Mercury

Environmental Chemistry 

Part 5 Typical Pollutants 

5.1 Typical Pollutants in the Environment

Typical Pollutants in the 

Environment 

• Typical inorganic pollutants 

Heavy metals: Hg, Cd, Pb, Cr, Zn, Cu, Sn, Ba; 

As, etc. 

Inorganic salts: cyanide、Nitrogen 

salts(ammonium salts 、nitrates、 nitrites)、 

sulfides、 fluoride, etc.; 

Radioactive species:Natural( 3 H, 235 U, 226 Ra)、 

Man-made ( 60 Co, 137 Cs)

• Typical organic pollutants PAHs 

Organic halides:halogenated hydrocarbon 、 

PCBs、Dioxins 

Surface active agent : anionic surfactant 、 

cationic surfactant 、 amphoteric surfactant 、 

nonionic surfactant



5.2 Mercury (Hg)

Mercury (Hg) 

1. Source and Distribution of Mercury 

in the Environment 

• Abundance ratio :63 rd in the Earth’s Crust,80 

mg/kg; 40 th in the Ocean,0.15 mg/L 

• Forms:nonvalent mercury、univalent mercury、 

bivalent mercury 

• Distribution:low concentration、broad 

distribution;all kinds of rocks;absorption 

medium;animals and plants 

• Source of pollution:waste water containing 

mercury、waste gas and waste residue-from 

factories using or producing mercury or mercuric 

compounds.

Water: industrial sewage - chlorine alkali 、 

plastics、 electronics industry 、 

amalgamative ore-refining industry and 

fulminating mercury ; 

Soil:pesticides containing mercury and sludge 

manures; 

Air:waste gas containing mercury and 

grainnessed mercury-ore-refining、burning 

of coal and oil 

Air→Soil→Water 

Annual produced quantity:>10,000t → 

“three wastes”

2. Transport and Transformation of 

Mercury in the Environment 

• Properties of Mercury 

II subgroup element(Cu, Zn), similar to Cu in 

chemical and geochemical properties 

Specificities: 

1) Relatively high oxidation-reduction potential, 

presents metallic state; 

2) Elementary Substance Hg and its chemical 

compounds are highly volatile,p300 chart 6-1 

Hg>Hg 2 Cl 2 >HgCl 2 >HgS>HgO; organic 

mercury>inorganic mercury; methyl mercury / 

phenyl mercury>other organic mercury;

3) Hg: the only metal in the form of liquid 

under normal temperature;can 

dissolve many metals and form 

amalgam ( 汞齐 ) (Na, K, Au, Ag, Zn, Cu, 

Sn, Pb); 

4) Covalence( 共价性 ): Mercury 

compounds>Znic compounds 

The high volatility, mobility and covalence of 

mercury and its compounds make easy their 

transport and distribution in the environment.

Mercury in the air 

• come from volatilization of mercury and its compounds 

• The volatility and forms of mercury compounds are closely 

related to their solubility in water, surface absorption and 

atmospheric relative humidity (RH), etc. p300 chart 6-1 

• Due to their high volatility, mercury compounds can be 

easily released into the air through transpiration( 蒸腾作用 ) 

of soil and plants. 

• Mercury in the air are mostly absorbed onto particulate 

matters( 颗粒物 ) 

• Gaseous mercury finally enter into soil and marine 

sediments.

Mercury in the water 

• The existing forms of mercury compounds and their 

transport and transformation in the environment are 

directly related to solubility in water. 

1) Hg solubility at 25 o C: 60 mg/L in pure water,25 mg/L in 

deoxidized water; 

2) Water-soluble salts:HgCl 2 , HgSO 4 , Hg(NO 3 ) 2 , Hg(ClO 3 ) 2 ; 

3) Organic mercury: 

water insoluble: diethyl mercury( 乙基汞 ) (CH 3 CH 2 ) 2 Hg 

and ethylmercuric chloride( 氯化乙基汞 )CH 3 CH 2 HgCl; 

slightly soluble:mercury phenylacetate( 乙酸苯基 

汞 )PhHgAc; 

mercury acetate( 乙酸汞 )HgAc 2 has the highest solubility.

4) Hg 2+ can easily form complex compounds ( 络 

合物 ) in the water,ligancy( 配位数 ) is 

commonly 2 or 4; Hg 2 

2+ 

are much less likely 

to form complex compounds than Hg 2+ .

