Final Assessment

Synopsis

An assessment of triclosan has been conducted under the Canadian Environmental Protection Act, 1999 (CEPA) to determine if it poses a risk to Canadians and their environment. Triclosan was also scheduled for re-evaluation under Health Canada's Pest Management Regulatory Agency (PMRA) pesticide re-evaluation program pursuant to the Pest Control Products Act (PCPA). The preliminary assessment that preceded this assessment report included a proposed conclusion for triclosan under both CEPA and PCPA. As of December 31, 2014, the Canadian registrants voluntarily discontinued the sale of pest control products containing triclosan. Consequently, triclosan is no longer registered in Canada as a pest control product under the PCPA. Hence, this assessment does not include a conclusion under PCPA for these products.

Triclosan [phenol, 5-chloro-2-(2,4-dichlorophenoxy)] (CAS RN 3380-34-5) is used as a material preservative and as an antimicrobial agent in a wide range of products used by industry and consumers to stop the growth of bacteria, fungi and mildew and to deodorize.

Triclosan does not occur naturally in the environment. The potential sources of exposure to triclosan for Canadians include products used by consumers which are treated with or contain triclosan (including, but not limited to, cosmetics, non-prescription drugs and natural health products) as well as industrial manufacturing or formulation of products containing triclosan.

Exposure of the general population to triclosan was characterized using the available Canadian biomonitoring data for triclosan from the Canadian Health Measures Survey (CHMS) Cycle 2 (2009-2011), the Plastic and Personal-Care Product Use in Pregnancy (P4) Study, and the Maternal-Infant Research on Environmental Chemicals (MIREC) and MIREC-Child Development Plus (MIREC-CD Plus) studies. These data encompass exposure to triclosan from all potential sources and routes, and are considered the most accurate estimates of total exposure of the general population in Canada to triclosan. Similar levels were observed in the recent CHMS, Cycle 3 (2012-2013). Exposure estimates of children under the age of three were derived separately using a combination of Canadian biomonitoring data (for infants and children three to five years old) and additional estimates to account for potential exposures via breast milk, household dust and mouthing of triclosan-treated plastic products.

In examination of the toxicological database as a whole, the principal toxicity in rodents and dogs following ingestion of triclosan is mainly in the liver, with the mouse being the most sensitive species. Triclosan exposure also results in modest decreases in serum thyroid hormone thyroxine (T₄) levels (but not triiodothyronine [T₃] or thyroid-stimulating hormone [TSH]) in rats caused by disruption in the target organ (liver) due to rodent-specific metabolism of triclosan. Critical evaluation of the overall database shows that there are no indications of adverse effects on thyroid function in the animal database and available human data show no changes in thyroid hormone levels or liver function after long-term exposure to low levels of triclosan. Further, humans have a much greater capacity to adapt to deviations in T₄ levels than do rodents. Consequently, the overall database does not support the effects of triclosan on thyroid function as a critical effect for risk characterization in humans.

Considering the current available information on the adverse effects of triclosan, an overall database no-observed-adverse-effect level (NOAEL) of 25 mg/kg bw/day was identified from a 90-day oral toxicity study in mice and was conservatively selected to be protective against a number of effects observed in multiple species at higher doses. This NOAEL was considered protective against potential liver effects, if any, that could occur in humans as well as effects in other organs and systems.

Risk to human health from exposure to triclosan is estimated by comparing estimates of exposure in humans with critical effect levels in health effects studies conducted in laboratory animals in order to derive margins of exposure (MOEs). For the general population, comparison of the estimated mean and upper-bound daily intakes with critical effect levels in mice (based on liver effects) resulted in MOEs between 416 and 5 400. For children under the age of 3 years, comparison of aggregate exposure estimates with the critical effect levels resulted in MOEs greater than 3 300. These MOEs were considered adequate to address uncertainties in the health effects and exposure databases for triclosan.

A review of all available information on the potential for triclosan to induce antimicrobial resistance (AMR) was conducted. Although there is the potential for triclosan-resistant bacteria to exist in laboratory and clinical settings, this has not been documented outside of clinical use (e.g. household settings, toothpaste use). Based on available information, induction of AMR from current levels of triclosan has not been identified as a concern for human health.

