The Toxic By-Products of Triclosan
Lily Munsill
Chemistry 303
November 25, 2013
Professor Benoit
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Triclosan (TCS) is an antibacterial biocide introduced in 1968, found in
common household items. It is used in personal care products as an antiseptic in
soaps, mouthwash, facial cleansers, cosmetics, toothpaste, and other household
cleaning items. Additionally, it is an additive used to prevent bacterial growth in
carpets, wood treatment substances, and plastic children’s toys. The chemicals in
personal care products (PCPs) are the most prevalent contaminants of aquatic
systems and because they are still relatively new to the environment, longterm toxic
effects of PCP are still largely unknown (Brausch et al, 2011). Triclosan is of
emerging concern to the environment, as it is domestically disposed of “down the
drain” and doesn’t get entirely removed from wastewater during water treatment.
Triclosan enters our drinking water supply and pollutes aquatic environments. An
important and concerning chemical characteristic of triclosan is that it can degrade
into many different chemical compounds, including toxic substances. TCS can
degrade into many different chemical compounds. The methylation of TCS results in
methyl triclosan, the chlorination of TCS through wastewater treatment processes
leads to the formation of chlorinated phenols, and the photodegradation of these
compounds produces chlorinated dibenzodioxins. Despite efforts to improve water
quality in wastewater treatment, the toxic by-products of triclosan degradation
during wastewater treatment processes, including methyl-triclosan and chlorinated
dibenzodioxins, actually magnify the toxicity of the contaminant and its potential to
harm aquatic ecosystems.
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Triclosan
( http://www.alibaba.com/product-free/107750419/TRICLOSAN.html)
Before it degradation into toxic by-products, triclosan itself is toxic and can
have adverse effects on aquatic ecosystems (Chalew et al, 2009). The chemical
formula of triclosan is C12O2Cl3H7, it is a chlorinated compound belonging to the
group polychloro phenoxy phenols, or PCPPs (Levy, 1999). TCS can be found in all
aquatic systems, but it is ubiquitous in that it can also be found in soils, indoor dust,
and living organisms, including humans (Bedoux et al, 2012). TCS has a half-life of
11 days in a fresh water system (DeLorenzo et al, 2007). Its relatively long half-life
combined with its lipophilic nature makes TCS a prime toxin for bioaccumulation in
aquatic species. In a recent study in Sweden, it was found that high enough
concentrations of triclosan can kill rainbow trout and other fish. In the same article,
scientists reported TCS in three out of five randomly selected human breast milk
samples (Adolfsson-Erici et al, 2002).
TCS was produced to be used as a bacterial pesticide. It does not affect all
bacteria, but it has been shown to kill the malaria bacteria and E. coli (Surolla et al,
2002). TCS is also effective in killing the bacteria that cause staph infections, making
it a useful antibacterial agent in surgical settings; however, there is large concern in
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the medical community however that strains of the staphylococcus bacteria and E.
Coli bacteria can form triclosan-resistant strains (Suller and Russel 2000).
TCS acts as a toxin in bacteria and living organisms due to the lipophilic
tendencies of the molecule. TCS inhibits synthesis of fatty acids by binding to
enzymes that catalyze fatty acid synthesis, thereby reducing the affectivity of the
enzyme. By inhibiting fatty acid synthesis, TCS slows growth and inhibits successful
reproduction (Tatarazako et al, 2004). In aquatic environments, TCS can be lethal to
phytoplankton which are particularly sensitive to the toxin as it impairs growth and
metabolism (DeLorenzo et al, 2007). High accumulation of TCS in the primary
producers of the food web leads to bioaccumulation of TCS throughout the aquatic
system.
Of greater concern, however, is the ability of TCS to degrade further into
other toxic intermediate substances. TCS can undergo photolytic degradation and
biodegradation by bacteria, as well as chlorination, which occurs while TCS is being
treated in waste water treatment plants (Bedoux et al, 2012). These processes form
many by-products of TCS including those in the main groups of chlorinated
dibenzodioxins, methyl triclosan and chlorinated phenols (Bedoux et al, 2012).
Wastewater treatment plants are one of the primary reaction vessels for the
breakdown of triclosan, which can be attributed to the high levels of microbial
organisms introduced in wastewater treatment, as well as an abundance of chlorine
(Buth et al, 2011). As triclosan becomes chlorinated through wastewater treatment
processes, it becomes more toxic. The direct photolytic degradation of the
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chlorinated form of triclosan can produce by-products that are more toxic than
triclosan itself (Buth et al, 2010).
