THE VARIED ROLES OF SNAILS - National Universities Commission

environmental quality. These gastropods were
particularly suitable as they are widely distributed in
rural and urban environments. They tend to have
specific home ranges and habitat preferences
The distribution of metals in the tissues of these slugs
collected from relatively unpolluted sites and those
collected from sites near disused lead and zinc mines
where manganese levels are so high were compared
(Irland, 1979). The comparison showed that all metals,
except manganese were higher in tissue concentrations
in the slugs found in the polluted areas when the
concentrations in the mollusks where compared with
situation in other invertebrates, it was found that
molluscs accumulated higher concentrations of mental
ions than other groups of invertebrates. Marigomez et
al; (1986) however observed that the higher
concentrations of these metals in the tissues did not
translate to higher mortalities thus making the molluscs
potential bioindicator tools for the environmental
pollutions with metals Greville and Morgan (1990)
reached similar conclusion and stated that the intrinsic
variability in metal levels increase the likelihood of
using gastropods as biological monitors of metal
contamination in terrestrial environment.
Hydrogen sulphide and methage are produced during
anaerobic bacterial decomposition and when these
substances come into contact with the upper oxygenated
layers, they produce deleterious effects on snail.
Similarly, high concentrations of zinc, copper, cadmium
or lead ions, are highly toxic to snails at levels above
1.0ppm. At intermediate levels (0.05 – 1.0ppm), they
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