Mercury wet deposition: An Australian study to assess impact of coal fired power stations

Near-power station (coal-fired) sites are believed to be prone to elevated Hg deposition fluxes. Total Hg (THg) in daily rainfall samples at a near-field and a far-field station have been monitored, employing ultra-clean sampling techniques and cold vapour atomic fluorescence spectrometry (CVAFS) analysis. For samples collected between June to December 2006, THg concentrations varied between 0.9 - 12.5 ng/L and 5.8 - 21.3 ng/L with average daily wet deposition fluxes of 4.7 and 24.0 ng THg/m²-day for the far and near-field sites respectively. While a two-sample t-test reveals the near-field site to have higher rainfall mercury (significant at the 95% level), at this stage because of differences in sampling periods we cannot infer the near-field site to be relatively "impacted". Strong correlation of THg fluxes with precipitation volume was found which suggests scavenging of reactive gaseous mercury species and particulate mercury by precipitation as a mechanism for mercury deposition. Thus, where wet deposition is concerned, the magnitude of the THg fluxes is likely to be dependent on the rainfall patterns, in addition to emission source strength.