Mercury Amalgams in Soil and Demolition Debris Samples.

Between 1920 – 1950, Hg was used by a former Dupont chemical facility in Waynesboro, VA for the catalytic synthesis of acetate flakes. During this period, spilled Hg catalyst (recycled as liquid Hg) periodically entered the plant storm drainage network, and the South River, contaminating the sediments, waters, and associated floodplains some 30 river miles downstream. For the past 3 years, our group has focused on the difficult problem of resolving the nature and complexation of Hg with floodplain soils (given its connection with methylmercury (MeHg) production and its subsequent accumulation in river biota) and debris samples collected beneath the Dupont plant using the solid-phase speciation technique of XAS. However, we have found it difficult to conclusively explain some of our bulk EXAFS data based on the classical view of Hg complexation in soils (which we observe in some samples) involving mixtures of sulfide, carbon, and oxygen coordinating atoms. Recently, we noticed that some samples show a large amplitude increase in one of the Fourier-transformed EXAFS peaks (< 0.26 nm) with increased k-weighting. Such behavior indicates the presence of metallic atoms in the Hg first shell. Electron microscopic and ?-XRF mapping data support this conclusion, showing Hg domains closely overlapping Cu, Zn, and Fe domains. Taken together, the data shows the Hg exists in some soil and debris samples as a mixture of oxygen/sulfur bound complexes and covalently bound metal-amalgams. To our knowledge, this is the first time metal-amalgams have ever been demonstrated in contaminated solids in the environment.