Sources of Water Pollution
尽管人们可以直接面对肮脏引起的疾病，但是直到十九世纪中期人们还没有意识到由污染水源引发的疾病传播。百老汇街上的水管就可以明显的看出水可以传播疾病。
1854年，一名叫Jonh Snow的公共卫生医师接到任务来控制霍乱的传播，在伦敦部分地区引起了高度重视。大多数人们都在百老汇中央水管喝水而染上疾病，而在附近一家啤酒厂工作的工人们却没有被传染。Snow意识到啤酒厂的工人们对霍乱有免疫的原因是由于啤酒厂工人喝的水是来自他们自己的地下水，而不是百老汇水管里的水（因此免疫应归功于啤酒）。Snow的证据说服了市政府禁止污染水的供应，最后拆毁了水管，不再使用了。传染源被切断了，霍乱的蔓延也平息了，公众也开始了解干净饮水的重要性。
直到最近，由于水传播疾病和传播细菌，因此水污染被认为是威胁人类健康的主要因素。在一些不发达的国家，或者在一些战乱的国家里，水传播疾病仍然是公众健康威胁的主要问题。在美国和其它无微生物污染的国家，水处理及分配方式基本上是无微生物污染的。我们现在意识到水污染构成更广泛的威胁，而且还在威胁着公众卫生安全，同时也威胁水生物的安全。在本章，我们讨论水污染源及河流、湖、海污染的影响。
水污染源
水污染物分为点源和非点源，前者认为所有干燥空气污染物通过水管或管道进入水道。雨水排水也会通过水管或管道进入水道，这都被认为是非点源污染。其它非点源污染来自匀在第十一章讨论过的农业上的排水，建筑工地和其它土地施工。点源污染主要来自工业工厂和城市废水处理厂。污染源的范围很广，仅仅根据什么可以产生污染。
牛奶加工厂、酿酒厂、或造纸厂、以及市政废水处理厂是构成污染物需氧量最重要类型, 这些物质在水道中分解会消耗掉的水中的溶氧。
1. We can’t live without water, but now many rivers are polluted. Hundreds of dead fish can be found on the surface of Haihe because of serious pollution. It is dangerous to drink such water.Besides Haihe, there are other rivers like this.
People come to know the seriousness of water pollution. Our government is taking measures to protect the rivers against pollutions. Peopie also try their best to protect rivers and keep them clean.
Water is used in homes, in farming, and in manufacturing. The water used by the people comes from oceans, lakes, rivers, and streams. Many water sources are becoming polluted. People are throwing things into the water. Factories are dumping waste materials into the water. Cities are dumping sewage into the water. Some water sources have become so badly polluted that the water cannot be made fit to use. Would you like to drink water that came from a source that had been so badly mistreated? Now is the time that we should take up our responsibility to protect our environment from being polluted.
2.Water pollution is caused by waste from factories and cities. Oceans are able to clean themselves, but certain seas, once they become dirty, are not able to do so. One example is the Mediterranean which lies between Europe and Africa. It has onlyeone narrow entrance to the ocean in the west. On quarter of the shores of the Mediterranean are polluted and are no longer safe for swimming, as a lot of diseases are present in the water. In most places it is not safe to eat the fish.
Lakes also have the same problems. Lake Baikal in Asia was once the cleanest in the world, with over 700 different kinds of plant and animal life. Now, however, the waters of this great lake, which is also the world\'s deepest (over 1,740 metres), have been dirtied by waste from a chemical factory.
In 1989 an oil tanker hit a rock off the northwest coast of Alaska. 35,000 tons of oil poured into the sea. The accident was one of the worst in history. More than 34,000 birds and 10,000 animals were killed. 4,800 square kilometres of ocean were polluted.
3. Spring is the best season of the year. The weather gets warmer and warmer. My clas i\'amates and I took a one-day sightseeing around our city.The scene was pretty. But when we saw the rivers along our city, I felt very sorry, and thoughit a lot.
With the development of modern agriculture and industry, more and more waste water is being poured into rivers. It has caused serious pollution. The river is becoming so dirty that no living things can live in it. The river is giving off a terrible smell.
We make an urgent appeal that measures should be taken to cope with the situation. Our government should start building various facilities such as sewage treatment!plant and encourage scientists to work out more and better ways to reduce the pollution of water.
Water is tho source of our lives. It is very important to protect water.
4. My classmates and I had an outing this spring. We had a good time. But meanwhile I noticed that water pollution in our city was becoming more and more serious.
On our way, we could see women washing clothes in the river. Litter was floating on the river. Waste water produced by a chemical factory was being discharged into the river. We did not see any fish in the river. The fiver was not so clear as before. Water quality was very bad. I am worried about it because water is important to all living things. Man can not live without water. I hope people pay more attention to this problem, especially the government. Try to control the pollution of water as early as possible.
At last I would like to say, "To protect water is to protect life."
Klaus-Dieter Balke
Institute for Geosciences,University of Tuebingen,Sigwartstr.10,D-72076 Tuebingen,Germany
Yan Zhu
Dept.of Earth Sciences,Zhejiang University,Yuquan Campus,310012 Hangzhou,P.R.China
1 Water quality
The quality of surface water in rivers,lakes or artificial reservoirs,depends nowadays not only on the natural composition of the water but also on the intensity and kind of man-made pollution.
