Step 2.3 Evaluating Exposures for Possible Health Effects

Focus of Literature Review

Health assessors look for the following when researching chemical information:

• The no-observed-adverse-effects-level (NOAELs)
• The lowest-observed-adverse-effects-level (LOAELs)
• The mechanisms of toxic actions
• The strengths and weaknesses of the studies

no-observed-adverse-effects-level (NOAEL)
The NOAEL is the dose of a chemical at which no adverse health effects are identified between the study animals or population (the group exposed to the chemical) and the control animals or population (the group with no exposure to the chemical). Effects or changes in the study animals or population may be produced at this dose, but the effects are not considered harmful.

lowest-observed-adverse-effects-level (LOAEL)
The LOAEL is the lowest dose of a chemical at which adverse health effects are identified between the study animals or population (the group exposed to the chemical) and the control animals or population (the group with no exposure to the chemical). Examples of possible adverse health effects identified at the LOAEL may include decreases in strength or lower birth weights for offspring.

mechanism of toxic action
A mechanism of toxic action describes how a chemical acts in the body to cause harm. For example, the chemical may react with cell membranes and prevent normal cell repair.

strengths and weaknesses of the studies
The literature often discusses the strengths and weaknesses of studies. A strength may be that an epidemiologic study considered exposures to both males and females, whereas a weakness may be that the study did not consider exposure to pregnant females and effects on the fetus. Identifying the strengths and weaknesses in a study can help a health assessor decide whether the study has enough similarities to site-specific conditions and concerns to use the study as part of the evaluation.

Epidemiologic studies that are reviewed should be studies similar to those at the site under evaluation in regards to the exposed population, exposure conditions, and chemicals.

Sources of Toxicity Data and Epidemiologic Studies

“ATSDR’s toxicological profiles (https://www.atsdr.cdc.gov/toxprofiledocs/index.html) are a primary source of information for toxicity data and epidemiologic studies.”

ATSDR’s approach to evaluating studies on which exceeded health guidelines are based can be found in ATSDR’s Public Health Assessment Guidance Manual, Section 8.3.

ATSDR’s approach to evaluating site-specific health effects data can be found in ATSDR’s Public Health Assessment Guidance Manual, Section 8.6 .

Other toxicity data and epidemiology study results can be found through searches of TOXNET (https://toxnet.nlm.nih.gov/) or PUBMED (https://www.ncbi.nlm.nih.gov/pubmed/), which are maintained by the National Library of Medicine.