Environ. Sci. Technol. 2002, 36, 2322-2329
Occurrence and Environmental Behavior of the Bactericide Triclosan and Its Methyl Derivative in Surface Waters and in Wastewater ANTON LINDSTRO ¨ M,† IGNAZ J. BUERGE,‡ T H O M A S P O I G E R , * ,‡ PER-ANDERS BERGQVIST,† MARKUS D. MU ¨ LLER,‡ AND HANS-RUDOLF BUSER‡ Institute of Environmental Chemistry, Umeå University, S-90187 Umeå, Sweden, and Swiss Federal Research Station, CH-8820 Wa¨denswil, Switzerland
The bactericide triclosan and methyl triclosan, an environmental transformation product thereof, were detected in lakes and in a river in Switzerland at concentrations of up to 74 and 2 ng L-1, respectively. Both compounds were emitted via wastewater treatment plants (WWTPs), with methyl triclosan probably being formed by biological methylation. A regional mass balance for a lake (Greifensee) indicated significant removal of triclosan by processes other than flushing. Laboratory experiments showed that triclosan in the dissociated form was rapidly decomposed in lake water when exposed to sunlight (half-life less than 1 h in August at 47° latitude). Methyl triclosan and nondissociated triclosan, however, were relatively stable toward photodegradation. Modeling these experimental data for the situation of lake Greifensee indicated that photodegradation can account for the elimination of triclosan from the lake and suggested a seasonal dependence of the concentrations (lower in summer, higher in winter), consistent with observed concentrations. Although emissions of methyl triclosan from WWTPs were only ≈2% relative to those of triclosan, its predicted concentration relative to triclosan in the epilimnion of the lake increases to 30% in summer. Passive sampling with semipermeable membrane devices (SPMDs) indicated the presence of methyl triclosan in lakes with inputs from anthropogenic sources but not in a remote mountain lake. Surprisingly, no parent triclosan was observed in the SPMDs from these lakes. Methyl triclosan appears to be preferentially accumulated in SPMDs under the conditions in these lakes, leading to concentrations comparable to those of persistent chlorinated organic pollutants.
Introduction Anthropogenic compounds may undergo various transformation reactions in organisms and in the environment, leading to more hydrophilic derivatives with higher mobility * Corresponding author phone: ++41 1 783 6289; fax: ++41 1 783 6439; e-mail:
[email protected]. † Umeå University. ‡ Swiss Federal Research Station. 2322
9
ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 36, NO. 11, 2002
FIGURE 1. Structure of triclosan and methyl triclosan, an environmental transformation product. in the aquatic environment and less potential for bioaccumulation. Sometimes, however, transformation reactions may render a compound more lipophilic and thus more bioaccumulative than the parent compound itself. One such reaction is biological methylation such as the transformation of phenolic compounds into methyl ether derivatives (1-4). Triclosan (5-chloro-2-(2,4-dichlorophenoxy)phenol; for structure, see Figure 1) is an important bactericide used in various personal care (shampoo, toilet soap, deodorants, tooth paste) and consumer (footwear, plastic wear) products (5-8). In Sweden, for example, 25% of the total amount of toothpaste sold in 1998 contained triclosan, corresponding to ≈2 tons of active ingredient (9). Triclosan is a relatively stable, lipophilic compound. It has been found in human milk, but little is known about the effects on exposed infants (9). The compound is acutely toxic to aquatic organisms such as fish (EC50, rainbow trout ) 350 µg L-1) (9, 10). Of further concern is the transformation of triclosan into chlorodioxins upon incineration and under the influence of sunlight (11). The environmental occurrence of triclosan has been reported and the compound has been detected in wastewater, surface water, and sediments (12-16). In fish, the presence of the methyl ether of triclosan, methyl triclosan (5-chloro2-(2,4-dichlorophenoxy)anisole), was also reported (17). However, it remained unclear whether methylation had taken place prior to or following uptake by the fish and whether triclosan itself was also accumulated. During an investigation on the occurrence of lipophilic contaminants in surface water using semipermeable membrane devices (SPMDs), the presence of methyl triclosan was observed but not the parent compound itself (18). This observation prompted a more thorough study on the environmental occurrence of triclosan and its methyl ether derivative. In this study, we report on these data and on the elimination behavior of triclosan in the aquatic environment. We document the transformation of triclosan into methyl triclosan, and we assess the occurrence of the two compounds in the aquatic environment.
Experimental Section Chemicals and Reference Compounds. The sources and purities of the compounds were as follows: triclosan, purity 99% with
