Endocrine Disrupting Chemicals
Endocrine disruptors are chemicals that interfere with the endocrine (or hormone system) in animals, including humans. These disruptions can cause cancerous tumors, birth defects, and other developmental disorders. Specifically, they are known to cause learning disabilities , severe attention deficit disorder , cognitive and brain development problems, deformations of the body (including limbs); sexual development problems, feminizing of males or masculine effects on females, etc. Any system in the body controlled by hormones, can be derailed by hormone disruptors. The critical period of development for most organisms is between the transition from a fertilized egg, into a fully formed infant. As the cells begin to grow and differentiate, there are critical balances of hormones and protein changes that must occur. Therefore, a dose of disrupting chemicals can do substantial damage to a developing fetus (baby). The same dose may not significantly affect adult mothers—for a more scientific explanation, see below.
Endocrine disruptors are substances that "interfere with the synthesis, secretion, transport, binding, action, or elimination of natural hormones in the body that are responsible for development, behavior, fertility, and maintenance of homeostasis (normal cell metabolism)." They are sometimes also referred to as hormonally active agents, endocrine disrupting chemicals , or endocrine disrupting compounds (EDCs).
EDC studies have shown that endocrine disruptors can cause adverse biological effects in animals, and low-level exposures also cause similar effects in human beings. The term endocrine disruptor is often used as synonym for xenohormone although the latter can mean any naturally occurring or artificially produced compound showing hormone-like properties (usually binding to certain hormonal receptors).
Endocrine systems are found in most varieties of animals . The endocrine system consists of glands that secrete hormones , and receptors that detect and react to the hormones.
Hormones travel throughout the body and act as chemical messengers. Hormones interface with cells that contain matching receptors in or on their surfaces. The hormone binds with the receptor, much like a key would fit into a lock. The endocrine system regulates adjustments through slower internal processes, using hormones as messengers. The endocrine system secretes hormones in response to environmental stimuli and to orchestrate developmental and reproductive changes. The adjustments brought on by the endocrine system are biochemical, changing the cell's internal and external chemistry to bring about a long term change in the body. These systems work together to maintain the proper functioning of the body through its entire life cycle. Sex steroids such as estrogens and androgens , as well as thyroid hormones, are subject to feedback regulation, which tends to limit the sensitivity of these glands.
Dichloro-diphenyl-trichloroethane (DDT) was first used as a pesticide against Colorado potato beetles on crops beginning in 1936. An increase in the incidence of malaria , epidemic typhus , dysentery , and typhoid fever led to its use against the mosquitoes, lice, and houseflies that carried these diseases. Before World War II, pyrethrum , an extract of a flower from Japan, had been used to control these insects and the diseases they can spread. During World War II, Japan stopped exporting pyrethrum, forcing the search for an alternative. Fearing an epidemic outbreak of typhus, every British and American soldier was issued DDT, who used it to routinely dust beds, tents, and barracks all over the world.
DDT was approved for general, non-military use after the war ended. It became used worldwide to increase monoculture crop yields that were threatened by pest infestation, and to reduce the spread of malaria which had a high mortality rate in many parts of the world. Its use for agricultural purposes has since been prohibited by national legislation of most countries, while its use as a control against malaria vectors is permitted, as specifically stated by the Stockholm Convention on Persistent Organic Pollutants.
As early as 1946, the harmful effects of DDT on bird, beneficial insects, fish, and marine invertebrates were seen in the environment. The most infamous example of these effects were seen in the eggshells of large predatory birds, which did not develop to be thick enough to support the adult bird sitting on them. Further studies found DDT in high concentrations in carnivores all over the world, the result of biomagnification through the food chain. Twenty years after its widespread use, DDT was found trapped in ice samples taken from Antarctic snow, suggesting wind and water are another means of environmental transport. Recent studies show the historical record of DDT deposition on remote glaciers in the Himalayas.
More than sixty years ago when biologists began to study the effects of DDT on laboratory animals, it was discovered that DDT interfered with reproductive development. Recent studies suggest DDT may inhibit the proper development of female reproductive organs that adversely affects reproduction into maturity. Additional studies suggest that a marked decrease in fertility in adult males may be due to DDT exposure. Most recently, it has been suggested that exposure to DDT in utero can increase a child's risk of childhood obesity. DDT is still used as anti-malarial insecticide in Africa and parts of Southeast Asia in limited quantities.
