Kadmium in Valsbaai : moniteringspotensiaal van die mariene slak, Oxystele tigrina (Mollusca)

Reinecke, A. J. ; Mdzeke, N. P. ; Reinecke, S. A. (2009-06)

CITATION: Reinecke, A. J., Mdzeke, N. P. & Reinecke, S. A. 2009. Kadmium in Valsbaai : moniteringspotensiaal van die mariene slak, Oxystele tigrina (Mollusca). Suid-Afrikaanse Tydskrif vir Natuurwetenskap en Tegnologie, 28(2):101-118, doi:10.4102/satnt.v28i2.52.

The original publication is available at http://www.satnt.ac.za/

Article

’n Opname is onderneem van die kadmiumvlakke in die tussengetygebied van Valsbaai, Suid- Afrika. Kadmiumkonsentrasies is seisoenaal bepaal in die water en sediment in verskillende lokaliteite. Die metings is oor ’n periode van een jaar gedoen deur seisoenaal monsters te versamel by ses verskillende versamelpunte in en een buite die baai. Dit is met behulp van atoomabsorpsiespektrofotometrie ontleed vir kadmium en die hoogste kontaminasievlakke is by die noordelike kusstreek gevind tussen Strand en Muizenberg waar die digsbevolkte gebiede en die meeste industriële aktiwiteit voorkom. Betekenisvolle variasie in konsentrasies van kadmium het seisoenaal en ruimtelik voorgekom. Die gemiddelde konsentrasies in die water en sediment was in sommige gevalle effens hoër as die vlakke wat deur die Suid-Afrikaanse waterkwalitetisriglyne aanbeveel is. Kadmiumkonsentrasies is ook in versamelde eksemplare van die mariene slak Oxystele tigrina vir verskillende seisoene vir drie lokaliteite bepaal. Laboratoriumeksperimente is uitgevoer om die opname, akkumulasie en verlies van kadmium in verskillende organe van die tussengetyslak, Oxystele tigrina te ondersoek. Weefselspesifi eke kadmiumkonsentrasies in kontrolesowel as blootgestelde lewende eksemplare is vergelyk oor ’n blootstellingsperiode van veertien dae. Die eksperimentele slakke is aan twee subletale konsentrasies van onderskeidelik 0.20 en 0.40 μg/ml watergedraagde kadmium in die vorm van CdCl2 blootgestel. Die proefdiere is gereeld gemonitor en kadmiumkonsentrasies is in verskillende organe, na suurvertering, atoomabsorpsiespektrofotometries bepaal. Die resultate het ’n algemene toename van kadmium in die liggame van die slakke uitgewys. Kadmium is in variërende konsentrasies in alle weefsel gevind. ’n Ongeveer liniêre patroon van akkumulasie het aangetoon dat die metaal waarskynlik nie deur O. tigrina gereguleer is nie. Die metaal se teenwoordigheid het verskil tussen die sagteweefsel en skulp op so ’n wyse dat die sagteweefsel normaalweg ’n hoër opnamekoers van die kadmium weerspieël het. Nadat die blootgestelde organismes in kadmiumvrye seewater oorgeplaas is, het gedeeltelike kadmiumverlies wel plaasgevind. Die variasie in kadmiumverlies van die verskillende organe dui moontlik daarop dat slegs ’n gedeelte van die geakkumuleerde kadmium sterk gebind was in sekere weefsels of organe. Die behoud van kadmium in beide sediment en diereliggame was sodanig dat afgelei kan word dat kadmium teen huidige omgewingskonsentrasies in sekere dele van Valsbaai, wat algemeen as laag beskou word, steeds met verloop van tyd in hierdie tussengetydiere kan akkumuleer tot vlakke wat nadelig is vir die spesies self, maar ook vir hulle predatore. Dit sal veral kan gebeur indien fi siese toestande verander om die biobeskikbaarheid te verhoog.

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.

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