Process for Selecting ATSDR Comparison Values (CVs) and/or Non-ATSDR Screening Levels

This diagram shows the process for selecting ATSDR comparison values (CVs) and/or non-ATSDR screening levels.

First, ask are any of these ATSDR CV(s) available for the contaminant(s) in the site-specific medium? These include the following by medium:

In drinking water:

• Chronic EMEG child or adult
• CREG
• Intermediate EMEG child or adult
• RMEG child or adult
• Acute EMEG child or adult (to consider for acute exposure)
• Maximum Contaminant Level (MCL is not an ATSDR CV, but is included as a potential screening value in PHAST)

In soil:

• Chronic EMEG child or adult
• CREG
• Intermediate EMEG child or adult
• RMEG child or adult
• Acute EMEG child or adult (to consider for acute exposure)
• Acute EMEG pica (to consider for pica scenario)
• Intermediate EMEG pica (to consider for pica scenario)

In air, SVI-subslab/near-source SG¹, and SVI-groundwater²:

• Chronic EMEG/MRL
• CREG
• Intermediate EMEG/MRL
• RMEG/RfC
• Acute EMEG/MRL (to consider for acute exposure)

If none of these ATSDR CVs are available for the site-specific medium, then you have the option to add a non-ATSDR screening level. If you don’t add a non-ATSDR screening level, retain the contaminant for further evaluation. Then an optional step is to ask are non-ATSDR screening levels (like EPA RSLs or state guidelines) available in the site-specific medium? If yes, you have the option to identify appropriate non-ATSDR screening levels to include in your screening.

If one or more of the ATSDR CVs are available in the site-specific medium, then select the PHAST recommended CV for screening the contaminant(s) in each media (if only acute CVs are available, retain contaminant for further evaluation). Then an optional step is to identify appropriate non-ATSDR screening levels to include in your screening.

Definitions for terms used include:

CREG = cancer risk evaluation guide
CV = comparison value
EMEG = environmental media evaluation guide
EPA = U.S. Environmental Protection Agency
MCL = maximum contaminant level
MRL = minimal risk level

PHAST = Public Health Assessment Site Tool
RfC = reference concentration
RMEG = reference dose media evaluation guide
RSL = regional screening level
SG = soil gas
SVI = soil vapor intrusion

¹Soil vapor intrusion CVs identify subsurface concentrations that indicate the need for indoor air sampling to evaluate air exposures. See ATSDR’s Vapor Intrusion Guidance pdf icon[PDF – 1,769 KB] for details.

²Non-ATSDR screening levels might be used if they are lower (i.e., more health protective) than ATSDR CVs, in addition to ATSDR-derived CVs, or when ATSDR CVs are not available. In cases where a non-ATSDR screening level is adequately protective of public health and lower than ATSDR’s recommended CV for the same exposure duration, health assessors can use that lower level after receiving approval by the Associate Director for Science (ADS). In their document, health assessors need to discuss all of the screening levels used in their evaluation.