An alkylphenol is a phenol molecule to which a C„H2b +1 chain is bonded (Figure 2).
About 500 million kg of alkylphenols are produced annually for use in surfactants, herbicides, gasoline additives, dyes, polymer additives, lubricant oil additives, and antioxidants. Nonylphenol (a 9-C alkyl chain) and related compounds have been much studied because they are widely used, relatively persistent, and have endocrine-disrupting (estrogenic) properties in fish, birds, and mammals.
Figure 2 (a) 4-Nonylphenol, an example of an alkylphenol; (b) triclosan; (c) urushiol (one of the several active ingredients in poison ivy).
Bisphenol A (BPA; Figure 1) is produced from phenol and acetone. Globally, very large quantities of BPA are used in polycarbonates (hard, clear plastics) and resins. More than 100 million kg of polycarbonates are produced annually; polycarbonates have many uses, including the electronic industry (CDs, for example) and the food industry (e.g., water bottles, can linings, etc.). BPA has estrogenic properties and has been investigated with respect to risks to mammals, fish, and amphibians. It can strongly affect reproduction in mollusks at concentrations as low as 1 mgl _1, and is under study because it appears to disrupt the function of estrogen in the developing brain, even at parts per trillion (ppt) concentrations.
PCP was widely used as a wood preservative (the purchase and use of PCP in the US was restricted in the 1980s). Commercial formulations of PCPs often contained other significant toxicants, such as dioxins, as production by-products. Based on freshwater field and laboratory studies, the probable no-effect concentrations for PCP have been shown to be on the order of 0.2-2 mgl"1 for water and 12.4-124mgkg-1 for freshwater sediment. Some isolates of white rot fungi can biodegrade PCP efficiently via laccase, a phenol oxidase.
Brominated phenols and biphenols, and polybrominated diphenyl ethers, came into widespread use in the 1970s, especially as flame retardants (>200 million kgyr-1). Some of these compounds are highly toxic and lipophilic; many are relatively slow to biodegrade, and some have endocrine-disrupting properties. Polybrominated biphenyls (PBBs), much like their polychlorinated counterparts (PCBs), are toxic and lipophilic: they are bioaccumulation and reproductive hazards.
Triclosan (Figure 2) has broad-spectrum antimicrobial properties and is used in many personal-care products, including deodorants, soaps, toothpaste, anti-perspirants, lotions, and cosmetics. It is also used in the production of polymers, plastics, and textiles. Triclosan has been found in 58% of the natural waters in the US, and is troublesome in two ways: it is relatively persistent, and when in water, it can be converted to a dioxin by exposure to UV components of sunlight. Some dioxins are very toxic, others are less so: however, most dioxins readily bioaccumulate, and some of the less-toxic dioxins can convert to a more toxic form if they react with chlorine, which is often used as a disinfectant for drinking water.
Salicylic acid (2-hydroxybenzoic acid) is prepared by treating the sodium salt of phenol with CO2 under pressure. This yields sodium salicylate, which is treated with sulfuric acid to form salicylic acid. The acetyl derivative of salicylic acid is aspirin. Aspirin is believed to act against fever, pain, and inflammation by interfering with the production of particular prostaglandins. Before the commercial production of aspirin was possible, salicin (the active ingredient of aspirin) was extracted from willow bark. Aspirin now is used in more than 50 over-the-counter cold, flu, and analgesic preparations. Some 80 billion tablets of aspirin are consumed annually in the US alone.
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