Abstract
M.Sc. (Zoology)
Tilapia sparrmanii (Smith) was exposed to sub-lethal doses
of chromium, manganese, zinc and iron for 96 hours at an
acidic pH (5), a physiological pH (7,4) and an alkaline pH
(9), as well as a prolonged exposure (2 - 4 weeks) at an
uncontrolled pH. In the laboratory fish were kept in
aquaria which were supplied with continuously flowing
borehole water. Controlled laboratory conditions existed
during experimentation. Blood and liver samples of the
experimental fish were sampled after exposure. The
bioconcentration and the effect of the selected metals at
the mentioned conditions, were thereby determined on
bloodcoagulation, total and differential leucocyte counts,
and liver enzYmes to investigate the possible damage to the
liver.
As metals have the ability to enter and concentrate in the
body, the bioconcentration of each metal was determined by
atomic absorption sPectrophotometry in the blood and liver.
Chromium showed an increase in concentration in both the
blood and liver, with an increase in pH after short term
(96h) exposure. The statistical significant increases of
manganese concentration in the blood over a short term were
not reflected in the liver. It may be indicative of
homeostatic control. A similar phenomenon was found with
.zd.nc , The concentration of zinc in the liver did not
reflect the progressive decrease in the blood wi th a
increase in pH. Iron revealed a statistical significant
increase in bioconcentration in the liver with, an increase
in pH, which is indicative of the activity of the liver.
The long term exposure of fish to chromium and manganese
caused a significant increase in the concentration of the
metals in the blood and liver. The only significant
increase in concentration after exposure to iron, occured
. in the Iiver. Exposure to zinc however caused a
statistical significant decrease in concentration in both
the blood and liver.
Differential leucocyte counts reflected lymphocytosis,
eosinophilia, monocytopenia and neutropenia, after short
term exposure. These conditions nearly always resulted in
leucopenia. Long term exposure to manganese and zinc
reflected both eosinophilia and neutropenia. Chromium
reflected eosinophilia, and iron, neutropenia. The only
statistically significant change in the number of
leucocytes after long term exposure, was caused by zinc and
resulted in leucopenia.
According to the photokymographic observation of blood
coagulation by the thrombelastograph, exposure to the
selected heavy metals lead to a prolonged clotting time and
thrombocytopenia. Long term exposure (4 weeks) to manganese
caused another bleeding disease, called hemophilia. It
was thus evident that the exposure to heavy metals led to
clotting defects, which caused bleeding.