First, the main pollutants
1, pathogenic pollutants?
Livestock and poultry rearing industrial wastewater, as well as tanning, wool washing, slaughtering, medical industry and other wastewater discharged, often containing a variety of pathogens, such as viruses, germs, parasites. Pollution of water bodies by pathogens can spread diseases such as schistosomiasis, cholera, typhoid, dysentery, and viral hepatitis. Some of the plagues that have been prevalent throughout history have been waterborne infections. Such as 1848 and 1854, two cholera epidemics in the United Kingdom, the death of more than 10,000 people; 1892 cholera epidemic in Hamburg, Germany, the death of more than 750 people, are caused by water pollution.
Pathogen-contaminated water, microbial proliferation, many of which are pathogenic bacteria, pathogenic eggs and viruses, they tend to exist with other bacteria and E. coli ****, so it is usually specified with the total number of bacteria and E. coli index and the number of bacterial values for the direct indicators of pathogen contamination. Pathogen contamination is characterized by: (1) large number; (2) wide distribution; (3) long survival time; (4) rapid reproduction; (5) easy to produce resistance, it is difficult to extinction; (6) the traditional secondary biochemical wastewater treatment and chlorination disinfection, some pathogenic microorganisms, viruses can still survive in large numbers. Common coagulation, sedimentation, filtration, disinfection treatment can remove more than 99% of the virus in the water, such as the turbidity of the effluent is greater than 0.5 degrees, will still be accompanied by virus penetration. Pathogenic pollutants can enter the water body through a variety of ways, once the conditions are suitable, it will cause human disease.
2, oxygen-depleting pollutants?
Industrial wastewater, such as food processing and paper, contains carbohydrates, proteins, oils and fats, lignin and other organic substances. These substances exist in suspension or dissolved state in the sewage, can be decomposed through the biochemical action of microorganisms. Oxygen is consumed during their decomposition, and they are called oxygen-consuming pollutants. Such pollutants can cause a decrease in dissolved oxygen in the water, affecting the growth of fish and other aquatic organisms. When the dissolved oxygen in the water is depleted, the organic matter undergoes anaerobic decomposition, producing unpleasant odors such as hydrogen sulfide, ammonia, and mercaptans, further deteriorating the water quality. Organic matter in the water column is very complex, the concentration of oxygen-depleting organic matter commonly used per unit volume of water in the biochemical decomposition of oxygen-depleting substances in the process of oxygen consumption, that is, expressed in biochemical oxygen demand (BOD). Generally 20 ℃, five days of biochemical oxygen demand (BOD5) that.
3, plant nutrients?
Plant nutrients mainly refers to nitrogen, phosphorus and other substances that can stimulate the growth of algae and water plants, interfere with water purification, so that the BOD5 rise. Excessive nutrients in the water body caused by the "eutrophication" of lakes and slow-moving water bodies caused by the harm has become a serious problem of water conservation.
Eutrophication (eutrophication) refers to the influence of human activities, biological nitrogen, phosphorus and other nutrients into lakes, estuaries, bays and other slow-flowing bodies of water, caused by algae and other plankton rapid reproduction of the body of water, the decline in dissolved oxygen, water quality deterioration, fish and other organisms die a large number of phenomena. Under natural conditions, lakes will also transition from a nutrient-poor state to a nutrient-rich state, with increasing sediments, first becoming a marsh and then a land. This natural process is very slow and often takes thousands or even tens of thousands of years. And man-made discharge of nutrient-containing industrial wastewater and domestic sewage caused by the eutrophication of water bodies can appear in a short period of time.
Plant nutrients from a wide range of sources and large quantities of domestic sewage (organic matter, detergents), agriculture (fertilizers, farmyard manure), industrial wastewater, garbage and so on. Nitrogen brought into the sewage per person per day is about 50 g. Phosphorus in domestic sewage mainly comes from washing wastewater, while 50% to 80% of fertilizers applied to farmland flow into rivers, lakes, seas and groundwater bodies. The content of phosphorus and nitrogen (especially phosphorus) in natural water bodies is to some extent a controlling factor for plankton growth. When a large amount of nitrogen and phosphorus plant nutrients are discharged into the water body, certain organisms (e.g., algae) are prompted to reproduce and grow dramatically, and the growth cycle becomes shorter. Algae and other plankton die and are decomposed by aerobic organisms, constantly consuming dissolved oxygen in the water, or are decomposed by anaerobic microorganisms, constantly producing hydrogen sulfide and other gases, which deteriorates water quality and causes the death of a large number of fish and other aquatic organisms. Algae and other plankton residues in the decay process, and the biological needs of nitrogen, phosphorus and other nutrients released into the water for a new generation of algae and other organisms to use. Therefore, after eutrophication of the water body, even if the source of external nutrients is cut off, it is very difficult to self-purify and restore to the normal level. When the eutrophication of the water body is serious, the lake can be silted up by some flourishing plants and their remains, becoming a swamp or even a dry land. Local sea area can become "dead sea", or "red tide" phenomenon.
