Why Our Approach to Toxicology Must Change

Exposures to endocrine disrupting chemicals (EDC) are a particular concern for children. Because children are developing rapidly, hormone disruption can have a greater impact; resulting in chronic health problems or making children susceptible to the development of illnesses later in life.

Research has shown that chemicals in a mother's body are able to cross the placenta, and therefore, children are being exposed to environmental chemicals even while they are in the womb. As infants, they are exposed to chemicals at higher levels because consume more food relative to body weight, but also because their immune systems are less developed, and therefore, less able process and remove chemicals from their bodies.

For lead, proper regulation took several decades because we initially had a poor understanding of its health effects. We face the same problem today with EDCs.

The famous adage the "dose makes the poison" describes the assumption toxicologists use when determining safe chemical exposure levels. Toxicology studies currently assume that a greater dose, or exposure level, will produce a greater effect.

To determine safe exposure levels, animals are exposed to varying amounts of a chemical and a dose that does not produce observable effects is identified. Then, a series of uncertainty factors are applied to that dose in order to calculate an acceptable level for human exposure. The uncertainty factors account for different sensitivities between the animals studied and humans but also to account for varying sensitivities between humans.

So, what is wrong with the current approach?

Scientists who study the endocrine system have recognized for a while that hormones have a different relationship between dose and effect. Hormones and hormone mimicking chemicals, like EDCs, can produce opposite effects at different exposure levels. A low level exposure can turn a process on, while a high level exposure could shut the process off.

Since EDCs have a different dose-effect relationship, the current assumptions used in toxicology studies are outdated. High-dose experiments can not be effectively used to predict low-dose results for EDCs, and therefore, safety testing needs to be adapted to make sure that potential low-dose effects are investigated. In order to address our evolving understanding of endocrine disruption, the Endocrine Disruptor Screening Program was established by the Environmental Protection Agency to develop a battery of tests to properly identify EDCs, information that will enable us to update the way we conduct toxicology studies.

The scientific understanding of how endocrine disruption can be identified and measured is still in the early stages, and research will be our best chance to close these knowledge gaps and identify chemicals that are a real public health threat.


This is Part 6 in the Chemical Exposures and Public Health series.
Part 1 - From Interest to Passion
Part 2 - An Environmental Health Risk
Part 3 - Lead: A Regulatory Success Story
Part 4 - Something My Body Needs Anyway?
Part 5 - Obesity's Elephant: Environmental Chemicals
Part 6 - Why Our Approach to Toxicology Must Change
Part 7 - Failures of U.S. Chemical Regulation
Part 8 - Cleaning Up Our Act
Part 9 - Environmental Health Research Saves Lives and Money
Part 10 - Call to Action