Alkylphenols are a family of organic compounds obtained by the alkylation of phenols. The term is usually reserved for commercially important propylphenol, butylphenol, amylphenol, heptylphenol, octylphenol, nonylphenol, dodecylphenol and related "long chain alkylphenols" (LCAPs). Methylphenols and ethylphenols are also alkylphenols, but they are more commonly referred to by their specific names, cresols and xylenols.
Alkylphenols such as nonylphenol and octylphenol are mainly used to make alkylphenol ethoxylate (APE) surfactants (detergents), though alkylphenols themselves can be used as plasticisers in plastics, and the derivatives alkylphenol phosphites can be used as UV stabilisers in plastics.
In Europe alkylphenol ethoxylates are used in:
- industrial detergents, such as those used for wool washing and metal finishing.
- some industrial processes, such as emulsion polymerisation
- the spermicidal lubricant nonoxynol-9.
- various laboratory detergents, including Triton X-100.
- some pesticide formulations.
Outside Europe alkylphenol ethoxylates are also used in many domestic products; for example in the USA they are in many liquid clothes detergents. In Europe these products contain the slightly more expensive, but much safer, alcohol ethoxylates.
Hormone disrupting effects
Alkylphenols were first found to be oestrogenic (oestrogen-mimicking) in the 1930s, and more evidence was published in 1978. However, it was only in 1991 that publication of the effects of nonylphenol on cultured human breast cells led to health concerns (Soto et al., 1991). This and more recent research has shown that the growth of these cells is increased by alkylphenols at concentrations 1000 to 10000 times higher than the oestradiol levels required to produce the same growth. Oestrogenic effects have also been shown on rainbow trout hepatocytes, chicken embryo fibroblasts and a mouse oestrogen receptor. Oestrogenic effects are present at tissue concentrations of 0.1 µM for octylphenol and 1 µM for nonylphenol. A recombinant yeast screen using the human oestrogen receptor has shown similar results.
Recent research is showing oestrogenic effects of nonylphenol at ever lower concentrations. Levels of 0.05 micro-g per litre were enough to increase the number of eggs produced by minnows, as well as increasing vitellogenin levels. This research also suggested that nonylphenol was leading to an increase in natural oestrogen levels.