Cellular stress responses to cadmium contamination as measure of sensitivity in intertidal molluscan species
Date
2007-03
Authors
Schoeman, Werner
Journal Title
Journal ISSN
Volume Title
Publisher
Stellenbosch : University of Stellenbosch
Abstract
The ability of various molluscan species to accumulate toxicants such as
cadmium from natural waters in quantities that are many orders of magnitude
higher than background levels are well-known. This phenomenon of
bioaccumulation might cause certain stress responses in these organisms at the
cellular level, which can be measured using biomarkers. A biomarker response
test known as the neutral red retention assay was employed in this study to
measure responses in four intertidal species. Specimens of Cymbula oculus
(Born), Scutellastra longicosta (Lamarck), Cymbula granatina (Linnaeus) and
Scutellastra granularis (Linnaeus) were collected at two localities on the coast of
False Bay, South Africa. Laboratory exposures in static flow tanks at three
different concentrations i.e. 0.8, 1 and 1.2 mg/L of CdCl2 were done respectively
for each species over a three day exposure period i.e. each exposure
concentration had an exposure period of 24, 48 and 72 hours. After every 24
hour exposure period the lysosomal membrane integrity was determined using
the neutral red retention method to establish which species is the most sensitive
to Cd. Both control and exposure groups for all species showed a decrease in
retention times with an increase in Cd concentration over the exposure period.
This decrease was particularly prominent at the highest exposure concentration
after 72 hours. At 0.8 and 1.2 mg/L CdCl2 exposures an indirectly proportional
relationship between neutral red retention time and heavy metal concentration
was prominent in C. oculus, indicating a dose related response. In all species
there was a moderate increase in heavy metal concentration over the 72 hour
exposure period. EC50 values indicated that S. granularis and C. granatina had a
“high” sensitivity to Cd contamination, while C. oculus had “medium” sensitivity
and S. longicosta “low” sensitivity to Cd contamination. The sensitivity data
obtained from the analysis of the experimental species in this study may
contribute to the eventual establishment of a species sensitivity distribution
model (SSD).
Description
Thesis (MSc (Botany and Zoology))--University of Stellenbosch, 2007.
Keywords
Intertidal molluscs, Cadmium sensitivity, Toxic stress, Neutral red retention assay, Mollusks -- Physiology, Mollusks -- Effect of heavy metals on, Mollusks -- Effect of pollution on, Intertidal animals -- Effect of pollution on, Cadmium -- Physiological effect, Dissertations -- Zoology, Theses -- Zoology