WHAT ARE TOXIC SUBSTANCES?
Toxic substances can be defined as broad group of chemicals capable of causing harm to plants and animals including humans. There are several classes of toxic substances that have the potential to affect surface waters in Vermont. While many Vermonters are aware that toxic mercury contaminates fish and fish-eating wildlife, there are many other types of toxic compounds that merit attention in this Strategy. For the purposes of this Strategy, toxic compounds have been grouped into five categories: atmospherically deposited compounds; organic and inorganic contaminants that result from industrial, manufacturing or other point and non-point discharges from facilities; pesticides; contaminants of emerging concern (CECs); and biological contaminants. These groupings reflect the commonality of management options that are applied to address each contaminant group.
CLASSIFICATIONS OF TOXICANTS
A. Carcinogens: Toxicants that causes cancer. E.g Radiations, Chemicals such as Polycyclic aromatic hydrocarbons, aromatic amines and halides, benzene, vinyl chloride, certain metals, diet, and tobacco smoke
B. Mutagens: Mutagens are toxicants that cause mutations in DNA. Many mutagens have also been shown to be carcinogens as well. Commonly found mutagens that are of most concern to humans include UV light, ionizing radiation, microtoxins, and organic and inorganic chemicals. Some chemicals are also mutagens, they include: Nitrosamines found in Pyrolysis products of tryptophan such as broiled meat, beer and whisky, Benzo(a)pyrene in cigarettes and wood smoke, Benzidine found in textile dyes and manufacture of paper and leather.
C. Teratogens: toxicants that causes birth defects E.g Thalidomide. Thalidomide was a drug used in the 1950s as a sleeping pill during pregnancy but turned out to be a potent teratogen. Pregnant women who had taken the drug gave birth to children suffering from different malformations of organs.
D. Allergens: Toxicants that causes unnecessary immune response. E.g Pollens and Dust. E. Neurotoxins: Affect nervous system E.g Clostridium toxins and Heavy metals.
F. Endocrine Disruptors: Toxicants that interfere with hormonal function in the body. e.g. DDT, and DES. Endocrine Disrupters mimic the hormones in the body. They interfere with the production, release, metabolism, binding or elimination of natural hormones.
SOURCES OF TOXICANTS
A. Point Sources: These are discrete discharges of chemicals that are usually identifiable and measurable, such as industrial or municipal effluent outfalls, oil spills and other stationary atmospheric discharges.
B. Non-point Sources: These are sources that are more diffuse over large areas with no identifiable single point of entry such as agrochemical (pesticide/fertilizer) runoff, mobile sources emissions (automobiles), atmospheric deposition, and groundwater inflow.
TOXICITY OF TOXICANTS
Types of Toxicity/Exposure
i. Acute Toxicity: Toxicity elicited as a result of short-term exposure to a toxicant. The effect of toxicants in acute toxicity is immediate and is usually associated with accidents. Example: corrosive chemical effect on the skin.
ii. Chronic Toxicity: Toxicity elicited as a result of long-term exposure to a toxicant. In chronic toxicity, the effect is delayed and do not occur until after the lapse of some time. For example Carcinogenic effects of many chemicals usually have a long latency period, often 20 to 30 years after the initial exposure, before tumors are observed in humans . V. Factors Affecting Toxicity Not all individual organisms are equal. Sensitivity to toxicant can vary with sex, age, weight, etc.
Environmental chemistry is the study of the chemical and biochemical phenomena that occur in nature. It involves the understanding of how the uncontaminated environment works, and which naturally occurring chemicals are present, in what concentrations and with what effects. Without this it would be impossible to study accurately the effects that humans exert on the environment through the release of chemical species. It is a multi-disciplinary science that, in addition to chemistry, involves physics, life science, agriculture, material science, public health, sanitary engineering, and so on. More or less, it is the study of the sources, reactions, transport, effects, and fate of chemical species in the air, water, and land, and the effect of human activities upon the various environmental segments, such as atmosphere, hydrosphere, lithosphere, and biosphere.
At present, many environmental issues exist that have grown in size and complexity day by day, threatening the survival of mankind on earth.
There are four environmental segments: atmosphere, hydrosphere, lithosphere consisting of abiotic or physical environment, and biosphere— the fourth segment of environment that consists of flora and fauna. Abiotic and biotic components together constitute the biome environment.