Polychlorinated biphenylsMain article: Polychlorinated biphenyls
Polychlorinated biphenyls (PCBs) are a class of chlorinated compounds used as industrial coolants and lubricants. PCBs are created by heating benzene, a byproduct of gasoline refining, with chlorine. They were first manufactured commercially by the Swann Chemical Company in 1927. In 1933, the health effects of direct PCB exposure was seen in those who worked with the chemicals at the manufacturing facility in Alabama. In 1935, Monsanto acquired the company, taking over US production and licensing PCB manufacturing technology internationally.
General Electric was one of the largest US companies to incorporate PCBs into manufactured equipment. Between 1952 and 1977, the New York GE plant had dumped more than 500,000 pounds of PCB waste into the Hudson River. PCBs were first discovered in the environment far from its industrial use by scientists in Sweden studying DDT.
The effects of acute exposure to PCBs were well known within the companies who used Monsanto's PCB formulation who saw the effects on their workers who came into contact with it regularly. Direct skin contact results in a severe acne-like condition called chloracne. Exposure increases the risk of skin cancer, liver cancer, and brain cancer. Monsanto tried for years to downplay the health problems related to PCB exposure in order to continue sales.
The detrimental health effects of PCB exposure to humans became undeniable when two separate incidents of contaminated cooking oil poisoned thousands of residents in Japan (Yusho disease, 1968) and Taiwan (Yu-cheng disease, 1979), leading to a worldwide ban on PCB use in 1977. Recent studies show the endocrine interference of certain PCB congeners is toxic to the liver and thyroid, increases childhood obesity in children exposed prenatally, and may increase the risk of developing diabetes.
Bisphenol A (BPA)
Bisphenol A is commonly found in plastic bottles (including many baby bottles), plastic food containers, dental materials, and the linings of metal food and infant formula cans . Another exposure comes from receipt paper commonly used at grocery stores and restaurants, because today the paper is commonly coated with a BPA containing clay for printing purposes.
It is a known endocrine disruptor, and "hundreds of studies published in the decade" have found that laboratory animals exposed to low levels of it have elevated rates diabetes , mammary and prostate cancers , decreased sperm count, reproductive problems, early puberty , obesity , and neurological problems. Some scientists believe that humans, especially infants, are currently exposed to levels that are known to cause harm in laboratory animals. The US FDA and the chemical industry maintain that it is safe, but the US Congress has taken steps to restrict the use of bisphenol A and has asked the FDA to reexamine it. Canada recently announced it plans to phase out the use of bisphenol A in baby bottles and metal formula cans. Nalgene , Playtex , and Wal-Mart have agreed to remove this substance from their products by the end of 2008. In August of that year, the FDA issued a draft reassessment, reconfirming their initial opinion that, based on scientific evidence, it is safe. However in October 2008, FDA's advisory Science Board sent FDA back to the drawing board, concluding that the Agency's assessment was "flawed" and hadn't proven the chemical to be safe for formula-fed infants. In January 2010, the FDA issued a report indicating that, due to findings of recent studies that used novel approaches in testing for subtle effects, both the National Toxicology Program at the National Institutes of Health as well as the FDA have some level of concern regarding the possible effects of BPA on the brain and behavior of fetuses, infants and younger children.
Polybrominated diphenyl ethers
Polybrominated diphenyl ethers (PBDEs) are a class of compounds found in flame retardants used in plastic cases of televisions and computers, electronics, carpets, lighting, bedding, clothing, car components, foam cushions and other textiles. Potential health concern: PBDE's are structurally very similar to Polychlorinated biphenyls (PCBs), and have similar neurotoxic effects. Research has correlated halogenated hydrocarbons, such as PCBs, with neurotoxicity. PBDEs are similar in chemical structure to PCBs, and it has been suggested that PBDEs act by the same mechanism as PCBs.
In the 1930s and 1940s, the plastics industry developed technologies to create a variety of plastics with broad applications. Once World War II began, the US military used these new plastic materials to improve weapons, protect equipment, and to replace heavy components in aircraft and vehicles. After WWII, manufacturers saw the potential plastics could have in many industries, and plastics were incorporated into new consumer product designs. Plastics began to replace wood and metal in existing products as well, and today plastics are the most widely used manufacturing materials.
