Toolkit for Exposure Assessment: More Advanced

When to Perform and Who Performs Quantitative Exposure Assessments?

ACA's Screening Level Evaluation Process

 

Screening Level Evaluation Process
Below is a process for evaluating screening level exposure with the basic elements shown in the following outline. There are many considerations that must be a part of this decisionmaking process, and these may vary significantly from one situation to another.

1. Understanding how a specific chemical flows through commerce. ...from chemical manufacturing, through distribution, handling, processing, end products, and release to the environment.

2. Determining the key routes by which a chemical might reach the public or the environment, including:

• Occupational and Community exposures at industrial facilities where chemicals are either manufactured, handled, or processed;
• Product-related exposures where a chemical is an ingredient. Consistent with the U. S. EPA's PMN framework, this includes sub-sets of industrial (e.g., a degreaser for cleaning machine tool parts), commercial/institutional (e.g., janitorial products), or consumer (e.g., household products) applications; and
• Other exposures, such as when chemicals are released to the environment from industrial facilities or product disposal in ways that may reach humans (e.g., via drinking water or food), or natural sources of a chemical.

3. Estimating key exposures, using available predictive models and/or direct observations such as monitoring data. This step may also include assessing the potential for aggregate exposures (where an individual or the environment might be exposed simultaneously to the same chemical through several pathways). Consistent with the screening-level nature of the evaluation, work is focused on estimating key exposures for the above routes, based on predictive models and/or available direct observations (e.g., monitoring data). Where appropriate, the results from individual routes of exposure can also be used to estimate aggregate exposures for multi-purpose/multi-use chemicals.

4. Comparing exposures to relevant hazard data. The comparison of exposure to hazards may involve, for example, estimating margins of exposure (i.e., the ratio of exposure to a threshold for adverse effects). Such a calculation is often used as a surrogate for the potential of a chemical to cause harm.

5. Evaluating whether a chemical is sufficiently studied, or there is a need for further action. This typically involves a weight-of-evidence approach that takes into account the uncertainties associated with both the hazard and exposure analysis, severity of the potential harm, reliability of numerical estimates, etc... Four basic options are included:

• An early conclusion, after identifying the potential pathways for exposure, that there is either very limited or no potential for exposure based on how or where a chemical is used, or that the chemical is widely recognized as being a low level hazard for a particular pathway. As a result, the chemical can viewed as sufficiently studied, based on a qualitative analysis.
• Chemicals/exposure pathways that are viewed as sufficiently studied, based on a qualitative or quantitative screening level comparison of potential exposures to applicable hazards.
• Chemicals/pathways that need further work based on a screening level analysis. This recognizes that many screening level approaches for estimating either exposures or hazard are inherently conservative, and may overestimate their respective endpoints. Thus, when the difference between exposure and hazard thresholds is small, a more comprehensive and accurate analysis may be needed for to determine whether the margins are meaningful, or simply due to the conservativeness of the screening data. Further work may include collecting more complete use and exposure information, or using more sophisticated and accurate "higher tier" exposure analysis or hazard evaluations.
• Chemicals/pathways that indicate the need for management, where a screening level evaluation indicates that exposures are significant relative to the hazards, and sufficiently well understood, after considering uncertainties, severity of effects, etc...