• In oxidizing natural water, 

mercury are mostly in the forms of 

bivalent mercury (HgCl 2 , Hg(OH) 2 ) 

and elementary mercury (Hg 0 ) ; 

• In the forms of HgCl 3- 、 HgCl 4- in 

marine water with high Cl - 

concentration; 

• In the forms of ethiopsite ( 硫化汞 ) 

in reduced water containing sulfur 

(e.g. soil seeper) ; 

• In the substrate sludge of water, 

inorganic mercury can be 

transformed into methyl mercury 

by microorganizm.

Mercury in the soil 

• Over 95% of the mercury entering the soil can be 

retented or fixed by soil. Clay minerals and 

organic matter in the soil have strong absorption 

toward mercury. Thus, mercury accumulates 

easily in the surface of soil. 

• Amicrobic transformation:2Hg + = Hg 2+ + Hg o 

• Microbic :HgS(thiobacillus 硫杆菌 )→ Hg 2+ (antimercury 

bacteria 抗汞菌 )→ Hg 0 

• Methylation of mercury (See Bioconversion of 

Pollutants)

Mercury in the organizm 

• Inorganic mercury compounds can easily be discharged 

from organizm. 

• Combined with macromolecules in the organizm, mercury 

can form stable organic complex compounds which are 

difficult to be discharged. 

e.g. cysteine( 半胱氨酸 ) and albumin( 白蛋白 ) can form 

highly stable complex compounds with mercury, even 

higher is the stability constant K of complex compounds 

with methyl mecury, logK=15.7, 22.0

The methylation process of 

mercury inside the organizm 

1) Main products: aerobic, CH 3 Hg + ; anaerobic, (CH 3 ) 2 Hg 

2) CH 3 Hg+: water-soluble, taken by organizm and enter the 

food-chain 

(CH 3 ) 2 Hg : water-insoluble, volatile, photolytic 

3) Formation speed: methyl mercury>dimethyl mercury 

4) reciprocal transformation: 

CH 3 Hg + 

H 2 S 

pH4-5 

(CH 3 ) 2 Hg 

6,000 times 

5) peccant materiel( 致病性物质 )of minamata disease: 

methyl mercury, dimethyl mercury, propyl mercury 

6) Accumulation: With high fat-solubility, mercury alkyl is 

more easier to be concentrated than non-alkyl mercury 

and is difficult to degrade.

Methyl mercury 

Inorganic mercury in waste water is absorbed by particulate 

matter and settle to the bottom of the water body, then 

methylated by the microbic transferase. 

Methyl mercury can also combine with Cl - or OH - and 

generate methyl mercuric chloride ( 氯化甲基汞 ) or methyl 

mercuric hydroxide ( 氢氧化甲基汞 ) 

neutral or acid conditions, methyl mercuric chloride is 

dominant 

pH=8, [Cl - ]

Dimethyl mercury 

Under anaerobic conditions, undersaturated methyl 

metals are completely methylated. 

p303

• Demethylation of methyl mercury and 

reduction of mercury ion 

Pseudomonas( 假单胞菌属 ) 

Methyl mercury is degraded into methane and 

mercury.

Transport and Transformation of 

Mercury in Environmental Elements 

• Due to high volatility, mercury and mercury 

compounds entering the soil can be released 

into air through the transpiration by soil and 

plants and can also enter into surface or 

underground water through precipitation. 

• In natural water body, mercury is mainly aborbed 

by the suspended particulates and finally 

become water sediments. 

• Environmental factors such as pH and contents 

of suspended particulates affect the absorption.

• In the bottom material of a river, mercury is 

• related to the transport and transformation of 

organic matter, of which suspended mercury is the 

main form of mercury transport. Under the effect 

of microorganizm, mercury in the bottom soil can 

be transformed into methyl mercury, which is 

water-soluble and thus released back into water. 

• Methyl mercury taken by Aquatic organizm can 

accumulate inside the organizm and concentrate 

along the food-chain. Fish contaminated by 

mercury has an inside concentration of mercury 

over 100 times higher than the outside 

concentration of mercury in the water.

. Hazards of Mercury Pollution 

• Mercury’s damage to human health depends on the chemical 

state, environmental conditions of mercury and the ways of 

entering the human bodies. 