Commonly used nitrogen and phosphorus content, productivity (O2) and chlorophyll-alpha as an indicator of the degree of eutrophication of water bodies. Prevention and control of eutrophication, must control the nitrogen and phosphorus content into the water body.
4, toxic pollutants
Toxic pollutants refers to the organisms that enter the accumulation of a certain number of body fluids and tissues can make changes in biochemical and physiological functions, causing temporary or persistent pathological state, or even life-threatening substances. Such as heavy metals and organic pollutants that are difficult to decompose. The toxicity of a pollutant is closely related to the amount ingested into the body. The toxicity of the same pollutant is also closely related to the form in which it exists. Different valence or form, its toxicity can have a great difference. For example, the toxicity of Cr(VI) is greater than that of Cr(III); the toxicity of As(III) is greater than that of As(V); the toxicity of methylmercury is much greater than that of inorganic mercury. In addition the toxicity of pollutants is closely related to a number of combined effects. From the traditional toxicology, toxic pollutants have three kinds of integrated effects on living things: (1) additive effect, i.e., more than two kinds of toxicants **** existence, its total effect is roughly the sum of the effect of the components. (2) synergistic effect, i.e., more than two toxicants * * * existence, a component can promote another component of the toxicity of a sharp increase. Such as copper, zinc *** existence, its toxicity for their individual existence of 8 times. (3) antagonistic effect, more than two kinds of poison *** existence, its toxicity can offset part or most. Such as zinc can inhibit the toxicity of cadmium; selenium can produce antagonistic effect on mercury under certain conditions. In short, in addition to considering the content of toxic pollutants, but also to consider its presence of form and integrated effect, so that a comprehensive and in-depth understanding of the pollutants on water quality and human health impact.
Toxic pollutants are mainly the following categories: (1) heavy metals. Such as mercury, cadmium, chromium, lead, vanadium, cobalt, barium, etc., of which mercury, cadmium and lead are more harmful; arsenic, selenium and beryllium are also more toxic. Heavy metals are generally not easy to disappear in nature, and they can be enriched through the food chain; in addition to the direct effect of such substances on the human body to cause disease, some metals may also promote the development of chronic diseases. (2) Inorganic anions, mainly NO2-, F-, CN- ions. NO2- is a carcinogen. The highly toxic substance cyanide comes mainly from industrial wastewater discharges. (3) Organic pesticides, PCBs. At present, there are about 6,000 kinds of organic pesticides in the world, and about 200 kinds of them are commonly used. Pesticides are sprayed on farmland and enter the water body through leaching and other effects, resulting in pollution effects. Organic pesticides can be divided into organophosphorus pesticides and organochlorine pesticides. Although the toxicity of organophosphorus pesticides is large, but generally easy to degrade, accumulation is not strong, so the impact on the ecosystem is not obvious; while the vast majority of organochlorine pesticides, toxicity, almost no degradation, accumulation is very high, the ecosystem has a significant impact. Polychlorinated biphenyl (PCB) is a general term for a mixture of various isomers formed when a portion or all of the hydrogen in the biphenyl molecule is replaced by chlorine.
Polychlorinated biphenyls are highly toxic, fat-soluble, easily absorbed by organisms, chemically very stable, difficult to act with acids, alkalis, oxidizers, etc., highly heat-resistant, and can only be completely decomposed at high temperatures of 1000-1400 ℃, and thus are difficult to be degraded in the water column and organisms. (4) Carcinogenic substances. Carcinogenic substances are divided into three categories: thick ring aromatic hydrocarbons (PAHs), such as 3,4-benzopyrene, etc.; heterocyclic compounds, such as aflatoxin, etc.; aromatic amines, such as methyl, ethyl aniline, benzidine, etc.. (5) General organic substances. For example, there are more than 2000 kinds of phenolic compounds, and the simplest one is phenol, which are highly toxic; nitrile compounds are also toxic, among which acrylonitrile has the most attention to its environmental impact.
5, petroleum pollutants?
Oil pollution is one of the important types of water pollution, especially in estuaries and offshore waters are more prominent. Discharge into the ocean of oil is estimated to be as high as millions of tons to tens of millions of tons per year, accounting for about five thousandths of the world's total oil production. Oil pollutants mainly from industrial emissions, cleaning the oil transportation ship's cabin, machine parts and accidents, offshore oil extraction, etc. can cause oil pollution. And oil tanker accidents belong to the explosive concentration of pollution sources, the harm is devastating.?
