CHAPTER VII

CHAPTER VII

ANTHROPOGENIC COMPOUNDS

A. INTRODUCTION

So many compounds that have been found to be harmful to humans or to some aspect of nature owe their presence in the biosphere in large part to human activities. Sometimes its a case of relocating a chemical substance from an environment where it cannot cause any harm to a place where it will. In many cases, however, completely new compounds are formed. Man-made compounds that do not normally exist in nature are called xenobiotics. In other cases compounds will be formed whereby further examination reveals the existance of natural processes that result in their formation. When most of the total mass of a harmful chemical released into some environment can be attributed to human activities, it is said to be an anthropogenic pollutant.

B. NATURALLY-OCCURRING POLLUTANTS

There are some types of naturally-occurring substances that are also considered anthropogenic pollutants. Although they were not created by humans, they were extracted and re-distributed by them. Generally this means that these compounds were placed in environments where they could easily come into contact with living organisms. Whereas previously they were isolated, with far less opportunity for contact with environments that might be harmed by them. A few examples of such naturally-occurring pollutants are petroleum products and heavy metals.

1. Petroleum Products

Petroleum or fossil fuels are naturally-occurring complex mixtures of organic compounds, mostly hydrocarbons. The compounds in crude petroleum may range in molecular weight from 16 (methane) up to 20,000 and above. Petroleum may also contain small amounts of oxygen, sulfur and nitrogen as well as the aforementioned carbon and hydrogen.

The precise composition of this enormously complex mixture is somewhat site specific. Nevertheless, it is useful to classify the constituent organics into three groups:

aliphatics

alicyclics

aromatics

The aromatic component is often dominated by the BTEX compounds: Benzene, Toluene Ethylbenzene and Xylene.

There are many methods for analysis of petroleum hydrocarbons. These differ in cost, method detection limit (MDL) and extent of characterization possible (Table 7.1). The non-specific or non-qualitative methods (the first 3 in table 7.1) are primarily used as a screening tool and for mapping the size and movement of petroleum plumes. They can only provide a single-number assessment of the total hydrocarbon concentration. Detailed site investigations require the use of one or more gas chromatographic (GC) methods. These are capable of providing fingerprints of the hydrocarbon mixture or even compound-specific concentrations.

Table 7.1

Methods for Analysis of Liquid-Phase Petroleum Hydrocarbons

(from DEP, 1994)

Method	Approx. MDL (µg/L)	Approx. Cost ($)	also Qualitative	Identification & Confirmation
Gravimetric	10,000	50	No	No
Infra-red	2000	65	No	No
UV Fluroescence	10	50	No	No
GC/FID Screen	10,000	125	Yes	No
GC with PID/FID	1	175	Yes	No
GC/FID with clean-up	100	250	Yes	No
GC/MS	10	700	Yes	Yes

Crude petroleum is refined to give a wide range of useful fractions. Some of these are discussed below.

Figure 7.1

Typical Size Ranges for Petroleum Products

Figure 7.2

Typical Densities for Petroleum Products

a. Gasoline

Gasoline is a blend of light hydrocarbon fractions from petroleum. There are the familiar automotive gasolines as well as aviation gasoline (Av Gas), used in piston-driven propeller aircraft. Virgin gasoline is probably about 50% alkanes, 40% cycloalkanes and 10% aromatics. However, this is blended with catalytically cracked gasoline and thermally reformed gasolines at the refinery. The blending process substantially changes the makeup, elevating the alkene content up to as much as 30%. Blending is done with the very practical objective of improving performance in combustion engines. Gasoline may contain a number of additives aimed at improving certain aspects of performance. These include anti-knock agents (or octane enhancers: e.g., methyl t-butyl ether [MTBE] and some alcohols), antioxidants (N,N'-dialkylphenylenediamines, and some phenols), metal deactivators (N,N'-disalicylidene-1,2-ethanediamine and related compounds), lead scavengers, anti-rust agents (carboxylic acids, phosphoric acids), anti-icing agents (isopropanol), upper cylinder lubricants, detergents and dyes. In particular, the use of MTBE is significant. Unleaded gasoline accounts for nearly all of the MTBE use in the U.S. It contrasts with many of the other gasoline constituents in that it is highly water soluble, while still quite volatile and resistant to biodegradation. As a result, MTBE has a high potential for exposure to humans by a water route, and especially following volatilization from water.

Since, gasoline is not blended to any specific chemical composition, its precise makeup is hard to characterize. Of all the major petroleum products, gasoline probably has the highest alkane content, a low alicyclic content, and a low to medium aromatic content. It differs from jet fuel in that the latter is higher in alicyclics and lower in alkanes. The fuel oils have higher aromatic contents, average alicyclic contents and very low levels of alkanes. Refer to chapter III for a listing of the major constituents in two commercial automotive gasolines. A general accounting by compound type is in Table 7.2. This breakdown is highly variable.