Groundwater contained in the subsurface fills pores and joints of rocks,see Fig.1.
Fig.1 Kinds of subsurface water（after Davies ＆ DeWiest,1966）
Fig.2 Concentration of dissolved salts increases from shallow to deep aquifer
Regarding groundwater quality particularly the climatic parameters precipitation and temperature influence the hydrochemical properties.They govern weathering processes which cause a removal of soluble ions and molecules out of rocks.These substances,transported by percolating water,finally reach groundwater bodies.
During the groundwater flow through an aquifer,chemical interactions between ground-water and the rocks of the aquifer take place.
The main dissolved ions in groundwater are Ca2+,Mg2+,Na+,K+,
Additionally,there are many other compounds of minor concentration such as Fe,Si,Sr,B,NO3,CO3,etc.
and trace substances such as Al,Cd,Cr,Co,Cu,Pb,Ra,Se,NO2,NH4,PO4,H2S,etc.
Generally,the concentration of dis-solved salts increases from shallow to deep aquifers and the dominant ions change see Fig.2.
cations;Ca2+-Ca2++Mg2+-Na+,
anions:
At a global scale, the amount of dis-solved substances in shallow groundwater in-creases from the arctic areas via the temper-ate zones towards the arid regions and decreases again towards the humid tropics,see Fig.3.
In most cases,between surface-and groundwater there exists a hydraulic connection,e.g.along river banks,see Fig.4.Surface-and groundwater influence each other and contamination can be transferred from surface water into groundwater and vice versa.
Besides natural components dissolved in water a huge variety of artificially produced chemical substances may contaminate the water resources.
Fig.3 Hydrochemical distribution of groundwater types of the European part of the USSR（after Alekin,1962）
1.Zone of hydrogencarbonatic-SiO2-groundwater
2.Zone of hydrogencarbonatic-Ca-groundwater
3.Zone of prevailing sulphatic and chiloridic groundwater
4.subzone of continental salt fringe
5.Zone of hydrogencarbonatic-Ca-groundwater of montaneous areas
Fig.4 effluent system（a）and influent system（b）
2 Artificial contamination of water
2.1 Agriculture
The increase of food production in many areas around the world requires the application of increasing amounts of fertilizers.
Among them especially nitrogen N as nitrate NO3,phosphorus P as phosphate PO4 and potassium K are essential elements for phytogenic and animal organisms.
Especially high concentrations of nitrate and phosphate are to be found in water of rivers passing farm land and in groundwater below over-fertilized farm land where inorganic nitrate and phosphate are applied excessively.
Another important source of contamination is often cattle breeding,respectively the removal of manure.Manure contains a lot of nitrate and is often spread out on farmland,from where it is washed into rivers and downwards into groundwater.
In order to avoid harvest losses and to increase the crop yield,pesticides are usually applied to exterminate plant pests,weeds,destructive insects and parasites.The toxic components of these agents are organic compounds,especially chlorinated hydrocarbons,and inorganic chemicals such as heavy metals,hydrogen cyanide,phosphorus,sulphur,etc.
Another group of contaminants with yet minor importance are veterinary pharmaceuticals which percolate the subsurface contained in fluid manure.
2.2 Industry
Industry and handicraft use numerous substances for their production:salts,heavy metals,hydrocarbons,chlorinated hydrocarbons,chlorofluorocarbons,radioactive compounds,pharmaceuticals,etc.These compounds are accumulated near the locations of the processing industries,in the working range of their products and in waste and sewage.
Mineral oil products such as gasoline,diesel,kerosene,fuel oil,etc.are lighter than water.After having percolated the vadose zone they spread out above the groundwater surface,see Fig.5.There,lenses of oil are formed.The soluble parts of the mineral oil diffuse into the groundwater.
If halogenated hydrocarbons seep downwards they infiltrate the vadose zone,percolate the aquifer and accumulate on its bottom,see Fig.5.That is an essentially different behaviour in an aquifer than that of oil.
Fig.5 Behaviour of hydrocarbons and halogenated hydrocarbons
The most important properties of chlorinated hydrocarbons are shown in Table 1:
Table 1 Properties of some chlorinated hydrocarbons
The water solubility of chlorinated hydrocarbons is relatively high,in many cases it exceeds by far the limiting values for drinking water.The boiling point is often below 100℃，i.e.such substances evaporate more easily than water.Their mass density,often above that of water,allows them to percolate through water bodies.
Halogenated hydrocarbons are easily volatile and chemically very persistent,they are even able to penetrate clay layers and concrete;moreover,they are lipidophilic i.e.they can penetrate cell membranes and accumulate in organic cells.Therefore,they can be found nowadays in the atmosphere,in rain water,surface water,sea water and shallow groundwater as well as in plants,animals,and even within human beings.