Atmosphere is a protective blanket of gases surrounding the earth, which supports life and protects it from the hostile environment of outer space. Atmosphere absorbs most of the cosmic rays from outer space and a major portion of the electromagnetic radiation from the sun, and also maintains the heat balance of the earth. It transmits only near-ultraviolet, visible, near-infrared (IR) (300–2500 nm), and radio waves (0.14–40 m), and absorbs energy re-emitted from the earth in the form of IR radiation. It serves as an insulator against heat loss from the surface of the earth, and stabilizes weather and climate owing to the heat capacity of the air.
What are substances that damage the atmosphere?
The release into the air of chemicals and particles can cause direct damage to the troposphere (air pollution); alter the composition and function of atmospheric layers (greenhouse effect) or other indirect damages (ozone layer depletion).
An air pollutant is a substance in the air that can cause harm to humans and the environment. Indoor air pollution and urban air quality are listed as two of the world”s worst pollution problems in the 2008.
Pollutants can be classified as primary or secondary. Usually, primary pollutants are directly emitted from a process, such as ash from a volcanic eruption, the carbon monoxide gas from a motor vehicle exhaust or sulfur dioxide released from factories. Secondary pollutants are not emitted directly. One example is ground-level ozone.
The transport sector has become one of the main emitters of polluting compounds in the world and one of the main causes of the greenhouse effect. Also, a report by the European Environment Agency (EEA) points out that road transport is the single largest air polluter in Europe. Through the burning of fuel, motor vehicles, cars and trucks emit a range of health damaging pollutants, such as particulate matter, nitrogen oxides, sulphur dioxide, carbon monoxides and Volatile Organic Compounds (VOCs). Some of the substances in motor vehicle exhaust also cause ‘secondary pollutants’ such as ozone, which are formed through chemical reactions in the air.
Air pollution is especially a problem in urban areas, where there is a lot of traffic. Some pollutants however can travel long distances and may accumulate in suburban or rural areas because of weather conditions such as wind or low pressure.
Compared with traffic, industrial activities are responsible for a larger total emission per year.
Main air pollutants are:
1. Sulphur oxides (SOx) – Mainly Sulphur dioxide (SO2). It is one of the causes for concern over the environmental impact of the use of fuels as power sources.
2. Nitrogen oxides (NOx) – NO2 is one of the most prominent air pollutants. Nitrogen (N) compounds, emitted as NOX and NH3, are now the principal acidifying components in our air and cause eutrophication of ecosystems.
3. Particulate matter – Particulates, alternatively referred to as particulate matter (PM) or fine particles, are tiny particles of solid or liquid suspended in a gas. Human activities, such as the burning of fossil fuels in vehicles, power plants and various industrial processes also generate significant amounts of aerosols.
4. Carbon monoxide (CO) – It is a product by incomplete combustion of fuel such as natural gas, coal or wood. Vehicular exhaust is a major source of carbon monoxide.
5. Carbon dioxide (CO2) – emitted from sources such as combustion, cement production, and respiration.
6. Heavy metals, such as arsenic (As), cadmium (Cd), lead (Pb) and nickel (Ni)
Benzene and benzo(a)pyrene
7. Ammonia (NH3) – emitted from agricultural processes.
8. Volatile organic compounds – VOCs are an important outdoor air pollutants
9. Chlorofluorocarbons (CFCs) – harmful to the ozone layer
Health impacts of air pollution
Air pollution is a major environmental risk to health.
Numerous scientific studies have linked air pollution to health effects including: harm to the respiratory system, leading to the development or aggravation of respiratory diseases, decreased lung function, increased frequency and severity of respiratory symptoms such as coughing and difficulty breathing, or increased susceptibility to respiratory infections; harm to the cardiovascular system; harm to the nervous system, affecting learning, memory and behaviour; harm to the reproductive system; cancer
Some of these impacts may result in premature death. Sensitive individuals, such as older adults and children and people with pre-existing heart and lung diseases or diabetes, appear to be at greater risk of air pollution-related health effects.
Asthma and respiratory conditions are among the most common effects on human health and they raise especial concern in the case of children. 10% of European children suffer asthma, allergies and respiratory conditions associated with air pollution (particles).
In 2005, an estimated 5 million years of lost life were caused by fine particulate matter pollution (PM2.5) alone in the EEA-32 countries (EEA, 2010).
