Chemicals are constantly being pumped into our environment. They are in the air we breathe, the food we eat, and the water we drink. They’re also in the products we use every day. It is impossible not to come into contact with them. Chemicals typically enter the body in one of three ways: through inhalation (breathing them in), skin contact, or ingestion (swallowing them). Once inside the body, chemicals can alter many processes essential for proper cell development. They may impact a single cell, a group of cells, an organ system, or the entire body.

A toxic effect may leave visible damage, or result in decreased performance or function that is only revealed when tested. The body’s liver, kidneys, and lungs can change most chemicals to a less toxic form and eliminate them. However, if the rate of exposure to a chemical exceeds the rate at which these systems can eliminate it, some of the chemical will accumulate in the body—in bones, internal organs, body fat—and may remain there for long periods.

Most people assume that products they routinely use or surround themselves with are safe. But scientists are concerned that some of the chemicals they contain might be hazardous. Lead is one chemical whose dangers are now widely known. Long considered harmless, lead has been phased out of many of the products in which it was traditionally used, such as gasoline and household paint. Once this toxic metal enters the body, it travels in the blood to the nerves, kidneys, brain, muscles, and heart. In adults, lead exposure can lead to reproductive problems, high blood pressure, nerve disorders, memory deficiencies, and muscle and joint pain. In children, whose developing brains and nervous systems are more sensitive to the effects of chemicals, it can cause significant behavior problems and learning disabilities.

While adults and children are exposed to less lead today than they once were, other chemicals have caught the attention of public health scientists and officials. Collectively referred to as “chemicals of concern,” these chemicals are known or suspected toxins or endocrine disruptors, meaning they interfere with the normal functioning of hormones in the body. Bisphenol A, or BPA, is a compound used in manufacturing polycarbonate plastic and epoxy resins. This means it is found in a wide range of commonly used products. Studies using the same toxicity tests used globally for regulatory decision making suggest that BPA levels in humans and the environment are below levels of potential concern. However, other studies—in particular, those that focus on low-dose exposure to the chemical—have prompted some health officials and consumer groups to take action to protect especially sensitive populations, including infants and young children. It’s worth noting here that children, in general, are especially vulnerable to chemical exposure. If an adult and a child take in the same amount of a particular chemical, the concentration will be a lot higher in the child due to the child’s much smaller body size.

In traditional toxicology, a single chemical is tested in one cell or in an animal to assess its harmful effects. In studying environmental hazards, several variables must be factored in. To accurately model real-world conditions, tests need to incorporate different combinations of chemicals, given in a wide range of doses, at different times of the day and year, and over different ages of a subject’s life. This makes it difficult to determine whether emerging chemicals of concern like BPA are inherently safe or not, and whether the risks of using them outweigh the benefits.

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