Site remediation can be a costly process for owners experiencing contamination issues. Evaluating bioavailability is the process of identifying only the concentration of contaminants that need to be removed from sites to address human or ecological risks. This method reduces site remediation costs by eliminating the need to remove the entirety of contaminants identified in soil or sediments, while still meeting health and environmental standards.

Accurately Assessing Contaminants

Established cleanup goals for contaminated soil and sediments are typically based on total contaminant concentrations at the identified site. In other words, potentially responsible parties tasked with site remediation often compare the total chemical concentration measured in soil or bulk sediment samples to cleanup criteria mandated by a regulatory agency, such as the state or U.S. Environmental Protection Agency (EPA). Site contamination risks may also be calculated using total chemical concentrations in soil and sediment. 

However, often the amount of contaminants actually available to be uptaken by a receptor and potentially cause a toxic effect, also known as the bioavailable fraction, is less than 100% of the amount of contaminant present in soil or sediment. Factoring bioavailability into the evaluation of site contamination risks and development of cleanup goals can provide a more accurate estimate of risk and better focus remediation needs on the amount of contaminant that needs to be removed.

For certain contaminants, such as arsenic and lead, default bioavailability factors are available from the EPA. Other methods are also available for conducting site-specific evaluations for both metals and polycyclic aromatic hydrocarbons (PAHs). Well-established methods are available for both in vitro and in vivo options to measure arsenic and lead bioavailability. These bioavailability methods range from simplistic comparisons of concentrations in soil to plant matter to live animal studies involving feeding site soils to animals and measuring excreted metals concentrations.

Looking to the Future

Developing bioavailability methods for PAHs are early in the experimental development stage and could lead to significant change in the site remediation process. PAHs present greater challenges for measuring receptor uptake compared to excretion, due to their toxicokinetics involving complex absorption, metabolism and excretion processes. However, the ongoing research to develop methodologies suitable for widespread use in contamination risk assessments is promising.

Beyond its use in evaluating risk, manipulation of bioavailability is a widely practiced and effective remediation and treatment technology. Bioavailability can be decreased by adding amendments to stabilize or fix the contaminants present in the soil or sediment. By adjusting levels so that contaminants are not available to be absorbed by receptors, the toxicity of the identified soil or sediment is significantly reduced without having to undergo the process of removing all contaminants present.

Project owners can reap the benefits of bioavailability by finding a solution that fits their specific needs. Site remediation costs can be greatly reduced by incorporating bioavailability as an assessment tool or remediation strategy to meet established cleanup standards and eliminate the need of unnecessarily removing contaminants not posing a significant risk to the environment.

 

Every environmental site has unique challenges. An experienced team can provide you with site remediation solutions fit to your needs.

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by
Diana Marquez is a site remediation project manager at Burns & McDonnell. Her more than 20 years of experience includes working with large Potentially Responsible Parties on complex sites that require careful negotiations with regulators.