THE VARIED ROLES OF SNAILS - National Universities Commission

when mineral ions form chelate complexes with humic
acids, snails begin to establish in such habitats. Studies
with sedimentary core sampling for molluscan analysis
have been used to identify areas that were the lower
limits of littoral zones in the past geologic times. The
value of snails in applied palaeoecology has been
further demonstrated by using carbon dating
technologies. The pulmonate snails which breathe
atmospheric oxygen were found to be completely
replaced by clams and prosobranch snails as a result of
eutrophication of their aquatic environment. This was
the first indication of the possibility of using snails as
valuable palaeoindicators of human impacts on aquatic
systems.
Soils normally contain at least trace quantities of the
heavy metals e.g. copper, lead, zinc, Nickels, Cadmium
and mercury. In some areas, levels of these metals have
been substantially increased from mining waste tips
from industrial fallouts e.g. from smelting industries or
by lead derived from car exhausts and by the use of non
biodegradable pesticides (i.e. insecticides, herbicides
and molluscicides). Snails are often used to monitor the
concentrations of these metals because when they reach
certain levels in the environment they become toxic to
plants and animals including snails. Cavalloro and
Ravora (1966) suggested that the gastropods are good
biological indicators of manganese contamination in
terrestrial environments. A study of the concentration of
nine metals in the tissues of A. ater from locations close
to, or far away from highways in Canada by Rophazard
D’auria (1980) made them to suggest that these
molluscs, might be useful as bio monitors for assessing
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