presence of large vacuoles and residual bodies were
indicative of the fragmentation phase of digestion, suggesting that Pb was also processed
chemically in the digestive cells.
The podocyte cells of the pericardial gland of bivalves are involved in the ultrafiltration of
the hemolymph (Giamberini and Pihan, 1996). A microanalytical study of the podocytes in
Dreissena polymorpha exposed to Pb revealed lysosomal-vacuolar storage/processing similar to
that in the digestive cells of Nerita saxtilis. The lysosome is thought to be the target organelle
for trace metal accumulation in various organs of bivalves (Giamberini and Pihan, 1996).
Epithelial secretion is the principal detoxification mechanism of the tiger prawn Penaeus
monodon. Vogt and Quinitio (1994) found that Pb granules tended to accumulate in the
epithelial cells of the antennal gland (the organ of excretion) of juveniles exposed for 5 and
10 days to waterborne Pb. The metal is deposited in vacuoles belonging to the lysosomal
system. Continued deposition leads to the formation of electron-dense granules. Mature
granules are released from the cells by apocrine secretion into the lumen of the gland, and
presumably excreted through the nephridopore (i.e., the opening of the antennal gland).
Apocrine secretion is predominant, so that as granules form, they are kept at low levels.
Excretion was also found to be a primary and efficient detoxification mechanism in the shrimp
Chrissia halyi (Prasuna et al., 1996).
Crayfish exposed to Pb have been shown to concentrate the metal in their exoskeleton and
exuvia through adsorption processes. More than 80% of Pb found in exposed crayfish has been
found in exoskeletons (Knowlton et al., 1983; Anderson et al., 1997). Following exposure,
clearance is most dramatic from the exoskeleton. The result of a 3-week Pb-clearance study with
red swamp crayfish Procambarus clarkia, following a 7-week exposure to 150 µg Pb/L, showed
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