Triclosan can be released to the environment as a result of its use in many products used by consumers, or as a result of the industrial manufacture of products containing triclosan. The use in products is considered to be the major contributor to releases of triclosan down the drain. Triclosan released into wastewater reaches wastewater treatment plants^Footnote1 (WWTP), where it is partly removed from wastewater, depending on the type of treatment. Triclosan is released to aquatic ecosystems as part of WWTP effluents. Some triclosan partitions to sludge during the wastewater treatment process. As a result, triclosan also reaches terrestrial ecosystems by way of biosolids amendment to agricultural land.

Triclosan degrades relatively quickly in the environment through biotic and abiotic processes. However, it is ubiquitous in the environment due to the continual release to surface water through WWTP effluents. Therefore, chronic exposure of organisms to triclosan is expected in aquatic ecosystems, especially when close to effluent sources. Exposure to soil organisms is also likely through land application of biosolids.

Triclosan is highly toxic to a variety of aquatic organisms, such as algae, macrophytes, invertebrates, amphibians and fish. Adverse effects that have been observed include reduction in growth, reproduction and survival, and there is evidence of effects on the endocrine system at environmentally relevant concentrations.Triclosan can also be highly bioconcentrated in fish, and there is evidence of bioaccumulation in algae and aquatic invertebrates. Triclosan is also highly toxic to certain soil organisms.

Based on an extensive review of the available toxicity data, a predicted no-effect concentration of 376 ng/L was derived for the aquatic compartment. This threshold includes consideration of endocrine disruptive effects in fish and amphibians.

Exposure of aquatic organisms was estimated using measured concentrations of triclosan in the receiving surface waters, including at or near WWTP effluent discharge points. Measured concentrations of triclosan in surface waters across Canada indicate that triclosan may cause harmful effects in aquatic ecosystems.

Concentrations of triclosan in soils were estimated based on the measured concentrations of triclosan in biosolids in Canada, and using parameters such as triclosan half-lives in soil and the regulated application rates for biosolids. Risk characterization that considered the high toxicity to certain soil organisms indicated that triclosan is not likely to cause harmful effects, given the low predicted soil concentrations.

The most notable transformation products of triclosan, formed through metabolism and degradation or chlorination, are methyl-triclosan and certain lower chlorinated dioxins. While most of the triclosan-derived dioxins are considered to be transient in the environment and of low toxicity, methyl-triclosan has similar properties to triclosan, such as high toxicity and bioaccumulation potential. Although chronic exposure to methyl-triclosan is likely in the environment, it has been detected at concentrations much lower than those of triclosan.

Triclosan is always present in aquatic ecosystems due to its continuous releases. It is a very potent chemical that can accumulate in organisms and cause adverse effects even at low exposure levels in the environment. Triclosan can transform to methyl-triclosan and to certain lower chlorinated dioxins. Overall, considering the potency of triclosan its widespread occurrence and the current exposure levels observed in the Canadian environment, it is concluded that potential for harm exists from exposure to triclosan in aquatic ecosystems.

Conclusions under CEPA

Based on the adequacy of the MOEs between estimates of aggregated exposure to triclosan and critical effect levels, it is concluded that triclosan is not entering the environment in a quantity or concentration or under conditions that constitute or may constitute a danger in Canada to human life or health; thus, it does not meet the criteria under paragraph 64(c) of CEPA.

Considering all available lines of evidence presented in this assessment report, there is risk of harm to organisms, but not to the broader integrity of the environment from triclosan. It is concluded that triclosan meets the criteria under paragraph 64(a) of CEPA as it is entering or may enter the environment in a quantity or concentration or under conditions that have or may have an immediate or long-term harmful effect on the environment or its biological diversity. However, it is concluded that triclosan does not meet the criteria under paragraph 64(b) of CEPA as it is not entering the environment in a quantity or concentration or under conditions that constitute or may constitute a danger to the environment on which life depends.

Therefore, it is concluded that triclosan meets one or more of the criteria set out under section 64 of CEPA.

Even though it is continuously present in the environment, triclosan has been determined not to meet the persistence criteria as set out in the Persistence and Bioaccumulation Regulations of CEPA. Similarly, while triclosan accumulates in organisms to levels that can cause adverse effects, it does not meet the bioaccumulation criteria as set out in the Persistence and Bioaccumulation Regulations of CEPA.