• Mercury vapor is highly diffusible and fat-soluble. It gets 

through the respiratory tract and is carried through the whole 

body by blood circulation. A large inhalation of mercury vapor 

can cause acute toxication such as hepatitis( 肝 

炎 ),hepatonephritis( 肾炎 ),hematuria( 尿血 ) and uraemia( 尿 

毒 ),etc. 

• The toxicity effect of organic mercury inside the human body is 

related to the organic radicals. Short-chained derivatives of 

mercury alkyl are more toxicant than aryl mercury( 芳基汞 ) and 

methoxyl-ethide mercury compounds( 甲氧基乙基汞化合物 ).

Hazards 

• Inhibiting a series of SH enzymes, thus damaging 

the basic functions and metabolism of cells as well 

as the detoxificating function of liver, destroying the 

cellular ionic equilibrium by changing the 

membrane permeability, preventing the nutrition 

from entering the cells and causing the ions to 

diffuse from inside the cells, finally bringing death 

to the cells. 

• Chronic intoxication of mercury includes 

neuropathic 

symptoms such as headache, faintness, limp 

numbness, aches, muscle quivering and ataxia, etc.

. Prevention of Mercury pollution 

• Improve traditional techniques, adopt substitute 

materials and reduce the use of mercury. 

• Sealed storage; prevent leaking when using; in case of 

dropping, cover with sulfur powder. 

• Treatment of waste water containing mercury 

Settling method :add sulfide to form HgS, through 

settlement and centrifugation. 

Ion-exchange method:pump in chlorine gas to transform 

elementary mercury into ionic mercury, then add chloride to 

change it into anionic complex compounds, and then 

remove it using anion exchange resin. Sometimes using 

cation exchange resin to treat waste water with a low 

concentration of Cl-.

Coagulation method:using alum, iron salts and limes, 

etc. as the coagulant 

Absorption method:Using active carbon or other 

natural macromolecular compounds with strong chelating 

power. 

Reduction method:ionic mercury is reduced to 

elemetary mercury and then filter the waste water. 

reducing agent: Al, Zn, SnCl2 etc. 

Ion-exchange method/ Coagulation method using iron 

salts or aluminum salts/ Absorption method using active 

carbon can reduced the concentration of dissolved 

mercury in the water to lower than 0.01 mg/L; 

The combination of Settling method using sulfide and 

Coagulation method can reduce the concentration of 

dissolved mercury to 0.02 mg/L;Reduction method is 

used when the concentration of mercury in the waste 

water is very low.



5.3 Polychlorinated Biphenyls (PCBs)

polychlorinated biphenyls 

(PCBs) 

• Structure and characteristics of PCBs 

209 isomers ( 异构体 ) 

Commonly 3~6 hydrion is substituted by chlorine ion, the 

content of Cl is as much as 42%~54% 

PCBs with less Cl content is usually in the liquid state. The 

more Cl content, the higher the viscosity. As for the external 

appearance, it varies from transparent liquid to white 

crystallines.

asic characteristics of PCBs 

1) Highly stable both chemically and physically; resistant to 

heat, acid, alkali, corrosion and oxidation; non-corrosive to 

metals. 

2) Difficult to dissovle or insoluble, soluble to oil or organic 

dissolvant (particularly chloride with high Cl content), also 

inter-soluble with plastics. 

3) Incombustible except monochloro and dichlor substitutes. 

4) Fine adhesive and extensive propeties. 

5) Low vapor pressure and volatility (particularly chloride with 

high Cl content) 

6) High specific inductive capacity (SIC), fine insulativity and 

electrochemical properties.

The uses of PCBs 

• As the insulative fluid in the transformers and capacitors; 

• As the medium in the heat-exchange systems and hydrolic 

systems; 

• As the additives in the production of lubricant, cutting oil, 

pesticide, paint, manifold paper, mastic and encapsulant, 

etc; 

• As the plasticiser in the production of plastics. 

Commercial production of PCBs began in 1930 and 

were gradually banned after 1977. PCBs is listed 

among the organic pollutants in priority control in 

many countries.

Transport and transfomation of 

PCBs in the environment 

• Since the production of PCBs, it is estimated that over half of 

the related products have entered the gabbage dumps. The 

combustion of such kinds of gabbage release PCBs to the 

atmosphere. 

