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Relating Metal Speciation to Bioavailability in Contaminated Sediments

Zn-contaminated area at the Indian Head site. Zinc-laden slag and soil have eroded from the hillside into the nearby river sediment.
For decades, metal-contaminated sediments have been an important concern for EPA. The purpose of this research is to use spectroscopic techniques to determine the chemical speciation of metals in contaminated sediments from around the country, and correlate the metal form to biological availability via assays.

During WWI, a zinc recovery furnace was located adjacent to Mattawoman creek at the Indian Head Naval Warfare Center in Charles County, Maryland. As a result of the recovery furnace's operation, the shore sediments of Mattawoman Creek contain zinc in the pore water at levels of 25 mg/L, and in excess of 20 g/kg in the sediment. The goal of the Indian Head Sediments project is to develop and evaluate in situ remediation strategies for the sequestration of zinc along the shore. EXAFS performed on a sample of Indian Head sediments at Argonne National Labs in February and March 2005 identified the zinc in the sediment as zinc hydroxide, zinc carbonate, and a phase likely associated with iron.

Contaminated sediments at Quantico. The tidal basin sediments have converted the transported lead into galena due to the anoxic conditions of the wetland.
The Chopawamsic Creek, a tributary to the Potomac River, has elevated levels of lead due to the migration of contaminated groundwater and sediment (exceeding five grams of lead per kilogram of sediment) from an erstwhile firing range.

The goal of the pilot metal sequestration project at Quantico is twofold:

  1. to evaluate lead speciation in sediments as related to toxicity, mobility, and bioavailability; and
  2. to evaluate the application of apatite (calcium phosphate) as a remedial strategy to sequester and immobilize lead.

In the sediments, lead was found to exist primarily as a lead sulfide. In addition to the field tests, laboratory experiments are investigate the chemistry of the sediments, and the transport of lead to the wetland through streams characterized by high levels of iron.

Contacts: Kirk Scheckel; Aaron Williams; James Ryan (EIMS#135364)

Office of Research & Development | National Risk Management Research Laboratory

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