Oil is a mixture of alkanes, olefins and aromatic hydrocarbons, the harm is manifold after entering the water body. Such as the formation of oil film on the water, can hinder the role of water reoxygenation, oil adhering to the gills of the fish, can make the fish asphyxiation; adhering to the algae, plankton, can make them die. Oil can inhibit water birds from spawning and hatching, and in severe cases, kill birds in large numbers. Oil pollution can also reduce the quality of aquatic products.
6, radioactive pollutants?
Radioactive pollution is caused by radioactive substances into the water body. Radioactive pollutants mainly from the cooling water discharged from nuclear power plants, radioactive waste to the ocean cast discarded, nuclear explosions landed in the water column of the fallout, nuclear fuel leaked from nuclear-powered ship accidents; mining, refining and the use of radioactive substances, if not properly handled, will also cause radioactive contamination. Radioactive contaminants in water bodies can attach to the surface of living organisms or enter them and accumulate, and can also cause internal irradiation of people through the food chain.
The main naturally occurring radioactive elements in water are 40K, 238U, 286Ra, 210Po, 14C, and tritium. At present, 90Sr, 137Cs can be measured in almost any sea area in the world.
7, acid, alkali, salt inorganic pollutants
A variety of acids, alkalis, salts and other inorganic substances into the water body (acid, alkali and neutralization to generate salts, and their interactions with some of the minerals in the body of water to produce certain salts), so that the freshwater resources to increase the degree of mineralization, affecting the quality of water for a variety of water. Salt pollution comes mainly from domestic sewage and industrial and mining wastewater, as well as certain industrial wastes. In addition, due to the increasing scale of acid rain, resulting in soil acidification, groundwater mineralization increased.
An increase in inorganic salts in water bodies can increase the osmotic pressure of water, which has an adverse effect on the growth of freshwater organisms and plants. In salinized areas, salt in surface water and groundwater will have a greater impact on soil quality.
8, thermal pollution
Thermal pollution is a kind of energy pollution, which is caused by industrial and mining enterprises to discharge high-temperature wastewater into the water body. Some thermal power plants and a variety of industrial processes in the cooling water, if you do not take measures, directly discharged into the water body, can make the water temperature, chemical reactions in the water, biochemical reactions speed up the speed of the chemical reaction, so that some toxic substances (such as cyanide, heavy metal ions, etc.) toxicity, dissolved oxygen reduction, affecting the survival of the fish and reproduction, accelerating the reproduction of certain bacteria, contributing to the aquatic grasses, anaerobic fermentation, malodor.
There is an optimal water temperature range for fish growth. Too high or too low a water temperature is not suitable for fish growth, and may even lead to death. The adaptability of different fish to the water temperature is also different. For example, tropical fish are suitable for 15-32℃, temperate fish are suitable for 10-22℃, and frigid fish are suitable for 2-10℃ range. Another example is that although trout live in 24℃ water, their breeding temperature is lower than 14℃. The upper limit of water temperature in which aquatic organisms in general can live is 33 to 35 degrees Celsius.
In addition to the above eight types of pollutants, detergents and other surfactants on the water environment, the main harm is to make the water foam, preventing the air and water contact and reduce the dissolved oxygen, and at the same time, due to the biochemical degradation of organic matter in the water to use up the water dissolved oxygen and lead to the lack of oxygen in the water body. The high concentration of surfactant has obvious toxicity to microorganisms.
There are many examples of water pollution, such as the Beijing-Hangzhou Grand Canal (Hangzhou section) on both sides of the banks of many factories, every day there is a large amount of wastewater discharged into the Canal, so that the water in the solid suspended solids, organics, heavy metals (Zn, Cd, Pb, Cu, etc.) and phenol, cyanide, etc. greatly exceed the ground water standards, some more than dozens of times, so that the water body is in the anaerobic reduction state, black and smelly, fish and shrimp extinct, can not be used for living, agriculture and other water;
There are also some examples of water pollution. Can not be used for life, agriculture and other water; poor self-purification capacity of the water body, if not managed, and control the source of pollution, water pollution will further expand.
The pollutants in the water environment can be divided into two categories of inorganic and organic pollutants in general. More important in the chemistry of the water environment, the more researched pollutants are heavy metals and organic matter. China's water pollution chemistry research began in the 1970s, from heavy metals, oxygen-depleting organics, DDT, six six six pesticide pollution, the focus of research has shifted to organic pollutants, especially difficult to degrade organics, because of its long retention period in the environment, easy to pass along the food chain (network) accumulation (enrichment), threatening the growth of organisms and human health, and therefore is increasingly being paid attention to. This chapter focuses on the environmental chemical behavior of heavy metals and organic pollutants transported and transformed in the water body.