• For the difference in climatic, biological, hydrographical and 

geological factors, etc. , the PCBs in the environment 

undergo a series of transport and transformation. PCBs are 

finally stored up mainly in soil, rivers and the bottom soil 

along the water bodies. 

• PCBs is water-insoluble and have high octanol-water 

partition coefficient, thus are more easily distributed among 

settled organic matters and soluble organic matters.

Transport and transfomation of 

PCBs in the atmosphere 

• PCBs enter into the atmosphere during the process of 

using and disposing. 

• The depletion of different PCBs depends on their 

environmental, phycial and chemical properties. 

• There are two main ways of depletion of PCBs in the 

atmosphere: direct photodecomposition; reaction with 

radicals like OH and NO 3 and also ozone. 

The radical OH has the most influence. The half-life of 

the reactions with PCBs activated by OH is 2~34 days; with 

every one more Cl ion in the PCBs molecule, the reactivity is 

reduced in half.

The atmosphere is purified of PCBs through 

rainwater flush and dry or wet precipitation, the 

process of which transports the pollutants from 

atmosphere to water or soil. 

Hydrophobic organic matters in the atmosphere 

are mainly in gaseous state or absorpt state. PCBs in 

the gaseous state and PCBs absorpt by particulate 

matters can reach the earth’s surface through dry or 

wet precipitation such as gas phase absorption, 

gravitational settling and eddy diffusion, etc.

he transport of PCBs in soil 

• PCBs continuously enter into soil in different ways. 

• Precipitaion of particulate matters is the main resource of 

PCBs in soil, while they are also partly from the sludge manure, 

leakage from the landfill and the prepartion of pesticides, etc. 

It is reported that the content of PCBs in the soil are in 

most cases over 10 times higher than that in the air above. 

• Except temperature, some other environmental factors such as 

clay content and the level of choloridization of PCBs also have 

some effect on the volatilization of PCBs in the soil. 

Biodegradation and invertible absorption contribute little to 

the depletion of PCBs. 

• Only the process of volatilization is most likely to cause the 

depletion of PCBs, especially those having more Cl content.

The transport of PCBs in water 

• PCBs enter into water (rivers, lakes and coastal water 

bodies) mainly through the process of atmospheric 

precipitation and the discharge of industial sewage, 

etc. 

• PCBs in water is low in amount is low due to their 

high volatility and low solubility in water. 

• PCBs are absorpt easily by particulate matters so that 

PCBs in water are mostly contained on the surface of 

suspended particulate matters and finally settle to the 

bottom soil. Thus, PCBs in the substrate sludge is 1 to 

2 times higher in amount than that in the water around.

PCBs in the substrate sludge can not easily be 

transported or distributed, which makes them stay in the soil 

for a long time. Also due to their high fat-solubility, PCBs are 

easily accumulated and concentrated in the organism. 

Hydrolic systems including substrate sludge and soil, etc. 

act as a very important deposition utensil to PCBs and other 

hydrophobic organic compounds. With the disappearing of 

primary pollution sources, they are likely to become the 

secondary pollution sources and release PCBs to the 

environment. 

The settled PCBs in the environment will continuously 

disperse to the oceans and cause the decreasing biotic 

population and aggravate the damage to the biological 

environment.

The transformation ways of PCBs 

in the environment 

• PCBs become persistent organic pollutants in the envrinment 

(POPs) due to its chemical inertia. 

• Main transformation ways of PCBs include photochemical 

decomposition and biotransformation. 

• Photochemical decomposition :p314 The agitation of ultra 

violet can cause the breaking of C-Cl bond and produces aryl 

radicals and chlorine radicals. 

• Biodegradation:PCBs can be degraded by pseudomonads( 假单 

胞菌 ), etc. The less Cl content, the more easy the biodegradtion. 

• Transformation in internal animals:except accumulation, PCBs 

can also undergo transformation through metabolism, the 

speed of which is reduced with more chlorine ions in the 

molecule.

Hazards of PCBs 

• Affect the growth of aquatic plants; 

at 0.1-1 mg/L, reduce photosynthesis; 

at 10-100 mg/L, inhibit the growth of aquatic plants. 

• Most species of fish are senstitive to PCBs during all stages 

of their growth. 。 

• The absorbtion of PCBs by birds can cause the expansion 

and damage of liver and kidney, internal bleeding, collapse 

of lien and thickened eggshell, etc. 

