Persistent Organic Compounds and Health

Persistent Organic Compounds and Health.


Persistent organic compounds (POPs), also known as POPs (Persistent Organic Pollutants) are a set of chemical compounds that resist photochemical (solar), chemical and biological degradation to varying degrees, causing their half-life to be high in the environment (persistent organic pollutant), may remain for several decades and even centuries in the environment.
They are harmful as they contaminate food especially dairy products and meat. They pass to the foetus through the placenta and are excreted in breast milk, threatening the reproductive health of both men and women and the health of future generations.
Although there are naturally occurring POPs, most of them are xenobiotic (a chemical structure that does not exist in nature). Pesticides (insecticides, fungicides, nematicides, herbicides), polychlorinated biphenyls (PCBs), dioxins and furans are part of persistent organic compounds (POPs).
Due to their physicochemical characteristics, POPs have been identified in all environmental compartments such as: water, rain, snow, air, sediments and soils, in all areas of the world including those that are very remote from the site of their environmental release.
People are not exempt from this as they have been found in the tissues of people living in places where there are no and there have been no sources of these substances. The global concern about these pollutants is due to their persistence and environmental mobility, their concentrations in the environment that will not diminish in the short term, even if the activities and use of these cease. Recently (December 2018) France has banned the use of 5 nicotinoid pesticides to protect the bee population.
-Environmental sources:
Their sources can be fixed or diffuse:
Industrial processes, including the generation and final disposal of waste and the production and use of energy. The use of pesticides that contain them, in agricultural, industrial, forestry and public health applications. Combustion, including accidental fires and the incineration of municipal and domestic or hospital waste.
-Natural sources:
Volcanic eruptions
Forest fires
Once POPs have entered the environment, they cannot be recovered, so proper management of them must be based on avoiding their generation and/or release, and replacing them with less dangerous compounds, since even the use of POPs in closed systems can represent a serious risk in the case of accidents such as leaks, spills or fires.
In general terms, the most important absorption of POPs for the majority of the population occurs orally and is facilitated in the presence of foods rich in fat (also by dermatological contact). Because of their lipophilicity, the main deposition site of POPs are fat-rich tissues and, of these, in addition to adipose tissue, the liver, nervous system, bone marrow and gonads. The excretion of POPs is difficult, which contributes to their accumulation.
Because POPs are lipophilic, bioaccumulation in organisms of the trophic chain is their main route of affection in the environment, and may cause immunodeficiency in fauna. Therefore, when their concentration increases, they become toxic. Although the acute effects of these pollutants are well documented, the effects derived from chronic exposure to low levels are of greater interest.
Immunotoxicity is the ability of a substance to adversely affect the immune system and the immune response of affected individuals, may induce immunodeficiency and may cause vitamin and thyroid deficiencies and a high susceptibility to microbial infections and reproductive disorders, along with hormonal disorders.
Effects on human health:
A number of adverse effects on different human organs, devices and systems have been associated with acute or chronic exposure to POPs. These effects have been demonstrated through clinical and epidemiological studies in humans.
Within the effects of POPs in humans are found:
Immune diminution.
Neurological dysfunctions.
Reproductive dysfunctions.
Hormonal alterations.
Developmental alterations.
Neurobehavioral disorder.
Cancer among others.