Table 7.2

Typical Components of Unleaded Automotive Gasoline

(from Domask, 1983)

Type	Carbon #	No. of Isomers		% by	Major Contributors
		Possible	Analyzed	Volume	Number	% of total
n-alkanes	C₃-C₁₀	8	8	11.4	3	10.2
isoalkanes	C₄-C₁₃	>600	51	46.5	17	38.0
cycloalkanes	C₅-C₁₃	>600	49	4.7	5	1.9
mono-alkenes	C₂-C₁₂	>600	29	9.0	8	3.3
aromatics	C₆-C₁₃	>200	14	28.4	9	20.8
TOTAL		>2000	151	100.0	42	74.2

b. Naphtha or Light Petroleum Distillates

These are fractions that include mineral spirits, gasoline blending stocks and a wide range of petroleum solvents.

c. Kerosene

Kerosene is heavier than gasoline, but still considered a light distillate. Since it is used in vaporizing burners, it is designed to have a high volatility. Kerosene is a straight-run distillate, prepared without blending. Petroleum products that are largely kerosene include Fuel Oil No. 1 and Diesel Fuel No. 1. The diesel fuel contains some special additives. Kerosene's typical composition is: 35% alkanes, 60% cycloalkanes, and 15% aromatics.

d. Fuel Oils

These are broad mixtures having properties defined by ASTM standars. Number 1 fuel oil is actually in the kerosene category. The category of fuel oil represented by number 3 has now been included in number 2. Numbers 4, 5 and 6 are collectively called the heavy fuel oils (HFO), or residual fuel oils.

Fuel Oil Number 2 is also known as heating oil or diesel oil or diesel fuel no.2. It is designed for use in atomizing burners, such as those found in homes. It is easier to handle but more costly than the residual fuel oils. The ASTM has defined three grades; 1-D, 2-D, and 4-D; of increasing weight. The average composition of these oils is: 30% alkanes, 45% cycloalkanes, and 25% aromatics.

Fuel Oil Number 4 is used for higher viscosity atomizing burners. However, it generally does not require pre-heating.

Fuel Oil Number 5 is so viscous that it requires heating prior to pumping.

Fuel Oil Number 6 is commonly called Bunker C Fuel Oil. It is obtained by blending residues from cracking or distillation with certain distillates. Like #5, this mixture requires heating prior to use. Use of this oil is only practical in large industrial settings. Fuel Oil Number 6 is typically composed of about: 34% aromatics, and 20% alkanes. It also contains substantial amounts of 3 to 7-ring polynuclear aromatic hydrocarbons (PAHs); from 6 to 20% or more.

e. Turbo and Missile Fuels

These include a range of turbo jet fuels and ram jet fuels designed for use in gas turbine-powered aircraft and missles and ramjet-powered missles. These have different properties than aviation gasoline which fuels piston-engine aircraft. The majority of the jet fuels are composed of distillates which are quite similar to Kerosene and Fuel Oil Number 1 (JP-4, JP-5 and JP-8). JP-4 is blended with the more volatile gasoline fractions. This fuel contains as much as 80% alkanes, with 20% aromatics making up the rest. Both JP-5 and JP-8 are composed of kerosene-based distillates, and resemble Commercial Jet A-1 fuel. Like gasoline, jet fuels can contain a number of additives.

The higher density ram jet fuels are all synthetic, and are only included here because they are used like distillate jet fuels. Three of these are made from pure compounds: exo-tetrahydrodi(cyclopentadiene) is JP-10; tetrahydrodi(methylcyclopentadiene) is RJ-4, and endo,endo-dihydro(norbornadiene) is RJ-5. JP-9 is a blend of methylcyclohexane, JP-10 and RJ-5. RJ-6 is a blend of RJ-5 and JP-10.

f. Lubricating Oils and Crankcase Oils

These are fractions that have been reduced in their aromatic content. Aromatics result in poorer viscosity characteristics and are more susceptible to unwanted oxidation. Their general composition is: 45-76% alkanes, 13-45% cycloalkanes, adn 10-30% aromatics. Used crankcase oils often have elevated levels of polynuclear aromatic hydrocarbons (PAHs) produced by combustion processes (see part D, below). They may also contain heavy metals from engine wear.

2. Heavy Metals

Many contaminated groundwaters contain elevated concentrations of heavy metals. Among the more frequently reported metals are lead, chromium, arsenic and zinc. Drinking water standards currently exist in the US for aluminum, antimony, barium, beryllium, cadmium, chromium, copper, lead, mercury, nickel, selenium, and thallium. Metals in drinking water may be grouped into three classes: (1) those that are present in the raw water and incompletely removed through treatment, (2) those that are purposely added over the course of treatment, and (3) the corrosion byproducts. The second group primarily includes aluminum. Members of this last group include lead, copper, and to a lesser extent, cadmium and chromium. The transition metals are generally less volatile than other water contaminants, although they may be transported by aerosol formation and even dry deposition.

