Cadmium contamination levels in the False Bay intertidal zone in South Africa were assessed in the water and sediments over a period of one year. Samples were collected seasonally from six sites within the bay, and from a reference site situated just outside the eastern arm of False Bay in order to obtain a general overview of contamination levels to which invertebrates in the coastal areas are exposed. The results from the chemical analyses of water and sediment samples revealed that most contamination was associated with the northern shore of the bay between Strand and Muizenberg, where the most populated and industrialised catchments occur. The high contamination factors calculated for Cd for sediments from some sites suggested a strong input of industrial and other discharges containing this heavy metal. There were signifi cant seasonal and spatial differences in the cadmium concentrations, with spatial variations indicating localised contamination, while seasonal variations were assumed to be predominantly related to changes in precipitation and runoff at different times of the year. The mean cadmium concentrations in the water and sediments were occasionally higher than the levels recommended by the South African Water Quality Guidelines, and indicated an increase in the levels compared to the previous water quality surveys. Laboratory experiments were conducted to examine the uptake, accumulation and loss of cadmium by the different organs of the periwinkle, Oxystele tigrina, from the False Bay intertidal zone. Tissue-specific cadmium accumulation in the control and exposed individuals were compared over a 14-day exposure period to sub-lethal concentrations (0.2 and 0.4 µg/ml) of water-borne cadmium in the form of CdCl2. The animals were sampled at regular intervals and the cadmium concentrations in the different organs measured by atomic absorption spectrophotometry. The results showed a general pattern of cadmium increase in the exposed individuals over a relatively short period. Cadmium was detected in all the tissues, with varying degrees of bioaccumulation. A more or less linear pattern of cadmium accumulation indicated that the metal was not regulated by O. tigrina. The metal was partitioned differently into the soft tissues and shells, with the soft tissues generally displaying a higher rate of cadmium uptake. There was a loss of the accumulated cadmium from the organs of the contaminated individuals upon transfer to clean seawater, with variations in the percentage of cadmium loss probably indicating that only part of the accumulated cadmium was firmly bound to the different tissues. The cadmium loss in the group that was exposed to 0.40µg/ml was not significant, indicating that the cadmium may have been more tightly bound in the tissues of this group compared to the group exposed to 0.20 µg/L. The amounts of cadmium in sediments and animal bodies in some parts of False Bay were such that cadmium could at current relatively low levels be expected to accumulate over time in these animals. Under changed physical conditions that may increase bioavailability, body levels could be reached that could affect the long term survival of this species and possibly its predators.
Due to the availability and chemical nature of some heavy metals, sub-lethal toxicant levels may persist in the ocean waters and may cause physiological problems and toxicity in invertebrates and other marine organisms. Although studies of metal concentrations in False Bay showed relatively low mean concentrations of Cd, invertebrates such as molluscs, crustaceans and many other groups are able to accumulate high levels of heavy metals in their tissues and still survive in the heaviest polluted areas. They can accumulate numerous pollutants from natural waters in quantities that are many orders of magnitude higher than background levels. Bioaccumulation ofcadmium in intertidal species could cause stress which may be measurable at the cellular level. A variety of limpet species that may serve as suitable ecotoxicological monitoring species occur in abundance on rocky shores along the South African coastline. The aim of this study was to obtain sensitivity data which could contribute to the selection of a suitable monitoring species and the eventual establishment of a species sensitivity distribution model (SSD) with a biomarker responseas endpoint. The limpets Cymbula oculus, Scutellastra longicosta, Cymbula granatina and Scutellastragranularis as well as water samples were collected at two localities in False Bay, South Africa. Analysis of water and biological samples were done by atomic absorption spectrometry. Exposures were done to three different sublethal concentrations of cadmium in the laboratory in static flow tanks over three days. There was a moderate increase in cadmium body concentrations over time. Results obtained at three exposure concentrations showed no significant differences in metal concentrations between the different C. oculus samples. Significant differences were obtained between the control and the exposure groups for each exposure time except between the control and the 1mg/L CdCl2 exposure group after 24 and 72 hours of exposure. Cd body concentrations(soft tissue) varied between 4.56 and 21.41µg/g (wet mass).Mean Cd concentrations in soft tissue of S. longicosta was considerably lower (varying between 1.18 and 19.58 µg/g Cd ) than in the tissues of C. oculus. The control group differed significantly from the 0.8 and 1 mg/L CdCl2 exposures after 48 and 72 hours. Mean Cd body concentrations in S. granular is were the highest of all exposed species, reaching a level of 148 µg/g Cd at the highest exposure concentration and differed significantly from the means of the other samples of the 0.8 mg/L CdCl2 exposure group after 72 hours and from the 1 mg/L CdCl2 group after 24 hours. Significant differences were also obtained between theCd body concentrations of C. granatina for the three exposure concentrations and three exposure times. Lysosomal membrane integrity was determined for both exposed and control animals, using the neutral red retention assay. Three of the four species showed a significant decrease in retention times with an increase in Cd concentration. Inter-species differences in sensitivity to environmentally relevant cadmium concentrations were reflected in the biomarker responses. Based on reduction of NRR times, the order of relative sensitivity to cadmium was S. granularis >C. oculus> S. longicosta.> C.granatina.
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