Selective Sequential Extractions (SSE)

When investigating mercury contaminated soils at legacy mining and industrial sites, measurements of the concentrations of total mercury in the soil are clearly necessary. However, the best approach to site remediation sometimes requires a fuller understanding of the environmental bioavailability and mobility of the particular mercury compounds found at the site.

There is growing interest in the regulatory community concerning bioavailability and Brooks Applied Labs (BAL) remains one of the foremost experts in providing commercially practical solutions to determine the concentrations of various mercury compounds or fractions. Through advanced separation techniques, we are able to quantify mercury concentrations in sediments according to specific compound or fraction of interest.

One of the methods used at BAL to assess the concentrations of mercury compounds in soils that belong to these specific classes is a selective sequential extraction (SSE) procedure. These selective sequential extractions represent the mobility of specific classes of mercury compounds and can be classified as fractions that are water soluble, weak acid soluble, organo-complexed, strongly complexed, or mineral bound. The first three of these fractions have been shown to be significantly more mobile, bioavailable, and susceptible to methylation.

Data regarding of the concentrations and ratios of these mercury compounds in contaminated soils can be critical to successful site remediation and containment of potentially hazardous materials.

It has become increasingly common for risk assessment and treatability studies to require speciation analyses to determine the potential mobility of toxic contaminants at varying sites. Looking at extractable speciation results can be helpful for these studies; however, this approach can only provide a snapshot of how much of each contaminant molecule is readily leachable at any given time.  In reality, the conditions in soil and sediment samples can change over time depending on many factors, including the amount of rainfall, contaminant plume movement, and the hydrogeology at each individual site. Contaminants trapped in various mineral phases can be mobilized under varying site conditions, and even the treatment technologies used to remediate a site can affect the chemistry of the targeted environment and the subsequent lability of certain metals.

At BAL, we have proprietary procedures for the SSE of certain metals in soils, sediments, and similar solid matrices using a series of solutions with an increasing ability to solubilize and extract the solid-phases. Rather than identify specific metalloid species, the metals are fractionated in accordance with their interaction with the substrate components. For specific metals we also have more focused SSE procedures that have the capacity to elucidate molecular forms or groups of molecular forms of the each specific metal.

Brooks Applied Labs currently has selective sequential extraction procedures for the following metals:

To learn more about our innovative analytical methods and how they can benefit your projects, contact us today.