Although aluminum is one of the most abundant elements in the earth’s crust, it is rarely present in water at high concentrations. This is due to its strong tendency to form insoluble hydroxides. For this reason, addition of aluminum in the form of alum for the treatment of water does not generally lead to elevated levels of the metal in finished water. However, problems may occur when the pH of the water drops to low (e.g., 5 or below). Under these conditions, aluminum hydroxide precipitates will not form to as great an extent, and aluminum solubility rises sharply.

Antimony has toxic effects, which manifest themselves in the gastrointestinal tract, the cardiovascular system, the skin and liver. It exists in two oxidation states, (+III) and (+V). Antimony is normally present at very low concentrations in water, and as a result, little is known about its speciation. Of the 50 elements studied by the US Geological Survey in soil and rock samples, antimony was the third least abundant, with an average composition of 0.5 ppm (Shacklette and Boerngen 1984). Antimony may become methylated in aquatic environments, which can substantially elevated its solubility (Andreae 1983).

Barium readily forms insoluble sulfate and carbonate precipitates, which renders the metal highly insoluble. For this reason alone, barium is not considered a major threat to human health. Barium is, however, a common contaminant at hazardous waste sites in the US.

Beryllium is not widely found in the natural environment. The presence of high concentrations of this metal suggest contamination from industrial wastewater, especially non-ferrous metal manufacturers. The atmosphere may also serve as an important Beryllium source for natural waters (EPA 1987). The US EPA has determined that Beryllium is a probable human carcinogen.

Cadmium can accumulate in the kidneys, eventually causing damage to that organ, and it can also cause bones to become fragile and break. The US EPA has determined that cadmium is a probable human carcinogen by inhalation. Water is rarely a major route of exposure to cadmium; food and incidental ingestion of dust, being much more important. However, in some instances, significant amounts of cadmium have been found to leach from plumbing fixtures.

Chromium exists in water in either the +III or the +VI oxidation state. Although chromium is an essential nutrient for the human diet, high atmospheric levels of Cr(+VI) have been associated with lung cancer in workers. For this reason, there is some concern over the hexavalent form. Chromium will adsorb to metal oxides and form strong chelates in natural waters. As a result, it is primarily found in water in a particulate form, with some soluble chromium complexes. The mean US chromium level for river water has been estimated at 10 mg/L(Eckel and Jacob 1988). Concentrations in tap water have been found to be lower (1.8 mg/L average,Greathouse and Craun 1978), but corrosion of plumbing fixtures can drive these up. Some contaminated groundwaters may contain very high levels of chromium.

Copper is one of those metals that is primarily present in tap water as a result of corrosion of pipes and plumbing fixtures. While copper corrosion is a nuisance, it is rarely a human health concern. However, those afflicted by Wilson’s disease (a copper metabolism disorder) may find levels of a few mg/L intolerable.

Lead can be a major concern in water systems subject to high levels of corrosion. Lead can cause damage to the brain and kidneys. In children, it can be especially damaging to mental development. Because lead readily precipitates as carbonates and hydroxides, it is rarely present at high concentrations in natural waters. Nevertheless, elevated lead levels can be found in tap water if the water is corrosive and if there is contact with lead in the pipes. Possible sources of lead include lead service connections, lead-tin solder and lead-containing brass fixtures. As with all corrosion byproducts, concentrations of lead are highest at the tap during the “first flush” of water in the morning.

Mercury can lead to permanent damage of the brain, kidneys, and the growing fetus. Mercury exists in three oxidation states (0, +I, +II). Metallic-mercury readily volatilizes and can be transported through the atmosphere. Under reducing conditions, certain microorganisms, such as the sulfate-reducing bacteria, can methylate mercury, which further aids its transport (Gilmour and Henry 1991). Mercury is characterized by its ability to form strong complexes and concentrate through the food chain.

Nickel is another trace metal that is thought to be an essential human nutrient. It does not appear to be very toxic, but it is probably carcinogenic when inhaled in the form of dust. Nickel is strongly bound to particle surfaces in water, and therefore is rarely present at high dissolved levels. It is not as readily concentrated through the food chain as other metals, such as mercury, can be. Unpolluted surface and groundwaters have nickel concentrations in the low ppb range (Shiller and Boyle 1987;Page 1981). In general, drinking waters have similar levels, although in at least one study (Ohanian 1986) evidence was found for contributions from corrosion.

Thallium can adversely affect the human nervous system, lung, heart, liver and kidney. Amounts as small as 1 gram can be fatal. Thallium is most commonly found in the monovalent form, and it tends to be bound to soil particles. It is normally present in very low concentrations in water; below 1 ppb in tap water (EPA 1988). When higher concentrations are found, it is usually due to contamination from mining operations or metal manufacturing wastewaters.