Ecosystem impacts of air pollution
Air pollution also damages the environment. For example, ozone can damage crops and other vegetation, impairing growth. These impacts can reduce the ability of plants to take up CO2 from the atmosphere and indirectly affect entire ecosystems and the planet”s climate. The atmospheric deposition of sulphur and nitrogen compounds has acidifying effects on soils and freshwaters. Acidification causes disturbances in the function and structure of ecosystems with harmful ecological effects, including biodiversity loss. Likewise, deposition of nitrogen compounds can lead to eutrophication, which constitutes an oversupply of nutrient nitrogen in terrestrial and aquatic ecosystems. Consequences include changes in species diversity, invasions of new species and leaching of nitrate to groundwater.
The stratosphere, a high layer of the atmosphere contains a high concentration of ozone. Ozone layer depletion allows a greater amount of ultraviolet (UV) radiation to reach the surface of the earth. An increase of UV radiation levels implies a significant harm to human health (skin cancer, cataracts, damage to the immune system) and to ecosystems, wild life and agriculture.
Air pollution may also impact the Earth”s climate. Some air pollutants interfere with the Earth”s energy balance and are therefore known as “climate forcers”.
These can either be gases (e.g. ozone) or airborne particulate matter (aerosols). Some climate forcers reflect solar radiation (e.g. sulphate aerosols) leading to net cooling, while others (e.g. black carbon aerosols) absorb solar radiation, thereby warming the atmosphere. In addition, aerosols influence the formation, microphysics and optical properties of clouds, resulting in indirect climatological effects.
Deposition of certain aerosols (e.g. black carbon) may also change the Earth”s surface reflectivity (albedo), especially on ice- and snow-covered surfaces, thereby accelerating melting.
The “greenhouse effect” is an increase of the average global temperature due to the accumulation of polluting gases in higher atmospheric levels that causes regional and global climate change.
The most visible greenhouse effects include:
1. increased frequency of extreme weather events (floods, draughts, retreating glaciers)
2. increase of sea level
extreme winter/ summer temperature differences
3. reduction of agricultural production in certain regions
alteration of natural systems
4. Climate change and ozone depletion are serious environmental problems that alter the stability of ecosystems and affect social structures.
What to do?
i. Avoid or reduce atmospheric emissions of these chemicals.
ii. Suggest the elimination or substitution of products or processes that generate those pollutants, replacing them with alternatives that eliminate or reduce air pollutants.
iii. When elimination or substitution is not possible, due to technical limitations, the second priority is to reduce the amount of air emissions, through plans to minimize the consumption of resources and raw materials and plans for minimizing emissions, discharges and waste generation, the reuse or recycling in situ, i.e. within the process or the introduction of best practices that reduce the risk inside and outside the facility, among other measures.
iv. Control and monitor the company’s compliance with legal air emission requirements.
Promote saving and energy efficiency measures (e.g. knowledge of data on energy consumption, study facilities and equipment, identify opportunities for energy savings, opportunities for good practices for saving energy)
Promote sustainable mobility plans in companies to reduce the use of private motor vehicles (e.g. promotion of public transport access to the workplace, in coordination with the metropolitan transport authorities and transport companies, information for workers on daily mobility alternatives to private vehicles: on foot, by bicycle, public transport, car pooling, promotion of education for the mobility of workers to make them aware of the risks associated with current mobility model).
Hydrosphere, which covers more than 75% of the earth’s surface, includes all types of water resources—oceans, sea, rivers, lakes, streams, reservoir, glaciers, polar ice caps, and groundwater (that is, water below the earth’s surface). About 97% of the total water available on earth is in the form of oceans, which cannot be used for human consumption owing to its high salt content. About 2% of the water resources are locked in the polar ice caps and glaciers, while only 1% is available as freshwater (surface water—river, lakes, streams, and groundwater) for human consumption and other uses. Freshwater is also available in the form of rains, snow, dew, and so on.
