In this article we will discuss about:- 1. Introduction to Persistent Organic Pollutants (POPs) 2. Global Action against POPs 3. Sources 4. Personal Action on POPs to Reduce Risk 5. Factsheet 6. POPs Problem in India 7. Collective Action 8. “The Dirty Dozen” POPs 9. Additional POPs 10. Notes 11. Factsheet.
- Introduction to Persistent Organic Pollutants (POPs)
- Global Action against POPs
- Sources of POPs
- Personal Action on POPs to Reduce Risk
- Factsheet of POPs 6. POPs Problem in India
- Collective Action to be taken on POPs
- “The Dirty Dozen” POPs
- Additional POPs
- Notes on POPs
- Factsheet about POPs
1. Introduction to Persistent Organic Pollutants (POPs):
Of all the pollutants released into the environment by human activity. Persistent Organic Pollutants (POPs) are among the most dangerous. They are ubiquitous- found in the most remote areas, far from any industrial activities. Even though they are present in the environment at extremely low levels, they have been linked to many health and environmental effects.
With the evidence of their long- range transport to regions where they have never been used or produced, and the consequent threats they pose to the environment of the entire planet, the international community has called for urgent global action to reduce and eliminate releases of these POPs.
Stockholm Convention is DDT, aldrin, dieldrin, endrin, chlordane, heptachlor, mirex. toxaphene, hexachlorobenzene (HCB), polychlorinated biphenyls (PCBs), dioxins and furans. Of these, nine are organochlorine pesticides. PCBs are compounds with varied industrial applications, while HCB, PCBs, dioxins and furans are produced unintentionally, industrially as well as otherwise.
2. Global Action against POPs:
In 1997, efforts were made on a global level to deal with the problem of POPS under the aegis of United Nations Environmental Programme (UNEP)-
1. POPs are most hazardous of all pollutants released into the environment every year by humans.
2. Among these, dioxins and furans are unintentionally produced by processes such as incineration and are of most concern because of their significant toxicity.
3. POPs travel globally on wind and marine currents to regions far from where they are produced.
4. Collective global action is the only way to stop the spread of POPs. The Stockholm Treaty lays guidelines for their phase-out.
5. POPs are transported via convection currents to colder regions, where they persist for longer periods. The Himalayas could possibly be a major sink for POPs to reenter the ecosystem through rivers.
A multilateral, internationally legally binding treaty to ban POPs was signed on May 23, 2001, in Stockholm by 87 countries. It has come to be known as the Stockholm Convention.
The Stockholm Convention sets out control measures covering the production, import, export, disposal and use of POPs. Governments are to promote the best available technologies and practices for replacing existing POPs while preventing the development of new POPs.
While the control measures will apply to an initial list of 12 chemicals, a POPs Review Committee will consider additional candidates for the POPs list on a regular basis.
3. Sources of POPs:
Sources of POPs can be classified according to their type. Pesticide POPs have similar source characteristics. PCBs have specific uses in different industrial sectors and have source characteristics accordingly similarly; unintentionally produced POPs have commonalities in terms of the kinds of sources and release mechanisms associated with them.
Sources of pesticides can be typically characterized as point and non-point.
i. Point sources of POPs pesticides are in the form of pesticide manufacturing facilities (both technical grade manufacturers as well as formulators) and stockpiles of obsolete, unwanted or date-expired pesticides.
ii. Non-point sources arise due to the general application of pesticides (such as in agriculture) resulting in crop run-offs or leaching into ground water reserves. POPs pesticides have been banned for use in agriculture, though they are present in food, water, etc. The use of DDT as part of the malaria programme also constitutes a non- point source.
Potential hotspots exists in closed factory premises which still house stocks of manufactured POPs. It is expected that the environment around such sites might also be contaminated due to exposure to toxics during the period of manufacture.
A variety of industrial and non-industrial processes (typically involving high temperatures’) result in the release of POP chemicals dioxins, furans, PCBs and HCB) into the environment. Among these POPs, dioxins and furans are of most concern because of their significant toxicity.
(A) Industrial Sources with Potential Tor Comparatively High Formation and Release of Pops:
(i) Waste incinerators, including co-incinerators of municipal, hazardous or medical waste or sewage sludge.
(ii) Cement kilns firing hazardous waste.
(iii) Production of pulp using elemental chlorine or chemicals generating elemental chlorine for bleaching.
(iv) Thermal processes in the metallurgical industry, including secondary copper production, sinter plants in the iron and steel industry, secondary aluminum production, secondary zinc production, etc.