Methyl-Triclosan (M-TCS)
(Dann et al, 2011)
While most by-products of triclosan are highly toxic, methyl-triclosan is of
particular concern as it has high persistence in aquatic environments. Methyltriclosan (M-TCS) is more lipophilic than TCS and has less potential to undergo
photolytic degradation, allowing for greater bioaccumulation in aquatic species
(DeLorenzo et al, 2007). In a Balmer et al study, concentrations of M-TCS in fish
were found to have been higher than the concentration of M-TCS in the ambient
water, suggesting that there are high rates of bioaccumulation of M-TCS in fish and
the potential for high bioaccumulation in other aquatic species. In the same study,
M-TCS was only found in lakes with a direct input from wastewater treatment
plants (Balmer et al, 2004).
TCS can degrade into M-TCS in various environments. The process by which
triclosan transforms into methyl-triclosan is called methylation, and this process is
carried out by microbial organisms. Methylation involves the replacement of a
hydrogen atom with a methyl group, CH3 (Delorenzo et al, 2008). The methylation of
TCS has been observed in wastewater treatment plants, in the soils of lake
environments, and it is also possible for TCS to accumulate in living organisms and
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later biodegrade into M-TCS (Coogan et al, 2007). Studies have shown that there is
more M-TCS in effluent water than influent water in wastewater treatment plants,
meaning M-TCS usually forms during the wastewater treatment process (Coogan et
al, 2007).
M-TCS is prevalent in aquatic environments as it bioaccumulates in
vulnerable species, especially algae, snails, and aquatic invertebrates, which causes
biomagnification throughout aquatic food webs (Dann et al, 2011). High levels of MTCS in upper trophic predatory species can have toxic effects. Studies show that
chronic exposure to M-TCS has adverse effects on thyroid hormone responses and
stress indicators in cells (Bedoux et al, 2011). M-TCS is also an inhibitor of lipid
synthesis, and this can be damaging to mitochondria and energy metabolism in
animal cells (Coogan et al, 2007).
Chlorinated Dibenzodioxins
(www.inchem.org)
Chlorinated Dibenzodioxins are formed from multiple stages of photolytic
degradation of triclosan. Triclosan is chlorinated in wastewater treatment plants,
typically using sodium hypochlorite, and while this aims to remove triclosan from
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wastewater, it produces three chlorinated triclosan derivatives (CTDs) of which are
two forms of dichlorophenoxy phenols, and a trichlorophenoxy phenol, also known
as tetraclosan and pentaclosan (Buth et al, 2011). CTDs are unstable and can further
photochemically transform into polychloro dibenzodioxins (PCDDs), the most
common of which are dichloro dibenzodioxins (DCDDs) (Bedoux et al, 2012). The
chlorinated derivatives of triclosan are a large supplier of toxic dibenzodioxins to
aquatic systems (Buth et al, 2010). While chlorination in wastewater treatment is
typically beneficial in breaking down harmful chemicals, it leads to unwanted side
effects in the case of triclosan.
PCDDs and DCDDs are in the chemical group dioxins, which are toxic to
aquatic organisms. Like triclosan and methyl-triclosan, dioxins also accumulate in
fat due to their lipophilic qualities, also making them detrimental to organisms at
the top of the food chain as it bioaccumulates in fatty tissues (Toxipedia, 2011).
Chlorinated dioxins are known carcinogens and cause reproductive and
development issues in humans (Yu et al, 2006). Additionally, dioxins are toxic to the
immune system function and are endocrine disruptors. (WHO, 2010) While the
effect of dioxins in aquatic organisms have been proven to be toxic, there still
remains little to be known about the specific chlorinated dioxin products of
triclosan.
These phototransformation products of the chlorinated form of triclosan are
ten times as toxic as the phototransformation products of unchlorinated triclosan
(Buth et al, 2011). The products of photodegradation of unchlorinated triclosan
were found to be nontoxic to the environment (Yu et al, 2006). It may be worthwhile
7
to investigate a strategy in which triclosan is eliminated from wastewater through
UV radiation exposure before it is chlorinated, so as to prevent the formation of
more toxic products and mitigate the effects of triclosan degradation on the
environment.
Conclusion
Triclosan can be toxic to aquatic organisms, and the degradation of triclosan
leads to the formation of higher toxicity by-products, including methyl triclosan and
chlorinated dibenzodioxins, which can be particularly detrimental to aquatic
organisms due to their lipophilic nature and ability to bioaccumulate. Triclosan and
its by-products are endocrine disruptors, inhibiting growth, reproductive success,
the immune system, and other essential processes of life. Two toxic by-products of
triclosan, methyl-triclosan, and chlorinated dibenzodioxins, can be produced during
wastewater treatment processes. An implementation of different wastewater
treatment strategies could prevent the production of higher magnitude toxicity in
by-products of contaminants. Further studies about these contaminants and
alternative wastewater treatment processes are required to protect aquatic
ecosystems that are exposed to triclosan contamination.
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