Halogenated Aromatic Hydrocarbons

Some of the commonly used aromatic HHCs include chlorinated benzenes, benzyl chloride, chlorinated phenols, chlorinated pyridines, chlorinated naphthalenes, chlorinated biphenyls, chlorinated dibenzodioxins, chlorinated dibenzofurans, chlorinated terphenyls, chlorinated benzoyl toluene, chlorinated phenoxyacetic acids, chlorobutyl rubber, Grignard's reagent, Friedel-Crafts's reagent, Diels-Alder Reaction, and alkanolamine.

Monochlorobenzene, dichlorobenzene (w-and/>-dichloro-benzenes), trichlorobenzenes (1,2,3-, 1,3,5-, and 1,2,4-trichlorobenzenes), and their derivatives (1-chloro-3-nitro-benzene, 1-bromo-4-chlorobenzene) have been widely used as chemical intermediates and solvents.^ยป-Dichlorobenzene is used as a fumigant (insecticide) and disinfectant. A mixture of trichlorobenzene isomers is used in termite control. 1,2,3-and 1,3,5-trichlorobenzenes have been used as heat-transfer media, transformer fluids, and solvents. Hexachlorobenzene (HCB) is used as a fungicide and as an intermediate for dyes and hexafluorobenzene, synthetic rubber, PVC, an additive for military's pyrotechnique compositors, and as a porosity-controlling agent in manufacture of electrodes.

Benzoyl chloride is an intermediate in the synthesis of benzyl compounds, quaternary ammonium chloride, dyes, tanning materials, pharmaceuticals, and perfume preparation. It is used in the textile and dyes industries as a fastness improver for dyed fiber and fabrics. Hexachlorophene is a topical anti-infective agent, used in detergents and as an antibacterial agent for soaps, surgical scrubs, hospital equipment, cosmetics, etc. It is used as a fungicide for vegetables and ornamental crops. Benzethonium chloride is used as a topical anti-infective agent in medicine and as a germicide for cleansing food and dairy utensils, and as a controlling agent for removing pool algae. It is an additive in deodorants and hairdressing preparations. Tri-, tetra-, penta-, hexa-, and octachloronaphthalenes have been formerly used in heat-transfer media, solvents, lubricant additives, dielectric fluids, and electric insulating material.

In addition to the agrochemicals, a few other HHCs that have caused most serious ecotoxicological and health effects include polychlorinated biphenyls (PCBs), poly-brominated biphenyls (PBBs), chlorinated naphthalenes, terphenyls, dioxins, dibenzofurans, and diphenyl ethers.

PCBs are mixtures of various congeners/isomers (Table 3). Mixtures of various congeners are marketed as Aroclors (Clophen outside USA) in which the last two digits indicate the degree of chlorination, such as Arochlor 1254 and 1260 (and Clophen A 60) (Table 4). These are chemically stable, unreactive, viscous liquids of low volatility. These have been used in closed, semiclosed, and

Table 2 HHC production in USA

Million metric tonsyr

Table 3 Numbers of possible congeners (isomers) of halogenated aromatics

Table 2 HHC production in USA

Million metric tonsyr

Chemical

Current

Past

Vinyl chloride

6-12 (1O)

O.599 (694 in 1978)

Solvents

Methyl chloride

O.198 (1971)

Methyl bromide

O.O36 (1975)

Chloroethanes

2.1

1,2-Dichloroethane

O.3

11 (1978)

1,2-Dibromoethane

O.23O (1978)

1,1,1-Trichloroethane

>1.O

O.644 (1978)

Hexachloroethane

O.228

Ethylene dichloride

O.O16 (198O)

Ethylene dibromide

O.OO85 (198O)

Trichloroethylene

O.3

O.299 (1978)

Tetrachloroethylene

O.7

O.725 (1978)

Carbon tetrachloride

O.5

O.737 (1978)

Chloroform

O.3

O.349 (1978)