Out of all natural resources, water is the most essential for the existence of living beings. Water sustains life on the earth. Unfortunately, civilization has perished it and is responsible for its pollution. Water pollution may be defined as the deterioration in the physical, chemical, and biological properties of water, brought about mainly by anthropogenic activities. It can also be caused by natural weathering of the product of rocks, minerals, soil sediments, nutrients, as well 22 Introduction to Environmental Sciences as organic matters of soil (decomposed animals, microorganisms, and vegetable materials) that are transported by erosion. This deterioration in quality of water body (both surface and ground) has increased during the past few decades mainly by enhanced human activities in industrial and agricultural sectors. In recent years, there has been an increasing concern around the world regarding the widespread distribution of the pollutants stemming from human activities and the potential harmful effects of these pollutants on human or the ecological systems. Some environmental problems such as contaminated water have arisen from poorly controlled discharges of industrial effluents into the water bodies, while others such as air pollution have arisen from poor emission control on the energy generation industry and motor vehicles.
Parameters of Pollution
The following parameters determine the nature and extent of pollution in water:
Physical parameters—colour, odour, turbidity, density, temperature, and so on
Chemical parameters—pH, total dissolved solids (TDS) and their ionic composition, suspended solids, dissolved oxygen (DO), residual chorine, COD, biochemical oxygen demand (BOD), redox potential, radioactive substances, organic materials, metallic ions (including heavy metals), oxides, by-products of industries, and so on
Biological parameters—different types of microorganisms, bacteria, algae, small animals such as protozoa and crustaceans, and so on Water Pollutants Nature and concentration of the pollutants depend upon their sources, physical and chemical conditions, and reactivity with the surrounding environment. The large number of water pollutants may broadly be classified under the following categories:
(i) Organic pollutants—These include degradable and non-degradable products, as well as disease-causing agents, plant nutrients, sewage, synthetic organic compounds, and oil. DO is an essential requirement for aquatic life. Its level in the water body should be 4–6 ppm. Decrease in this value is an indication of pollution mainly caused by organic matter, for example, sewage, industrial wastes, and run-off from agricultural lands.
(ii) Inorganic pollutants—These pollutants consist of inorganic salts, finely divided metal or metal compounds, trace elements, complexes of metal with organic moiety mineral acid, etc
(iii) Sediments—Sediments are insoluble soil particles of unknown composition that enter water bodies by soil erosion. In fact, sediments are the most extensive pollutants of surface water. It has roughly been estimated that suspended solids loading reaching natural waters are about 700 times as large as the solids loading from sewage discharge. Several factors such as agricultural practices, construction activities, and strip mining activities have great influences on solid erosion rates in the given area.
(iv) Radioactive substances—Radioactive pollution is the worst pollution among all and it is detrimental to health. Sources of environmental radioisotopes may broadly be grouped as natural and artificial. Natural radioisotopes produced by cosmic rays find their way into soil and water courses through precipitation (rainfall and snow) and run-off, whereas those occurring on the surface of the earth and below enter the water-bearing formulations through weathering. On the other hand, man-made radioisotopes enter the environment mainly through nuclear installations and research organizations. Some of the radioisotopes such as K-40; Ra-222, Ra-226, and Ra-228; Pb-210; and C-14 are incorporated into the human body through different pathways.
(v) Thermal pollutants—Coal-fired or nuclear fuels used by steam power plants are among the most important sources of thermal pollutants, as only a fraction of the heat generated using these fuels is successfully converted to work and the remaining is wasted. Even in the modern coal-fired plants, the efficiency does not exceed 40%. The condensers used in these plants utilize water from nearby river or lake or municipal source.
This is the outer mantle of the solid earth, consisting of minerals occurring in the earth crust and the soil. The earth is a cold, spherical solid planet of the solar system, which spins on its axis and revolves around the sun, maintaining a certain constant distance. It comprises a complex mixture of minerals, organic matter, air, and water. 18 Introduction to Environmental Sciences Lithosphere mainly consists of three layers: crust, mantle, and outer and inner core. The surface of the crust is covered with soil, which is the most important part of lithosphere. Soil is a mixture of organic as well as weathered rock and materials necessary for the growth of plants. It is a storehouse of minerals, a reservoir of water, a conserver of soil fertility, a producer of vegetative crops, and a home of wildlife and livestock.
Biosphere denotes the realm of living organisms and their interaction with the environment, that is, atmosphere, hydrosphere, and lithosphere. Both the biosphere and the environment are influenced by each other considerably. Thus, the levels of oxygen and carbon dioxide in the atmosphere depend entirely on the plant kingdom. As a matter of fact, green plants alone are responsible for the accumulation of oxygen in the atmosphere, through photosynthesis and decay; the original atmosphere was devoid of oxygen.
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