(b) Other Sources Listed:
(i) Open burning of waste including burning of landfill sites.
(ii) Thermal processes in the metallurgical industry not mentioned in Part II.
(iii) Residential combustion sources.
(iv) Firing installations for wood and other biomass fuels.
(v) Specific chemical production processes releasing unintentionally formed POPs, especially production of chlorophenols and chloranil.
(vii) Motor vehicles, particularly those burning leaded gasoline.
(viii) Destruction of animal carcasses.
(ix) Textile and leather dyeing (with chloranil) and finishing (with alkaline extraction).
(x) Shredder plants for the treatment of end-of- life vehicles.
(xi) Smoldering of copper cables.
(xii) Waste oil refineries and furans released are accompanied with PCBs and HCB as well.
POPs pervade the environment through a variety of media. Pesticides, though intended for the target pest species, end up in the food chain, water and air and into non-target species and ecological systems. Unintentional and industrial POPs are released in an unregulated manner and are assimilated into environmental systems owing to their properties of persistence, lipophilicity and volatility.
Exposure of humans to pesticide POPs can be intentional (suicides and homicides) and unintentional (accidental, occupational and non-occupational exposure from water and air.
POPs that are already in the environment will be around for decades. Still, we can reduce our exposure to POPs and help stop more POPs from getting into circulation.
To reduce the risks of POPs, the following steps should be considered:
1. Try to Eat Lower on the Food Chain or Avoid Fats:
This will reduce lifetime accumulation of POPs and is especially relevant for children.
2. Choose Unbleached Paper Products:
Chlorine bleaching processes unintentionally generate POPs by-products such as dioxins furans and others.
3. Avoid Polyvinyl Chloride (PVC or Vinyl) Plastics:
This might be an impossible task given that there is an endless list of common vinyl items that include packaging material, utility items, wall coverings, blood and infusion bags, medical equipment, credit cards, office supplies, etc. Don’t burn these items.
4. Avoid Using Weed Killers Containing Pops Chemicals:
A useful hint for the customers is to check the label for the active ingredient 2, 4-D; they may contain dioxins and other POPs byproducts food). Amongst unintentional exposures in the environment are the direct toxic effects during application to non-target groups such as pollinators, predators, wildlife, etc., as well as post application hazards due to pesticide residues in food, air and water.
Pesticide POPs can get into the ecosystem at various junctures such as during production, transport, storage and application.
Once in the environment, POPs are transported within the region mainly through natural media like fresh water systems (rivers and streams), atmospheric currents (usually adsorbed to suspended sediment) and marine currents.
Air transport can also occur through precipitation and the movement of dust particles with adsorbed POPs. The persistence of POPs in soil/sediments may result in their re-suspension and re-mobilization back to the atmosphere under favourable high temperature conditions through volatilization and to the surface waters through run-offs during monsoon/flood periods.
Most inflows into the marine environment occur due to the outflows of rivers into the oceans and seas.
5. Factsheet of POPs:
1. POPs are highly stable compounds and can circulate globally through a process known as the “grasshopper effect”. According to UN, the breast milk of the average Inuit mother has five times as much dioxin as that of her counterpart in the industrialized world. However, breast milk is still recommended for infants.
2. On entering the environment, POPs can alter the normal bio-chemical and physiological functions of plants and animals, including humans. Effects may include molecular changes (enzyme activity, DNA damage), cellular changes (tumour formations), tissue changes (organ functioning), individual changes (behaviour, deformities), population changes (mortality, abundance, distribution), and community changes (numbers of species and their interactions).
3. POPs concentrate in living organisms through another process called bioaccumulations. POPs are readily absorbed in fatty tissue, where concentrations can become magnified by up to 70,000 times the background levels.
4. Fish, predatory birds, mammals and humans are high up the food chain and so absorb the greatest concentrations.
5. Human health impacts may be felt most acutely in populations that consume large amounts of fish (for example, subsistence fishermen), since fish have a high fat content and thus can contain high concentrations of POPs.
6. Though most of the 12 POPs have been banned or subjected to severe use restrictions in many countries for more than 20 years, many are still in use and stockpiles of obsolete POPs exist in many parts of the world.
7. Humans can be exposed to POPs through diet, occupational accidents and the environment.
8. Exposure to very low doses of certain POPs can lead to cancer, damage to the central and peripheral nervous systems, diseases of the immune system, reproductive disorders, and interference with infant and child development.
