Triclosan Reactivity in Chlorinated and Chloraminated Waters

Sponsor: American Water Works Association Research Foundation

This recently completed project examined the reactivity of the antimicrobial agent triclosan in waters containing either free chlorine or chloramines. Triclosan is the most commonly utilized anti-microbial agent and is present at concentrations of 0.3-1.0% in numerous handsoaps and personal-use products.

As a result of its widespread use, significant quantities of triclosan are washed down the drain and are ultimately dispersed throughout the environment. The environmental prevalence of triclosan when coupled with concerns about its biological ramifications, made it an obvious choice for the study of its interactions with drinking water disinfectants. Free chlorine and the chloramines (of which monochloramine is the dominant species under water treatment conditions), are the most commonly utilized drinking water disinfectants in the U.S...

The major findings of this project are summarized below:

• Triclosan in its phenolate form readily reacts with hypochlorous acid, but is essentially unreactive with hypochlorite ion.

• The pH dependent speciation of triclosan and hypochlorous acid causes the reaction rate to exhibit hyperbolic behavior, with the fastest rates observed at near-neutral pH values and lower rates observed at acidic and alkaline pH. The rate constant (k_ArO-HOCl) for the reaction between hypochlorous acid and triclosan was determined to be 5.4 x 10³ M^-1s^-1.
  
• Triclosan decay is observed in monochloraminated waters, albeit at considerably slower rates.
  
• In both chlorinated and chloraminated solutions, a number of reaction intermediates and products were produced. In the absence of bromide, these include: 5,6-dichloro-2-(2,4-dichlorophenoxy)phenol, 4,5-dichloro-2-(2,4-dichlorophenoxy)
  phenol, 4,5,6-trichloro-2-(2,4-dichlorophenoxy)phenol, 2,4-dichlorophenol,
  2,4,6-trichlorophenol, and chloroform. The relative concentrations of each species were a function of the bromide content, the solution pH, as well as the ratio of total oxidant to triclosan. As expected, the intermediate and product concentrations were considerably lower in chloraminated waters than in chlorinated waters.
  
• In studies conducted with triclosan containing dish soap it was found that chloroform formation can occur in the presence of free chlorine. The risk, if any, associated with dermal and inhalational exposures to chloroform produced via these reactions should be examined.

Presentations