Radionuclides

The major radionuclides of concern in drinking waters are radium 226 and 228, uranium, and radon 222. Because it is a gas, radon poses a special concern. It is found in many groundwaters, depending on the local geology, and its concentrations can be highly variable. Based on data from the National Inorganic and Radionuclides Survey, 17 million Americans are expected to have radon levels in their water in excess of the MCL (300 pCi/L), and 2.7 million are thought to have water above 1,000 pCi/L.

Inorganic Non-metals

Nitrogen species can present toxicity to humans under certain circumstances. One of the best known examples is the condition known as methemoglobinemia. This occurs when infants ingest water with high levels of nitrate or nitrite.

Selenium is toxic at high doses, yet it is also an essential nutrient. For this reason, its regulation is quite complex. Symptoms of excessive selenium uptake include brittle hair and deformed nails. From a chemical standpoint, selenium behaves much like sulfur. It has four oxidation states (-II, 0, +IV, +VI), and the two most oxidized states tend to form the more soluble compounds. Both of these forms (selenites and selenates) are common in aerated waters. Selenium is relatively bioactive, and microorganisms, such as cyanobacteria are known to be able to methylate the metal (Bender et al. 1991).

C. SYNTHETIC ORGANIC CHEMICALS

1. Industrial Solvents

a. Chlorinated Solvents

These compounds include trichloroethylene, tetrachloroethylene, 1,1,1-trichloroethane, dichloromethane (methylene chloride), chloroform, carbon tetrachloride and many more (Figure 7.3). They are all produced in large quantities for industrial use. Furthermore, they are relatively persistent and mobile, especially in the subsurface. All of these 1 and 2-carbon haloaliphatics are readily volatilized from water. For this reason, they are considered members of the group, volatile organic compounds or VOCs.

Trichloroethylene Tetrachloroethylene 1,1,1-Trichlorethane

Dichloromethane Chloroform Carbon Tetrachloride

Figure 7.3

Some Common Industrial Chlorinated Solvents

Dichloromethane is used in paint strippers, and as a decaffeinating solvent. Chloroform was used as an anesthetic around the turn of the century. Like its cousin, carbon tetrachloride, it is a good general solvent. Production of the common solvent, 1,1,1-trichloroethane is being phased out due to its detrimental effect on the stratospheric ozone layer. This chemical is a popular degreaser and can be found in household glues, spot cleaners and aerosol sprays. Tetrachloroethylene (also known as perchloroethylene) has replaced carbon tetrachloride as the solvent of choice among dry cleaners.

2. Propellants and Refrigerants

These encompass primarily the chloro-fluoromethanes: trichlorofluoromethane (CCl₃F), dichlorodifluoromethane (CCl₂F₂) and chlorodifluoromethane (CHClF₂). As a group they are called chlorofluorocarbons (CFCs). Although, small amounts of the CFCs may be produced by volcanoes, they are primarily man-made. They are being phased out of use in favor of compounds that are less harmful to the ozone layer.

3. Pesticides

Pesticides may be used to control a wide range of plants and animals deemed undesirable. Most are either chlorinated compounds (e.g., DDT, methoxychlor, mirex, lindane, endrin, 2,4-D, 2,4,5-T), organo-phosphorus compounds (e.g., parathion, malathion), triazines (e.g., atrazine) or carbamates. These are all man-made chemicals. Some of the more current occurrence data may be found in Thurman 1992 and Stamer 1996.

One of the most celebrated of these compounds is DDT. Although it was first synthesized as early as 1873, it wasn't until 1939 when Paul Muller of J.R. Geigy studied the compound that its utility as a pesticide was fully recognized. DDT found widespread use during World War II, helping to control the insects that spread Typus, Malaria, Typhoid and Dysertery. Later, in 1948 Muller was awarded a Nobel Prize for his work with DDT.

In general, chlorinated organic compounds are associated with man-made pollutants. However, there are over 2000 known naturally-produced halogenated organics (Gribble, 1994). Many marine and terrestrial organisms produce halo-organics that serve as pesticides or related compounds which can give the organism a feeding advantage.

4. Phthalates

Phthalates are esters of phthalic acid. They are produced in very large quantities, and used primarily as plasticizers. For example, they are used to make polyvinyl chloride (PVC) flexible.

5. Surfactants

Surfactants are of three major types: anionic, nonionic and cationic. The anionic surfactants comprise the soaps (sodium salts of simple, aliphatic fatty acids), linear alkylbenzene sulfonates, secondary alkyl sulfonates, and fatty alcohol sulfates The nonionic surfactants are mostly polyethylene glycol ethers of a phenol or an aliphatic alcohol. The cationic surfactants are quaternary ammonium chloride derivatives.