• PCBs can induce a series of symptons to mammals such as 

adenoma and cancer. 

• PCBs can cause skin ulcers, acnes, hydatoncus, liver 

damage and the increase of leukocytes, etc. Except causing 

cancers, PCBs can also be spread to infants and cause 

monstrosity.

Degradation of PCBs 

• Substrate sludge contains more PCBs with less Cl 

content while upper sludge contains more PCBs with 

more Cl content, because in the upper strata active soft 

soil, PCBs with less Cl content are easily degraded by 

microorganizm while PCBs with more Cl content are 

relatively stable. 

• Water solubility is also a factor. PCBs with higher solubility 

are easily biodegraded. 

• There is a marked concentration of PCBs when it comes 

to biodegradation, which is the lowest required 

concentration of PCBs for them to be biodegraded.

Treatment of PCBs 

• Mainly include sealing and storage, hightemperature 

treatment, chemical treament and 

biodegradation, etc. 

• Combustion at high temperature is a developed 

treatment way for PCBs which will be degraded 

completely in 2 seconds at 1200 o C but needs to 

prevent the production of dioxins, a significant 

canceroge. 

• Sealing and storage is a temporary way of 

treatment and can’t solve the problem of PCBs 

pollution fundamentally.

1) Sealing and storage 

• To seal and store the disposed transformer oil 

containing PCBs in certain stockhouses or 

bury them deeply in concrete pools or store 

them in remote caves, waiting for further 

treatment. 

• However, it would bring risks to the 

environment due to the possible leakage of 

PCBs from the rusty crust to the surounding 

area.

2) High-temperature treatment 

• It’s the most common way for treatment of PCBs at 

present. 

• Simple combustion: By adding a large amount of 

fuel and dissolvant, the temperature is raised to up 

to 1200 o C-1600 o C in several seconds so that the 

disposed transformer oil containing PCBs can 

combust and transform into other compounds. 

disadvantages: the production of dioxins, benzfuran 

and other secondary pollutants.

Fusion medium method( 熔融介质法 ):using some 

inorganic medium such as metals and inorganic 

salts, etc. instead of air as the medium for heat 

transfer and reaction during the process of 

combustion. 

This method would not produce dioxins and other 

related pollutants and doesn’t have strict 

requirements for the samples, but high expense is 

needed in the treatment of waste gas and residue. 

Plasma method: a technology using plasma as the 

heat source, high cost.

3) Chemical removal method 

• Under certain conditions, reaction between the 

added reagents and PCBs would remove chlorine 

from PCBs and produce diphenyl compounds or 

other intoxicant or slightly toxicant matters. 

• Advantages: complete treatment of waste; simple 

equipment that can be easily carried by car after 

simple design; applicable to the treatment of 

centralized and concentrated PCBs waste, while 

also applicable to scattered waste with a low 

concentration of PCBs. 

• Mainly include:metal reduction method, 

hydrogenation method, vulcanization method and 

oxidization and chlorinization method, etc.

4) Biodegradation 

• A potential method only applicable to waste with 

a low concentration of PCBs and slow reaction. 

• A combination of primary UV treatment and 

secondary microorganizm treamtment is also 

practical for the degradation treatment of PCBs. 

A thorough and environment-friendly way 

for PCBs degradation is badly needed to 

solve this tough global problem.



5.4 Surface Active Agent

surface active agent 

• Definition: under a low concentration, surface 

active agent can fix on to the surfaces of two 

phases of a system, through changing the interface 

properties, significantly reducing the surface 

tension and altering the interface state, thus 

causing wetting and dewetting, emulsification and 

deemulsification, bubbling and debubbling and 

producing solubilizing matter under relatively high 

concentration.

Principles 

• Surface active agent’s ability to fix on to the interface and 

change its properties is due to its amphiphilicity( 两亲性 ). 

• Molecular structure nonpolar lipophilic group and polar 

hydrophilic group; 

• Lipophilic group: hydrocarbon chain, polyoxyalkylene chain( 聚 

氧丙烯链 ) , fluorocarbon chain( 碳氟链 ), silane chain( 硅烷链 ), 

etc. 

