There is a wide and growing concern about environmental toxins and human health. These chemicals, the product of pesticides, plastics, fire-retardants, and industrial waste, are found in our sofas, our soil, our food. Their ability to persist in the environment and accumulate in our bodies over time is the reason why they pose such a serious health risk. This cumulative effect of environmental toxins, particularly on the health of developing fetuses and young children, has made them a public health issue.
Toxic chemicals are rarely found in amounts that can be seen or tasted. They are more often airborne molecules that exert a subtle, disrupting influence, usually at a hormonal level, that can have serious consequences. Leukemia, brain tumors, neurodevelopmental and behavioral problems, birth defects, low birth weight and other acute and chronic problems are among the possible short- and long-term consequences of childhood exposure to pesticides detailed in a recent report by the American Academy of Pediatrics.
Toxic chemicals are rarely found in amounts that can be seen or tasted.
Dioxins, a group of chemically-related compounds that are persistent environmental pollutants, have been reported to be linked to genital abnormalities in male newborns whose mothers were exposed to them. Other studies document poorer attention, a lack of fine motor coordination, and problem solving/thinking skills in children exposed to polybrominated diphenyl ether (PDBE) during fetal development and early childhood.
What is going on and what do we know about the threat to our and our children’s health?
The compounds of concern are part of a group of chemicals called endocrine disrupting compounds (EDCs). They include natural and synthetic hormones, plant constituents, pesticides, compounds used in the plastic industry, and other industrial by-products and pollutants.
The list of substances which have been in the news for their proven or possible association with health problems includes PCBs, BPA, DDT, dioxin, phthalates and phytoestrogens.
EDCs enter the environment through numerous routes including hazardous waste sites, burning of industrial waste and improper dumping of industrial pollutants, exposure through use of food and beverage containers containing the chemicals, children’s toys, plastic pipes, lining of medical or even soup cans, medical supplies, and certain polymers used in dental treatment to name a few of the best studied exposure sites.
Endocrine disruptors have been found in virtually all regions of the world, even minimally populated and non-industrialized areas.
Some EDCs are transported long distances in the water and air supply. Some are rapidly degraded in the environment, while others persist for years. In fact, certain EDCs are stored in body fat and have been found in women’s breast milk and transmitted to their breastfeeding infants. Children are uniquely vulnerable to environmental toxins in the soil since they play outdoors, crawl on the ground, and put their fingers and toys in their mouths. Endocrine disruptors have been found in virtually all regions of the world, even minimally populated and non-industrialized areas.
An endocrine disruptor is a chemical or compound that changes the way the endocrine system functions and causes negative health consequences to a living being or its offspring. They interfere with the formation, secretion, transport, action or elimination of natural hormones in the body. Hormones are responsible for how we grow and mature and age; they affect our behavior, fertility and cell metabolism.
Exposures to EDCs cause different effects depending on when they occur. Developing fetuses and young children may be most vulnerable because they are at periods of rapid organ development, differentiation and growth but EDCs have been suspected of causing health problems in all age groups.
It has been difficult for researchers to prove that EDCs cause certain problems because the timing of exposure and the onset of the abnormality may be years apart… a newborn may ingest a toxin from breast milk but not exhibit a negative effect until much later in life.
The endocrine system is responsible for the regulation of all body systems including the nervous system, reproductive system, and metabolic system. It is made up of glands — including the ovaries, testes, thyroid, pituitary and adrenals — that produce a variety of hormones that are released into the blood stream and travel to body tissues. In addition to the sex hormones estrogen and testosterone, there are thyroid hormone, growth hormone, insulin, the stress hormone cortisol and many others. Different hormones make reproduction possible, stimulate growth, build bone, make us hungry, move sugar into cells to provide energy and promote feelings of attachment. New hormones are still being discovered; at present, over 50 hormones have been identified.
There are two major classes of hormones. One class is made up of proteins, peptides, and modified amino acids; steroids form the second class. Each type of hormone is a chemical messenger, produced in one part of the body and acting somewhere else. In order to be appropriately effective, hormones must attach to specific receptors.
In general, hormone molecules bind to receptors on the surface of "target" cells, cells able to respond to the presence of the hormone. This binding of the hormone to its receptor triggers intracellular signals that may alter the behavior of the cell (such as by opening or closing membrane channels) or affect gene expression in the nucleus by turning on (or off) the promoters and enhancers of the genes.
Endocrine disruptors may act in a variety of ways. They may interfere with the production of hormones, prevent their attachment to the receptor sites, or block the transport, metabolism and activation of hormones. When the normal function of the endocrine system is disrupted or malfunctions, significant abnormalities in growth and development result which may appear across the life span.
