Toxicological Evaluation

Introduction

The Public Health Assessment Training (PHAT) module 7 teaches you that a toxicological evaluation is a step in the health effects evaluation. During this step, health assessors evaluate human exposure to a specific contaminant to determine whether people could become sick from their exposure. This evaluation guides ATSDR’s recommendations to protect public health. A toxicological evaluation is conducted under the following conditions:

Site-specific hazard quotients (HQs) meet or exceed 1.
Site-specific cancer risks (CRs) meet or exceed 1E-6.
No health guideline is available to evaluate noncancer effects for a contaminant.
No oral cancer slope factor (CSF) or inhalation unit risk (IUR) is available for a known or suspected carcinogen.
A contaminant is a community concern.
Other factors (such as mixtures or concerns about specific sensitive populations) warrant further evaluation (even if no HQs or CRs were above acceptable levels).

This primer contains detailed information you need to know before performing a health effects evaluation.

Let’s take a look at the public health evaluation process and see where the topic in this primer—the toxicological evaluation—fits in. As you will see, this part of the process is circled in the flowchart below.

Important: The values and reference documents used in this primer were current when this training was developed. These can be updated periodically, so be sure to use the most current information at your real sites.

public health evaluation process highlighting the toxicological evaluation step

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Identify completed, potential and eliminated exposure pathways
Define exposure units to evaluate, as appropriate
Compile data for each contaminant in each completed and potential exposure pathway (by exposure unit, if appropriate)
Perform a screening analysis to identify potential contaminants of concern requiring further evaluation
Estimate exposure point concentration (EPC) for each potential contaminant in each completed and potential exposure pathway
Calculate doses using the EPC or adjust air concentrations by duration
Calculate hazard quotients (HQs) for noncancer hazards and see if >1
Calculate cancer risks (CRs) for carcinogens and see if >1.0E-6
Perform tox evaluation for contaminants with HQ >1 or CR >1.0E-6, no health guidelines, no cancer risk values for known or suspected carcinogens, community concern, or other factors that warrant it
Evaluate health outcome data, if available and appropriate for site
Summarize health effects evaluation findings, including discussing uncertainty

Note

It is important to remember that the PHA process has many steps. Typically, the four primary technical components involve evaluations of 1) exposure pathways, 2) screening analyses, 3) EPCs and exposure calculations, and 4) in-depth toxicological effects.

The sequence of steps laid out in the previous flowchart may differ slightly, depending on site-specific factors. For instance, health assessors may define an exposure unit before or after the screening analysis. With large data sets, the health assessor may decide to complete the media-specific screening on the entire data set to identify potential contaminants of concern at the site, and then define appropriate exposure units for further analysis.

For smaller or more defined data sets, the health assessor may decide to define the exposure units before the screening analysis. Health assessors will use professional judgement to decide when to define exposure units; however, they must define them before determining EPCs.

What Questions Will the Toxicological Evaluation Help Me Answer?

In the public health assessment (PHA) process, a toxicological evaluation includes reviewing information to answer questions such as the following:

How does the contaminant get into the body?
What happens to the contaminant after it gets into the body?
What data were used to develop the health guidelines and cancer risk values?
What effects are associated with the contaminant and at what doses or concentrations?
How do site-specific doses or concentrations compare to health effects doses or concentrations in published studies?

When to Conduct a Toxicological Evaluation

Perform toxicological evaluations to examine contaminants that meet any of the following criteria:

Yield HQs >1
Yield CRs >1E-6
Have no noncancer health guidelines
Have no cancer risk values for known or suspected carcinogens
Are a community concern
Have factors that warrant further evaluation, even if no HQ/CR exceedances