• Hydrophilic group: -COOM, -SO 3 M, -CH 2 -CH 2 -O-( 聚氧乙烯链 ) 

• Not all molecules with amphiphilic structure are surface active 

agents, like sodium formate with a short lipophilic group, thus 

it’s not lipophilic enough to become surface active.

Classification and properties 

of surface active agent 

• Ways of classification: according to the use, 

properties and chemical structure; 

• Surface active agents are internationally 

classified according to the type of the 

dissociated surface active ions in water, as the 

following: 

1. anionic surfactant 

2. cationic surfactant 

3. amphoteric surfactant 

4. nonionic surfactant

1. Anionic surfactant 

• The hydrophilic group linking with hydrophobic group is an 

anion when anionic surfactant dissovles in water. 

• carboxylate:eg. soap RCOONa 

• xanthagenate :eg. sodium alkyl benzene sulfonate( 烷基苯 

磺酸钠 ) 

• sulfuric acid ester salts( 硫酸酯盐 ):eg. sodium lauryl 

sulfate( 硫酸月桂酯钠 ) C 12 H 25 OSO 3 Na 

• organic phosphate salts( 磷酸酯盐 ):eg. sodium alkyl 

phosphate( 烷基磷酸钠 )

2. Cationic surfactant 

• The hydrophilic group linking with hydrophobic 

group is a cation when cationic surfactant 

dissovles in water. ; 

• Mainly include the derivatives of orgainic amine( 有 

机胺 ), commonly quarternary ammonium salt( 季胺 

盐 ) like hexadecyl trimethyl 

ammonium bromide 

( 十六烷基三甲基溴化铵 ) 

• Aqueous solution of ationic surfactant is highly 

disinfectant and thus broadly used as fungicide.

3. Amphoteric surfactant 

• It’s the surface active agent composed of both 

anionic and cationic ions, the molecular structure of 

which is similar to amino acid and the properties of 

which in aqueous solution varies with pH. 

• Under alkaline condition it presents 

anionic properties; 

• At isoelectric point it presents nonionic properties; 

• Under acid condition it presents cationic properties; 

• Can form internal salts inside the molecule; 

• Low toxicity, easy biodegradation, fine effects of 

rinsing, emusifying, anti-corrosive, disinfectant and 

antistatic, etc.; 

• High cost, low dosage, potential and promising

4. Nonionic surfactant 

• Nonionic surfactant doesn’t disassociate as ions in 

aqueous solution but appears in the forms of 

molecule or micelle. 

• lipophilic group: commonly hydrocarbon chain or 

polyoxyalkylene chain( 聚氧丙烯链 ) ; 

• Hydrophilic group: etheriality( 醚基 ) and hydroxy( 羟 

基 ) 

• Nonionic surfactants are stable in netrality, acid, 

slight alkaline conditions and hard water. 

• Broadly used in textile, dye printing, metal purging, 

food production and pesticide emulsification and 

some other industries.

The properties of surface active agent depends 

on their chemical structure, related to the 

following factors: hydrophilicity, the relative 

position of hydrophilic groups, the size of 

molecules and the hydrophobic groups 

1) hydrophilicity (HLB) is the equilibrium ratio of 

the surface active agent’s hydrophilicity and 

lipophilicity: 

HLB=hydrophilicity of hydrophilic groups 

/hyrophobicity of hydrophobic groups 

Surface active agent’s HLB value is related to the 

HLB value of each of its radicals, the computing 

of which is : 

HLB=7+Σ(HLB of hydrophilic groups)-Σ(HLB of 

hydrophobic groups)

2) the relative position of hydrophilic 

groups 

• A molecule has stronger wettability when its 

hydrophilic groups are located in the middle rather 

than at the end of the chain, like the following 

molecule, a famous penetrant: 

• A molecule has better dirt removing power when its 

hydrophilic groups are located at the end rather 

than in the middle of the chain, e.g.: 

• C 16 H 33 OCOCH 2 CH(SO 3 Na)COOH has better dirt 

removing power

3) the size of molecules 

• Small-sized surface active agents have better 

wettability and permeability; 

• Large-sized agents have better ablution ( 洗涤 

作用 ) and dispersant effect ( 分散作用 ). 

e.g. the order of the ablution effectiveness of 

alkyl sodium sulfate surface active agent is as 

follows: 

C 16 H 33 SO 4 Na> C 14 H 29 SO 4 Na> C 12 H 25 SO 4 Na 

• Concerning wettability, it appears the 

opposite.

