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Accumulation of cadmium and zinc in the marine sponge Suberites domuncula and its potential consequences on single-strand breaks and on expression of heat-shock protein: a natural field study

The marine sponge Suberites domuncula (Porifera ; Demospongiae) was used in a natural field study (in the vicinity of Rovinj, Croatia) as a bioindicator to assess the genotoxic risk of cadmium exposure for sponges as a model for invertebrates, and as an early stress marker of expression of heatshock protein 70 (Mr 73 kDa ; termed HSP73). Significant differences in 'natural' cadmium levels of S. domuncula were found among sponges collected from differently polluted sites ; in contrast zinc levels were relatively similar. Sponges living at polluted sites contained 15 to 24 times more cadmium than sponges at unpolluted reference sites. The capacity of S. domuncula to accumulate cadmium after an additional exposure to 5 mg/l of cadmium for 5 d, was markedly higher (increase in cadmium content of 42 to 49 mg Cd/kg) for sponges collected from polluted sites compared to those from uncontaminated or less contaminated sites (increase of 8 to 29 mg Cd/kg) ; a strong increase in cadmium level was accompanied by a reduction in zinc level in the sponges from polluted sites. In this study we have used the rapid, sensitive and cheap Fast Micromethod to determine the number of DNA single-strand breaks in S. domuncula collected from differently polluted sites and some of those sponges additionally exposed to cadmium. The strand scission factor (SSF) was found to depend on the pollution load ; it further increased by 1.7- to 8.6-fold after additional exposure to cadmium (5 mg/l). Similarly, the levels of HSP73 were found to be highest in S. domuncula living at polluted sites. Additional exposure of the sponges to cadmium strongly increased HSP73 level. This increase in HSP73 level was higher in sponges from polluted sites compared to those collected from uncontaminated or less contaminated control sites. From these data we conclude that the sponge S. domuncula is a useful bioindicator regarding the cadmium load of the aquatic environment.

cadmium; zinc; DNA damage; heat-shock protein; field study; marine sponge; suberites domuncula

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