Risk Assessment

Environmental Contaminants and Toxicology Reader

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Source: Environmental Health Perspectives.


Humans have been producing and releasing environmental contaminants ever since the discovery of fire. Contaminants include both naturally occurring chemicals released in unnaturally high concentrations, and chemicals that are novel to natural environments, produced by human activity and released either intentionally or accidentally.

Toxicology is the science devoted to understanding the impact of these chemicals on plant and animal (including human) individuals and populations. Understanding adverse effects of chemical contaminants leads to improved regulation, management and control of potentially toxic chemicals. Of course, new chemicals are produced, used and released constantly into the environment, requiring continuing research, monitoring, analysis, assessment and risk communication. As the ability to detect lower and lower concentrations of contaminants in the environment continues to increase, toxicologists continue to reveal adverse impacts of exposure to smaller and smaller amounts. Significantly, they are acknowledging increasingly the potential for the combined  and cumulative impact of multiple contaminants present in small quantities.

This e-text is designed to introduce the reader to contaminants and toxicology. All content was written by qualified scientists who are experts in their respective topic area. Content is reviewed thoroughly by a Topic Editor prior to publication.

Authors are welcome to expand and edit the contents list; please contact Emily Monosson with suggestions. If you are interested in writing an article for this collection, please consult the How to Contribute page for more information on getting involved.

Toxicology Basics


The following sections will provide basic concepts that will help you to ask appropriate and informed questions about the impacts of contaminants on living systems.  We begin with a historical perspective:

Dose makes the poison

One of the basic tenets of toxicology is "The Dose Makes the Poison." Though in reality toxicity processes and outcomes are a little more complicated. The point is: One cannot begin to evaluate the impacts of chemical contaminants without considering exposure and dose.

Interaction of contaminants with living systems

Once an organism (or biological/ecological system) is exposed to a toxicant, the effect of that substance will depend on what happens to it as it travels through the organism's body (or through the biological/ecological system). Consideration of absorption, distribution and excretion (ADE) are essential to understanding the potential for a chemical to cause harm.

Impacts on specific systems

Beyond the basics of ADE, a toxicologist considers how chemicals interact at the cellular level. For example, sometimes chemicals are detoxified by enzyme systems within certain cells, and sometimes, they are activated. Sometimes they need no activation, and can bind to receptors meant for other chemicals in the body.

Combined contaminant exposures

Until most recently, most toxicologists studied the impact of chemicals as they acted singly, an unrealistic scenario in many human health or environmental cases. The study of chemical mixtures is a growing field of toxicology.

Toxicity Testing and Risk Assessment

When new chemicals are developed, and as various producers, users and regulators try to evaluate their potential impact on both humans and the environment, chemicals are tested and monitored, exposures are estimated and potential risk is evaluated. For commentary see Role of science in regulation 

Government agencies and legislation in the United States

A number of Federal agencies are charged with protecting humans and the environment from potentially adverse impacts caused by chemical substances through various laws, policies and regulations. (This is not a complete list. Please feel free to contact Emily Monosson to add.) 



Federal Laws and regulations (for summaries see: Environmental Laws and Regulation of toxic chemicals

European Legislation

Environmental Justice and communities

The realization that many contaminated sites are located disproportionately near communities of color and near low-income communities led to a growing Environmental Justice movement and field of research-based, academic study. Additionally, researchers are beginning to realize that traditional and community knowledge about exposure, contamination, and environmental change provides valuable information to environmental and health assessment.

Reducing contaminant impacts



Chemical contamination worldwide

(In)famous sites and disasters

Chemicals of note

Chemical contaminants of recent concern


Air Pollutants








Monosson, E. (2013). Environmental Contaminants and Toxicology Reader. Retrieved from http://www.eoearth.org/view/article/51cbedbb7896bb431f693819