DETERMINATION OF HEAVY METAL SPECIATION IN SEDIMENTS BY SEQUENTIAL EXTRACTION IN TWO ESTUARINE ENVIRONMENTS IN SALEM, MA

Heavy metals introduced into sediment by anthropogenic activity can cause concern due to the toxic nature of the metals, especially if the potential for remobilization exists. One important variable that can control the post depositional mobility of toxic metals is the speciation of the metal within the sediment. To assess the potential for metal mobility in the North River and Forest River estuaries in Salem, MA, a sequential extraction procedure was used. Previous studies of bulk concentrations of metals in sediments from the North River indicate toxicity values of lead and chromium that exceed the effects range median (ERM) sediment quality guideline, while all other measured heavy metals from both locations are above the effects range low (ERL) guideline. These concentrations of toxic metals strongly reflect the similarities in land use history in both estuarine environments. To better understand where metals reside, sediments were introduced to four stages of chemical solutions to obtain exchangeable, reducible, oxidizable, and residual fractions. Each extraction fluid was analyzed using an ICP-OES for arsenic, cadmium, chromium, copper, nickel, lead, and zinc concentrations. Initial results indicate total metal concentrations in the North River sediments are between 9 and 1150 ppm, while total metal concentrations in sediments from the Forest River are between 3 and 392 ppm, which is consistent with previous work. The speciation results indicate nickel predominantly resides in the exchangeable fraction and therefore is susceptible to mobility with subtle changes in aqueous chemistry. Results also indicate that lead is found in the reducible fraction while chromium is in the oxidizable fraction. Thus, it can be expected that individual metals will be mobilized separately in response to chemical change.