By the 1960s, all homes were wired with electricity and had numerous electrical appliances. Cotton and wood had been the dominant textile used to produce home furnishings, but now their home furnishings were composed of mostly synthetic materials. More than 500 billion cigarettes were consumed each year in the 1960s, as compared to less than 3 billion per year at the turn of the century. When combined with high density living, the potential for home fires was higher in the 1960s than it had ever been in the US. By the late 1970s, approximately 6000 people in the US died each year in home fires.
In 1972, in response to this situation, the National Commission on Fire Prevention and Control was created to study the fire problem in the US. In 1973 they published their findings in America Burning, a 192-page report that made recommendations to increase fire prevention. Most of the recommendations dealt with fire prevention education and improved building engineering, such as the installation of fire sprinklers and smoke detectors. The Commission expected that with the recommendations, a 5% reduction in fire losses could be expected each year, halving the annual losses within 14 years.
Historically, treatments with alum and borax were used to reduce the flammability of fabric and wood, as far back as Roman times. Since it is a non-absorbent material once created, flame retardant chemicals are added to plastic during the polymerization reaction when it is formed. Organic compounds based on halogens like bromine and chlorine are used as the flame retardant additive in plastics, and in fabric based textiles as well. The widespread use of brominated flame retardants may be due to the push from Great Lakes Chemical Corporation (GLCC) to profit from its huge investment in bromine. In 1992, the world market consumed approximately 150,000 tonnes of bromine-based flame retardants, and GLCC produced 30% of the world supply.
PBDEs have the potential to disrupt thyroid hormone balance and contribute to a variety of neurological and developmental deficits, including low intelligence and learning disabilities. Many of the most common PBDE's were banned in the European Union in 2006. Studies with rodents have suggested that even brief exposure to PBDEs can cause developmental and behavior problems in juveniles and exposure interferes with proper thyroid hormone regulation.
Phthalates are found in some soft toys, flooring, medical equipment, cosmetics and air fresheners. They are of potential health concern because they are known to disrupt the endocrine system of animals, and some research has implicated them in the rise of birth defects of the male reproductive system.
Although an expert panel has concluded that there is "insufficient evidence" that they can harm the reproductive system of infants, California and Europe have banned them from toys. One phthalate, Bis(2-ethylhexyl) phthalate (DEHP), used in medical tubing, catheters and blood bags, may harm sexual development in male infants. In 2002, the Food and Drug Administration released a public report which cautioned against exposing male babies to DEHP. Although there are no direct human studies the FDA report states: "Exposure to DEHP has produced a range of adverse effects in laboratory animals, but of greatest concern are effects on the development of the male reproductive system and production of normal sperm in young animals. In view of the available animal data, precautions should be taken to limit the exposure of the developing male to DEHP". Similarly, phthalates may play a causal role in disrupting masculine neurological development when exposed prenatally.
Certain alkylphenols are degradation products from nonionic detergents . Nonylphenol is considered to be a low-level endocrine disruptor owing to its tendency to mimic estrogen.
PFOA exerts hormonal effects including alteration of thyroid hormone levels. Blood serum levels of PFOA were associated with an increased time to pregnancy — or "infertility" — in a 2009 study. PFOA exposure is associated with decreased semen quality. PFOA appeared to act as an endocrine disruptor by a potential mechanism on breast maturation in young girls. A C8 Science Panel status report noted an association between exposure in girls and a later onset of puberty.
Other suspected endocrine disruptors
Some other examples of putative EDCs are polychlorinated dibenzo-dioxins (PCDDs) and -furans (PCDFs), polycyclic aromatic hydrocarbons (PAHs), phenol derivatives and a number of pesticides (most prominent being organochlorine insecticides like endosulfan and DDT and its derivatives, the herbicide atrazine , and the fungicide vinclozolin ), the contraceptive 17-alpha ethinylestradiol , as well as naturally occurring phytoestrogens such as genistein and mycoestrogens such as zearalenone .
The molting in crustaceans is an endocrine-controlled process. In the marine penaeid shrimp Litopenaeus vannamei , exposure to endosulfan resulted increased susceptibility to acute toxicity and increased mortalities in the postmolt stage of the shrimp.
Compiled by Rami E. Kremesti M.Sc.