Mercury volatilization from a floodplain soil during a simulated flooding event

Purpose Middle-European floodplain soils are often contaminated with mercury (Hg) and periodically flooded. In this study, the influence of a flooding event and subsequent dewatering on the volatilization of elemental Hg and methylated species was investigated in a laboratory experiment. Material and methods Undisturbed soil cores were taken from a topsoil (12.1 ± 0.75 mg kg −1 Hg) at the Elbe River in Lower Saxony, Germany. Soil columns were incubated at 20 °C with varying soil moisture (water-saturated for 2 weeks, 95 and 90 % water content for 1 week each), and the redox potential (E H ) was recorded. The gaseous Hg that accumulated in the headspace of the flux chamber of the columns was pumped over cooled traps filled with adsorber material and analyzed by gas chromatography/inductively coupled plasma mass spectrometry for the various Hg species. Results and discussion The watering of the soil resulted in a rapid decrease in the E H and the achievement of strongly reducing conditions (E H < −100 mV). Mercury concentrations of the pore waters decreased continuously from 68.3 μg L −1 Hg at the beginning to 5.78 μg L −1 Hg at the end of the experiment. Species analyses revealed that exclusively elemental Hg volatilized. The volatilization rate was between 1.73 and 824 ng m −2 h −1 Hg, which is consistent with other studies at the Elbe River. Conclusions Even when flooded for a longer period of time, floodplain soils should show neither emission of methylated Hg nor exceptionally high volatilization of elemental Hg.