Some of these ubiquitous chemicals, along with natural plant compounds called phytochemicals, can interact with the endocrine system, especially during critical developmental stages. These endocrine disrupting chemicals (EDCs) interfere by mimicking, blocking, or altering hormones and their signaling systems. Hormones work with the immune and nervous systems to regulate growth, reproduction, metabolism, immunity, cognition, and behavior.
What's the fuss?
Altering hormone signals can change how the body works and may lead to health problems. Some people speculate that EDCs may be linked to many health concerns, such as cancer, diabetes, obesity, learning disabilities and behavior changes. Solid evidence linking EDCs with these kinds of effects is lacking, but increasing anecdotal evidence suggests there might be something to the claims.
However, studies of cell cultures, laboratory animals, wildlife, and accidentally exposed humans do show EDCs can cause a wide range of reproductive, developmental, growth, and behavior problems. The most attention has been given to those compounds that produce estrogenic, androgenic, antiandrogenic, and antithyroid actions. Less is known about interactions with other hormones and possible effects on immunity (infections), metabolism, (obesity), the brain (intelligence, behavior), the heart, the lungs, and multiple generations.
But effects vary. Distinct health effects can occur in different organs and at different life stages. Exposed adults may not show ill effects. But, fetuses and embryos, whose growth and development are highly controlled by the endocrine system, are more vulnerable to exposure and may suffer overt or subtle lifelong health and/or reproductive abnormalities (Bern 1992). Prebirth exposure, in some cases, can lead to permanent alterations and adult diseases.
For example, testicular cancer in young men takes root before birth during fetal development. Certain cancers and uterine abnormalities in women are associated with exposure to DES in the womb. In another case, phthalates in pregnant women’s urine was liked to subtle, but specific, genital changes in their male infants – a shorter, more female-like anal-genital distance and associated incomplete descent of testes and a smaller scrotum and penis (Swan et al. 2005). The ubiquitous compounds, found in plastics and cosmetics, are known to block the androgens that control development of the normally longer male anal-genital distance.
Biomonitoring: They’re in Us, Too
We all carry a heavy mix of hormonally active compounds within us. Synthetic contaminants are passed to us by our parents and picked up at home, at work, in the car, and outside via skin, while breathing, and through food and drink. We accumulate the longer-lasting chemicals (the PCBs, dioxins, and organochlorine pesticides) just by living, store them in fat, and often pass them on to our children through the womb and breast milk. Our exposure to other widely used but less persistent toxic chemicals - such as phthalates, phytochemicals, hormonal drugs, and additives like bisphenol A - is also widespread and occurs throughout life.
According to the Centers for Disease Control’s (CDC) 2005 National Report on Human Exposure to Environmental Chemicals, Americans harbor dozens of chemicals from pesticides, consumer products, and cigarette smoke in their blood and tissue. In its third report, the agency checked 2,400 people for 148 chemicals and found more than 90 percent have a mix of pesticides. And although almost everyone is contaminated with phthalates, children carry a bigger load of the plasticizer and of pesticide ingredients than adults (CDC 2005a).
Although the CDC’s and other recent biomonitoring projects carried out by interest groups confirm people’s chemical body burdens, it is not clear if the contaminants in us pose health threats. While certain individuals or populations in specific regions of the world could face higher risks, no one is sure exactly how or to what extent EDCs affect human health.
As with any risk, factors such as length of exposure, dose, age, genetics, lifestyle, and other individual differences will influence the kinds and severity of associated health problems. That is, one person may experience many problems while another may experience none.
But, some evidence does point to human impacts. Because experimenting on people is illegal and unethical, pinpointing troubles or establishing cause and effect in humans is darned near impossible. Researchers rely on accidental exposures, job-related exposures, and epidemiology studies (using surveys and health clinic data) to obtain evidence of EDCs effects in people.
In general, health effects associated with EDCs include a range of reproductive problems (reduced fertility, male and female reproductive tract abnormalities, and skewed male/female sex ratios, loss of fetus, menstrual problems); changes in hormone levels; early puberty; brain and behavior problems; impaired immune functions; and various cancers.
