Properties Use and Environmental Problems

Polycyclic aromatic hydrocarbons (PAHs) are contained mainly in the tar of hard coals and in all kinds of mineral oils. During the various preparation processes for intermediate products in the chemical industry and for numerous fuels, PAHs enter the wastewater, groundwater and solid wastes. Because of their toxicity, 13 PAHs are included in the EPA list. Four of these and two further PAHs are presented in Table 9.7. Two characteristics are of notable importance: their low solubility in water, but high solubility in mineral oil, and their toxicity (LD50). With increasing number of rings and molecular mass, their solubility in water decreases and their toxicity increases dramatically.

Table 9.7 Some polycyclic aromatic compounds, their properties, and use (Rippen 1991). For symbols used, see Table 9.1.

Compound

LD50

EPA No.

Naphthalene Anthracene

Phenanthrene

Benzo(e)pyrene

Benzo(k)fluorethene

Acenaphthene

25 (20 °C) Rat: 1780 Raw material for the produc tion of dyes

0.048 (20°C) Daphnia magna: Intermediate in the produc- 78

Rat: 10000

tion of dyes and anthra-chinone

Raw material for the production of explosives, pharmaceutical products, drugs, herbicides, tanneries

Raw material for the production of textile pigment dyes and synthetics, insecticides and fungicides

75 77

Therefore, toxic PAHs are mostly dissolved in other organics such as mineral oils. Mineral oils and their biodegradability will be discussed first before continuing with the biodegradability of PAHs.

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