9. Shifting from POPs to chemical and non- chemical alternatives is the key to reducing the impact of these hazardous substances. A high priority is finding alternatives to hazardous chemicals for insect control.
10. There are many safer chemical and non- chemical alternatives, but their development and dissemination will require time, money and training.
11. Many countries face barriers to identifying and controlling releases of POPs. These include high prices of some alternatives, the need for training on the hazardous nature of POPs, a lack of information on alternatives, a lack of reliable data about the current uses of POPs and the need for regulations/infrastructure to manage their use.
Dietary exposure of POPs takes precedence over other pathways like air, water and dermal exposure. Primary exposure by dietary pathways is, however, not applicable occupational and accidental exposure where dermal, atmospheric and water pathways can assume significance.
The presence of POPs residues in human and animal samples is the most effective way to confirm the exposure and magnitude of POPs in the population. POPs exposures even at low doses can cause undesirable health effects, especially in the more vulnerable sections of the population, such as pregnant mothers and young children.
6. POPs Problem in India:
Despite the fact that most short-listed POPs are banned from use, production, import or export in India, a combination of factors has led to their continued production, trade, use and release into the environment.
Chlordane has been imported in India subsequent to its ban, while aldrin, chlordane and heptachlor have been exported subsequent to their ban. It is suspected that DDT which is allowed for vector control but banned for agricultural purposes is pilfered and used as an insecticide.
Though stockpiles of obsolete POPs exist, there is no known government programme to monitor them. Electrical equipment, such as transformers containing PCBs, are indiscriminately disposed into the waste stream.
Some developed nations, are pushing for the expansion of POPs producing technologies such as waste incinerators, waste-to-energy and PVC manufacturing plants.
Extensive use of DDT for malaria control has led to a high level of contamination of all quarters of the environment and food commodities.
The problems associated with POPs are too large, complicated and expensive for any individual nation to tackle.
Suggested ways of doing so are as follows:
i. Elimination of All POPs Sources:
The sources of POPs must be properly identified, and then phased out, replaced or removed. This is true for POPs that are produced intentionally as well as unintentionally, such as dioxins.
ii. Technological and Other Resource Assistance:
The global POPs treaty includes measures to discourage wealthy countries from promoting and exporting POPs-generating technologies, processes and materials to newly industrialized nations. At the same time, measures must be included to encourage wealthy countries and aid programmes to assist newly industrialized countries in developing and implementing non- POP technologies and materials.
iii. No Incineration:
Since incineration itself has been identified as a minor source of dioxins and furans, it cannot be used as a disposal route for existing POPs stockpiles. While so-called state-of-the- art incinerators can steady reduce stack emissions, they cannot stop the formation of dioxins and other POPs which may be present in fly ash and bottom ash. Those would still require further treatment and disposal.
Alternative destruction and detoxification methods and technologies which do not generate POPs should be used instead.
These 12 POPs are often referred to as the “dirty dozen” information about them is given below:
An organochlorine insecticide; Acts as stomach and contact poison.
(i) A pesticide used to control soil insects termites and ants ‘It has been widely used to protect crops such as corn and potatoes, to protect wooden structures from termites.
(ii) It is oxidized in the insect to form dieldrin, a neurotoxin.
(iii) It is a carcinogen as well as a mutagen.it is most toxic to aquatic invertebrates
(iv) It binds strongly to soil particles, is resistant to leaching into ground water. It is released from soil by volatilization.
(v) Due to its persistent nature, aldrin is known to bio-concentrate.
(vi) Aldrin is toxic to humans causing headache, dizziness, nausea, general malaise, and vomiting, followed by muscle twitching.
(vii) Myoclonic jerks and convulsions. Lethal dose is 80 mg/kg if adult body weight MRLs range from 0.006 mg/kg meat fat and 0.1 to 180 mg/kg for water quality
(viii) Occupational exposure to aldrin, in conjunction with dieldrin and endrin, has been associated with a significant increase in liver and biliary cancer. Aldrin may affect immune responses.
(ix) Many countries, including India have ended its usage manufacture, import and export.
(x) It is a carcinogen as well as a mutagen.
(xi) Half-life in soil ranges from 20 days to 1.6 years.
(i) Chlordane is a contact insecticide that has been used on agricultural crops as well as being used extensively in the control of termites, household pests. Uses as fumigant, acaridae, most effective on termites.
(ii) Banned in US in 1988 and India also used manufacture, import and export.