6. Miscellaneous Synthetics

a. PCBs

The polychlorinated biphenyls (PCBs) are aromatic hydrocarbons that have been used as capactor dielectrics, transformer coolants, hydraulic fluids and heat transfer fluids. These compounds all share the biphenyl structure, with varying numbers of chlorine atoms (1-10) substituted for hydrogens. For example, there would be 12 unique arrangements for 2 chlorine atoms on the biphenyl structure. These would all be isomers of each other. However, the total number of possible structures of varying chlorine content is 209. Related compounds of this type are called congeners.

Most PCBs were produced by one manufacturer (Monsanto Corp.) under the trade name, Arochlor®. Actually are were mixtures of PCBs which vary in the average chlorine content (see Table 7.3). The first two numbers in the numerical code indicate the number of carbon atoms (12), and the last two indicate the average percent chlorine (by weight). These compounds were sold in large quantities in the US from 1930 to 1977.

Table 7.3

Average Composition of 6 Arochlors by Weight

(from Erickson, 1986)

Number of	Arochlor
Chlorines	1221	1232	1242	1248	1254	1260
0	10
1	50	26	1
2	35	29	13	1
3	4	24	45	2	1
4	1	15	31	49	15
5			10	27	53	12
6				2	26	42
7					4	38
8						7
9						1

D. UNCONTROLLED REACTION BYPRODUCTS

1. Combustion Byproducts

a. Polycyclic Aromatic Hydrocarbons or Polynuclear Aromatic Hydrocarbons (PAHs)

PAHs are common byproducts of the combustion of fossil fuels, wood, cigarettes, and charcoal-broiled foods. While they are present in crude oils, and can be produced by natural combustion processes (e.g., forest fires, volcanoes), it is the anthropogenic sources that are of greatest concern. Several of these compounds (e.g., anthracene, acenaphthene, fluorene, and phenanthrene) are commercially prepared for use primarily in the manufacture of dyes.

Most of the PAHs in natural surface waters are thought to have come from atmospheric deposition. These compounds are relatively insoluble. Accordingly, they tend to readily adsorb to particles and sediments, or they can volatilize. Due to their insoluble, hydrophilic nature, they accumulate in aquatic organisms, and readily move up the food chain.

Quite a few of the PAHs studied are now classified by the US EPA as probably human carcinogens. This groups includes benzo(a)pyrene, benzo(a)anthracene, benzo(b)fluoranthene and many others.

b. Dioxins

This group of compounds is more correctly called the chlorodibenzo-p-dioxins. The most important is probably 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8-TCDD). There are 22 isomers of TCDD. The chlorinated dibenzodioxins and dibenzofurans may also be produced in very small quantities by some animals (Gribble, 1994).

2. General Chlorination Byproducts

Active chlorine is used as a disinfectant, a bleaching agent, a halogenating agent and a general oxidant for a wide range of purposes. Most common to our everyday experience is chlorine's use in the production of drinking water, and in swimming pools. However, chlorine is also used to bleach wood pulp in the manufacture of paper, to disinfect municipal wastewaters, and in the synthesis of many industrial chemicals. Since chlorine is so reactive, it will attack many types of compound in water, not just the target substance (e.g., pathogenic organisms, colored wood fibers). Some of the organic byproducts that are formed will contain organically-bound chlorine. Concern over the general toxicity of organo-chlorine compunds has opened a national debate. Many are questioning the need for chlorine, and proposing a national ban on chlorine's use. A well-studied example is that of the chlorination byproducts produced during drinking water treatment. These will be discussed in detail below.

Chlorine reacts with naturally-occurring organic matter during drinking water treatment to form a diverse group of organic byproducts; some hazardous, and some not. The hazardous compounds that have concerned the US EPA and state regulatory agencies are the halo-organic mutagens or suspected carcinogens (Bull et al., 1982; Kringstad et al., 1983). Researchers at the US EPA Health Effects Laboratory in Cincinnati have been actively pursuing the identity of these compounds. Their approach has included the use of the Ames mutagenicity test in conjunction with GC/MS analysis to determine the specific compounds responsible for the mutagenic activity in chlorinated natural waters. Despite extensive studies of this type, only 7-8% of the overall mutagenicity in chlorinated humic acid solutions could be accounted for by 1985 (Meier et al., 1985). The discovery, in 1986, of low concentrations of an extremely potent mutagen, 3-chloro-4-(dichloromethyl)-5-hydroxy-2(5H)-furanone (more commonly referred to as MX, see equation 1), in chlorinated humic acid solutions and drinking waters has significantly advanced this effort (Coleman et al., 1986). In a survey of 6 chlorinated drinking waters, MX alone was found to account for 22%-44% of the overall mutagenicity (Holmbom et al., 1987). A subsequent study of 26 chlorinated Finnish waters found MX to account for 15-57% of the overall mutagenicity (Kronberg & Vartianinen, 1988). The likely effects of MX on humans still remains to be determined (Daniel et al., 1994). The next most important mutagen may be 2,3,3-trichloroprepenal. This compound may account for 4% of the overall mutagenic activity from chlorinated humic acid solutions (Meier et al., 1985), although it has not yet been isolated from drinking waters. Despite recent advances in this area, more than 50% of the mutagenicity of chlorinated drinking waters remains unaccounted for.

