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Abstract

Man's activities impose an increasingly heavy burden
of metals on the marine environment. An excess of the
transitional element zinc, which is essential for life,
is suspected of causing ecological disruption. Before
stable zinc can be regarded as a pollutant, harm to marine
organisms will have to be demonstrated.
Histochemical and physical methods of analysis have
been applied to the tissues of the native oyster, Ostrea
angasi to determine whether or not the accumulation of
zinc is associated with any cytopathological effect or
histological change.
Oysters were gathered from the south and east coasts
of Tasmania and compared with specimens collected from
sites in the Derwent Estuary, where commercially grown
oysters containing up to 10% of their dry weight as zinc,
had previously been responsible for cases of food poisoning.
Tissue was prepared for light and.electron microscopy
by fixation in glutaraldehyde saturated with hydrogen
sulphide. The concentration of zinc in the visceral mass
was determined by atomic absorption spectrophotometry and
zinc in adjacent tissue located histochemically by the
sulphide-silver and alkaline-dithizone techniques. Resin-embedded
thin sections of the intestinal tract were examined
in a transmission electron microscope and both thin and
thick sections were analysed in a combined scanning electron microscope-electron probe microanalyser.
Zinc was located intracellularly as electron dense
granules 1 gm in diameter. In the scanning electron
microscope these granules were electron reflective
and appeared as bright spherules, which in the transmission
electron microscope had a ring-like structure. The presence
of zinc in these granules was confirmed by energy dispersive
and wavelength dispersive systems of X-ray analysis.
Zinc-laden granulocytes were widely distributed
throughout the connective tissue and vascular spaces and
concentrated beneath the epithelia of the intestinal tract,
palps, digestive diverticula, gills and mantle. The
granulocytes were also conspicuous within these epithelia.
There was no evidence of a pathological tissue reaction,
although in some instances large collections of granulocytes
beneath the intestinal epithelium were associated with
abundant fibrous connective tissue.
The concentration of zinc in the visceral mass was
- the same order of magnitude ( 10 4pg g dry weight ' ) in
all specimens. Circumstantial evidence suggests that each
specimen came from a 'high-zinc' environment, despite their
wide geographical separation. Specimens would have to be
obtained from a proven /low-zinc' environment before
definite conclusions can be drawn from the observed
histological features.
The function of the zinc granulocyte is in debate.
One school of thought claims that the cell is part of a microscope-electron probe microanalyser.
Zinc was located intracellularly as electron dense
granules 1 gm in diameter. In the scanning electron
microscope these granules were electron reflective
and appeared as bright spherules, which in the transmission
electron microscope had a ring-like structure. The presence
of zinc in these granules was confirmed by energy dispersive
and wavelength dispersive systems of X-ray analysis.
Zinc-laden granulocytes were widely distributed
throughout the connective tissue and vascular spaces and
concentrated beneath the epithelia of the intestinal tract,
palps, digestive diverticula, gills and mantle. The
granulocytes were also conspicuous within these epithelia.
There was no evidence of a pathological tissue reaction,
although in some instances large collections of granulocytes
beneath the intestinal epithelium were associated with
abundant fibrous connective tissue.
The concentration of zinc in the visceral mass was
- the same order of magnitude ( 10 4pg g dry weight ' ) in
all specimens. Circumstantial evidence suggests that each
specimen came from a 'high-zinc' environment, despite their
wide geographical separation. Specimens would have to be
obtained from a proven /low-zinc' environment before
definite conclusions can be drawn from the observed
histological features.
The function of the zinc granulocyte is in debate.
One school of thought claims that the cell is part of a metal detoxification system, whereas others believe that
the cell plays a physiological role in the cellular defence
mechanism of the host against injury. The precise function
of these cells will have to be established before definitive
statements can be made about contamination of oyster tissue
by zinc.

Item Type:	Thesis - Unspecified
Authors/Creators:	Lytton, David Gordon
Keywords:	Oysters, Ostrea angasi, Zinc, Zinc
Copyright Holders:	The Author
Copyright Information:	Copyright 1979 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 (M.Env.St.)--University of Tasmania, 1980. Bibliography: l. 137-139
Item Statistics:	View statistics for this item

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