More specifically, women could face higher risks of breast and reproductive organ tissue cancers, fibrocystic disease of the breast, polycystic ovarian syndrome, endometriosis, uterine fibroids, and pelvic inflammatory diseases.
For men, most of the health effects fall under what is called testicular dysgenisis syndrome. This term describes a range of effects that are tied to disrupted gonadal development during fetal life, possibly caused by exposure to hormone-like compounds (Sharpe and Skakkeback 1993). Human health trends in some countries loosely support trends of decreased sperm quality and increased cancer. Animals studies, however, have confirmed the links between chemical exposure during critical development times and the associated problems. The male effects, then, include: poor semen quality (low sperm counts, low ejaculate volume, high number of abnormal sperm, low number of motile sperm), increases in testicular cancer, malformed reproductive tissue (undescended testes, small penis size, hypospadias), prostate disease, and other recognized abnormalities of male reproductive tissues.
High Dose Exposures: Known Human Effects
Two examples where people were exposed to very high doses illustrate that EDCs can affect humans health: the drug diethylstilbestrol (DES) and the accidental exposure of the population of Seveso, Italy to dioxin (TCDD or tetrachloro-dibenzo-p-dioxin).
DES, a strong synthetic estrogen banned since the 1970s, was given to pregnant women for about 40 years to prevent miscarriages. It was not until the daughters were grown that the negative side effects became known. Daughters of mothers who took the synthetic estrogen during pregnancy have higher rates of reproductive problems, reproductive cancer (vagina, cervix) and malformed reproductive organs (uterus, cervix) (Noller et al. 1990). Sons may also face higher rates of malformed or small penises, undescended testicles and abnormal sperm (Gill et al. 1976). However, there is no evidence of reduced fertility in DES sons. Mice studies confirmed that DES caused the reproductive problems and certain cancers (including the rare rete-testicular cancer in males). More recent animal studies show multigenerational effects and find granddaughters and sons may also be affected (CDC 2005b).
DES is not only a potent estrogen, similar in strength to the natural estrogen estradiol, but it also has the unique ability to concentrate in target tissues, such as the reproductive tracts of birds, reptiles and other animals, during development and cause abnormalities. This drug serves as an example of what potent estrogenic compounds can do and may illustrate the health effects that other environmental estrogens can produce.
The Seveso, Italy, dioxin event, though not the only known case, is probably the most studied population following a chemical disaster in the world. On a quiet July day in 1976, a cloud of industrial chemicals rose in the air from the Industrie Chimiche Meda Societa Azionaria chemical plant and engulfed the unsuspecting town and region. The chemicals, a mix of herbicide ingredients, contained about 30 kilograms (66 pounds) of dioxin, a long-lived, hormonally active, cancer causing poison. It took hours for the first burns to appear on children, days for animals to die, months before the classic dioxin-associated skin disease chloracne developed, and years before the more insipid effects were found. Decades later, people’s health is still affected. Residents have been poked, prodded, and studied since the explosion and continue to be part of research to determine the long-range effects from a heavy dose of a strong pollutant. Studies evaluating cancers, endometriosis, reproduction, immune function, menopause, miscarriages, and other parameters are numerous. Some effects have not correlated with the dioxin. Other effects have taken years to manifest. For example, a significant increase in breast cancer risk with higher dioxin exposures was found more than 10 years after initial exposure (Warner 2002) and life-long immune system problems continue with lowered ability to resist disease.
Other Exposures: Some Examples
Human health is affected by direct exposure to large doses of EDCs. Less clear are effects from everyday exposures to complicated mixes of pollutants. Circumstantial evidence suggests there might be reason to be worried. Below are some examples of less cut and dried cases of possible human health effects from various sources and unclear doses of exposure.
Brain, behavior, intelligence
Concern is Warranted
Although large exposures produce known effects, impacts from long term, low level adult exposure is less clear and more controversial. It’s the kids, though, that cause the most concern. Because, even more unknown is the prospect that developing embryos, fetuses, infants, and children, whose growth and development is highly controlled by endocrine signals, may be more vulnerable to exposure at certain times and may suffer lifelong effects from those encounters. Although the 1993 global assessment found insufficient data to reach concrete conclusions about impacts to human health, it concluded there is sufficient evidence to warrant concern (IPCS 2002).