Others researchers have identified and quantified numerous halo-organics in an effort to account for all of the Total Organic Halide (TOX) produced by drinking water chlorination. Table 6 summarizes some of these findings. In this endeavor, roughly 50% of the TOX has been identified (Christman et al., 1983).

(1)

Table 6

Major Halo-organic Byproducts of Chlorination

Compound(s)	% of TOX	Early References
Trihalomethanes	15 - 25	Sander et al., 1977
Trichloroacetic Acid	5 - 20	Reckhow & Singer, 1984, Norwood et al., 1986
Dichloroacetic Acid	5	Christman et al., 1983; Reckhow & Singer, 1984
Other Aliphatic Chloroacids		Norwood et al., 1980; De Leer et al., 1985
1,1,1-Trichloropropanone	0.8	Coleman et al., 1984; Reckhow & Singer, 1984
1,1-Dichloroacetone	0.2	Coleman et al., 1984
Other Aliphatic Haloketones		Coleman et al., 1984; Sato et al., 1985
Aliphatic Chloroaldehydes		Kopfler et al., 1985
Dihaloacetonitriles	0.5	Reckhow & Singer, 1984; Oliver, 1983
Other halonitriles		Coleman et al., 1984
Halophenols		Coleman et al., 1984; Kringstad et al., 1985
Chloroaromatic Acids		De Leer et al., 1985; Seeger et al., 1985
Halothiophenes		Coleman et al., 1984
Chlorinated PAHs		Shiraishi et al., 1985

The reason that efforts to identify all of the chlorination byproducts has not been 100% successful is two-fold. First, there may be many chlorination byproducts that are not readily amenable to gas chromatography (e.g., complex, high molecular weight compounds). Second, many of the byproducts may not be sufficiently stable to survive the various extraction, separation and derivatization procedures used, as well as the high injector temperatures often employed. Indeed, Kopfler and co-workers (1985) found that 50% of the mutagenic activity of chlorinated humic acids decomposed upon heating (in aqueous solution) to 220^oC for one minute. Others have noted a complete loss at 250^oC (Kool et al., 1985). Kopfler and co-workers also found that less than 10% of the original mutagenic activity was recoverable by trapping all of material in the GC column effluent. One important heat-labile compound is the potent mutagen, MX. This important chlorination byproduct undergoes complete decarboxylation to form 3-chloro-2-(dichloromethyl) propenal, which is probably far less mutagenic that the parent compound (see equation 1, below).

The trihalomethanes are the best known of the chlorination byproducts (see Figure 8). They are also the most easily measured. Chloroform has been shown to cause cancer in laboratory animals and the other trihalomethanes (THMs) have been found to be mutagenic in the Ames Salmonella assay. The chloroacetic acids are also widespread, with the di and tri compounds being found in all chlorinated waters. Although dichloroacetic acid (DCAA) and trichloroactic acid (TCAA) are not apparently mutagenic, some preliminary evidence indicates that they may be carcinogenic to laboratory animals (NRC, 1987).

Trihalomethanes (THMs)

Haloacids (HAAs)

Figure 8

The Trihalomethanes and Chloroacetic Acids

The haloacetonitriles (Figure 9) are thought to be products of the chlorination of amino acids and proteinaceous material (Trehy & Beiber, 1981). In addition, de Leer and co-workers (1985) have shown that isolated humic materials react with chlorine to give cyano acids which continue to react to form haloacetonitriles. Dichloracetonitrile and bromochloroacetonitrile have been determined to be direct acting mutagens. Trichloroacetonitrile, bromochloroacetonitrile and dibromoacetonitrile all showed varying carcinogenicities in tests with laboratory animals. Another N-containing chloro-organic, chloropicrin (see Figure 11), was found to be an indirect acting mutagen and proved negative in several carcinogenicity tests.

Figure 9

The Haloacetonitriles

Among the chlorination byproducts of concern are many halogenated aldehydes and ketones (see Figure 10). Chloral is a mutagen although its carcinogenicity is uncertain. 1,1,3-Trichloropropanone, 1,1,3,3-tetrachloropropanone, pentachloropropanone and hexachloropropanone were all found to be direct acting mutagens. They have not yet been tested for carcinogenicity.

Figure 10

Some Chloroketones

Figure 11

Chloral and Chlorpicrin

An extensive list of C₃-C₁₀acids have been isolated as chlorination byproducts of aquatic humic materials. Figure 12 shows some of the more common low molecular weight members of this group. Dichlorosuccinic acid may be the most prevalent halogenated byproduct containing more than three carbon atoms.

