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Abstract

A strategy for the use of the mussel Mytilus edulis planulatus
in assessing heavy metal (Cd, Cu, Pb, Zn) levels in open marine waters
is suggested. Metal accumulation by mussels was linear, in laboratory
experiments and the rate was directly proportional to the external
concentration. Depuration was minimal, and dependent on tissue concentration.
Physiological and environmental factors were observed to
influence accumulation rate. Smaller sized mussels accumulated metal
at greater rates, while rates were higher at low water temperatures.
Mussels collected from populations in areas where metal levels were
high had lower rates of accumulation than mussels from more pristine
areas. Rate of accumulation was shown to be a sensitive index of
external metal concentration if the influence of external factors was
minimized or eliminated.
When metals were presented singly, the mussel accumulated zinc
and lead in direct proportion to exposure time, while this was not the
case for cadmium and copper. Under combined exposure to all four metals,
cadmium and lead accumulation was proportional to exposure time, while
zinc and copper accumulation was not. This apparent interaction between
metals during simultaneous exposure was shown to be between cadmium,
copper and zinc. In general, cadmium accumulation was decreased in
the presence of the other metals, while that of copper and zinc was increased.
Previous exposure to either the same or another metal had no
influence on the subsequent accumulation of cadmium, lead or zinc.
Copper accumulation was markedly increased in mussels initially exposed
for 20 days to either cadmium or zinc. The fact that these interactions
occurred predominantly at high external concentrations (e.g. Cd>10 µg ℓ-1,
Cu>10 µg ℓ-1, Zn>100µg ℓ-1 ) suggests that they would not seriously
interfere with the monitoring strategy.

In the light of experimental results, a mechanism for accumulation
of each metal by M. e. planulatus is proposed. Cadmium and
copper appear to share a similar carrier-assisted uptake mechanism,
while zinc and lead appear to diffuse across membranes passively.
The method of storage of lead within cells appears to be distinct from
that of the other three metals.
Cadmium, lead and zinc were found to be taken up at both the
gills and digestive tissue, and were generally evenly distributed
throughout the mussel body, but with high concentrations in the kidney.
Zinc levels were also high in the muscle and byssus/foot tissues.
Copper, on the other hand, was taken up only at the gills and stored
in the foot and digestive tissue (liver). The byssal threads appear
to be a major excretory system for copper, and may also be important
for the other three metals as well.
Field trials of the proposed monitoring techniques, involving
cage suspension of organisms, revealed that the mussel provides a very
sensitive and time-integrated assessment of the biologically available
metals in seawater. Biomonitoring using mussels would be less costly
and labour intensive than conventional techniques currently available
for measuring metal levels in seawater.

Item Type:	Thesis - PhD
Authors/Creators:	Elliott, N. G.(Nicholas Grant),1953-
Keywords:	Marine pollution, Heavy metals, Environmental monitoring
Copyright Holders:	The Author
Copyright Information:	Copyright 1982 the Author - The University is continuing to endeavour to trace the copyright owner(s) and in the meantime this item has been reproduced here in good faith. We would be pleased to hear from the copyright owner(s).
Additional Information:	Thesis (Ph.D.)--University of Tasmania, 1983. Bibliography: l. 172-192
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