Increasing urbanization and industrialization along the coastal areas of False Bay in SouthAfrica can endanger coastal ecosystems because of increasing metal pollution. To obtain baseline data on contamination levels in the intertidal zone, cadmium (Cd) body loads of four invertebrate species were measured seasonally over a period of 15 months from different sites within the bay. Specimens of Tetraclita serrata (barnacle), Oxystele sinenses (periwinkle), Cymbula oculus (limpet) and Choromytilus meridionalis (mussel) were collected and analysed to determine temporal changes in Cd body burdens. Cd concentrations were also measured in water and sediments. Cd concentrations in the intertidal animals varied considerably between sampling sites and between seasons and also occasionally between species. All four species accumulated Cd in their bodies to levels several times higher than environmental concentrations. No significant difference could be shown between the Cd concentrations in the gastropod grazers and the filter-feeders. The highest mean body load of Cd (70.67 µg/g dry weight) for a single sampling occasion was measured in the sessile barnacles (T. serrata) collected at Rooi-Els. The highest mean Cd concentration (11.95 µg/g) for the bay as a whole was measured in the limpet C. oculus. Two-way analysis of variance indicated that spatial (location) rather than temporal (seasonal) factors affected Cd concentrations in the invertebrates. Cd concentrations in False Bay sometimes exceeded the norms or water quality standards.
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.
The development of methods to monitor the South African coastal waters offer major challenges. Knowledge and availability of suitable species that may serve as biomonitors will be valuable to obtain information to support good management decisions. It is therefore important to identify local species that show the basic characteristics required for biomonitoring. The aim of this study was to compare, as part of a wider seasonal field study of metals in the intertidal zone of False Bay, South Africa, the body loads of copper (Cu), nickel (Ni), lead (Pb), cadmium (Cd) and zinc (Zn) in the black mussel (C. meridionalis) and the barnacle (T. serrata), and to compare these with environmental concentrations. Also to draw conclusions about the animals’ relative abilities to accumulate priority metals. Specimens of both species were collected over several seasons at different points in False Bay and analysed chemically. The mean body load (soft tissue and shell) of metals was higher in the black mussel than in the barnacle during all seasons. A comparison between the body loads and environmental concentrations in water and sediment showed that the priority metals Cd, Ni and Pb are accumulated strongly by both C. meridionalis and T. serrata. The mean Cd body loads varied between 6.43 µg/g and 14.73 µg/g for the various seasons but was not statistically significantly different between seasons. Metal concentrations were in most cases highest during winter. Multiple regression analysis showed a strong correlation between body load of metals in the black mussel and the environmental concentration for most seasons, which indicates that the black mussel can be useful as an active rather than a passive biomonitor. The concept of biomonitoring has merit because it may show long-term tendencies, but it does not offer an absolute measure of immediate, varying pollution levels. It could serve as an additional management tool in a national marine programme for the protection of the intertidal zone’s biodiversity.
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