CH₃Cl₂COOH CCl₂=CHCOOH CCl₂=CClCOOH

2,2-Dichloropropanoic 3,3-Dichloropropenoic 3,3-Dichloropropenoic

Acid Acid Acid

HOOCCH₂CHClCOOH HOOCCH₂CCl₂COOH

Chlorosuccinic Acid Dichlorosuccinic Acid

HOOCCH=CClCOOH HOOCCCl=CClCOOH HOOCCCl=CClCOOH

Chloromaleic Acid Dichloromaleic Acid Dichlorofumaric Acid

Figure 12

Miscellaneous Chloroaliphatic Acids

A limited amount of work has been done on chlorination byproducts not containing carbon-halogen bonds. Chlorine is known to react with a wide range of organic amines to form N-chloro-organic compounds (i.e., organic chloramines; Morris, 1967). The significance of these byproducts to human health is unknown. Because the TOX only represents a small fraction of the total chlorine demand, most of the organic chlorination byproducts probably do not contain chlorine. A number of these non-halogenated byproducts have been identified (Christman et al., 1983). Most are aliphatic mono- and di-acids, and benzenepolycarboxylic acids. Because these compounds are probably not of health concern, they have not been extensively studied. It should be noted that many of these compouds are quite biodegradable, and therefore contribute to a water's Assimilable Organic Carbon (AOC).

In addition to the toxic chlorination byproducts there are others that may be classified as aesthetically unpleasing; compounds that impart a taste & odor to finished water. In an indirect way, tastes and odors are also a health concern. Consumers may reject a disagreeable, yet safe, treated water for a better tasting and unsafe substitute. Chlorophenols have long been known as offensive byproducts of chlorination (Burttschell et al., 1959). Similarly, the chlorination of naturally-occurring phenolic type precursors has been blamed for chronic taste and odor problems (Walker et al., 1986). While chlorination byproducts have been indicated as the source for many taste and odor problems, the identities of the troublesome compounds are generally not well known (Jestin et al., 1986). Nevertheless, it is clear that chlorine taste is most closely related to chlorine demand (i.e., to formation of organic byproducts), rather than to residual chlorine concentrations (Bablon et al., 1986).

2. Chloramine Byproducts

Inorganic chloramines are formed by the reaction of free chlorine with ammonia. The reaction is stepwise, giving monochloramine (equation 2) followed by dichloramine (equation 3). The dichloramine is quite unstable, forming nitrogen gas (equation 4) and some nitrate. This decomposition is responsible for the classic breakpoint chlorination phenomenon.

NH₃+ HOCl --------> NH₂Cl + H₂O (2)

NH₂Cl + HOCl --------> NHCl₂+ H₂O (3)

NHCl₂+ NHCl₂+ H₂O --------> HOCl + 3H⁺+ 3Cl^-+ N₂(4)

Normally when chloramines are prepared "in situ" by the addition of ammonia followed by chlorine, reaction 2 occurs so fast as to preclude any direct reaction of free chlorine with organic matter. If, however, the reverse order is used (i.e., chlorine then ammonia) some free chlorination byproducts may be formed before the hypochlorous acid is consumed by added ammonia.

Monochloramine is known to add chlorine to the nitrogen of amines and amino acids forming organic chloramines (Crochet & Kovacic, 1973). This reaction also occurs with free chlorine. Model compound studies have shown that monochloramine can add chlorine to activated aliphatic carbon-carbon double bonds (Minisci & Galli, 1965). The adjacent carbon may become substituted with an amine group or with oxygen. Other types of reactions involve the simple addition of amine or chloramine. Chlorine substitution on to activated aromatic rings has been observed. For example, monochloramine will slowly form chlorophenols from monochloramine (Burttshcell et al., 1959). Unfortunately, many of these studies were carried out at extremes of pH or monochloramine concentration, and their relevance to drinking water treatment conditions is uncertain.

Monochloramine is far less reactive with most organic compounds than free chlorine. Studies with aquatic fulvic acid have shown 24-hour oxidant demands of 0.24 moles/mole carbon for chlorine and 0.06 mole/mole carbon for monochloramine (Jensen et al., 1985). About 100 times as much monochloramine was required to achieve the same degree of fulvic acid bleaching as free chlorine. The bleaching of humic substances is probably related to the destruction of carbon-carbon double bonds. Identifiable byproducts include dichloroacetic acid, cyanogen chloride and very small amounts of chloroform and trichloroacetic acid. While its not clear that TCAA and the THMs are true byproducts of chloramines (i.e., they may be formed due to the presence of a small free chlorine residual), it does seem that DCAA and cyanogen chloride are true byproducts. Backlund and co-workers (1988) found that monochloramine also formed MX from humic materials, although the amount measured was less than 25% of that formed during chlorination. Mutagenic activity was less than 50% of the level produced by chlorine. Shank and Whittaker (1988) have proposed that small amounts of the known carcinogen, hydrazine (H₂N-NH₂), may be formed when drinking waters are chloraminated. However, they have not yet been able to detect this compound in drinking water distribution systems.