Alternatives to the use of chemical pesticides:
All the pollution problems associated with chemical pesticides have aroused great interest in seeking alternatives to their use. The investigations are oriented in different fields, among which we can mention:
Use of biological controls: through the use of natural predators or parasites.
Development of varieties of plants more resistant to insects and diseases.
Use of attractants (sexual, light, sound).
Genetic control through sterility, e.g. insects.
Hormonal manipulation to avoid development to adult stage of insects.
Bioenvironmental control through the use of agricultural practices that negatively affect pests (delay of sowing, elimination of remains after harvest…).
Organochlorine insecticides
Most of these pesticides are organochlorine active ingredients, many of which have remarkable properties:
– Stability to decomposition or degradation in the environment.
– Low solubility in water
-High solubility in hydrocarbon media, such as fat.
-Relatively high toxicity to insects, but relatively low for humans.
Polychlorinated biphenyls (PCBs)
Molecular structure of PCBs.
Polychlorinated biphenyls (PCBs) are a mixture of up to 209 chemicals that refer to a group of individual organochlorine chemicals made up of two aromatic molecules linked by a Carbon-Carbon bond. Their fundamental characteristic is that their hydrogens are replaced by up to ten chlorine atoms. Each PCB differs in the amount and location of the chlorine atoms. There are no known natural sources of PCBs.
The Stockholm Convention on POPs:
In May 2001, in Stockholm, Sweden, 127 countries adopted a United Nations treaty to prohibit or minimize the use of twelve of the world’s most widely used toxic substances, considered to cause cancer and birth defects in humans and animals. The object substances polychlorinated and hexachlorobenzene) and two by-products of various combustion processes (dioxins and furans).
The objective of the Stockholm Convention is to eliminate or restrict the production and use of internationally manufactured persistent organic pollutants. In addition, it seeks to minimize the generation of unintentionally produced contaminants, such as dioxins and furans.
The Stockholm Convention was established to promote public participation and the dissemination of information and to carry out research, development and monitoring activities. Among the main activities committed by Mexico within the Stockholm Convention are:
Measures to reduce or eliminate releases from intentional production and use: Prohibition and/or adoption of the legal and administrative measures necessary to eliminate the production and use, as well as imports and exports, of the most dangerous persistent pollutants, among which are the following:.
The dirty dozen:
-Aldrin: is an insecticide used in soils to kill termites, grasshoppers, among others. Humans are exposed to aldrin primarily through everyday products and animal meat.
-Clordane: insecticide used to control termites in a wide range of agricultural crops, has been postulated to affect the immune system.
Dieldrin: pesticide used to control termites, insect-borne diseases that live on agricultural soils, and textile pests. In soil and insects, aldrin can oxidize, resulting in rapid conversion to dieldrin. The half-life of the dieldrin is approximately five years. Dieldrin has been linked to Parkinson’s disease, breast cancer, and is classified as an immunotoxic and neurotoxic capable of disrupting the endocrine system.
Endrin: insecticide that is sprayed on the leaves of crops, and is used for the control of some rodents, in soils, endrin has a long half-life greater than 12 years. In humans it can act as a neurotoxin and exposure occurs mainly through food.
Heptachlor: is a pesticide used primarily to kill soil insects and termites, along with cotton insects, grasshoppers, other crop pests, and the malaria-carrying mosquito. It is classified as a possible carcinogen.
-Hexachlorobenzene (HCB): is an industrial chemical first introduced in 1945-1959 to treat seeds because it could kill fungi in food crops. Consumption of HCB-treated seed grains is associated with skin lesions, colic, weakness, and a metabolic disorder called Porphyria Turcica, which can be lethal.
-Mirex: insecticide used to fight ants and termites or as a flame retardant in plastics, rubber and electrical appliances. Mirex is one of the most stable and persistent pesticides, with a half-life of more than ten years, with a carcinogenic capacity suggested in humans.
-Toxaphene: insecticide used in cotton, cereal, grains, fruits, nuts and vegetables, as well as for the control of ticks and mites in livestock. Human exposure results primarily through food. It is classified as a possible carcinogen.
-Polychlorinated biphenyls (PCBs): industrial and technical chemicals used as heat exchange fluids, in electrical transformers and capacitors, and as additives in paints, carbonless copying paper and plastics.
Dichlorodiphenyltrichloroethane (DDT): very persistent and bioaccumulable and has a half-life of more than 10 years.
Dioxins: are accidental by-products of processes carried out at high temperatures, such as incomplete combustion or the production of pesticides. Dioxins are normally emitted by the burning of hospital waste, municipal waste and hazardous waste, along with emissions from cars, peat, coal and wood.
Furans: are by-products of high-temperature processes, such as incomplete combustion after waste incineration or in automobiles, the production of pesticides, and the production of PCBs.
-New POPs
Other additions to the «Dirty Dozen» derived from the 2001 Stockholm Convention are:
-Clordecone, mainly responsible for the contaminated bananas that come from the French Antilles (Guadeloupe and Martinique), although their use has been banned for more than 20 years, due to their persistence that some calculate in hundreds of years, the problem continues; Hexachlorocyclohexane, hexabromodiphenyl ether, Lindane, hexachlorocyclohexane, Pentachlorobenzene, tetrabromodiphenyl ether (tetraBDE) and pentabromodiphenyl ether (pentaBDE), Perfluorooctane sulfonic acid, Endosulfants, Hexabromocyclodecane.


The hormonal or endocrine system is a complex communication system that acts in conjunction with the nervous and immune system and is responsible, among other functions, for the internal stability of the body, regulate growth, development and reproduction, and produce, use and store energy.
As we can see, it regulates vital functions of the organism, including embryonic development. It is made up of glands (which secrete hormones), hormones (chemical substances that act as messengers) and hormone receptors (which are activated by hormones).
Hormones travel in the bloodstream to cells in different organs that contain specialized proteins called receptors, which recognize that hormone and bind to it. The hormone changes the state of the receptor from inactive to activated, making it possible for it to bind to cellular DNA and activate or repress the expression of nearby genes.
Each endocrine gland secretes only a very determined and very small amount of a hormone, at a specific time, circulating through the blood very small amounts, as the hormones are very effective and produce their effect at very low concentrations (picograms or nanograms /ml of blood).
In recent decades, the incidence of diseases of the reproductive system (infertility, malformations, precocious puberty, etc.), cancer (ovaries, breast, testicles, thyroid), neurological and metabolic diseases (metabolic syndrome), obesity and diabetes has increased, especially in the most industrialized countries.
How they act:
– Mimicking (replacing) the action of hormones, for example, those that act as estrogens are called environmental estrogens, among these are DDT or some PCBs.
-Antagonizing (inhibiting or nullifying) the action of hormones, for example antiestrogens such as some PCBs or PCBS, such as the fungicide vinclozine.
– Altering the pattern of synthesis and metabolism of hormones, such as PBDE-99 which alters the synthesis of thyroid hormone.
-Modulating the levels of the corresponding receptors, such as bisphenol A that interferes with the estrogenic receptor.
-Activate peroxisome proliferating receptors (PPARs), which are related to the differentiation of fat cells that produce body fat, and diabetes, there must be a balance between the different isoforms of PPARs, (especially PPARbeta and PPARgamma) to maintain a balance between synthesis and oxidation of fatty acids, as an imbalance in the balance is associated with the development of obesity and insulin resistance, this is the case of the solvents trichloroethylene and perchloroethylene.
-Changes in thyroid hormones should be considered with special attention because even minor changes in a pregnant woman can have significant consequences, especially in sensitive populations such as the embryo or fetus.

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