*3.2.4. Municipal waste*

synthesis in plants. Typically, phenylalanine is deaminated to cinnamate through phenylala‐ nine ammonia‐lysase catalysis. A hydroxylation process catalysed by cinnamate‐4‐hydroxy‐ lase then results in the conversion of cinnamate to coumaric acid which becomes the starting material for the synthesis of stilbenes, flavonoids and furanocoumarines including other classes of phenolics catalysed by different enzymes [20]. These compounds are stored in the leaves, roots and stems of plants. Roots and leave exudates of plants contain these phenolic compounds, which are finally introduced into the soil by the exudates. Decomposition of dead leaves, roots and plants also introduces the phenolic compounds into the soil. Runoff

Phenolic compounds have varied applications in the day‐to‐day lives of human beings. Phenol is widely used in different industries such as the chemical industry where it is used in the production of other derivatives such as alkylphenols, cresols, aniline and resins [21]. Its application in the oil and gas and coal industries is also noteworthy [1]. Phenolic resins, which are also produced from phenol, are used heavily in appliance, wood and construction indus‐ tries for various purposes. Dyes, textiles and explosive industries all depend on phenol as raw material. Other phenolic compounds such as bisphenol A serves as the raw material from which non‐polymer additives, polycarbonate plastics and epoxy resins are manufactured. Nylon 6 (polycaprolactam) and some fibres (synthetic) are produced using caprolactam as raw material [22]. Phenolic compounds are also constituents of some pesticides and other insecticides. Other industrial activities such as wood distillation, use of chlorine for water disinfection, cooking processes and paper production all result in the formation of chloro‐ phenols [23]. Direct or indirect discharge of effluents and/or influents from these industrial activities into water bodies culminate in their pollution with phenolic compounds. Some of these compounds are also released into the atmosphere through vehicular activities and are

Application of pesticides, insecticides and herbicides constitutes the main source of water pollution with phenolic compounds through the agricultural source. Availability or detec‐ tion of phenol and some chlorophenols such as 2‐chlorophenol, 2,4‐dichlorophenol and some catechols in the aquatic environment have been attributed to biodegradation of some of these pesticides. Among these pesticides are 2,4‐dichlorophenoxyacetic acid, 4‐chloro‐2‐methyl‐ phenoxyacetic acid, 2,4,5‐richloro‐phenoxy acetic acid [24, 25]. Another pesticide vastly used in the agricultural sector is pentachlorophenol which finally degrades to other chlorophenols with lower chlorine substituents [26]. These herbicides, fungicides, and pesticides with their degradation by‐products are washed into the water bodies through agricultural runoff.

Phenol is a component of many household chemicals. It is present in disinfectants, antisep‐ tics and slimicides. Medical or pharmaceutical products including body lotions, ointments,

from land then washes these compounds into the nearby water bodies.

424 Phenolic Compounds - Natural Sources, Importance and Applications

**3.2. Anthropogenic sources**

finally washed into water bodies as rain water.

*3.2.1. Industrial waste*

*3.2.2. Agricultural waste*

*3.2.3. Domestic waste*

Effluents and influents emanating from municipal waste treatment plants, and leachates from municipal solid waste landfill sites, are another source of phenolic compounds into water bod‐ ies. p‐Cresols have been identified in leachates from a municipal waste landfill site and are believed to originate from incineration residues. Similarly, 2,4,6‐trichlorophenol, 4‐tertrabutyl‐ phenol and bisphenol A were also found in leachates and are believed to emanate from fly ash while combustibles were deemed to be the source of 4‐tert‐octylphenol in landfill leachates. Some chlorophenols, 4‐nonylphenol and phenol have all been identified in municipal waste landfill sites [27]. Thus, the release of untreated leachates from landfill sites, the release of resi‐ dues of incineration such as solid fly ash and the release of incombustible materials into nearby water bodies result in the pollution of the aquatic environments with phenolic compounds.
