March 29, 2021

Adjusting Remediation Goals Based on Bioavailability Measurements at Sediment Sites

Meg Jalalizadeh

Sediments are sources of organic and metal contaminants that are potentially available to the aquatic food chain. Responsible parties and regulators develop Preliminary Remediation Goals (PRGs) to define remedial actions that reduce risk at contaminated sediment sites. A PRG value for a specific contaminant is typically based on the total measured concentration of that contaminant in sediment. However, since the concentration of total contaminant in bulk sediment is often not related to bioaccumulation or sediment toxicity, the need to refine PRG values based on the concentration of bioavailable contaminants in sediment has emerged. Bioavailability-based PRG values are typically higher than PRGs that are developed based on bulk sediment. Therefore, the use of bioavailability-based PRGs can result in a more targeted, cost- and time-effective management plan for reducing risk.

Passive samplers (such as polyethylene sheets) are cost-effective and convenient tools for measuring the bioavailability of contaminants. An example of the application of passive sampling for refining PRGs at a contaminated site is reported by Burgess et al. (2017). This case study was conducted by the University of Maryland, Baltimore County at the South Wilmington Wetlands site in Delaware. Passive samplers were used to measure concentrations of bioavailable chemicals of concern in sediment (mainly polycyclic aromatic hydrocarbons and PCBs) through laboratory exposures. The bioavailability-based PRGs were higher than the PRGs based on bulk concentrations by two orders of magnitude. The results from this study and the refined PRG estimates were submitted to the Delaware Department of Natural Resources and Environmental Control and are currently being used to delineate the restoration area and the final remedy for the site.

Accurate assessment of PRGs for contaminated sediment sites is critical for selecting the most cost-effective remedy. Standard methods can result in PRGs that are orders of magnitude lower than site-specific PRGs. Bioavailability-based PRGs represent protective, site-specific cleanup levels for contaminated sediment sites, and passive samplers are convenient tools for determining bioavailability-based PRGs. The use of passive samplers is approved and highly recommended by USEPA for measuring the bioavailability of contaminants. (USEPA, 2012b; Burgess et al., 2017).

    Meg Jalalizadeh, Ph.D.

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    Meg Jalalizadeh, Ph.D., is a senior associate at Exponent, Inc (Pasadena, CA).