National Geochemical Survey of Australia The Mercury Concentrations Dataset

The 'National Geochemical Survey of Australia: The Geochemical Atlas of Australia' was published in July 2011 along with a digital copy of the NGSA geochemical dataset (http://dx.doi.org/10.11636/Record.2011.020). The NGSA project is described here: www.ga.gov.au/ngsa. The present dataset contains additional geochemical data obtained on NGSA samples: the Mercury Concentrations Dataset.<br>Abstract:Almost 2400 new total mercury (Hg) analyses were obtained on catchment outlet sediment samples from the NGSA regolith archive to document the range and patterns of Hg concentrations in the surface regolith and their relationships to geology and anthropogenic activity. The selected samples included 1214 NGSA Top Outlet Sediment (TOS) samples taken from 0 to 10 cm depth, and 1182 Bottom Outlet Sediment (BOS) samples taken, on average, from 60 to 80 cm depth. This included 1149 sites with both TOS and BOS analysed. Only the sieved &lt;75 µm (or ‘fine’) fractions were analysed in this study. In total, 2396 new Hg concentrations were obtained from 1141 NGSA catchments (~10% of which were sampled in duplicate).<br>Mercury concentration analyses were performed by James Taylor under the supervision of A/ Prof Larissa Schneider at the School of Culture, History and Language, College of Asia and the Pacific, The Australian National University. Mercury analyses were conducted using a tri-cell Direct Mercury Analyzer (tri-cell DMA-80; Milestone, Bergamo, Italy) on approximately 100 mg of sample weighed in nickel boats. The instrument was calibrated with aqueous Hg standard for AAS Sigma Aldrich TraceCERT® (1000 mg/L Hg in nitric acid). A calibration curve was constructed by plotting the absorbances of standards against Hg concentrations in nanograms, which was considered valid for an R2 value of 0.99 or higher. The DMA-80 determines total Hg mass through a sequence of thermal decomposition, amalgamation, and atomic absorption spectrometry. Samples were analysed using the USEPA method 7473 (USEPA, 1998), with a (mass) limit of detection of 0.01 ng Hg.<br>After every tenth sample, a replicate sample was analysed. When replicate recovery exceeded a variance of 10% compared to the original sample, a third replicate was run. At least two blanks and two Standard Reference Materials (SRMs) were analysed for every 40 samples. One hundred and thirty-eight analyses of National Institute of Standards and Technology SRM NIST-2706 (New Jersey soil) yielded a Hg concentration of 133.7 ± 14.2 ng/g (mean ± 2 SD), resulting in an RSD of 5.3%, compared to the certified value of 132.9 ± 3.3 ng/g (mean ± 2 SD), resulting in an analytical bias (recovery) of 100.6 ± 10.7% (mean ± 2 SD). Twenty-six analyses of Environment Canada SRM WQB-1 (Lake Ontario sediment) yielded a Hg concentration of 1135.1 ± 36.2 ng/g (mean ± 2 SD), resulting in an RSD of 1.6%, compared to the certified value of 1060 ± 250 ng/g (mean ± 2 SD), resulting in an analytical bias of 107.1 ± 3.4% (mean ± 2 SD). Fifty-four analyses of National Institute of Standards and Technology SRM NIST-1646a (estuarine sediment) yielded a Hg concentration of 35.4 ± 6.4 ng/g (mean ± 2 SD), resulting in an RSD of 9.1%, compared to the non-certified value of 40 ng/g (mean), resulting in an analytical bias of 88.5 ± 16.0% (mean ± 2 SD). Finally, 142 replicate analyses of internal project standard NGSA sample 2007190264002 yielded a Hg concentration of 9.2 ± 2.5 ng/g (mean ± 2SD), resulting in an RSD of 13.6%, which can be taken as a proxy for precision on matrix-matched samples for the project.<br>The results show a range of Hg concentrations (ng/g) in the NGSA TOS and BOS &lt;75 µm fraction samples across the continent:● Hg in TOS &lt;75 µm (N = 1214): Min = 0.97; Med ± Robust SD = 17.17 ± 12.48; Mean ± SD = 23.52 ± 27.53; Max = 556.00● Hg in BOS &lt;75 µm (N = 1182): Min = 0.90; Med ± Robust SD = 13.69 ± 11.40; Mean ± SD = 19.13 ± 22.30; Max = 525.28These new data allow the construction of continental-scale regolith Hg concentration maps of Australia for topsoil and subsoil and can be used to understand contributions of Hg from underlying bedrock (including Hg-bearing mineralisation), wind-blown dust and possibly from anthropogenic sources (industrial, transport, agriculture, waste handling).<br>The complete dataset is available to download as a comma separated values (CSV) file from Geoscience Australia's website (http://dx.doi.org/10.26186/150328). The data will be used in a forthcoming publication to analyse various sources, sinks and pathways for Hg cycling in the Australian near-surface environment (Schneider et al., https://doi.org/10.1021/acs.est.5c11189). Alternatively, the new Hg data can be downloaded from and viewed on the GA Portal (https://portal.ga.gov.au/).<br>

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