Triclosán y resistencia a los antibióticos
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
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
Triclosan has been
widely detected in the water coming in and out of
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.
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
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
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.
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
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
This lack of effect could be due to the particular types of
bacteria in that specific biofilm and it is possible that other
species could respond
differently. Alternatively, the coordinated effort of all the
bacteria in the biofilm could have been sufficient to degrade
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.