Triclosan und Antibiotikaresistenz

3. What happens to triclosan in the environment?

• 3.1 How does triclosan reach the environment?
• 3.2 To what extent does triclosan break down or persist in the environment?
• 3.3 Are microbial populations in the environment affected by triclosan?

3.1 How does triclosan reach the environment?

Because of it widespread use triclosan finds its way to waste water treatment plants. Depending on the technical capabilities of the plant, between 58% and 99% of the triclosan is removed before the treated water is released, but the rest will end up in surface waters.

When triclosan is removed it is partly broken down, but approximately half of the incoming mass of triclosan remains in the sewage sludge. Some of this triclosan will eventually end up in the soil, because the triclosan-laden biosolids are often spread over agricultural as fertilizer.

Triclosan has been widely detected in the water coming in and out of waste water treatment plants, in lakes, rivers and sea water in various countries in Europe, in the USA, in Canada, in Australia, in Japan and in Hong Kong. More...

3.2 To what extent does triclosan break down or persist in the environment?

Triclosan is chemically very stable but it brakes down rapidly in the environment when exposed to light and is also degraded by ozone. Some of the break-down products are more toxic than triclosan itself, but bacteria also attack and break these up further.

Triclosan does not react with water over a reasonably large pH range and it is stable in the presence of strong acids and bases. However, triclosan dissolved in water and exposed to light, degrades and forms radicals. Triclosan also degrades in chlorinated water.

When triclosan is dissolved in water in the presence of oxygen, it is easily broken down by several bacteria although very little is known on how this biodegradation takes place. In the absence of oxygen and light, triclosan is quite stable.

Because triclosan is not very soluble in water, it attaches itself to solid particles so it tends to accumulate in sediments. The presence of triclosan reduces significantly the ability of bacteria to deal with the solid sludge in wastewater treatment plants. More...

3.3 Are microbial populations in the environment affected by triclosan?

High levels of triclosan have been measured in some sediments, biosolids and activated sludge in wastewater treatment plants. In general, these levels would not be high enough to kill microorganisms but they would be sufficient to control their growth.

Triclosan does not seem to affect the activity of enzymes in the soil or respiration, but it can disturb the nitrogen cycle in some soils.

Bacteria often join in very large numbers to form colonies called biofilms and these are widespread throughout the environment. When such a biofilm from a domestic kitchen sink was exposed repeatedly to sub-lethal doses of triclosan, only a few types of bacteria were left but these did not show any increased resistance to antimicrobials. This lack of effect could be due to the particular types of bacteria in that specific biofilm and it is possible that other bacterial species could respond differently. Alternatively, the coordinated effort of all the bacteria in the biofilm could have been sufficient to degrade the triclosan.

Complex mixtures of bacteria are found in many environments, for instance inside the human mouth. In general, exposing these to repeated doses of triclosan does not seem to make them resistant but the results vary with the species considered. For instance, E. coli does become considerably less sensitive to triclosan when treated with it. More...