4) hydrophobic groups 

• The order of lipophilicity of surface acitve 

agents with different hydrophobic groups is as 

follows: 

Fatty alkane 脂肪族烷烃 >cyclane 

环烷烃 >fatty alkene 脂肪族烯烃 >fatty aromatic 

hydrocarbon 脂肪族芳烃 > aromatic hydrocarbon 

芳香烃 >hydrocarbon with weak hydrophilic 

groups 带弱亲水基团的烃

source and pollution of surface 

1. source: 

active agent 

• 1960s, already largely used in detergent industry 

• 1999, global annual use reached 9.3 million t 



• A large portion of used surface active agent enters 

waste water. 

• The problem of the degradation of surface active 

agent requires attention from environmentalists.

2. hazards 

1) Surface active agent is a source material for producing 

detergents. As organic matter, synthetic detergents can be 

bio-degraded, consuming the dissolved oxygen in the water. 

Permernant bubbles appear when the concentration of 

surface active agent reaches . 

Anionic surfactant produces bubbles in water more 

easily than other surfactants.e.g. in 1963,a 0.6 m-thick 

sheet of bubbles appeared on the surface of Ohio river 

of America, due to the pollution of detergents; 

The speed and level of reoxygenation in bubble-covering 

river will be largerly reduced. e.g. the pollution of 

detergents in Thames river of Britain caused water 

deoxidation and people could even smell hydrogen 

disulfide along the river.

2) The large amount of phosphates such as trimeric 

sodium phosphate ( 三聚磷酸钠 Na 5 P 3 O 10 ) 

contained in detergents can cause eutrophy( 富营 

养化 ) to the water bodies. It’s estimated in Britain 

and U.S. and other other countries that 30%~75% 

phosphorus in the urban sewage comes from 

detergents. Also due to the large amount of 

discharged waste water, it would constitute 

hazards to aquatic plants and fish. 

3) Surface active agents can accelerate the 

emulsification and dispersion of petrol, PCBs and 

other indissolvable organic matters in water, thus 

raising the difficulty of waste water treatment.

4) The sterilization of high-concentrationed cationic 

sufactant can make demages to the aquactic 

microorganizm communities. 

5) The strong dissolving capacity of detergents 

toward unctuous matters can damage the 

gustatory organ of fish, thus depriving them the 

ability to avoid toxicant matters and look for food. 

It’s reported that fish can not survive in water 

with detergents at a concentration of over 

10mg/L.

he degradation of surface active 

agent 

• It means under the environmental factors, 

the molecular structure of surface active 

agents is changeg, from environmentharmful 

matters to environment-friendly 

molecules such as CO 2 , NH 3 and H 2 O. 

• Mainly include bio-degradation and 

photodecomposition.

1. Bio-degradation of surface 

active agent 

• priciples:the depletion of surface active agent 

entering the water environment depends mainly on 

degradation by microorganizm, the principle of which 

includes the oxidation of methyl on the methyl-chain 

(ω-oxidation), β -oxidation, the oxidation of aromatic 

ring and 脱磺化。 

1) Methyl oxidation means the oxidation of the methyl at 

the end of the hydrophobic groups of surface active 

radical and then the respective production of of 

formyls ( 醛基 ) and carboxyls ( 羧基 ).

2) β -oxidation 

• Carboxylic acid in the surface active agent 

molecue is oxidized under the effect of A 

coenzyme ( 辅酶 A) and the second carbon 

bond breaks. 

3) The process of desulfonation 

The process of desulfonation happens in the 

alkyl chain oxidation of both branched-chain 

and linear alkylbezene sulfonates.

4) Oxidation of aromatic 

compounds 

• The ring-opening process of phenol ( 苯酚 ) and 

salicylic acid ( 水杨酸 ) and other compounds includes 

the primary production of pyrocatechol ( 邻苯二羟基 ), 

the secondary split of two hydroxyls ( 羟基 ), and then 

the production of dicarboxylic acid ( 二羧酸 ) and the 

final disappearing.