A newborn may ingest a toxin from breast milk but not exhibit a negative effect until much later in life.
The terrible health and environmental effects of endocrine disruptors were first publicized in 1962, when Rachel Carson published her book, Silent Spring, calling attention to the negative effect of pesticides, particularly DDT, on the environment. DDT is known to cause thinning of the eggs shells and decreased reproductive capacity in birds of prey and contributed to the severe decline in their population.
Since that time, numerous examples of the influence of endocrine disruptors on wildlife have been catalogued. These have included changes in immunity, behavior, skeletal structure and reproductive capacity in a variety of wildlife. Organochlorines have been shown to cause decreases in the reproductive and immune functions of Baltic seals. A pesticide spill in Florida resulted in developmental and gonadal abnormalities in reptiles exposed to the spill. The liquid run off from paper and pulp mills and from sewage treatment plants has been shown to damage exposed fish.
The damage done to wildlife strongly suggests that humans, too, are vulnerable to the negative health effects of endocrine disrupting compounds. But while exposure to EDCs has been associated with developmental, behavioral, immunological and reproductive problems in humans, there have been few direct cause and effect studies. As mentioned earlier, suspected problems include declining sperm counts, an increase in congenital malformations, a rising rate of hormone-related cancers of men and women, changes in the timing of the start of puberty and neurodevelopmental abnormalities.
There are a number of reasons why it has been difficult to come up with the kind of evidence that would enable researchers to prove that EDCs cause certain problems. One reason is that the timing of exposure and the onset of the abnormality may be years apart. There may be a lasting effect from an EDC exposure during a critical period of development even though the toxin in question is no longer measurable in the body at the time of diagnosis. For example, a newborn may ingest a toxin from breast milk but not exhibit a negative effect until much later in life.
EDC exposure also can be transmitted across generations, passed down from mother to child such that exposure only impacts the offspring. For example, when pregnant women were given DES (diethylstilbestrol) to prevent miscarriage, their female offspring were at increased risk of developing vaginal cancer years later when they reached puberty.
There are truly no safe doses for chemicals that act like hormones because the endocrine system is designed to act at very low levels.
The risk from EDCs on humans is also influenced by genetic predisposition, age, gender, diet, existing disease conditions and past exposures to similar or different toxins which may have a cumulative effect. An additional research challenge is the fact that studies have often measured pollutant levels for air and water quality but haven’t recorded how much actually is present in the human body by measuring blood and tissue levels of chemical contaminants.
There has been ongoing debate about what amounts of EDCs are necessary to cause problems in humans. When laboratory studies are done by exposing lab animals to EDCs and monitoring the outcome on specific systems, the dose is typically much higher than the expected human dose would be. Thus some scientists reason that it would be very uncommon for humans to be exposed to sufficiently high levels of EDCs to experience the negative effects seen in laboratory animals.
However, recently researchers have been focusing on the risks of very small levels of EDCs. They reason that naturally-occurring hormones in the human endocrine system work at very small doses and it would therefore take only a tiny dose of an endocrine disruptor to unbalance the finely tuned system.
A recent review of over 100 studies on the subject concluded that "low doses cannot be ignored and lead to wide ranging health effects from fetuses to aging adults including links to infertility, cardiovascular disease, obesity, cancer and other disorders....There are truly no safe doses for chemicals that act like hormones because the endocrine system is designed to act at very low levels."
The National Resources Defense Council suggests the following measures to decrease individual exposure:
- Buy organic food when possible
- Avoid using pesticides in home, yard or on pets
- Campaign for non-toxic alternatives to pesticides in children’s schools and day care
- Avoid fatty foods such as cheese and meat when possible
- Check for contamination of risk from lakes, rivers and bays
- Avoid heating food in plastic containers or storing fatty foods in plastic containers or plastic wrap
- Do not give young children soft plastic teethers or toys
- Support strong government regulation of increased research on EDCs
There is strong evidence for the dangerous role of endocrine distuptors in the health of wildlife. There is increasingly compelling data that similar processes are at work in humans causing changes in reproductive health, increases in some cancers, increases in chronic diseases such as diabetes, and neurodevelopmental problems. All these pose health challenges which may begin in childhood and persist into adulthood. There is a growing consensus that EDCs and their impact need to be thoroughly explored by increased research. Government intervention and regulation of suspected and proven EDCs may be necessary on a national and international level to decrease exposure. Public education and individual vigilance will be required if we are to reduce the threat of EDCs to our health.