Jensen and co-workers (1985) found that at high monochloramine/carbon mole ratios (~10) about 5% of the oxidant demand ended up as TOX. This is identical to the results for chlorine at an equally high chlorine/carbon ratio. At lower ratios more typical of drinking water treatment (i.e., 0.2) the percent TOX to oxidant demand for chlorine rises to 10-20%. There is no reason to believe that would not also be the case for monochloramine. In other words, to get the same degree of oxidation with monochloramine as with chlorine, one would have to apply a much higher dose, and this higher dose would produce about the same amount of TOX. Most of the chlorinated organic byproducts remain tied up in high molecular weight compounds. This contrasts with free chlorine, as monochloramine is a much weaker oxidant and it is much less likely to oxidatively fragment humic molecules to small ones that can be analyzed by gas chromatography.

3. Chlorine Dioxide Byproducts

Chlorine dioxide undergoes a wide variety of oxidation reactions with organic matter to form oxidized organics and chlorite (equation 5). Chlorite may also be formed, along with chlorate (ClO₃), by the disproportionation of chlorine dioxide. All three of these oxidized chlorine species (chlorine dioxide, chlorite and chlorate) are considered to be toxic, and their presence in finished water should be minimized.

ClO₂+ Organics ---------> ClO₂+ oxidized organics (5)

Equation 5 represents a one electron transfer, and by definition the oxidized organics contain a free radical (unpaired electron). Model compound studies have shown chlorine dioxide to be quite reactive with tertiary amines and phenols, moderately reactive with olefins and slightly less reactive with alcohols and aldehydes (NRC, 1980). Chlorine dioxide has a greater tendency to react with alcohols and aldehydes (to form acids) than other water treatment oxidant/disinfectants. Chlorine dioxide will not oxidize bromide to hypobromite, nor will it react with ammonia. Interestingly, it has been proposed that chlorite can react with certain types of organic compounds to give hypochlorite as a byproduct.

Chlorine dioxide will also undergo chlorine substitution reactions. Model compound studies have shown the formation of chlorinated aromatic compounds and chlorinated aliphatics. Trihalomethanes, however, have not been detected as reaction products. As with the other chlorine-containing oxidants, chlorine addition/substitution products are favored at low oxidant to carbon ratios and oxidation reactions are favored at high ratios.

Very little information exists on the chlorine dioxide byproducts from reaction with humic substances. Experiments with concentrated extracts of aquatic fulvic acid showed low reactivity, and very little material that could be analyzed by gas chromatography (much less than 10% of the starting TOC; Colclough, 1981). The major halogenated product was dichloroacetic acid, no trichloroacetic acid was detected. Chloromalonic and chlorosuccinic acids were also identified. Most of the identified byproducts consisted of aliphatic diacids, simple aromatic acids and furan acids not containing chlorine. In an earlier study using Ohio River water treatment with chlorine dioxide resulted in the formation of low molecular weight aliphatic aldehydes (Stevens et al., 1978). As with the model compound studies, no trihalomethanes were detected from either study using natural aquatic organic matter. Also, much less TOX is produced as compared to what is normally found for chlorination (Rav-Acha et al., 1983).

4. Ozonation Byproducts

Although many researchers have applied GC/MS techniques for the purpose of identifying organic ozonation products of raw waters and extracted humic materials, the identifiable yields are generally very small (i.e., <5% of the starting TOC). This is the case despite the very high reactivity of ozone for humic substances. Among the products reported are simple aldehydes (Schalekamp, 1977; Trussell et al., 1981; Glaze et al., 1990), a large variety of low molecular weight (MW) aliphatic acids, some keto-acids, hydroxy-acids, and benzene polycarboxylic acids (Lawrence, 1977; Lawrence et al., 1980; Benga, 1980; Paramisigamani et al., 1983; Anderson, 1984; Killops et al., 1985; Glaze, 1986). Among this group of identified ozonation byproducts, perhaps, only the aldehydes are suspected as being human health hazards (Glaze, 1986). In particular, formaldehyde seems to be a ubiquitous product of drinking water ozonation. In some waters, however, this formaldehyde is diminished by reaction with other constituents (Glaze et al., 1988). Since, the vast majority of the ozonation byproducts are not gas chromatographable, toxicological assessments of ozonation cannot be based solely on the identified compounds (Killops et al., 1985).

The tendency of ozone to form organic free radicals which can undergo subsequent condensation reactions (i.e., higher MW) may also help to explain the lack of gas chromatographable products. One group of transient byproducts, the peroxides & hydroperoxides, cannot easily be identified due to their high degree of reactivity. Studies employing general tests for oxidizing materials have suggested that these compounds are present. Research is currently underway using LC/MS to isolate and identify organic peroxides.

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