Simultaneous determination of mercury and organic carbon in sediment and soils using a direct mercury analyzer based on thermal decomposition–atomic absorption spectrophotometry

•A direct mercury analyzer was used to estimate total organic carbon.•Mercury and organic carbon were measured in oxbow lake sediment cores.•Temporal and spatial deposition of Hg in the Mississippi Delta were evaluated.

The purpose of this work was to study the feasibility of using a direct mercury analyzer (DMA) to simultaneously determine mercury (Hg) and organic matter content in sediment and soils. Organic carbon was estimated by re-weighing the sample boats post analysis to obtain loss-on-ignition (LOI) data. The DMA-LOI results were statistically similar (p < 0.05) to the conventional muffle furnace approach. A regression equation was developed to convert DMA-LOI data to total organic carbon (TOC), which varied between 0.2% and 13.0%. Thus, mercury analyzers based on combustion can provide accurate estimates of organic carbon content in non-calcareous sediment and soils; however, weight gain from moisture (post-analysis), measurement uncertainty, and sample representativeness should all be taken into account. Sediment cores from seasonal wetland and open water areas from six oxbow lakes in the Mississippi River alluvial flood plain were analyzed. Wetland sediments generally had higher levels of Hg than open water areas owing to a greater fraction of fine particles and higher levels of organic matter. Annual loading of Hg in open water areas was estimated at 4.3, 13.4, 19.2, 20.7, 129, and 135 ng cm−2 yr−1 for Beasley, Roundaway, Hampton, Washington, Wolf and Sky Lakes, respectively. Generally, the interval with the highest Hg flux was dated to the 1960s and 1970s.

Graphical abstractComparison of LOI data obtained by a conventional method and by the DMA. The dark line represents a 1:1 ratio.Figure optionsDownload full-size imageDownload as PowerPoint slide