Toxicology of endocrine disrupting chemicals

Nkemjika, Chinedu Frank
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Endocrine disrupting chemicals (EDCs) are defined by the World Health Organization’s International Program on Chemical safety as “An exogenous substances or mixture that alters the functions of the endocrine system and consequently causes an adverse effect in an intact organism or its progeny, or (sub) populations”. The clinical and public health significance of EDCs has been on the rise in recent years because increasing trends of many endocrine related human disorders have been detected. Large proportions up to 40% of young men in some countries have low semen quality and the incidences of breast, ovarian, prostrate, testicular and thyroid cancers are high in many parts of the world. The prevalence of obesity, type 2 diabetes, genetic abnormalities such as penile malformations and non descending testis have also increased. Our knowledge on the effects of these chemicals on wildlife and human health has improved immensely due to intense scientific work in this area. Therefore, the aim of this thesis to provide a summary of scientific literature concerning the various groups of EDCs, their occurrence in the environment, their health impacts as well as measures and regulations necessary for prevention of harmful exposures to these substances. Articles related to the toxicology of EDCs were collected from the PubMed database. All reviews published within the last 10 years were studied. Relevant information was also collected from the website of the World Health Organization. Hundreds of natural and synthetic chemicals are known to affect or disturb the physiology of the endocrine system. These EDCs were categorized into 11 major groups. They include the persistent organic pollutants (POPs), other persistent and bioaccumulative chemicals, plasticizers, polycyclic aromatic hydrocarbons (PAHs), halogenated and non-halogenated phenolic compounds, current use pesticides, pharmaceutical agents, growth promoters and personal care products, metals and organometallic chemicals, natural hormones and phytoestrogens. Sources of exposure include point sources from industries and homes, and diffuse sources from agricultural farm lands and vehicles. Humans or wildlife can be exposed to EDCs through major pathways such as air, water, food and soil. 4 The behavior and degradation of EDCs depend on their physicochemical properties which can affect their routes of exposure both to humans and wildlife. Factors that can enhance the decay of these chemicals include increased temperature, sunlight, and aerobic conditions therefore their breakdown is increased in warmer regions of the Earth. EDCs can be taken up by organisms via inhalation, oral intake and dermal contact. Following absorption they undergo metabolism and can be excreted from the body through urine, faces or breast milk depending on their chemical properties. The site of accumulation also depends on their physicochemical properties; lipophilic EDCs tend to accumulate in adipose tissues. Some EDCs can be metabolized into more toxic products than their parent molecules. A variety of animal species in the wildlife have been shown to be adversely affected by exposure to EDCs. They include mammals, birds, fishes and invertebrates. EDCs tend to cause abnormal behaviors, a decline in reproduction and thereby decrease in the population number of some species. Exposure to EDCs can adversely affect the growth and development, immune system, nervous system, urogenital system, thyroid functions and can be associated with development of breast, endometrial, ovarian, prostrate and thyroid cancers. To prevent and regulate exposure to EDCs more intense research is required. It is also necessary to identify more EDCs, strengthen the knowledge by creating a network in which information and resources about EDCs can be shared globally, decrease presently known exposures to the minimum level and also direct involvement or contribution of researches and the intellectuals in this field in policy making about this chemicals. In conclusion, although a lot of insight about these chemicals, the knowledge present is still the tip of the ice berg, further studies and researches are needed to investigate and identify other possible EDCs, their windows of exposure and how there effects may be passed on to generations.
toxicology, endocrine