sodium thiosulphate (green). (d) The FTIR spectra in the range from
900 to 1300 cm-1 are enlarged to enable comparison with the
spectra of the AgNP exposed sample (black), sodium sulphate (red)
and sodium thiosulphate (green). In (c) and (d), FTIR measurement
was operated in transmission mode.
The FTIR spectrum was obtained on the selected regions
marked in yellow rectangles, seen in fig. 4a (control sample)
and in fig. 4b (exposed sample); for comparison, fig. 4c shows
reference spectra of calcite (blue), sodium sulphate (Na2SO4)
(red) and sodium thiosulphate (Na2S2O3. 5H2O) (green). In fig.
4c, the peak at 864 cm-1 assigned to calcite in exposed sample
is weaker than in control sample, indicating loss of calcite in
the exposed sea urchins. One explanation is that silver might
inhibit the activity of the carbonic anhydrase enzyme that is
responsible for calcite formation in living organisms
(Bianchini et al., 2005). Comparison of the FTIR spectra (fig.
4d) of the exposed sea urchin (black) with sodium sulphate
(red) and sodium thiosulphate (green) indicates the presence
of sulphur-containing compounds. We suggest that the
presence of excess sulphur might be the results of a biological
response to reduce the concentration of Ag ions (Liu and
Hurt, 2010; Ayata and Yildiran, 2005; Feng and van Deventer,
2010). These results correspond to those from XANES
discussed above confirming the oxidized Ag species observed
are complexed with both S and O/N ligands in AgNP-exposed
sea urchins. Further detailed study of FTIR results will be
published elsewhere.