Toxicology is the study of the harmful effects of chemicals, substances, or environmental agents on living systems.
Introduction
What is toxicology?
Once a field that focused on studying poisons, toxicology has evolved into a broader discipline dedicated to evaluating potential risks of various exposures and promoting the safety of humans, animals, and the environment.
These exposures include many chemicals, of which two examples are bisphenol A (BPA), and perfluorinated chemicals known as PFAS. Potentially harmful chemicals and metals, such as lead and arsenic, can be found in environmental agents, such as traffic-related air pollution. In consumer products, chemicals such as phthalates are found in many items, including some food packaging, toys, and medical device tubing.
By discovering the ways in which environmental exposures can affect our health, toxicology research can point to strategies for preventing disease, birth defects, and other adverse conditions, and for improving the well-being of people.
What factors play a role in toxicology studies?
- Dose-response relationship: Toxicologists study the relationship between the amount of a substance and its effects on an organism. This analysis helps determine the level of exposure (dose) at which a substance may become harmful and pose a health risk to humans. All substances have the potential to be toxic under certain conditions or at certain doses.
- Exposure pathways: Understanding how chemicals enter the body is crucial for assessing risk and developing safety measures. Routes of exposure include inhalation, ingestion, or direct skin contact.
- Susceptibility factors: Individual differences, such as age, sex, genetics, and health status, influence how a person responds to an environmental exposure. Just because someone is exposed to a harmful substance does not mean they will get sick from it.
- Critical windows of exposure: During certain life stages, like pregnancy, early childhood, and adolescence, people are generally more sensitive to chemical exposures. Toxicologists tend to focus on these critical periods for studies. Even low-dose exposures that may seem insignificant could have biological effects or lead to an adverse health effect if the exposure happens during a critical window of development, such as when the brain and reproductive tract are forming.
How does the science of toxicology improve people’s lives?
Toxicology provides critical information that regulatory agencies, decision makers, and others can use to develop programs and policies that limit our exposures to toxic substances. These advances are intended to help prevent or reduce the likelihood of diseases or other adverse health outcomes. For example, the California state government used federal research findings to establish a drinking water standard for hexavalent chromium. Data from NIEHS studies was also been used by the Environmental Protection Agency to set drinking water limits for some PFAS. These standards will help reduce people’s exposure to these persistent toxicants.
Other benefits of toxicology include:
- Government agencies have a sound scientific basis for establishing regulations and policies aimed at protecting and preserving human health and the environment from toxic pollution.
- Companies, such as those in the pharmaceutical and chemical industries, are able to develop safer products, drugs, and workplaces.
- Consumers have access to information that helps them make decisions about their own health and prevent diseases.
How is federal toxicology research coordinated?
NIEHS is headquarters for the National Toxicology Program (NTP), an interagency partnership that includes the National Center for Toxicological Research of the U.S. Food and Drug Administration (FDA) and the National Institute for Occupational Safety and Health of the Centers for Disease Control and Prevention (CDC).
Researchers at NIEHS support NTP through toxicology testing, laboratory research, and literature-based assessments. They also oversee NTP databases, advisory groups, and peer review of draft reports.
What is NIEHS Doing?
NIEHS extramural research. NIEHS funds grants in toxicology and environmental health sciences, which primarily go to research universities or non-profit research institutions. For example, NIEHS-funded researchers are working to develop new and improved models of toxicity that can help predict cancer and other adverse health outcomes that may result from fetal or early life exposures.
NIEHS intramural research. In-house, or intramural research, is performed by scientists who are employed by the federal government and work onsite at NIEHS, particularly the Division of Translational Toxicology. That division’s mission is to improve public health through toxicological data and knowledge development that are translatable, predictive, and timely.
NTP Interagency Center for the Evaluation of Alternative Toxicological Methods (NICEATM). NIEHS, a key player in toxicology, is leading national efforts to reduce the use of animals in chemical safety testing, to keep pace both with emerging substances and the technology used to study them, and to communicate findings with stakeholders and the public.
NICEATM works to find and evaluate test methods that replace, reduce, and refine the use of animals in testing, particularly mammals. These methods might include computer models, cell-based systems, and non-mammalian model organisms. For example, NICEATM created the Systematic Evaluation of the Application of Zebrafish in Toxicology (SEAZIT) program to promote the broader adoption of zebrafish models for toxicological screening.
Integrated Chemical Environment (ICE). ICE is a resource developed by NICEATM. It includes curated toxicology data on thousands of chemicals and a collection of tools to assist in the prediction of the effects of exposures. Recent research shows that ICE data generated in the laboratory can be highly predictive of the effects of exposures seen in people in the real world.
Chemical Effects in Biological Systems (CEBS). CEBS is a comprehensive toxicology database that compiles individual and summary animal data from the NTP testing program and other depositors into a single electronic repository. The resource currently contains over 11,000 exposure agents and over 8,000 studies, including all available NTP carcinogenicity, short-term toxicity, and genetic toxicity studies.
Toxicology in the 21st Century. Tox21 is a unique collaboration among four federal agencies, including NIEHS. This program, formed in 2008 and is ongoing, develops innovative non-animal test methods to rapidly evaluate whether substances adversely affect human health. For example, Tox21 uses robotics in high-throughput screening, which is important for increasing the volume and speed of toxicity testing.
Public Health Impact
NIEHS and NTP toxicology research have significantly influenced public health policies. For example, NTP evaluates substances to determine if they should be labeled as human carcinogens, which are substances that could cause cancer in humans. This evaluation is included in the Report on Carcinogens, a congressionally mandated report that lists agents posing cancer hazards to many people in the U.S. Several states and federal agencies use this report as an authoritative source for decision-making and hazard communication.
An interactive tool, available to the public, highlights the important role that cancer hazard identification can play in preventing cancer.
Challenges and Future Directions
The field of toxicology faces several challenges, including the complexity of chemical mixtures, the need for better predictive models, and the ethical considerations of testing potentially harmful substances on animals. Future directions in toxicology research include the development of more sophisticated biomarkers, the use of big data and computational models, and a greater focus on personalized medicine to tailor interventions based on individual susceptibility.
Further Reading
Stories from the Environmental Factor (NIEHS Newsletter)
Additional Resources
- Toxlearn. A toxicology tutorial provided by the National Library of Medicine, covering key principles of toxicology.
- What is Toxicology? A website designed by the Toxicology Education Foundation to enhance public understanding of toxicology through access to objective, science-based information on the safety of chemicals and other agents.
- Becoming a Toxicologist. This webpage by the Society of Toxicology provides those considering a career in toxicology with information on the profession, schooling needed, and more.