Source: Williams and Burson (1985).

Source: Williams and Burson (1985).

kidney necrosis, and coronary degeneration. They react to form methemoglobin in the blood. Repeated exposure can produce strong allergic reactions. Aromatic amines or diphenylamine compounds are carcinogens, such as benzidine, 2-naphthylamine, or 4-aminodiphenyl, which cause "aniline tumors'' in dye industry workers. Any alkyl amine (such as those that can be produced in digestion of food) can react with nitrites in food and acid in the stomach to form nitrosamines, which can potentially cause liver cancer.

Analine itself is an important industrial compound that is also used in household products such as polishes, paints, and inks. It is considered very toxic and is easily absorbed through the skin. In the blood, aniline oxidizes Fe(II) to Fe(III), turning the blood to a brown-black color and eliminating its ability to transport oxygen.

Nitro compounds are mild irritants. Unsaturated compounds are easily absorbed der-mally. Nitrated aromatics produce a variety of effects, including methemoglobinemia. Some produce bladder tumors. Trinitrotoluene and dinitrobenzene are easily absorbed by all routes of exposure. Besides the other toxic effects, they can uncouple oxidative phosphorylation and cause liver damage. Nitriles (compounds with structure R—C=N) are easily absorbed, and many slowly degrade to cyanide. Acetonitrile is considered moderately to very toxic. Acrylonitrile is classified as highly toxic and is a suspected human carcinogen.

Single-ring aromatics include benzene and its derivatives. Aromatics tend to be more toxic than aliphatics with a similar number of carbons. CNS depression caused by aromatics differs qualitatively from that produced by aliphatics. Coma induced by aliphatics, such as by gasoline, exhibit inhibited reflexes. On the other hand, aromatics produce hyperactive reflexes, sometimes with convulsions.

Benzene is reportedly fatal at about 10 to 15 mL for an adult, and possibly as low as 2 to 5 mL. Inhalation at 250 ppmv produces headache, nausea, vertigo, and drowsiness; 3000 ppmv in air is irritating to the eyes and respiratory tract. Acute symptoms appear after 30 to 60 minutes at 7500 ppmv; 20,000 ppmv for 5 to 10 minutes has been reported to be fatal. Acute symptoms are respiratory inflammation, pulmonary edema and hemorrhage, renal congestion, and cerebral edema. Chronic dermal exposure can produce damage resembling first- or second-degree burns. Blood disorders progress through three stages: First is a reversible reduction in blood clotting and a mild anemia. Continued exposure produces increased leukocyte production. Finally, a more severe anemia and hemorrhage occurs. Less commonly, benzene also causes a cancer, leukemia. It is a class A carcinogen. Chomosome damage has also been observed in humans. Toluene is a stronger CNS depressant than benzene but is not known to cause permanent blood disorders. The xylenes are even stronger CNS depressants than toluene.

Phenols are cytotoxic, acting as a local anesthetic and CNS depressant. They are easily absorbed but produce strong irritation and burns. Phenol easily penetrates the skin, where it causes deep burns. Burns from ingestion can lead to extreme shock and death. Phenol can also cause necrosis systemically in the liver and kidneys as well as the heart and urinary tract. Death from systemic poisoning is usually from respiratory depression as a result of its CNS depression activity. Ingestion of as little as 1 or 2 g reportedly can be fatal. The dihydroxyphenols catechol, resorcinol and hydroquinone, and cresol, behave similarly to phenol, except that they are more toxic.

benzene phenol hydroquinone p-cresol benzene phenol hydroquinone p-cresol

Polynuclear aromatic hydrocarbons (PAHs, also referred to as PNAs or polycyclic aromatic hydrocarbons) are fused benzene rings and their derivatives. Many are prevalent in coal and crude oil. They also are significant products of partial combustion; that is, they are found in soot and smoke particles, and in pyrolytically produced tars and oils. The simplest PAH is naphthalene.

naphthalene anthracene phenanthrene naphthalene anthracene phenanthrene benzo[a]pyrene benzo[a]pyrene pyrene pyrene fluoranthene fluorene fluoranthene fluorene

PAHs are strongly absorbed to soil and sediment particles in the environment and can even be transported long distances by the wind. Aqueous solubility decreases with molar mass and is lower for linear ring arrangements than more condensed forms (compare anthracene and phenanthrene in Table 21.8). In aquatic environments, PAHs tend to be most concentrated in sediments, least in the water column, and intermediate in organisms.

Some bacteria and fungi can mineralize some PAHs, but others can only cometabolize them. Fungi and some animals utilize the cytochrome P450 (MFO) system to hydroxylate PAHs to diols. Certain intermediates of this conversion in mammals are thought to be responsible for carcinogenicity in this group. Injection of PAHs in fish can induce MFO activity severalfold within several days.

PAHs cause acute toxic effects in humans only at high doses that are not common in environmental or occupational settings. Napthalene inhalation causes headache, confusion, nausea, and profuse perspiration in humans. For a variety of marine and

TABLE 21.8. Transport Properties of Some PAHs and Bioaccumulation Factors for Daphnia pulex

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