The most important users of chlorinated hydrocarbons are:metal industry,chemical industry,pharmaceutical industry,dry cleaners,textile industry,plastics processing industry,paper and pulp industry,car industry and repair shops,production of paints and varnishes,production of feed-stuff,printing shops,production of cooling agents,recycling plants,re-fineries,production of aroma substances and essences,etc.
Heavy metals,67 metallic elements with specific weights greater than 5g/cm3,are natural constituents of rocks,enriched in ore deposits.
Being involved in many chemical reactions and technical processes they are ultimately incorporated in waste,sewage,sewage sludge from treatment plants,and exhaust fumes.
Since most of the heavy metals are toxic to human beings above individually specified concentration levels it is of great importance to control their existence in the environment.
Heavy metals are elements and therefore not degradable by natural decay.They can precipitate especially as hydroxides（e.g.Fe（OH）3）,oxides（e.g.Fe3O4）,and sulphides（e.g.FeS2）,and they can be adsorbed by some natural substances（clay,hydroxides,humicmatter,etc.）.In case of changing pH-values（into the acid range）and redox potentials（to low values）adsorbed or precipitated heavy metals can be dissolved again.
As a result of natural release（volcanic exhalations,weathering processes,burning of forests）and man-made release（traffic,industrial and private exhaust gases,plant protective agents,burning of oil,coal,and wood）,rainwater contains heavy metals.
2.3 Private households
In private households salts,diluting agents,paint remover,cleaning agents,pharmaceuticals,cosmetics,etc.are in use.
The waste from households is often deposited in uncontrolled municipal waste deposits which deliver contaminated waste water into the subsurface.Fluid contaminants percolate out of leaky sewage pipe systems into groundwater bodies.In developing countries septic tanks may release inorganic and organic pollutants.
2.4 Pharmaceutical contaminants
With growing population and rising living standard the application and use of pharmaceuticals increases.This group of chemical substances includes compounds such as hormones,vitamins,enzymes,beta-blocker,psycho pharmacological medicine,anti-epileptic drugs,antibiotics,disinfectants,etc.and their metabolites as decay products.In Germany about 45.000 different pharmaceuticals are licensed for sale.
Nowadays,pharmaceuticals can be found in surface-and groundwater.Concentrations up to 20μg/L have been measured in water which is released from sewage treatment plants after the treatment process into receiving rivers,and values up to 1μg/L in groundwater.Regarding these results it has to be taken into consideration that only a very limited number of compounds have been measured until now.The endangering potential may be higher than yet estimated.
Many pharmaceuticals are very persistent.In some cases 50% of the original dose is excreted from the body chemically unaltered,and they are not decayed by water treatment.Mainly released from sewage treatment plants into receiving rivers,from sewage of pharmaceutical industry,out of leaky sewer pipe systems,and dissolved in leachate from waste deposits,they pollute surface-and groundwater.A special source is cattle breeding with the application of antibiotics and hormones if liquid manure from these animals percolate into the subsurface.
In German rivers maximum concentrations have been measured of
lipid regulators 3.1μg/L,
anti-phlogistics 4.1μg/L,
beta-blockers 2.9μg/L,
anti-epileptics 1.2μg/L,
antibiotics 1.7μg/L,
X-ray contrast medium 2.8μg/L,
estrogens 0.0016μg/L.
The concentrations are mostly higher in small than in big rivers,but they can accumulate to remarkable values,see Fig.6.
Generally,the concentrations of pharmaceuticals and the number of substances involved are higher in surface water than in groundwater.
At the present time,an endangering of human beings by pharmaceutics in drinking water and acute poisoning is scarcely to be expected.But it is as yet unknown whether a long-term poisoning by a cumulative effect may happen.Chronic effects could include toxicity against genes,nerves,and the immune system.It also has to be considered that enrichment effects in animals and human beings may lead to concentrations exceeding acceptable values.Such enrichment effects happened in fresh water fishes in Germany and in farmed shrimps in the Philip-pines some yearsago.In any case,it can be expected that in the long run germs,bacteria,viri,etc.come into being which are resistant to antibiotics.Also in such a way humans and the ecosystem could be affected.
In order to reduce the occurrence of pharmaceutical compounds in surface-and groundwater it is necessary to optimise municipal and industrial sewage treatment processes,to repair defect sewage pipe systems,to use only controlled waste deposits,and to inform and train the population not to remove expired pharmaceutics by putting them into sewage.
Fig.6 Contamination of the Weschnitz with pharmaceutical residues（after Ternes,2001）
Another group of newly apparent substances in surface-and groundwater are cosmetics and perfumes（the production of cosmetics only in Germany amounted in 1993 to about 550.000 tons）.It has to be taken into consideration that most of these substances are finally washed off the body and disappear in the sewage system.
References
[1]Alekin O.A.1962.Grundlagen der Wasserchemie.-61 fig.,Leipzig（Dt.Verlag fur Grundstoffindistrie）,260p.
[2]Davies N.S.,DeWiest,R.J.M.1966.Hydrogeology.-New York（Wiley）,463p.
[3]Ternes Th.2001.Vorkommen von Pharmaka in Gew?ssern.-Wasser,Boden.53/4,ISSN 0043-0951,Berlin
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