We are in the midst of a vast, unplanned experiment.
During the past century we have created tens of thousands of chemicals that previously existed nowhere on Earth. With them we have intentionally transformed the material world, creating countless useful products that are now hard to imagine life without. But these chemicals are also changing the world in ways that extend well beyond their intended design. A great many, it has been discovered, are capable of altering life’s most fundamental biological building blocks and interfering with genes, hormones, and cellular receptors in ways that can adversely affect the body’s most vital systems.
Given the complexity of these biological systems and the multitude of chemicals to which we’re now exposed – even before birth – it remains difficult to pinpoint precise causes and effects of exposure at a population level. But there is now substantial evidence that environmental pollutants play an important role in most complex human diseases and disorders. As Germaine Buck-Louis, a senior scientist at the National Institute of Child Health and Human Development, told me recently: “Important signals are being picked up” about the coincidence of common and chronic health disorders and chemical toxicology.
How did this happen? People have been tinkering with molecules since ancient times, but it wasn’t until the 1930s that chemists designing products destined for mass-production began to shift their attention from synthetics based on alcohol, cellulose, corn, milk, and starch to synthetics based on petroleum products. The excess hydrocarbons made available by the burgeoning oil and gas industry provided a whole new world of molecules for chemists to work with, and their chemical properties enabled the creation of materials that could be manipulated in ways never before possible. Fast-forward several generations, and almost everyone alive today is accustomed to a world with lightweight, shatterproof, and flexible plastics, stretchy and water-repellant fabrics, and detergents that erase dirt and grease, to name but a few products of modern chemistry.
Moving invisibly through nearly all of our bodies are chemicals used to make nonstick cookware, grease-resistant food packaging, water repellant textiles, polycarbonate plastics, food can linings, flame retardants, antibacterial soaps, sunscreen, pesticides, preservatives, artificial fragrances, cosmetics, toys, and rocket fuel. Scientists have found more than 200 industrial chemicals in newborn babies’ umbilical cord blood. Many of these substances have been found in blood, urine, and breast milk samples taken from people all around the world. They have also been found in air, water, soil, and wildlife, often far from where these products were made or used. Some synthetic chemicals are so different from the products of natural chemistry that, says Terry Collins, director of Carnegie Mellon University’s Institute for Green Science, “it is as though they dropped in from an alien world.”
More than 400 million tons of chemicals are produced worldwide each year and that volume is expected to continue to grow. The exact number of chemicals produced commercially is not known, but it’s estimated that there are well over 100,000 on the market. Thousands of new chemicals are invented each year. A huge number of chemicals have been launched into commercial production without full knowledge of their environmental or health effects. And when these effects are characterized, it is done on a chemical-by-chemical basis, examining the impacts of a single chemical, while in reality we are exposed to multiple chemicals simultaneously.
A great many synthetic chemicals were designed to make life more convenient and, in some cases, safer. But many also behave in ways that are hazardous to human health and the environment. Some persist in the environment for years, even decades. Others are fat-soluble and can accumulate in plant and animal tissue and work their way up the food web. Many produced with the assumption that they would not be biologically active in fact have chemical structures and compositions that enable them to interfere with the natural chemistry of living cells. Some chemicals are not environmentally persistent and don’t bioaccumulate, but are used so widely that our exposure to them is virtually continuous. Prime examples are bisphenol A (BPA) – which makes up the polycarbonate plastics used in reusable food and beverage containers and the resins that line many food and drink cans – and the phthalates used to soften polyvinyl chloride plastics and as ingredients in cosmetics and a host of other consumer products.
We have also learned that industrial workplaces, smokestacks, drainpipes, and waste dumps are not the only sources of chemical exposure. Chemicals are being released constantly from finished products that surround us and that we use daily. They are in products we wear, sit on, sleep with, and deliberately rub into our skins. Their traces can be found in the food we eat, the water we drink, and the air we breathe. They are in us – just as they are in polar bears, sea turtles, salmon, snails, frogs, and seals. These chemicals have become so ubiquitous that, according to marine scientists studying their impact, “During the course of the last century, the planet has become chemically different from any previous time.”
Why does this matter? It matters because exposure to many of these synthetic chemicals can affect virtually every vital body system and function in animals – including humans. Some can disrupt the delicate balance of hormones in ways that can set the stage for fertility, metabolic, and behavioral problems, and also cause certain cancers. And we now know that extremely low levels of exposure to certain chemicals can have profound biological impacts, upending the earlier assumption that only high chemical doses can cause adverse health effects. We’ve also learned that a single exposure can affect not just one but several generations.
Early childhood and infant exposure to certain pesticides (organophosphates) and flame retardants, for instance, has been linked to irregular brain development and impaired cognitive and neurological function. Exposure to pesticides and chemicals used in plastics and cleaning products has been linked to early puberty. Exposure to plasticizers and fragrance agents has been shown to cause chronic respiratory and skin conditions. Prenatal exposure to certain chemicals (BPA, tributyltin, certain phthalates and perfluorinated compounds, among others) can prompt the body to produce an abnormally large number of fat cells, which can lead to obesity later in life. The list of potential health impacts linked to environmental chemical exposure grows daily, as does the debate about the nature of this problem and what to do about it.
Scientific societies, including the American Medical Association, representing tens of thousands of scientists, have voiced concern over the effect of chemical exposures, particularly those of endocrine disrupting chemicals on infants and children, and called for policies that reduce and eliminate their use. At the same time consumers, workers, policy-makers, and many businesses have been pushing and opting for safer products. We can’t turn back the clock. But the science and technology that have enabled the creation of amazing new materials can be put to work to make a new generation of chemicals – ones that are safe for the environment and human health.
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