June 19, 2018
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Expert Q&A

The Impact of Endocrine-Disrupting Chemicals

by David Tuller, DrPH  

Rachel Morello-Frosch, PhD, is a professor in the School of Public Health and the Department of Environmental Science, Policy and Management at the University of California, Berkeley. In her research, she examines social determinants of environmental health disparities, with a particular interest in air pollution, chemical exposures, and the impacts of climate change.

Dr. Morello-Frosch is also collaborating on a major study based at UC San Francisco on the effect of industrial compounds called endocrine-disrupting chemicals, or EDCs, on fetal and neonatal development. This category includes thousands of compounds, such as chemicals known as phthalates, which are widely used in cosmetics and other personal care products, and bisphenol A, which is found in plastics and food containers. We spoke with Dr. Morello-Frosch about her current research and the ongoing controversy over EDCs.

What is an endocrine-disrupting chemical?

In the simplest terms, an endocrine-disrupting chemical, or EDC, is a compound that affects your hormone system and the regulation of your hormone system. These chemicals can mimic hormones in different ways that can have adverse reproductive, neurological, and other human health effects throughout the life course.

One big issue of increasing concern is prenatal exposure and the way it affects fetal and childhood growth and development. In relation to this, scientists are beginning to understand the so-called epigenetic effects of EDCs. Rather than changing the DNA or genome itself, some of these compounds can affect genetic expression by turning genes on and off. So, for example, a compound might turn tumor suppressor genes off, which can increase the risk of some cancers. Animal studies looking at the transgenerational impacts of these chemical exposures suggest that the epigenetic effects can be passed on from the adult animal to its offspring, and then to the offspring of the offspring.

You recently published a study that looked at blood levels of various chemicals, including EDCs, in mothers and their newborn babies. What did you find?

Our study compared maternal blood and fetal cord blood taken at delivery and measured these samples for the presence and levels of a variety of different chemicals. The study is the first in the United States to measure exposure to 59 toxic chemicals in pregnant women and their newborns. Our results showed that the women and their newborns had widespread exposure to environmental chemicals, many of which showed up in higher levels in the newborns than in the mothers. Overall, four-fifths of the chemicals that we detected in maternal blood samples were also detected in the umbilical cord blood samples, indicating that they passed through the placenta and entered the fetal environment. This is concerning because many of these chemicals are EDCs and have been shown in other studies to have adverse neurological, cognitive, and other developmental effects.

What are the main ways in which we’re exposed to endocrine-disrupting chemicals?

They come from a variety of sources. We are exposed through indoor air, household dust, and the consumer products that we use to clean our homes. They’re also prevalent in personal care products like shampoos, lotions, and other scented products. They can also come from food packaging and fast food containers—the chemicals can leach from the packaging into the food we’re eating. EDCs can be very hard to avoid, even if you try to avoid them as a consumer by reading labels. The chemicals are also found in building materials and furniture, so that’s something you might not have a lot of control over as a consumer.

So what can consumers realistically do to protect themselves and their families?

It’s a really nuanced message that we as scientists need to convey to consumers. One of the challenges in public health is that we always feel compelled to give people messages about things they can do to protect themselves and their families and children. So the advice tends to be what you as a consumer can do to reduce exposures. You can avoid certain products, avoid buying certain foods and toys for your kids, avoid certain compounds on labels. A lot of that I think is very rational and useful advice and can reduce certain chemical exposures.

But I also think that, at the same time, we need to remind people that the impacts of those individual actions are limited, and people can’t shop their way out of this environmental chemical problem. We can’t each do our own personal risk assessment every single time we decide what shampoo or food product to buy. Individual actions can certainly help reduce some exposures—for example, by reducing your use of scented products, washing your hands regularly, or trying to eat organic or pesticide-free fruits and vegetables. But you and your children will still be exposed to chemicals, since many of the ingredients in the consumer products we use are not disclosed.

What we really need is a fundamental shift in environmental policymaking and a decisive move away from this notion that chemicals are considered safe until proven otherwise. The European Union is now requiring companies to provide data showing that compounds are safe to use before they can go to market. Although it seems unlikely given our new political reality in the U.S., where the EPA is under attack, ultimately that is a standard that we are pushing for in the U.S. as well.

Why is there still so much debate about the impact of EDCs on our health?

Some of the biggest challenges of assessing the human health effects of environmental chemicals are really capturing levels of exposures to multiple chemicals, and also understanding the timing of exposures during human development—from conception and even pre-conception into adulthood. When and how people are exposed to certain chemicals does matter, in terms of the risk of diseases later on. But in humans, we’re limited to doing observational studies. It’s unethical to put people in clinical trials that randomize people into exposure and control groups and expose one group deliberately to environmental chemicals to assess the potential damage.

So, you’re basically faced with observational studies where you’re trying your best to characterize people’s exposures during the moments that you think are important—for example, prenatal exposures at different times during pregnancy. And then you’re trying to control for other factors that might confound the relationship between chemical exposure and adverse health outcomes. That’s challenging from an analytical point of view. And the health effects that you see can be diseases that are multifactorial and can be caused by a lot of different things in addition to environmental chemicals, so you’re trying to account for that as well.

Due to the lack of human studies on many chemicals, for a lot of chemical regulation, we rely on toxicology evidence—that is, animal studies. That allows us to have more controlled experiments and more homogeneity in the study population—rodents that are genetically very similar to each other, for example. There’s always the challenge of extrapolating the results that we see in animals and assessing the relevance to humans, and also of whether or not the exposure levels that are being tested in animals are relevant to humans. Those calculations have uncertainties and are often contested. But overall, animal studies of environmental chemicals have been shown to be pretty predictive of potential adverse health effects in humans, which is why they are used to set regulatory standards by agencies like the EPA.


Also see Are Hazardous Chemicals in Your Cosmetics?