Environmental hormones

Daily use of chemicals is an essential habit of modern society. Large scale production and repeated use of synthetic chemicals introduce many toxic and persistent chemical residues into the environment. As a result, humans and wildlife are constantly exposed to the chemical residues through air, food and water. Some of these chemicals in the environment interfere with, block or mimic the effects of natural hormones. Such environmental contaminants which modulate the activities of natural hormones are called environmental hormones, endocrine disrupting chemicals (EDCs), or environmental estrogens (EE) or xenoestrogens. It has been scientifically shown that environmental hormones may elicit a variety of adverse health effects in both humans and wildlife including promotion of hormone- dependent cancers, reproductive organ disorders and reduction in reproductive fitness.

Kinds of hormone mimicking chemicals

The term ‘environmental estrogen’ is currently used to denote both plant – derived estrogens (phytoestrogens) and the anthropogenic (synthetic) estrogens (xenoestrogens). The naturally occurring estrogens in either humans or animals are called endogenous estrogens and all compounds with estrogenic properties entering the body from an outside source as exogenous estrogens.

Phyto-xenoestrogens

Phytoestrogens (phyto meaning plant) are naturally occurring estrogenic compounds that are found in a variety of plant foods such as beans, seeds and grains. These compounds are generally weak estrogens when compared to xenoestrogens. Many phytoestrogens belong to the large group of plant phenolics. Caffeic acid is one of the most common plant phenolics found in chicory coffee, artichoke, olive oil and red wine. The other major phytoestrogens consumed in excess quantities by humans are  isoflavonoids and lignans. Strong phytoestrogens are present in soy, red clover, caffeine and Chester berry.

Synthetic xenoestrogens

The word xenoestrogens is derived from the Greek words xeno, meaning foreign, estrus, meaning sexual desire and gene, meaning to generate and literally means ‘foreign estrogen’. The synthetic xenoestrogens include both chlorinated and non-chlorinated compounds. The synthetic xenoestrogens are found in plastics (BPA), pasticizers (phthalates), industrial chemicals (polychlorinated biphenyls,PCBs; dioxins), pesticides(DDT, methoxychlor),fungicides(vinclozolin), pharmaceuticals(diethylstilbestrol) and heavy metals(arsenic, lead, chromium, cadmium).

Mode of action

Environmental estrogens have been shown to directly bind to the estrogen receptor(ER) and function as either agonists or antagonists. The estrogen agonists are compounds that mimic the effects of natural estrogen. But estrogen antagonists block the action of estrogens by interfering with the normal functions of the estrogen receptor. In general environmental estrogens have the ability to mimic/ antagonize the effects of natural hormones. They also modify hormone receptor levels and the pattern of synthesis and metabolism of natural hormones.

Sources of synthetic xenoestrogens

Plastic additives- phthalates and bisphenol A(BPA) are plastic additives. Phthalates are used extensively in industry, plastic packaging, inks, paints, and vinyl products. Bisphenol A is used in the production of epoxy resins and polycarbonate plastics. They are lipophilic and accumulate in the fat. They cause human breast cancers.

Brominated flame retardants(BFRs) – are a group of industrial chemicals mainly used in electric devices, textiles and cars. They are highly lipophilic and bioaccumulate in adipose tissues. They have been reported to disrupt thyroid, androgen and estrogen signalling.

Perfluorinated chemicals(PFCs) – are used to make non-stick cookware. They are completely resistant to biodegradation. PFOA decreases sperm quality and causes kidney disease or thyroid disease.

Organotins,TBT (tributlytin) is an active ingredient in antifouling paints. Exposure to TBT causes obesity and metabolic disorders.

Dioxins – are the most deadly organochlorine chemicals found in pesticides, plastics, solvents, detergents, and cosmetics.  More than 90% of human exposure is through food, mainly meat and dairy products, fish and shellfish. They are highly toxic and bio- accumulate through food chain.

Human health effects

Synthetic xenoestrogens may act as false messengers and disrupt the process of reproduction.  Xenoestrogens induce precocious puberty in girls with premature secondary sexual characters.

They may be associated with the development of learning disorders, severe attention deficit disorders and developmental defects.

TBT may act as androgens and fungicide vinclozolin act as anti-androgens.

In males, exposure to xenoestrogens decreases sperm quality and counts, incidence of testicular cancers and crytorchidism (undescended testis). In females exposure causes endometriosis and endometrial cancer.

Exposure to dioxins can cause reproductive and developmental problems, damage the immune system, interfere with hormones and also cause cancers.