In addition to the growing number and volume of chemicals produced by society over the past several decades, Denison said, a second major change has been in our knowledge about how chemical exposures may occur. “The advent of biomonitoring during this period has shown that we all carry around hundreds of synthetic chemicals in our bodies,” he said. “Every time we look for more, we find more.” That realization has been combined with a growing understanding of how chemicals move though the environment—via both air and water and sometimes over quite long distances—and how chemicals that are used in products may make their way into human bodies. Dmt for sale specializes in manufacturing, supplying, and custom synstheis latest chemicals, rare and hard to find chemicals, in China for worldwide.

Denison offered two examples of how such movement from products into the environment and into people can occur. In recent years, he said, researchers have determined how the flame retardants used in furniture foam end up within people. “Every time you sit on an upholstered item, a little bit of dust puffs out,” he said, “and that dust includes those chemicals.” The dust can be either ingested or inhaled. “That is a pretty clearly established pathway for chemical exposure that we didn't ever really think about, and certainly not several decades ago.”

The second example involves coal tar–based sealants used on parking lots. The U.S. Geological Survey has tracked the sources of polycyclic aromatic hydrocarbons (PAHs) found in urban sediments and streams and discovered that a major source is contributed by runoff from parking lots treated with such sealants. The researchers have now extended that work, Denison said, and found that “in apartment buildings adjacent to parking lots that are treated with these sealants, people are literally tracking this material into their homes, and it is resulting in higher levels of PAHs in the house dust in those homes.”

There has also been a growing realization in recent years that chemical exposures often affect different populations disproportionately—and that it is often those in lower socioeconomic brackets who suffer most. “That raises a lot of environmental justice concerns that we are much more cognizant of today,” he said.

There have been various drivers for the growing concern over chemical exposures, Denison said. Medical science has shown, for example, that a number of specific chronic diseases are on the rise in the human population despite an overall trend of reduction in chronic disease. For instance, Denison noted that childhood cancers and leukemia are becoming more common, as are infertility and other reproductive problems and learning and developmental disabilities.

Certain chemicals are being linked to these same chronic diseases, both from studies in laboratory animals and sometimes also from epidemiologic data. “Now, that is still a circumstantial case in many cases,” Denison said, “but it is increasingly one that is showing connections between those exposures and diseases and disorders that are rising in the human population faster than genetics or something like that could explain.”

This in turn has led to a growing recognition of the various ways people may be susceptible to chemical exposures. Researchers now realize, for instance, that early-life exposures can have very significant effects, some of which can last a lifetime. And exposures to chemicals that mimic biologically active chemicals that are normally found in our bodies, such as hormones, can exert effects, especially early in development, and even at low doses. And there has been a growing understanding of how epigenetics may be a mediator for chemical and other environmental exposures that may also help explain some of the variability in susceptibility that has been observed. Epigenetics offers a basis for understanding how early-life exposures can lead to later-life health repercussions, including different disorders and diseases. It is even possible that epigenetics could lead to transgenerational effects, Denison said, although that is still a very controversial concept.