So far, at least, 45 chemicals have been identified as endocrine disruptors. Many of them are long-term organic compounds that remain in the environment for decades and accumulate in human tissues. This list includes certain herbicides, fungicides and insecticides (such as atrazine and chlordane); industrial chemicals and other waste products, such as polychlorinated biphenyls (PCB) and dioxin; and a number of compounds found in plastics such as phthalates and styrenes, used in food and beverage containers.
The publication Our Stolen Future, March 1996 brought to light a debate that had been simmering in the scientific literature for several years. In this book (widespread) the zoologist Theo Colborn, the World Wide Fund for Nature (WWF), along with two other co-authors raised the hypothesis that some very common industrial chemicals in the environment may be causing havoc on the human health by altering the hormonal system of the body. Specifically, the authors argue that these substances dubbed “endocrine disruptors” because they interact with the endocrine hormone system may be playing a significant role in a range of issues ranging from reproductive and developmental abnormalities to cancer, through defects immunological and neurological. The evidence suggests that, in large exhibitions, some of these substances, including DDT, PCBs, and some pesticides can cause reproductive problems and developmental nature in wildlife. The question is whether such substances can exert similar effects in humans when subjected to low doses in which, typically, are in the environment.
The lack of definitive evidence on these adverse effects in humans (although there is abundant evidence about the effect of these substances in animals) has not quieted the debate. Colborn and others believe that the weight of evidence in both animals and humans are enough to warn about the danger of these products for fertility, intelligence and, ultimately, for the most basic survival. Others, like Stephen Safe of Texas A & M University, believe that these concerns are overstated, appealing for it to rely on conflicting findings at least or not sufficiently used. Although many of these chemicals have been banned in developed countries by their duly proven adverse effects, dispersal, and persistence in the environment makes them potential threats to long-term.
So far, at least, 45 chemicals have been identified as endocrine disruptors. Many of them are long-term organic compounds that remain in the environment for decades and accumulate in human tissues. This list includes certain herbicides, fungicides and insecticides (such as atrazine and chlordane); industrial chemicals and other waste products, such as polychlorinated biphenyls (PCB) and dioxin; and a number of compounds found in plastics such as phthalates and styrenes, used in food and beverage containers.
The endocrine system
It is believed that the problems attributed to endocrine disruption arising mainly from the ability of these compounds to mimic or interfere with the normal functioning of sex hormones such as estrogen, testosterone, and progesterone, or thyroid hormones integral to the development of the brain and other organs and tissues. Comprehensive sex hormones play a crucial role in the government of a normal development. Estrogen, for example, not only helps orchestrate the sexual development of the human embryo and fetus but is also required for normal development of the brain, bones, muscles, immune system and other organs and tissues. Prenatal exposures or throughout life to sex hormones might influence the risk of developing various cancers.
These hormones travel through the blood and perform their function by binding to molecules known as hormone receptor cells. This, in turn, activates genes in the cell nucleus in order to produce a range of biological responses. Under normal conditions, the body carefully controls a number of active hormones to ensure proper operation of the system. For example, the body produces specific proteins that can attach to hormones and regulate access to the cells. The body is also protected from excessive production of hormones slowing or damping the sensitivity of the cell to them. Endocrine disrupters can work at the same time as imitators of hormones or block thereof; in both cases with the enormous potential to alter normal cellular activity. Scientists are still far from knowing what levels of exposure these effects can be seen.
The key wildlife
The first signs of the effects of endocrine disruptors on reproduction were detected as a result of alarming discoveries in wildlife. During the seventies and eighties, PCBs, DDT, dioxin and other substances associated with certain abnormalities of the reproductive tract, such as reducing the size of the penis and decreased fertility in alligators in Florida, abnormal behavior mating, and abnormalities in the reproductive organs seagulls the western United States.
These findings led the researchers investigated the possible role of these products and their impact on human health. The results have been contradictory and, therefore, controversial. It is difficult to ignore these issues in science, because many of these substances, such as DDT, have already shown their negative effects on animals and humans, whether endocrine disrupters or not. In other words, the adverse health effects could be separated from the added effect of hormones. To complicate matters further, many recent epidemiological studies have been preliminary or “organic” nature. This means that a study may determine an increase in cancer, for example, coincides with an increased use of a chemical suspected but cannot be evidence that people exposed to the chemical develop cancer. As one of the researchers, data may show that the stork population has declined and that the number of births has declined, but that does not lead us to conclude that they are the storks bring babies.