(iii) Chlordane sticks strongly to soil particles at the surface and is not likely to enter groundwater. As a result it can stay in the soil for over 20 years and breaks down very slowly. Its half-life in soil is 4 years.
(iv) Bio-concentrates in fish, mammals, and birds.
(v) In both humans and animals, it can damage nervous and digestive systems and liver has caused convolutions and death.
(vi) Recent human studies have linked chlordane exposure with prostate and breast cancers.
(vii) MRLs are 0.002 mg/kg milk fat and 0.5 mg/kg poultry fat for water – 1.5 to 6mg/litre.
A synthetic pesticide was earlier used on agriculture crops.
(i) DDT is toxicant; used for vector control of malaria, dengue and kala-azar.
(ii) It has a half-life of 2-15 years and is immobile in most soils. Half-life in air is 7 days.
(iii) Breakdown products in the soil environment are DDE and DDD, which are also highly persistent and have similar chemical and physical properties.
(iv) Banned in the US for most uses in 1972. In India, It is banned for agriculture uses but allowed for restrictive use in the public health sector.
(v) Subsequently banned for agricultural use worldwide, but is still used to a limited extent in mosquito control in certain parts of the world.
(vi) Concentrates significantly in fish and other aquatic species, leading to long-term DDT and its metabolic products DDE and DDD magnify through the food chain.
(vii) DDT bio exposure to high concentrations.
(viii) At the chronic level, individuals who consumed contaminated fish increased diabetes occurrences.
(ix) DDT is a probable human carcinogen. It exhibits estrogen like activity.
(x) The Cows milk samples found to contain detectable levels of DDE.
(xi) MRLs are 0.02 mg/kg if milk fat, 5 mg/kg of meat fat and 1 mg/litre of drinking water.
An insecticide for soil pests, used in wool processing industries and for termite control.
(i) Closely related to aldrin which itself breaks down to form dieldrin
(ii) It accumulates as it is passed along the food chain.
(iii) MRLs are 0.006 mg/kg milk fat. 0.2 mg/kg meat fat and 0.1 to 1.8 mg/litre of drinking water.
(iv) It acts as non-systematic stomach and contact poison.
(v) Long-term exposure is toxic to many animals (humans included) far greater than to the original insect targets.
(vi) Currently banned in most of the world including India (except use for locust control in the desert areas).
(vii) Linked to Parkinson’s disease, breast cancer and immune, reproductive, and nervous system damage.
(viii) It has a high half-life of 3-4 years in soil in temperate climates. Persistence in air for 4 to 40 hours.
Insecticide/rodenticide in cotton, rice, sugarcane and other crops.
(i) Banned in many countries including India.
(ii) It is likely to adsorb onto the sediments in surface water.
(iii) An insecticide used on cotton, maize, and rice; a rodenticide used to control mice. It is a contact and stomach poison, has a delayed neurotoxic action.
(iv) It can bio-concentrate in the fatty tissues, of organisms living in water. It is very toxic to aquatic organisms, namely fish, aquatic invertebrates, and phytoplankton. Bioconcentration up to 1800 has been reported in fish.
(v) Half-life in soil estimated 12 years.
(vi) Endrin poisoning in humans primarily affects the nervous system. Food contaminated with endrin has caused several clusters of poisonings worldwide, especially affecting children. It suppresses the immune system in humans.
An insecticide for soil pests, termites, household pests; also used for seed treatment.
(i) Similar to the insecticide chlordane; toxic to wildlife; in birds induces behavioral changes, reduced reproductive success and mortality.
(ii) The U.S. has banned the sale of heptachlor products and virtually eliminated its use for any purpose. In India also, it is completely banned.
(iii) Has a very stable structure, thus it can remain in environment for decades; its soil half-life is 0.75 to2 years in temperate climate.
(iv) Possible human carcinogen (Group 2B).
(v) MRLs are 0.006 mg/kg of milk fat, 0.2 mg/kg meat or poultry fat.
7. Hexachlorobenzene (HCB):
(i) A fungicide formerly used as a seed treatment, especially on wheat.
(ii) Known animal carcinogen (liver, kidney, and thyroid).
(iii) Probable human carcinogen; also causes urinary, arthritic, neurological and metabolic disorders in human.
(iv) After its introduction as a fungicide in 1945, for crop seeds, this toxic chemical was found in all food types.
(v) Banned in many countries. It is not registered in India.
(vi) In humans it can cause liver disease, skin lesions, ulceration, hair loss, thyroid damage colic, severe weakness, kidney damage, CNS effects and respiratory depression.
