Triclosan is an antibacterial and antifungal agent. It is a polychloro phenoxy phenol. Despite being used in many consumer products, beyond its use in toothpaste to prevent gingivitis, there’s no evidence by the FDA that triclosan provides an extra benefit to health in other consumer products.[1] Triclosan safety is currently under review by the FDA.[1]

Uses

Triclosan has been used since 1972, and it is present in soaps (0.10-1.00%), deodorants, toothpastes, shaving creams, mouth washes, and cleaning supplies, and is infused in an increasing number of consumer products, such as kitchen utensils, toys, bedding, socks, and trash bags. Triclosan has been shown to be effective in reducing and controlling bacterial contamination on the hands and on treated products. More recently, showering or bathing with 2% triclosan has become a recommended regimen for the decolonization of patients whose skin is carrying methicillin resistant Staphylococcus aureus (MRSA)[2] following the successful control of MRSA outbreaks in several clinical settings.[3][4]

Triclosan is regulated by the U.S. Food and Drug Administration, the Environmental Protection Agency, and the European Union. During wastewater treatment, a portion of triclosan is degraded, while the remaining adsorbs to sewage sludge or exits the plant in wastewater effluent.[5][6] In the environment, triclosan may be degraded by microorganisms or react with sunlight, forming other compounds, which may include chlorophenols and dioxin, or it may adsorb to particles that settle out of the water column and form sediment.[5][7] Triclosan was found in Greifensee sediment that was over 30 years old, suggesting that triclosan is degraded or removed slowly in sediment.[5]

Mechanism of action

At in-use concentrations, triclosan acts as a biocide, with multiple cytoplasmic and membrane targets.[8] At lower concentrations, however, triclosan appears bacteriostatic and is seen to target bacteria mainly by inhibiting fatty acid synthesis. Triclosan binds to bacterial enoyl-acyl carrier protein reductase enzyme (ENR), which is encoded by the gene FabI. This binding increases the enzyme’s affinity for nicotinamide adenine dinucleotide (NAD+). This results in the formation of a stable ternary complex of ENR-NAD+-triclosan, which is unable to participate in fatty acid synthesis. Fatty acid is necessary for reproducing and building cell membranes. Humans do not have an ENR enzyme, and thus are not affected. Some bacterial species can develop low-level resistance to triclosan at its lower bacteriostatic concentrations due to FabI mutations, which results in a decrease of triclosan’s effect on ENR-NAD+ binding, as shown in Escherichia coli and Staphylococcus aureus.[9][10] Another way for these bacteria to gain low-level resistance to triclosan is to overexpress FabI.[11] Some bacteria have innate resistance to triclosan at low, bacteriostatic levels, such as Pseudomonas aeruginosa, which possesses multi-drug efflux pumps that ‘pump’ triclosan out of the cell.[12] Other bacteria, such as some of the Bacillus genus, have alternative FabI genes (FabK) to which triclosan does not bind and hence are less susceptible.

Formation of dioxin in surface water

The use of triclosan in household anti-bacterial products introduces the chemical to surface waters where it can form dioxins. The dioxin compound that formed when triclosan degraded in sunlight was shown in a study by University of Minnesota researchers not to be of public health concern. Dioxin is not one compound, but a family of compounds of widely ranging toxicity. Of the 210 dioxin and furan family compounds, only 17 are considered to be of public health concern.[13]

Resistance concerns

An article coauthored by Dr. Stuart Levy in the August 6, 1998 issue of Nature[14] warned that triclosan’s overuse could cause resistant strains of bacteria to develop, in much the same way that antibiotic-resistant bacterial strains are emerging, based on speculation that triclosan behaved like an antibiotic. Based on this speculation, in 2003, the Sunday Herald newspaper reported that some UK supermarkets and other retailers were considering phasing out products containing triclosan.[15]

It has since been shown that the laboratory method used by Dr. Levy was not effective in predicting bacterial resistance for biocides like triclosan,[16] At least seven peer-reviewed and published studies have been conducted demonstrating that triclosan is not significantly associated with bacterial resistance over the short term, including one study coauthored by Dr. Levy.[17]

Some level of triclosan resistance can occur in some microorganisms, but the larger concern is with the potential for cross-resistance or co-resistance to other antimicrobials. StudiesHealth concerns

In August 2009 the Canadian Medical Association asked the Canadian government to ban triclosan use in household products under concerns of creating bacterial resistance and producing dangerous side products (chloroform).[19]

Reports have suggested that triclosan can combine with chlorine in tap water to form chloroform gas,[20] which the United States Environmental Protection Agency classifies as a probable human carcinogen. As a result, triclosan was the target of a UK cancer alert, even though the study showed that the amount of chloroform generated was less than amounts often present in chlorinated drinking waters.

Triclosan also reacts with the free chlorine in tap water to produce lesser amounts of other compounds, like 2,4-dichlorophenol.[20] Most of these intermediates convert into dioxins upon exposure to UV radiation (from the sun or other sources). Although small amounts of dioxins are produced, there is a great deal of concern over this effect, because some dioxins are extremely toxic and are very potent endocrine disruptors. They are also chemically very stable, so that they are eliminated from the body very slowly (they can bioaccumulate to dangerous levels), and they persist in the environment for a very long time.

Triclosan is chemically somewhat similar to the dioxin class of compounds. Its production leads to small amounts of residual polychlorinated dioxins, and polychlorinated furans, which are contained in small amounts, in the products that are using it.

A 2006 study concluded that low doses of triclosan act as an endocrine disruptor in the North American bullfrog.[21] The hypothesis proposed is that triclosan blocks the metabolism of thyroid hormone, because it chemically mimics thyroid hormone, and binds to the hormone receptor sites, blocking them, so that normal hormones cannot be utilized. Triclosan has also been found in both the bile of fish living downstream from waste water processing plants and in human milk.[22] The negative effects of triclosan on the environment and its questionable benefits in toothpastes[23] has led to the Swedish Naturskyddsföreningen to recommend not using triclosan in toothpaste.[24] Another 2009 study demonstrated that triclosan exposure significantly impacts thyroid hormone concentrations in the male juvenile rats.[25]

Triclosan is used in many common household products, including Clearasil Daily Face Wash, Dentyl mouthwash, Dawn, the Colgate Total range, Crest Cavity Protection, Softsoap, Dial, Right Guard deodorant, Sensodyne Total Care, Old Spice, Mentadent, and Bath and Body works hand sanitizers.

In the United States, manufacturers of products containing triclosan must now say so somewhere on the label.

Advertisements