The effects on human health
Some of the strongest evidence on reproductive effects of endocrine disruptors on humans come from long-term studies conducted on the potent synthetic estrogen not diethylstilbestrol steroidal (DES by its initials in English), delivered to thousands of women the fifties and sixties to prevent abortions. Studies of the evolution of the sons and daughters exposed to DES since the seventies have detected a significant enough number of abnormalities in the structure and function of their reproductive organs. Some studies have been documented that many of the men exposed to prenatal DES have the smallest penis, testicles also smaller and without having fallen enough, and semen is a very poor quality. In contrast, other studies contradict the above. As if that were not enough, since men have been exposed in the womb to estrogenic substances in larger quantities than is usually one finds in the normal environment, these findings are not easily extrapolated to the general population.
However, some researchers have suggested that endocrine disruptors may be associated with decreased sperm count of the population as a whole. This hypothesis emerged when Danish, French, Belgian and British noted a decline of 50 percent in sperm volume over a period of between 20 and 60 years, i.e. more or less the same time in which he extended and popularized the use of these disruptors. Other studies conducted in the United States, France, and Finland, however, have not detected this problem; in some cases even an increase was found in the amount of sperm. All reveals a great uncertainty whether has had an effect, first, a decrease in sperm count somewhere in the world; and, secondly, in the event that it has been so, to what extent this decline can be attributed to the influence of endocrine disruptors.
Similar doubts about exposure to these substances can be transferred to the male-female ratio at birth. Studies in animals indicate that exposure to certain pesticides may affect male-female gulls, alligators, and turtles, with the result of a sharp decline in the proportion of the birth of males index. In humans, studies have believed see a slight decline in the number of male births in the Netherlands between 1950 and 1994, and in Denmark between 1951 and 1995. Many other factors can influence the number of births to women, among which consider the age of the parents the time and cycles that pregnancy occurs, or hormonally induced ovulations in the eighties.
The fear that endocrine disruptors can cause cancer has arisen partly because of the evident role that DES has played in cancers of the female reproductive system. In addition, epidemiological studies have shown that a considerable exposure throughout life to estrogen in the body (from, say, early menstruation or late menopause) increases a woman’s risk of breast cancer (21). Could exposure to endocrine disruptors encourage the development of that type of cancer? (See – “invited signature” – Devra Davis). Trends, according to the data, suggest that breast cancers, testicular and prostate cancers are on the rise in some parts of the world.
A part of the increase in breast and prostate cancer seems to have to do with the progress experienced in detection techniques, with early diagnosis, and the longevity of the general population. Some researchers have suggested that the occupational and environmental exposure to endocrine disruptors could also be behind the increase. Thus, some studies have shown that farmers exposed to certain pesticides and herbicides have an additional risk of developing prostate and testicular cancer. Other studies, however, have not been able to determine that relationship, even having analyzed different chemicals.
Another serious potential effects resulting from exposure to endocrine disruptors is the neurological impairment. Much of the concern stems from the study conducted in the Great Lakes region in the United States, which showed that children exposed prenatally to PCBs suffered small but significant alterations intellectual type. Children who had experienced a very intense exposure were three times more likely to have lowered IQ scores were lower and twice more likely to go with two years behind in reading comprehension. These children also would suffer from problems related to attention span and memory. In addition, most worrisome: the levels of exposure to PCBs by those children were only slightly higher than those of the general population.
As for the possible mechanisms, laboratory analysis indicated that prenatal exposure or through breast, milk to PCBs may lower rates of thyroid hormones in the blood, needed to stimulate the growth and maturation of brain cells. However, the mechanism is not yet determined, and it is possible that PCBs are harming the intelligence through a mechanism not necessarily related to endocrine disruption.
Natural hormones also have to do with the prenatal development of the immune system and committed both children and adults, raising fears that endocrine disruptors may affect somehow the immune system and thus, provide an added risk for possible infections.
The role of endocrine disruptors in causing these and other effects are being investigated worldwide. At the moment, the general consensus among experts is that further studies are needed to determine if synthetic chemicals, which have helped the development of agriculture and industry, are also acting on the health of individuals or population as a whole. At the international level, both the World Health Organization and the Organization for Economic Cooperation and Development (OECD) and are conducting an international inventory of the status of investigations. National governments and other international organizations and even private companies are funding and / or research in order to overcome the gaps in the knowledge of these subjects. Meanwhile, countries strive to see how to regulate the use of these substances as scientific knowledge advances in this field.
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