(vii)Human and animal studies have demonstrated that HCB accumulate in fetal tissues and is transferred in breast milk.
(viii) Extremely toxic to aquatic creatures. Risk of bioaccumulation in an aquatic species is high and has a long half-life in biota.
(ix) Estimated half-life in soil is 2.7 to 5.7 years in soil and 0.5 to 4.5 years in air.
(i) An insecticide; flame retardant.
(ii) Listed as a persistent, accumulative, and toxic pollutant by EPA in the U.S. Capable of undergoing long range transport due to volatility.
(iii) It was used to control fire ants and as a flame retardant in plastic, rubber, paint, paper and electronics.
(iv) Mirex is transported across the placenta and can be passed from mother to child through breast milk.
(v) Most affected in animals in the. It has moderate acute toxicity for mammals.
(vi) Proven to cause cancer in mice and rats and is a carcinogenic risk to humans It has potential of endocrine disruption in humans.
(vii) Toxic for a range of aquatic organisms, with crustacean being particularly sensitive.
(viii) Mirex induces pervasive long-term physiological and biological disorders in vertebrates.
(ix) There is evidence of accumulation of mirex in aquatic and terrestrial food chains to harmful levels.
(x) Mirex is one of the most stable of the organochlorine insecticides and is it is widespread in the environment.
(xi) All uses of mirex as a pesticide were banned in the U.S. in 1978. It is never registered in India.
(xii) Mirex is still used in the USA mainly as a flame-retardant in plastics, rubber, paint, paper and electronics.
(xiii) Effects on organisms combined with its persistence suggest that mirex presents a long-term hazard for the environment. Its half-life is 10 years.
(xiv) It has a bioconcentration factor of2600 for pink shrimp and 51400 for fathead minnows.
9. PCBs (Polychlorinated Biphenyls):
(i) Used as coolants/insulating fluids, also used in flexible PVC coatings of electrical wiring and electronic components, pesticide extenders, cutting oils, flame retardants, hydraulic fluids, sealants (used in caulking, etc.), adhesives, wood floor finishes, paints, and in carbonless copy- paper.
(ii) PCBs are very stable compounds and do not degrade readily.
(iii) Despite being banned in the 1970s due to their high toxicity. PCBs still persist in the environment.
(iv) PCBs have been detected globally in the atmosphere, from the most urbanized areas that are the centers for PCB pollution, to regions north of the Arctic Circle, carried by wind currents.
(v) Bio-concentrates in animals.
(vi) PCBs can be transmitted to children via breast milk as well as through the placenta.
(vii) In humans, PCBs can cause liver disease, ocular lesions and lessened immune response.
(viii) Babies born to women exposed to PCBs have been shown to weigh less, have problems with motor skills, a decrease in short-term memory, and compromised immune systems.
(ix) PCBs alter estrogen levels in the body and contribute to reproduction problems.
(x) Endocrine Disrupting Chemicals (EDC’s) such as PCBs pose a serious threat to reproduction in top-level predators.
(xi) Biological magnification of PCBs has led to polar bears and whales that have both male and female sex organs and males that cannot reproduce.
(xii) Effects on animals are liver, stomach, thyroid damage, plus immune system changes, changes in behavior and impaired reproduction.
(xiii) Some studies indicate that PCBs are associated with cancer in humans, such as cancer of the liver and biliary tract.
(xiv) PCBs are known to induce Vitamin A deficiency in mammals, an affect that may be associated with impairment of the immune system, reproduction and growth.
Commonly Referred to as DIOXINS.
(i) Dioxins are teratogens (cause birth defects), mutagens, and potential human carcinogens.
(ii) Known to accumulate in humans and wildlife due to dioxins’ ability to dissolve in fats and oils and their tendency to be water insoluble. This means that even small amounts in contaminated water can bio-concentrate up the food chain to dangerous levels.
(iii) In humans, they can cause effects in reproductive/sexual development, plus immune system damage, thyroid disorders, nervous system disorders, endometriosis and diabetes.
(iv) In animals and fish, studies have shown dioxin exposure to cause cancer birth defects, liver damage, endocrine damage, and immune system suppression.
(v) Studies have shown that exposure to dioxin increases the ratio of female births to male births among a population.
(vi) Concentrations of dioxins are found in all humans today, with higher levels found in persons living in more industrialized countries.
(vii) The estimated elimination half-life for dioxins in humans ranges from 8 to 132 years.