Second, the movement of pollutants into the water column
Pollutants into the water column immediately after the occurrence of a variety of movements. The following is an introduction to the ocean as an example, the situation of other bodies of water, you can draw an analogy.
The ocean is home to a wide variety of aquatic animals and plants. Organisms and water, organisms and organisms carry out a complex exchange of material and energy, from the number of maintain a dynamic equilibrium relationship. However, under the influence of human activities, this balance has been disrupted. When human beings discharge pollutants into the water, some beneficial aquatic organisms will be poisoned and die, while some pollution-resistant aquatic organisms will intensify their reproduction and consume a large amount of oxygen dissolved in the water, so that beneficial aquatic organisms are forced to migrate elsewhere due to the lack of oxygen, or die. Especially some toxic elements, both difficult to dissolve in water and easy to accumulate in the organisms, causing great harm to human beings. For example, the content of mercury in water is very low, but the content in aquatic organisms is very high, and the content in fish is surprisingly high. Assuming that the concentration of mercury in the water body is 1, the concentration of mercury in the benthic organisms in aquatic organisms (referring to the small organisms living in the mud of the water body) is 700, and the concentration of mercury in fish is as high as 860. It can be seen that, when the water body is contaminated, it will lead to the disruption of the balance between the organisms and the water, between the organisms and the organisms, and on the other hand, the transfer of some poisonous substances will continue to be transferred and enriched, which will finally jeopardize the health and life of the human beings themselves. life.
Three, the impact of water pollution on human health
1, the harm of water pollution is multi-faceted, here is a brief introduction to the impact of water pollution on human health
(1), causing acute and chronic poisoning. After the water body is polluted by toxic and harmful chemicals, through the drinking water or food chain may cause poisoning. The famous Minamata disease and pain disease are caused by water pollution.
(2), carcinogenic effect. Some carcinogenic chemicals such as arsenic, chromium, nickel, beryllium, aniline, benzo (a) pyrene and other polycyclic aromatic hydrocarbons, halogenated hydrocarbons contaminated water, can be suspended, adsorption of sediment, but also in the aquatic organisms in the body of the accumulation of long-term consumption of water containing such substances, or consumption of the body of the organisms that have accumulated such substances (eg, fish) may be induced cancer.
(3), the occurrence of water-mediated infectious diseases. Human and animal feces and other biological pollutants contaminate water bodies, may cause bacterial intestinal infectious diseases such as typhoid fever, dysentery, enteritis, cholera, etc.; intestinal common viruses, such as poliovirus, coxsackievirus, infectious hepatitis viruses, etc., all through the water pollution caused by the corresponding infectious diseases. 1989 Shanghai's "Hepatitis A incident", is caused by water pollution. In developing countries, about 60 million people die of diarrhea every year, most of them are children.
(4), indirect effects. After the pollution of water bodies, often can cause the deterioration of the sensory properties of water, such as certain pollutants in a certain concentration, although there is no direct harm to human health, but can make the water odor, color, present foam and oil film, etc., impede the normal use of the water body. Copper, zinc, nickel and other substances in a certain concentration can inhibit the growth and reproduction of microorganisms, thereby affecting the decomposition of organic matter in the water and biological oxidation, so that the self-purification capacity of the water body to reduce the water body's health status.
(5), water pollution can seriously jeopardize the ecosystem as well as cause serious economic losses.
2, the impact of major pollutants
(1), lead: on the kidneys, nervous system hazards, children with high toxicity, carcinogenicity has been proved
(2), cadmium: on the kidneys have an acute injury
(3), arsenic: on the skin, the nervous system and other hazards, carcinogenicity has been proved
(4), mercury: on the human body (4) Mercury: extremely harmful to the human body, damage to the main organs for the kidneys, the central nervous system
(5) Selenium: high concentrations will harm the muscles and nervous system
(6) Nitrites: cause cardiovascular disease, the most obvious impact on infants (blue baby syndrome), carcinogenic
(7) Total trihalomethanes: chloroform has the greatest impact on the health of the most commonly occurring carcinogenicity is bladder cancer
(7) Total trihalomethanes: chloroform health impacts, the most common The most common carcinogenicity is bladder cancer
(8), trichloroethylene (organic): inhalation will reduce the central nervous system, heart function, long-term exposure to the liver is harmful
(9) carbon tetrachloride (organic): a wide range of human health effects, carcinogenicity, the liver, kidney function is extremely affected
(9), carbon tetrachloride (organic): a wide range of human health effects, carcinogenicity, liver, kidney function is extremely affected