Down the Drain: » Triclosan
Triclosan is an antimicrobial agent found in a broad variety of products, ranging from hospital and household liquid hand soap, detergents, and other sanitizing products, to toothpaste and hair products, pesticides, and plastic and foam products like cutting boards and shoe insoles. The popularity of antibacterial consumer products has led to increased consumer use of triclosan (Perencevich 2001; Tan 2002). This antimicrobial agent is marketed under a variety of trademarked names as well, including Microban, Irgasan DP-300, Lexol 300, Ster-Zac, Cloxifenolum, Biofresh, and others.
Triclosan has been detected in human breast milk and blood samples from the general population (Adolfsson-Erici 2002; TNO 2005), and in the urine of 61 percent of 90 girls ages 6 to 8 tested in a recent study spearheaded by Mount Sinai School of Medicine (Wolff 2007). EWG-led biomonitoring studies have detected triclosan in 17 of 21 people tested (EWG 2007a). Scientists recently found triclosan in 58 percent of 85 streams across the U.S. (Kolpin 2002), the likely result of its presence in discharges of treated wastewater.
The amount of triclosan in the wastwater stream is estimated to be as much as 3 to 5 milligrams per person per day from residences alone (McAvoy 2002); in addition, substantial discharges of this antimicrobial agent are expected from laundries, hair salons, medical facilities, and many other commercial and industrial sites. Optimal water treatment can result in degradation and removal of 95 percent of triclosan (Samsoe-Petersen 2003); however, small amounts may pass through the treatment plants to receiving waters.
Triclosan kills microbes by disrupting protein production, and also by binding to the active site of a critical carrier protein reductase that is essential for fatty acid synthesis. This target enzyme is present in microbes but not in humans. Though triclosan is known to be acutely toxic to certain types of aquatic organisms (Orvos 2002), available studies do not indicate it causes cancer or birth defects in humans (Bhargava 1996). Products containing triclosan may occasionally cause skin irritation in people with a specific sensitivity (Bhargava 1996).
Triclosan has the tendency to bioaccumulate (Samsoe-Petersen 2003), or become more concentrated in the fatty tissues of humans and other animals that are exposed to this chemical. The chemical structure of triclosan is similar to that of DES, a non-steroidal estrogen linked to cancer development in those exposed in utero, raising concerns about its potential to act as an endocrine disruptor. A recent study on fish showed that triclosan had weakly androgenic effects, but no estrogenic effects (Foran 2000).
In contrast, another study found that low levels of triclosan in combination with thyroid hormones triggered rapid transformation of tadpoles into frogs (Veldhoen 2006). Rather than mimicking the thyroid hormone, triclosan, in concentrations of less than 1 part per billion commonly measured in U.S. streams, appeared to make thyroid hormones more potent. This hormone signaling mechanism is similar in frogs and humans, suggesting that triclosan could potentially disrupt the human thyroid system.
The evolving interaction between microbes and antiseptic agents has led to concern that use of specific antimicrobial ingredients may provoke the development of strains of bacteria that are resistant to disinfection. Studies have described strains of bacteria that have acquired reduced susceptibility to triclosan (McMurry 1998; Chuanchuen 2001). The identification of a triclosan-resistant bacterial enzyme suggests that resistance to this antiseptic ingredient may develop more readily than to other agents (Heath 2000). In addition, exposing specific bacterial strains to triclosan appears to result in selection favoring bacteria that are resistant to multiple antibiotics (Chuanchuen 2001).
The American Medical Association has advanced an official recommendation against using antibacterial products in the home due to concern about antimicrobial resistance (Tan 2002). A Food and Drug Administration panel reviewed the existing research and found no evidence that households that use antibacterial products are healthier than households that use soap and water and other typical cleansing products (FDA 2005).
Studies indicate that in surface waters, triclosan can interact with sunlight and microbes to form methyl triclosan, a chemical that may bioacummulate in wildlife and humans (Adolfsson-Erici 2002; Lindstrom 2002). A recent European study found methyl triclosan in fish, especially concentrated in fatty tissue (Balmer 2004). Triclosan also can degrade into a form of dioxin, a class of chemicals linked to a broad range of toxicities including cancer (Lores 2005). New research shows that triclosan in tap water can react with residual chlorine from standard water disinfecting procedures to form a variety of chlorinated byproducts at low levels, including chloroform, a suspected human carcinogen (Fiss 2007).