« Le rêve séduisant selon lequel "les produits chimiques veillent à la vie" se transforme en un cauchemar où des hormones imposteurs détournent le comportement de nos cellules, affectent nos facultés intellectuelles, provoquent l’infertilité et le cancer. »

Endocrine Disruption:
Changing Times

  Lia A. Daborn
  Conservation Council of New Brunswick
  January 1999

hemicals in the environment are sabotaging fertility and development of wildlife in Canada and, in the long run, in humans. Developing children and fetuses are most vulnerable to the effects of toxic chemicals known as ‘hormone mimics’ or endocrine disruptors. These chemicals disrupt the normal hormonal messages that tell a body when and how to develop.

The effect of toxic contaminants in the environment first came to public attention in 1962 through biologist Rachel Carson’s book, Silent Spring, in which she described the potentially fatal effects on wildlife resulting from use of DDT. However, more than a quarter-century later, chemicals may still be undermining our ability to reproduce, to learn and to think.

How does hormone disruption work?

The endocrine system is one the body’s three integrating networks. It is made up of glands, hormones, and target cells that comprise a complex network of chemical signals and messages controlling many immediate and lifelong bodily responses and functions. Hormones produced by the endocrine system act as messengers, working with the nervous system to tell cells how and when to:

  maintain the body’s internal steady state (nutrition, metabolism, excretion, water and salt balance);

  react to stimuli from outside the body;

  regulate growth, development and reproduction; and

  produce, use and store energy.

In order to send messages, hormones lock into receptors and, like a key in a lock, send the required signal. At very low concentrations, synthetic compounds that mimic hormones can insert themselves into the receptor and either turn on cell activity at the wrong time, or block the appropriate activity by occupying the receptor site (see Figure).

(Diagram: C.C.N.B.)

Hormones are very potent chemicals that operate at low concentrations. Estradiol, for instance, is a natural hormone that can cause a response in the parts per trillion (ppt) range. This sensitivity allows for variations in offspring from the same genetic code. However, it also makes the endocrine system vulnerable to serious disruption if something interferes with normal hormone levels.

Interference with hormone functions is particularly dangerous to developing embryos and newborn babies. Such interference may emerge later in life as lower sperm counts, cancers, miscarriages and tubal pregnancies, impaired learning ability, reduced immunities and behavioural disorders such as hyperactivity. The most dramatic and troubling sign that hormone disruptors may already be taking a toll is found in reports that human male sperm counts have plummeted over the past century (Carlsen et al., 1992).

Children are most vulnerable to the potential effects of hormone disrupting chemicals due to the high level of hormonal activity taking place during development. Prior to birth the process of sexual differentiation is highly dependent on hormones to take the unisex embryo and guide its development into a male or a female. Hormonal cues delivered at the right moment guide the expression of the cells as tissues make "now or never" choices about the direction of development.

Damage by hormone disruption is trans-generational (can affect offspring); it may be apparent at birth, but often emerges later in life. The exposed mother may be completely unaffected, but her children may have trouble producing the next generation.

The timing rather then the level of exposure is crucial. For example, exposure to one very low dose of a hormone disrupting substance during a critical stage of embryonic development can cause permanent damage. The damage caused by hormone disrupting chemicals is cumulative (tending to accumulate or increase) and synergistic (tending to combine to even greater amounts). This makes it impossible to generalize what the effect of human exposure to a chemical may be. (For more about the process and effects of hormone disruption on humans and wildlife, see Colborn et al., 1996.)

"unless the environmental load of synthetic hormone disruptors is abated and controlled, large scale dysfunction at the population level is possible." (The Wingspread Consensus Statement [1991] is signed by 21 scientists. Reprinted in Colborn et al., 1996.)

Research into hormone imposters has increased, and reveals threatening information. Recent reports of PCB levels in breast milk of northern native populations demonstrate that no place on earth is safe from chemical contamination. To date, scientists have identified more than 50 chemicals that act as hormone disruptors (Aziz, 1998). Environmental estrogens are the most commonly discussed, but chemicals can also act as androgens (male hormones) and thyroid hormones (regulating metabolism and growth). Such chemicals will most drastically affect the reproductive organs, brain, thyroid, liver, kidney and immune system (Aziz 1998).

Despite the studies and research findings, some still do not believe that changes in populations and reproduction are related to chemical contamination in the environment. The problem is that there is no hard and fast proof that these effects are directly linked to one specific combination of chemicals or to one specific episode. Therein lies the real threat: how long do we have to wait before realizing there is a problem and attempting to do something about it? How many generations have to be affected before concrete action is taken to incorporate precaution into the everyday use of chemicals and increase the testing of chemicals, both before and while they are in common everyday usage? The longer we wait, the greater the implications will be, not only for wildlife populations but human as well.

OTHER RESOURCES ON THIS TOPIC: Aziz, L. 1998. "The Endpoint", in Equinox April/May pp 48-57 Colborn, Theo, Dianne Dumanoski and John Peterson Myers. 1996.   "Our Stolen Future" (A Dutton Book) Carlsen, E., A. Giwercman, N. Keiding, and N. Shakkebaek. 1992. "Evidence of Decreasing Quality of Semen During Past 50 years." British Medical Journal 305:609-13 Carson, R. 1962. Silent Spring. Environmental Health Perspectives, vol.106 No.1, Jan. 98 Jacobson, J., S. Jacobson, P. Schwartz, G Fein, and J Dowler. 1984. "Prenatal Exposure to Environmental Toxin: A Test of the Multiple Effects Model," Developmental Psychology 20 (4): 523-32 Mausberg, B. and P. Muldoon. 1997. "A Taste of Canada" Canadian Environmental Law Association, April The Environmental Working Group. n.d. The Pesticide Data Program. US. Dept. of Agriculture US Natural Resources Defense Council. 1989. "Intolerable Risk: Pesticides in our Children’s Food" http://www.ecologic-ipm.com ("Worst First: High Risk Insecticides, Children’s Foods and Safer Alternatives") http://www.monitor.net/rachel/   (Rachel’s Environment and Health Weekly) http://www.pmac.net (PANUPS: Pesticide Action Network North America Updates Service) http://www.wwfcanada.org (Endocrine Disruption Information)