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What are Regional Screening Levels (RSL) and why are they used?

The Regional Screening Levels (RSL) can be described as risk-based concentrations derived from standardized equations combining exposure information assumptions with EPA toxicity data (United States Environmental Protection Agency, 2020).

Why are SLs used?

The EPA Regional Screening Levels (RSL) are used for site screening and as initial cleanup goals. In site screening, the most crucial role of the RSL is to aid identify areas, contaminants, and conditions that need further federal attention at a particular site. In instances whereby the concentrations of a contaminant in a site fall below the stipulated RSLs, no further action or study is warranted under the Superfund program, so long as the exposure assumptions at a site match those taken into account by the SL calculations. Nonetheless, when the chemical concentrations are found to be above the RSL, that would not directly designate a site as 'dirty'. However, an area with chemical concentrations exceeding an RSL suggests that further evaluation of the potential risks by site contaminants is suitable.

Moreover, the RSL is also used for identifying initial cleanup goals at a site. In this context, RSLs provide long-term targets to use during the analysis of different remedial alternatives. By establishing RSLs early in the decision-making process, design staff may be able to streamline the consideration of remedial alternatives. 

Who sets SLs?

The Regional Screening Levels (RSL) is set by the United States Environmental Protection Agency.

EPA Environmental Standards

The Environmental Protection Agency (EPA) is an agency of the United States federal government whose principal mission is the protection of human and environmental health. Having been established in 1970, the agency has made significant steps in the protection and conservation of the natural environment, regulating the manufacturing, handling, supply, and use of chemicals, and establishing the safe tolerance levels for chemicals and pollutants in food, animal feed, and water. The agency has been successful in enforcing its findings mainly through fines and sanctions (Gillespie, 2016).

How often is the SL Table updated?

It is anticipated that the Screening Levels (SLs) will be updated approximately semiannually in the Fall and Spring (United States Environmental Protection Agency, 2020).

How and Why does the EPA use risk assessment when setting SLs?

EPA uses risk assessments to characterize the nature and magnitude of health risks to humans and ecological receptors from chemical contaminants and other stressors, that may be present in the environment. Following a planning and scoping stage, the risk assessment process begins by collecting measurements that characterize the nature and extent of chemical contamination in the environment, and the information needed to predict how the contaminants behave in the future.

Based on this, the risk assessor evaluates the frequency and magnitude of human and ecological exposures that may occur as a consequence of contact with the contaminated medium, both now and in the future. This evaluation of exposure is then combined with information on the inherent toxicity of the chemical to predict the probability, nature, and magnitude of the adverse health effects that may occur. In the ideal world, all risk assessments would be based on a very strong knowledge base. However, in real life, information is usually limited to one or more of these key data needed for risk assessment calculations. This means that risk assessors often have to make estimates and use judgment when performing risk calculations, and consequently, all risk estimates are uncertain to some degree. For this reason, a vital part of all proper risk assessments is a fair and open presentation of the uncertainties in the calculations and a characterization of how reliable the resulting risk estimates are. Risk managers then use this information to help them decide how to protect humans and the environment from stressors or contaminants.

 

For more information on Regional Screening Levels (RSL), you can use the fantastic resource available on the environmental standards page of the esdat.net website to search and use environmental standards and guidelines. Environmental Standards are available for air, water and soil for the United States, Canada, Australia, New Zealand, United Kingdom, Holland and from the World Health Organization.

References

United States Environmental Protection Agency. Regional Screening Levels for Chemical Contaminants at Superfund Sites. (June 18, 2020). Retrieved from https://www.epa.gov/risk/regional-screening-levels-frequent-questions#FQ1