Other halogens

Chlorobenzene

O.24O (1967)

p-Chloronitrobenzene

O.O5O (1967)

o-Chloronitrobenzene

O.O17 (1967)

Dichlorodifluoromethane

O.O83 (1967)

Trichlorofluoromethane

O.12O (1967)

Chlorinated paraffins

O.O28 (1967)

Hexachlorocyclopentadiene

O.O5O (1967)

Total Pesticides

1.388 (1.O)

Herbicides

O.674

2,4-D

O.O44 (197O)

2,4,5-T

O.O12 (197O)

Propachlor

O.O11

Insecticides

Silvex

O.OO2 (197O)

Methoxychlor

O.OO55 (1975)

Chloropicrin

O.OO5 7 (1975)

Toxaphene

O.31

DDT

O.O59 (197O)

Cyclodienes

O.89 (1975)

Aldrin/Dieldrin

O.OO9

Ethylene dibromide

O.28

O.O88 (1975)

Chloral

O.O26 (1967)

Alachlor

O.O89 (1976)

Fungicides

O.143

Trifluralin

O.O28

PCP

O.O4O (1975)

HCB

PCBs

USA

O.O13

9OO (1978)

Rest of the world

1OOO (1978)

Chlorofluorocarbons

O.12

aData from Anonymous (1979) Environmental Quality. The Annual Report of Council on Environmental Quality, 816pp. Washington, DC: US Government Printing Office.

aData from Anonymous (1979) Environmental Quality. The Annual Report of Council on Environmental Quality, 816pp. Washington, DC: US Government Printing Office.

'open-end' systems, such as hydraulic fluids, coolants, electric transformers, capacitors, insulations (electric wire and cable), heat-transfer systems, fluorescent light ballasts, lubricating oils, plasticizers, paints, inks, paper, dielectric fluids, heat-transformer fluids, lubricants, vacuum pump

Table 3 Numbers of possible congeners (isomers) of halogenated aromatics

Halogen substitution

Benzenes

Dioxin

Furans

Biphenyls

Mono

1

2

4

3

Di

3

1O

16

12

Tri

4

14

28

24

Tetra

3

22

38

42

Penta

1

14

28

46

Hexa

1

1O

16

42

Hepta

2

4

24

Octa

1

1

12

Nona

O

O

3

Deca

O

O

1

Total

13

75

135

2O9-265

oils, carbonless copying paper, wall coatings, surface treatment in textiles, wood, metal, and concrete; in caulking material, impregnated fruit wrappings, cutting oils, microscopic mounting and immersion oil, vapor suppressants; in insecticide and bactriocide formulations, etc., from agriculture to office buildings, automobiles, and homes. PCBs have caused widespread contamination. However, major environmental sources of PCBs include manufacturing wastes, careless disposition, and dumping. From 1929 to the mid-1970s, USA produced 1.4 billion tons of PCBs and rest of the world about the same amount. In USA about 300 0001 of PCBs have been disposed in dumps and landfills; and about 60 000 t in fresh water and coastal waters, while air contains less than 30 0001 of PCBs. The worst contamination with PCBs in USA occurred in Escamba Bay, FL; Lake Michigan, IL; the Ohio River, OH; Francisco Bay, CA; the Hudson River, NJ; and Puget Sound, WA (Table 5).

PBBs have been used mostly as flame retardants and have caused only local problems based on accidental contamination of cattle feed and waste disposition in Michigan. The brominated hydrocarbon flame retardant hexabromocyclododecane (HBCD) is blended with textile and polystyrene foam. It can leach out from these products and contaminate water and biota. Flame retardants bromodiphenyl ethers have become common environment and human contaminants.

Polychlorinated dioxins (PCDDs) and dibenzofurans (PCDFs) are present in halogenated aromatics as contaminants or are produced during their synthesis or incineration. Some of these are persistent and extremely toxic to wildlife, including higher animals and humans.

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