Health Effects and Toxicology Literature Review

Literature reviews are important steps in research processes, as they provide context and background knowledge for whatever situation you are interested in further exploring. There is a companion wiki to this one with detailed descriptions of literature review purpose and process, found here. In the present wiki, we focus on exactly how to conduct a literature review specifically about health effects of a contaminant. We delineate a guide including steps for how to conduct searches in the literature review, and include a template for how to write up a health effects literature review.

Guide

1. Make a rough list of information to find, including:
   • Sources of the contaminant to the environment
   • Various species or forms of the contaminant
   • Health effects of each contaminant species in humans
   • Short-term and long-term health consequences
   • Environmental concentrations and exposure concentrations that can be of risk to humans
   • Mechanism by which the contaminant affects humans
2. Go to the Center for Disease Control (CDC) and World Health Organization (WHO) websites to find out basic health effects and toxicology information about the substance of concern. Go to the Environmental Protection Agency (EPA) and Occupational Safety and Health Administration (OSHA) websites to find basic information regarding exposure pathways for the substance of concern.
3. From the CDC, WHO, EPA, and OSHA websites, or other reputable websites, write down key sentences relevant to the topics you listed in step (1). Write down any citations that accompany those sentences.
4. Find the Agency for Toxic Substance and Disease Registry (ATSDR) Toxicological Profile for the substance, which may have a link from the CDC website, the ATSDR website, or can be found through a search engine.
5. Read the Public Health Statement section of the ATSDR Toxicological Profile of the substance. Make notes of the citations for pertinent information, including the information listed in step 1.
6. Read the introduction or overview to subsequent sections in the ATSDR Toxicological Profile. Thoroughly read Health Effects sections and make note of citations for the most fundamental and/or pivotal studies.
7. Look up papers that are discussed in the ATSDR Toxicological Profile which appear to be most influential. Particularly influential papers may be discussed multiple times in the ATSDR Toxicological Profile, or be the sole citation for a whole section of the Profile. See the “How to Conduct a Literature Review” wiki for tips about how to look up scientific papers.
   • Read each paper with the following order for sections: abstract, conclusion, methods, discussion.
   • Take careful notes about who is (and who is not) included in the study population, the type of exposure (e.g. chronic or acute), and the chemical species or composition of the substance of interest.
8. In your literature review section, write paragraphs collating information you have learned regarding health effects and toxicology, clumping topics by biological system (e.g. respiratory or cardiovascular). Be sure to cite the primary literature papers you have read, and also include your general secondary source (e.g. ATSDR Toxicological Profile).
9. Use the following template to help structure your literature review.

Template

1st paragraph: Basic Information. Explain that X substance has health consequences ranging from Y to Z. State that we can be exposed to X through these ways. Provide the concentration range of X that can be harmful given various exposure durations.

2nd paragraph: Routes of Exposure / Kinds of Exposure Explain different ways people are exposed, such as occupational and environmental routes. If relevant, explain different exposure routes for different species of X. Detail typical or maximum likely exposure concentrations in a few relevant scenarios.

3rd paragraph: Most drastic health effect that is strongly associated with with exposure: Reference the ATSDR Toxicological Profile and specific studies. Clump health effects into whole body systems (e.g. respiratory) if several systems are affected. Discuss the populations studied (and identify the populations that are not well studied). Discuss health outcomes at various exposure levels.

4th - nth paragraph: Lesser health impacts strongly associated with exposure: Discuss less drastic health impacts, again lumping impacts into whole body systems. Follow the guide for the 3rd paragraph for content to include.

(n+1)th paragraph: Possible health impacts: Discuss studies with lower exposure-outcome associations and/or animal studies. Follow the guide for the 3rd paragraph for content to include. Be sure to include relative certainty or uncertainty of the association.

(n+2)nd paragraph: Toxicokinetics and Mechanisms: Discuss the mechanisms by which substance X impacts the human body. If the mechanism for interaction is highly varied, it may be better to structure the literature review by body system, with each section including a paragraph for health effects and a paragraph for toxicological mechanism.

(n+3)rd paragraph: Wrap-up Summary and Conclusion: Highlight the most well-known health effects and the possible/likely health impacts at various exposure levels, identify the populations who have not been widely studied, and potential exposure routes.