Paraben

The general chemical structure of a paraben is shown at the top right of this page, where R symbolizes an alkyl group such as methyl, ethyl, propyl or butyl.

para-Hydroxybenzoic acid is in turn produced industrially from a modification of the Kolbe-Schmitt reaction, using potassium phenoxide and carbon dioxide.

They are thought to act by disrupting membrane transport processes[2] or by inhibiting synthesis of DNA and RNA[3] or of some key enzymes, such as ATPases and phosphotransferases, in some bacterial species.

They are found in shampoos, commercial moisturizers, shaving gels, personal lubricants, topical/parenteral pharmaceuticals, sun-tan products, makeup,[6] and toothpaste.

[10] Studies in rats have indicated that parabens may mimic the hormone estrogen, raising concerns over possible contributions to breast cancer.

[citation needed] Concerns about endocrine disruptors have led consumers and companies to search for paraben-free alternatives.

[14] The European Scientific Committee on Consumer Safety (SCCS) reiterated in 2013 that methylparaben and ethylparaben are safe at the maximum authorized concentrations (up to 0.4% for one ester or 0.8% when used in combination).

The SCCS concluded that the use of butylparaben and propylparaben as preservatives in finished cosmetic products is safe to the consumer, as long as the sum of their individual concentrations does not exceed 0.19%.

[18] In one New York wastewater treatment plant (WWTP), mass load of all parent paraben derivatives (methylparaben, ethylparaben, propylparaben, butylparaben, etc.)

[21] This reaction can occur with free chlorine present in tap water or with sodium hypochlorite, which is often used in WWTPs as a final disinfectant step.

[22] In neutral water, Raman spectroscopy has confirmed that chlorine is predominantly present as hypochlorous acid (HClO).

[23] Parabens can react with HClO to form mono- and di- chlorinated products through electrophilic aromatic substitution.

[21] The electrophilic attack of the chlorine forms a carbocation that is stabilized by donated electron density from the hydroxyl group of the paraben.

[21] A base can then abstract a proton from the carbon containing the chlorine, which is followed by subsequent restoration of aromaticity by the involved pi electrons.

[24] The Arrhenius equation was used in a study to calculate activation energies for the chlorination of four parent parabens (methyl-, ethyl-, propyl-, and butylparaben) and was found to range from 36–47 kJ/mol.

When paraben-containing cosmetic products are discharged into community wastewater influent, they become exposed to an environment where the pH ≥ 8, and the base-catalyzed hydrolysis of the parent paraben ensues, forming PHBA.

Upon separation of the liquid and solid phases of the incoming influent, parabens have a greater tendency accumulate in the sludge.

[18][22] These levels have been accurately measured in tertiary effluent and sewage sludge, as these are the primary avenues for which parabens and their degradation products reach the environment upon discharge from WWTPs.

The second reason is due to the intermediate increase in levels of PHBA during the secondary clarifier phase of the WWTP through biological processes.

[31][32] In Daphnia magna, general toxicity conferred by chlorinated parabens occurs through non-specific disruption of cell membrane function.

These hazards include, but are not limited to, abnormal fetal development, endocrine disrupting activity, and improper estrogen-promoting effects.

[33] If the tertiary effluent is released to the environment in rivers and streams or if the sludge is used as fertilizer, it poses as a hazard to environmental organisms.

[35] Due to the electrophilic nature of ozone, it can easily react with the aromatic paraben ring to form hydroxylated products.