Synchrotron X-ray mapping of bio-accumulated metals in a tropical sponge

Synchrotron X-ray mapping of bio-accumulated metals in a tropical sponge

Publication TypeConference Proceedings
Year of Conference2011
AuthorsMunksgaard, NC, Padovan, AC, Gibb, KS, Parry, DL
Conference NameEnvirotox 2011 Darwin
Date Published04/2011

The marine sponge Spheciospongia vagabunda from Darwin Harbour contains high metal concentrations (dry weight): Co (≈140 ppm), Cd (≈100 ppm), Fe (≈4,000 ppm), Ni (≈1,400 ppm) and Zn (≈800 ppm) in spite of near-pristine metal levels in sediment and seawater. Metal levels in S. vagabunda greatly exceed those of several other sponge species in Darwin Harbour (Padovan et al., in review). Bio-concentration factors for Co, Cd, Fe, Ni and Zn in S. vagabunda tissue were ≈106-107 relative to 0.45 µm filtered seawater and for Co, Cd, Ni and Zn were ≈101-103 relative to sediment, suggesting a highly effective metal uptake mechanism in S. vagabunda. Inter-site differences in sponge metal concentrations are likely related to differences in sediment texture and metal availability. Mapping of Co, Cr, Fe, Mn, Ni and Zn concentrations in sponge tissue was carried out at the Australian Synchrotron using the X-ray fluorescence microprobe (XFM) beam line at a resolution of 2 µm. A Maia 384 silicon detector array (Ryan et al. 2010) allowed for high count rates and rapid mapping of large areas (approximately 1 M pixels per hour in this experiment). Detection limits were in the range 20-40 ppm for a 100 µm2 area. Cadmium could not be analysed in this experiment. Quantitative mapping showed that Co, Fe, Ni and Zn were often localised in highly concentrated ‘hotspots’ of (semi-) circular clusters up to 200 µm in size or, in linear seams several 100 μm in length adjacent to tissue water canals. A close correspondence of Co, Fe, Ni and Zn ‘hotspots’, suggests that a common mechanism is responsible for accumulation of these metals in S. vagabunda. The distribution pattern of ‘hotspots’ is similar to that of zooxanthellae reported in other sponges and we speculate that these dinoflagellates may be responsible for the metal accumulation in S. vagabunda. In contrast, Cr and Mn contents were highly dispersed throughout the tissue, mainly in small areas a few microns in size. These areas may represent small embedded inclusions of sediment grains. Further research is focused on coupling metal microanalysis to ultra structural features and molecular microbial community identification, to further investigate the mechanism of metal accumulation in S. vagabunda.


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