Determination of low-level mercury in coralline aragonite by calcination-isotope dilution-inductively coupled plasma-mass spectrometry and its application to Diploria specimens from Castle Harbour, Bermuda

We have developed a technique that combines a high temperature quartz furnace with inductively coupled plasma-mass spectrometry for the determination of Hg stored in the annual CaCO3 bands found in coral skeletons. Substantial matrix effects, presumably due to the discontinuous introduction of CO2 to the gas stream, were corrected for by simultaneously supplying a stream of argon containing highly enriched elemental Hg-202(o) and observing peaks in the Hg-200/(202) Hg signal as the sample was decomposed. Primary signal calibration for Hg was achieved using gas injections from a saturated vapor standard. The absolute instrument detection limit was low (about 0.2 fmol), with a practical limit of detection (3 sigma of blanks) of 2 fmol. Reproducibility of samples was (RSD) 15-27%. We applied this method to the determination of Hg concentrations in two colonies of Diploria labyrinthiformis collected from Castle Harbour, Bermuda, at a site about to be buried under the municipal waste landfill. The temporal reconstructions of Castle Harbour seawater Hg concentrations implied by the coral record show a decline throughout the period of record (1949-2008). The coral archived no apparent signal associated with waste disposal practices in the Harbour (bulk waste land-filling or, since 1994, disposal of waste incinerator ash), and mercury concentrations in the coral did not correlate to growth rate as assessed by linear extension. There was, however, a large and nearly exponential decrease in apparent Hg concentration in the Harbour which circumstantially implicates the dredging and/or landfilling operations associated with the construction of the airport on St. David's Island. (C) 2013 Elsevier Ltd. All rights reserved.