(viii) Dioxin enters the general population almost exclusively from ingestion of food, specifically through the consumption of fish, meat, and dairy products since dioxins are fat-soluble and readily climb the food chain.
(ix) Because Dioxins are lipophilic, breast fed children usually have substantially higher dioxin body burdens than non-breast fed children until they are about 8 to 10 years old.
(x) According to the EPA, 80% of Dioxin emissions are caused by coal burning plants, municipal waste incinerators, metal smelting, diesel trucks, land application of sewage sludge, burning treated wood and trash burn barrels. Dioxins are also generated in bleaching fibers for paper and textiles.
(a) Highly toxic
(b) Properties and chemical structure similar to dioxins.
A non-systemic contact and stomach insecticide. Used extensively for cotton pests, vegetables, fruits and cereal grains.
(a) Highly toxic to fish also used to combat livestock parasites.
(b) Banned in US in 1990, outlawed in 1991 by the Stockholm Convention. It has half-life of up to 12 years; bio concentrates in aquatic organisms.
(c) Exposure can cause damage to lungs, nervous system, kidneys and can be fatal. It has potential of endocrine disruption and is a possible human carcinogen.
9. Additional POPs:
(i) PBDEs are used in plastic, foam and textiles in clothing, computers, televisions, furniture and cars.
(ii) PBDEs have been found at high levels in indoor dust.
(iii) Research has linked some chemicals in the flame retardants to effects on thyroid function on brain function, reduced male fertility and damaged ovarian development and the development of the embryonic nervous system, impacting motor skills and behavior.
(iv) These chemicals were banned in Europe in 2004/2005.
(v) Levels of concentration in humans and marine mammals continue to increase.
(vi) Studies have found that PBDEs accumulate in human blood, fat tissue and breast milk. It has been found that a woman can pass these chemicals to her unborn child through the placenta.
(vii) In the United States levels in human breast milk are 40 times higher than in Europe and are steadily rising.
(viii) Marine mammals like bottlenose dolphins, harbor porpoises, pilot and beluga whales have been found to be contaminated with PBDEs. Birds including cormorants and glaucous gulls, and popular food fish including salmon and tuna have also been found to carry high concentrations of PBDEs.
(B) PFCs – Perflorinated Compounds:
(i) PFCs are used as industrial and commercial surfactants – wetting agents that lower the surface tension of liquid.
(ii) In contrast to the majority of organic pollutants that are deposited in fatty tissue, perflorinated contaminants circulate in the blood and accumulate primarily in the liver.
(iii) PFCs are synthetic molecules that are thought to bio accumulate and are believed to be extremely resistant to physical degradation, biodegradation, and biotransformation.
(iv) Clear links exist between chemicals such as phthalates, bisphenol A, and perflorinated compounds found in consumer products including baby bottles, toys, and cosmetics to reproductive disorders.
10. Notes on POPs:
Penetration and Deposition of Particles in the Human Respiratory Tract:
Particles small enough to stay airborne may be inhaled through the nose (nasal route) or the mouth (oral route, the inhaled particles may than either be deposited or exhaled again, depending on a whole range of physiological and particle-related factors. The five deposition mechanisms are sedimentation, inertial impaction, diffusion (significant only for very small particles < 0.5 μm), interception, and electrostatic deposition.
Sedimentation and impaction are the most important mechanisms in relation to inhaled airborne dust, and these processes are governed by particle aerodynamic diameter. There are big differences between individuals in the amount deposited in different regions.
The largest inhaled particles, with aerodynamic diameter greater than about 30 pm, are deposited in the airways of the head that is the air passages between the point of entry at the lips or nares and the larynx. During nasal breathing, particles are deposited in the nose by filtration by the nasal hairs and impaction where the airflow changes direction.
Retention after deposition is helped by mucus, which lines the nose. In most cases, the nasal route is a more efficient particle filter than the oral, especially at low and moderate flow rates.
Thus, people who normally breathe part or all of the time through the mouth may be expected to have more particles reaching the lung and depositing there than those who breathe entirely through the nose. During exertion, the flow resistance of the nasal passages causes a shift to mouth breathing in almost all people.
Other factors influencing the deposition and retention of particles include cigarette smoking and lung disease of the particles which fail to deposit in the head, the larger ones will deposit in the tracheobronchial airway region and may later be eliminated by mucociliary clearance or – if soluble – may enter the body by dissolution.
