Endocrine Disrupting Chemicals: Impacts on Human Health and Environmental Concerns, Study notes of Environmental Engineering

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Endocrin Distrupting Chemicals

and Toxic Effects II

Chemicals that affect any aspect of hormonal function are referred to as endocrine disruptors (EDs)

Exposure during critical periods of development, such as fetal and early postnatal life, may have particularly critical consequences with implications in research, patient care, prevention and public health

Fetal growth restriction, premature birth, reproductive disorders, alterations of pubertal timing, thyroid and immune dysfunction, certain cancers, especially of the reproductive organs, birth defects of the genitalia and poorer sperm quality, cryptorchidism, neurological effects, neuropsychiatric disorders, diabetes, obesity and other metabolic disorders have been associated with the exposure to EDs

EDs are divided into major classes of chemicals including

• various types of pesticides,
• industrial chemicals,
• plastic packaging components,
• fuels and other materials that are used in daily life

Inhalation, oral and dermal exposures are the main routes of adult exposure to environmental chemicals

EDs may act via classical nuclear receptors, nonnuclear steroid hormone receptors, nonsteroid receptors, orphan receptors, enzymatic pathways involved in steroid biosynthesis and/or metabolism and other mechanisms involved in endocrine and reproductive system function.

Effects may be not dose dependent, and even exposure to low doses of chemicals may induce disrupting effects.

Different animal species react differently to the same compound, making it impossible to reliably infer effects from the observation of what occurs in wildlife to human beings.

Age groups and sexes react differently.

• EDCs are also transferred to a developing fetus, or infant by transplacental route and breast milk.

• EDCs mimic or antagonize the effects of endogenous hormones, disrupt the synthesis of endogenous hormones or their receptors, or may alter target cell sensitivity.
• The mechanisms by which EDCs affect developmental events are identified to be numerous and include changes in the neuroendocrine system, epigenetic mechanisms and/or direct effects on gene expression

• Recent decades have witnessed an unusual spurt in the incidence of genital malformations, infertility due to low semen quality, adverse pregnancy outcomes, neurobehavioral disorders associated with thyroid disruption, endocrine-related cancers (breast, endometrial, ovarian, prostate, testicular, thyroid), premature thelarche, obesity and Type II diabetes mellitus
• Congenital disorders such as cryptorchidism, hypospadias, early puberty and thyroid dysfunction have also been shown to have clear endocrine association.

• Common examples of exposure to EDCs include Bisphenol A used in the manufacture of polycarbonate plastics and epoxy resins which have been found to be causative for obesity and polycystic ovarian syndrome
• Phthalates used in nail polish, hair spray, deodorants and shampoos have been found to be associated with impaired genital development in male children

• Chemicals such as persistent organic pollutants (POPs), methylmercury which enter the bodies of younger children persist for a longer time due to their long half- lives and present their harmful effects later in life or cause multigenerational effects.
• The Stockholm Convention (2011) ratified by the international community recommended the elimination or phasing out of POPs. Some EDCs like dichloro-diphenyltrichloroethane banned years ago in some countries, still persist in the environment and human bodies and manifest in older age groups

• EDCs often produce their impacts with relatively low doses
• Most EDCs do not have traditional dose response curves.
• The timing of exposure decides the magnitude of impact. Effects such as learning difficulties, increased susceptibility and sensitivity to infections, testicular dysgenesis syndrome, infertility, fibroids, premature menopause, obesity, atherosclerosis, cardiovascular disease, Alzheimer’s disease, Parkinson’s disease, breast and prostate cancers manifest after a variable latent period depending on the time and the specific tissue exposed.
• Multi-chemical exposures are frequent and often have additive or synergistic potential