The effect of the structure of 

surface active agent on bio-degradation 

1) Cationic surfactant 

The bio-degradation of cationic surfactant requires 

aerobic conditions. The order of the ability of being biodegraded 

of three types of alkylbenzene sulfonates (ABS) 

with different structures of hydrophobic groups is as follows: 

Linear ABS (LAS)>ABS substituted by a branch-chain at the 

end of the group>trimethy ABS 

As for those cationic surfactants difficult being degraded, we 

can prepare them together with other types of surface active 

agents in order to raise its bio-degradation. e.g. trimethyl 

dodecyl ammonium chloride ( 三甲基十二烷基氯化铵 ) 

couldnot be degraded even in 27h while it can be easily 

degraded once being mixed with LAS at the radio of 1:1.

2) Anionic surfactant 

• Anionic surfactants such as LAS and AES ( 脂肪醇醚硫 

酸盐 ) constitute a large portion of surface active agents 

contained in detergents. 

• LAS degrades the most quickly in all the detergents, 

which can be hydrolysed by sulfatase to sulfates and 

some related fatty alchohol ( 脂肪醇 ) and finally further 

oxidized to CO2 和 H2O. 

• As for LAS, the degradation speed grows with the 

farther distance between the sulfo ( 磺基 ) and the end of 

the methyl chian and it degrades the most quickly with 

the number of carbon atoms of the methyl between 

6~12. The effect of branch-chain is similar to that of 

nonionic surfactants.

3) nonionic surfactants 

• Easiness for degradation: 

linear molecule>normal branch-chain 

molecule 

molecule with alkyl>molecule with phenyl 

Linear carbinol and disubstituted carbinol 

oxyethyl compounds can be effectively 

degraded by microorganizm in the activated 

sludge.

The relationship between molecular 

structure and the bio-degradation of 


• The biological degradability of surface active agent depends 

mainly on the hydrophobic groups. With the linearity ( 线性程 

度 ) of hydrophobic groups, the degradability of the 

quaternary carbon atom at the end of the chain is 

significantly reduced with more hydrophobic groups; 

• The properties of the hydrophilic groups also have some 

influence on the biological degradability. e.g. LPAS( 直链伯烷 

基硫酸盐 ) has higher primary bio-degradation speed than 

other anions; short-EO-chain polyoxyethylene ( 聚氧乙烯 ) 

nonionic surfactants are bio-degraded more easily. 

• The increase of the distance between between the sulfo ( 磺 

基 ) and the end of the hydrophobic groups can raise the 

primary bio-degradability of methyl benzene sulfonates 

(distance principle).

2. Photodiscomposition of 


• Photocatalysic degradation and oxidation are technologies 

developed in the recent 30 years. 

• Advantages: low cost, mild reaction conditions, no 

secondary pollution. 

• Reaction speed: 

anionic>cationic 

aromatic ring part>methyl part 

• The degradation speed constant K is only related to the 

light source, catalysic activity and the reaction medium 

rather than the surface active structure. 。

3 steps for the photocatalysic 

degradation reaction ot the surface 

active agent on the surface of TiO2: 

1) Absorption of surface active agent on the 

surface of TiO 2 ; 

2) Absorption of UV by TiO 2 and the formation of 

electron/hole pair ( 电子 / 空穴对 ) (e - /h + ), and the 

further reaction between this pair and the 

aromatic ring (Ar) of the surface active agent 

and the production of aromatic cations (Ar + ); 

3) The ring-opening process of Ar + , and successive 

oxidation to the fnial production of CO 2.

3. Prospect for the surface 

active agent technology 

• The fixation of mixed bacteria using the technology of 

cellular fixation technoloy ( 固定化细胞技术 ) can enable 

several reuse of the reaction system and also reduce the 

cost and increase efficiency. 

• The foundation of engineering bacteria, produced with 

microorganizm in alternate or symbiotic relationship by the 

combination of cell fusion technology and gene 

engineering technology, can give the engineering bacteria 

both the fuction of mixed culture and the advantages of 

simple required nutrition, stable metabolism and easy 

control, making it the major research direction for the future.

One of the key points in the research of photocatalytic 

degradation is to choose the suitable carriers and 

develop nanometered TiO 2 , use photoactive matter in 

the preparation of photocatalyst agent to produce highefficient 

catalyst agent for photocatalyst degradation, 

further improve the modification and fixation technology 

of catalyst agent and increase the quantum efficiency of 

catalyst agent. 

The application of optimized combination of biodegradation 

and photocatalyst degradation in treating 

surface active agent will be more effective.

Mercury

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