The smaller particles may penetrate to the alveolar region the region where inhaled gases can be absorbed by the blood. In aerodynamic diameter terms, only about 1% of 10-μm particles gets as far as the alveolar region, so 10 μm is usually considered the practical upper size limit for penetration to this region.
Maximum deposition in the alveolar region occurs for particles of approximately 2-μm aerodynamic diameter. Most particles larger than this have deposited further up the lung. For smaller particles, most deposition mechanisms become less efficient, so deposition is less for particles smaller than 2 μm until it is only about 10-15% at about 0.5 μm.
Most of these particles are exhaled again without being deposited. For still smaller particles, diffusion becomes an effective mechanism and deposition probability is higher. Deposition is therefore a minimum at about 0.5 μm.
Figure below illustrates the size of the difference between nasal and oral breathing, and the role of physical activity on the amount of dust inhaled and deposited in different regions of the respiratory airways.
It presents the mass of particles that would be inhaled and deposited in workers exposed continuously, during 8 hours, to an aerosol with a concentration of 1 mg/m3, a mass median aerodynamic diameter equal to 5.5 μm and a geometric standard deviation equal to 2.3.
Respiratory parameters (tidal volume, Vt, and frequency, f -were associated with their physical activity as follows:
Vt = 1450 cm3 f= 15 min-1 (moderate physical activity)
Vt = 2150 cm3 f= 20 min-1 (high physical activity)
The results show that oral breathing increases dust deposit in the alveolar (gas-exchange) region when compared to nasal breathing, indicating the protective function of the nasal airways. A higher physical activity can increase dust deposition in all parts of the respiratory airways.
Fibres behave differently from other particles in their penetration into the lungs, fine fibres even as long as 100 μm have been found in the pulmonary spaces of the respiratory system. This is explained by the fact that the aerodynamic diameter of a fibre, which governs its ability to penetrate into the lung, is primarily a function of its diameter and not its length. However, for longer fibres, deposition by interception becomes increasingly important.
After deposition, the subsequent fate of insoluble particles depends on a number of factors. (Soluble particles depositing anywhere may dissolve, releasing potentially harmful material to the body.)
The trachea and bronchi, down to the terminal bronchioles, are lined with cells with hair like cilia (the ciliated epithelium) covered by a mucous layer. The cilia are in continuous and synchronized motion, which causes the mucous layer to have a continuous upward movement, reaching a speed in the trachea of 5-10 mm per minute.
Insoluble particles deposited on the ciliated epithelium are moved towards the epiglottis, and then swallowed or spat out within a relatively short time. The rate of clearance by the mucociliary mechanism may be significantly impaired by exposure to cigarette smoke.
Intermittent peristaltic movements of the bronchioles, and coughing and sneezing, can propel particles in the mucous lining towards the larynx and beyond.
The epithelium of the alveolar region is not ciliated; however, insoluble particles deposited in this area are engulfed by macrophage cells (phagocytes), which can then (1) travel to the ciliated epithelium and then be transported upwards and out of the respiratory system; or (2) remain in the pulmonary space; or (3) enter the lymphatic system. Certain particles, such as silica-containing dusts, are cytotoxic; i.e. they kill the macrophage cells.
Defence or clearance mechanisms for the retention of inhaled insoluble dusts have been broadly classified, based on results of experiments with rats, as:
(i) A fast-clearing compartment, linked to the ciliary clearance process in the tracheobronchial region (clearance time of the order of half a day),
(ii) A medium-clearing compartment, linked to the “first-phase” macrophage clearance action in the alveolar region (clearance time of the order of 10 days),
(iii) A slow-clearing compartment, linked to the “second-phase” macrophage clearance action in the alveolar region (clearance time of the order of 100 -200 days), and,
(iv) A “sequestration” compartment in which particles are stored permanently (e.g., “embedded” in fixed tissue).
It has also been shown that the accumulation of large enough burdens of insoluble particles in the lungs leads to impaired clearance. This so-called “dust overload” condition may occur as a result of prolonged occupational exposures, even at relatively low levels.
Wherever the particles are deposited, either in the head or in the lung, they have the potential to cause harm either locally or subsequently elsewhere in the body. Particles that remain for a long time have increased potential to cause disease. This is why inhaled particles are important in relation to environmental evaluation and control.
Used on crops like corn and to keep away birds. It has since been banned in India.
A carcinogenic pesticide widely used to control termites and since has been banned in India.
(iii) Dichlorodiphenyl Trichloroethane (DDT):
Small amounts of DDT are today used on crops; however, DDT is still widely employed as the cheapest means of controlling mosquitoes that carry malaria and other diseases. It is banned in 34 countries including India because of toxicity to mammals, including humans.
It is an insecticide with probably the strongest carcinogenic effect amongst all organochlorine pesticides and since has been banned in India.
Used mainly on field crops such as cotton and grains. Also used as a rodenticide and to keep away birds. It has since been banned in India.
Used in Mexico, Bulgaria and the US to kill insects in seed grains and on crops, and to fight termites. It is now banned in India.
(vii) Hexachlorobenzene (HCB):
Once widely used as a fungicide to protect seeds, HCB is also released into the environment as a by-product during the manufacture of chlorine gas and some chlorinated pesticides, and during waste incineration. It causes porphyria turcica, a metabolic disorder, and damages reproductive and immune systems.
Used as an insecticide and fire retardant in the US till 1987 and also known to cause cancer in laboratory animals. It has not been produced and not used in India.
It took over from DDT in 1970s as the world’s most popular insecticides, particularly used in cotton-growing. It is now banned in 37 countries including India. Toxaphene is still manufactured in China, Nicaragua and Pakistan.
(x) Polychlorinated Biphenyls (PCBs):
PCBs are the leading industrial POPs. Being chemically stable and heat-resistant, they are widely used in electrical equipment oils such as transformers and capacitors as a heat- exchange fluid, and as a lubricant and plasticizer. Acutely toxic in high concentrations, they damage immune and reproductive systems and cause birth defects. Though only small quantities are now produced, they are still being released into the environment due to the break-up of old electrical equipment.
(xi) Dioxins and Furans:
These chlorine based compounds are produced in high-temperature incinerators used for burning organic materials including plastics, as an unwanted by-product in industrial processes ranging from metallurgy to the bleaching of paper, and as a trace contaminant in chlorophenol compounds (such as wood preservatives) and herbicides (such as Agent Orange). They are more potent than PCBs, but the effects are similar.
a. Hexachlorocyclohexane (HCH):
This insecticide is widely used on cotton and on locust control. There are three chemical forms of HCH – alpha, beta and gamma. The crude manufactured from, known as technical HCH contains all the three forms. Only gamma-HCH is a useful pesticide, modern manufacturers make a pesticide formulation called lindane, which is exclusively gamma-HCH.
Widely used as an insecticide on many crops, including rice, and to control these flies. Endosulfan is being manufactured in Germany, Brazil, India, Israel, Indonesia and South Korea. Change of CCl4 by toluene in endosulfan production could be environmental relevance of the considered synthesis.
An insecticide mainly used as a timber preservative, especially for power line poles, railway sleepers and fence posts.
(i) Persistent organic pollutants (POPs) are organic compounds that resist environmental breakdown via biological, chemical, and photolythic processes, some taking as long as a century to degrade.
(ii) POPs exposed to the environment are proven to travel long distances from their origin via wind and ocean currents. Precipitation carries PCBs (polychiorinated biphenyls).
(iii) POPs therefore can be found globally, even in areas such as the Arctic and Antarctica, far from their source. Human exposures in certain Arctic areas are among the highest worldwide.
(iv) POPs bio-concentrate as they move up through the marine food chain and accumulate in the fatty tissues of living organisms at higher trophic levels.
(v) Marine mammals around the world carry high burdens of POPs.
(vi) Although many countries have banned these chemicals, they remain stockpiled, are produced or used illegally, or, because of lengthy half-lives, they continue to exist in soil, or other environmental media.
(vii) The United Nations is currently considering the elimination or reduction of twelve of some of the most damaging POPs through the formulation of an international treaty. Nine of the POPs chemicals under consideration are pesticides that have been extensively used in both developed and developing countries.
(i) POPs can disrupt the endocrine, reproductive, and immune systems the developing brain and nervous system may be most vulnerable.
(ii) POPs are capable of causing behavioral problems, cancer, diabetes and thyroid problems.
Babies whose mother ate large amounts of highly contaminated fish from Lake had lower birth weights, poor memory smaller head circumferences and shorter attention spans than babies whose mothers did not eat fish.
Marine mammals are affected with diseases associated with immune system dysfunction. Marine mammals present a metabolic imbalance, so they are considered one of the most vulnerable organisms with respect to long-term toxicity of man-made chemicals such as organochlorines. (Whales and dolphins) have a poor ability to detoxify organic pollutants because they lack isozymes that are required to detoxify DDT and PCBs.