Screening Assessment for the Challenge

1,4-Dioxane

Chemical Abstracts Service Registry Number
123-91-1

Environment Canada
Health Canada

March 2010

(PDF Version - 488 KB)

1. Synopsis
2. Introduction
3. Substance Identity
4. Physical and Chemical Properties
5. Sources
6. Uses
7. Releases to the Environment
8. Environmental Fate
9. Persistence and Bioaccumulation Potential
10. Potential to Cause Ecological Harm
11. Potential to Cause Harm to Human Health
12. Conclusions
13. References
14. Appendix 1: Upper-bounding estimates of daily intake of 1,4-dioxane by the general population in Canada
15. Appendix 2: Estimated intake of 1,4-dioxane from food additive uses
16. Appendix 3: ConsExpo sample calculation scenarios
17. Appendix 4: Summary of effects information for 1,4-dioxane
18. Appendix 5: Summary of margins of exposure for 1,4-dioxane

Synopsis

Pursuant to section 74 of the Canadian Environmental Protection Act, 1999 (CEPA 1999), the Ministers of the Environment and of Health have conducted a screening assessment of 1,4-dioxane, Chemical Abstracts Service Registry Number 123-91-1. The substance 1,4-dioxane was identified in the categorization of the Domestic Substances List as a high priority for action under the Ministerial Challenge. 1,4-Dioxane was identified as a high priority as it was considered to pose greatest potential for exposure of individuals in Canada and is classified by other agencies on the basis of carcinogenicity. Although this substance met the ecological categorization criteria for persistence, it did not meet the criteria for bioaccumulation and inherent toxicity to aquatic organisms. The focus of this assessment of 1,4-dioxane relates principally to human health risks.

According to information reported under section 71 of CEPA 1999, between 10 000 and 100 000 kg of 1,4-dioxane were both imported into and manufactured in Canada in 2006. In addition, Canadian companies reported using between 10 000 and 100 000 kg in that year. In terms of environmental releases, between 10 000 and 100 000 kg of 1,4-dioxane were released into the environment in 2006, with the majority entering water and air. In Canada , 1,4-dioxane is used primarily as a solvent for pharmaceutical processing and research and development and as an analytical reagent for laboratory use. However, it is also found as an impurity in ethoxylated substances, which are used in numerous industries (manufacture of personal care products, detergents, food packaging, etc.).

Based on available information on concentrations in environmental media and results from a survey under section 71 of CEPA 1999, the general population is expected to be exposed to 1,4-dioxane from environmental media (ambient air, indoor air and drinking water), from food and during the use of consumer products (personal care and household products) containing this substance.

Based principally on the weight of evidence–based assessments of several international and other national agencies and available toxicological information, critical effects associated with exposure to 1,4-dioxane are tumorigenesis following oral and inhalation exposure, but not following dermal exposure; and other systemic effects, primarily liver and kidney damage, via all routes of exposure (i.e., oral, dermal and inhalation). The collective evidence indicates that 1,4-dioxane is not a mutagen and exhibits weak clastogenicity in some assays, but not others, at high exposure levels often associated with cytotoxicity. Consideration of the available information regarding genotoxicity, and conclusions of other agencies, indicate that 1,4-dioxane is not likely to be genotoxic. Accordingly, although the mode of induction of tumours is not fully elucidated, the tumours observed are not considered to have resulted from direct interaction with genetic material. Therefore a threshold approach is used to characterize risk to human health.

The margins between upper-bounding estimates of exposure from environmental media and use of consumer products, taking into consideration multiple product use scenarios and levels associated with effects in experimental animals are considered to be adequately protective to account for uncertainties in the human health risk assessment for both cancer and non-cancer effects.

On the basis of the adequacy of the margins between conservative estimates of exposure to 1,4-dioxane and critical effect levels in experimental animals, it is concluded that 1,4-dioxane 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.

Based on available empirical data, 1,4-dioxane is expected to degrade only in air, but not in water, soil or sediment. It is not expected to bioaccumulate in organisms. The substance meets the persistence criteria but not the bioaccumulation criteria set out in the Persistence and Bioaccumulation Regulations. In addition, empirical aquatic toxicity data indicate that the substance poses a low hazard to aquatic organisms. Based on a comparison of a predicted no-effect concentration with an estimated reasonable worst-case environmental exposure concentration for Canadian surface water, it is concluded that 1,4-dioxane is not entering 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 or that constitute or may constitute a danger to the environment on which life depends.

Based on the information available, it is concluded that 1,4-dioxane does not meet the criteria set out in section 64 of CEPA 1999.

This substance will be considered for inclusion in the upcoming Domestic Substances List inventory update initiative. In addition and where relevant, research and monitoring will support verification of assumptions used during the screening assessment.

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Introduction

The Canadian Environmental Protection Act, 1999 (CEPA 1999) (Canada 1999) requires the Minister of the Environment and the Minister of Health to conduct screening assessments of substances that have met the categorization criteria set out in the Act to determine whether these substances present or may present a risk to the environment or to human health.

Based on the information obtained through the categorization process, the Ministers identified a number of substances as high priorities for action. These include substances that

• met all of the ecological categorization criteria, including persistence (P), bioaccumulation potential (B) and inherent toxicity to aquatic organisms (iT), and were believed to be in commerce in Canada ; and/or
• met the categorization criteria for greatest potential for exposure (GPE) or presented an intermediate potential for exposure (IPE) and had been identified as posing a high hazard to human health based on classifications by other national or international agencies for carcinogenicity, genotoxicity, developmental toxicity or reproductive toxicity.

The Ministers therefore published a notice of intent in the Canada Gazette, Part I, on December 9, 2006 (Canada 2006), which challenged industry and other interested stakeholders to submit, within specified timelines, specific information that may be used to inform risk assessment and to develop and benchmark best practices for the risk management and product stewardship of those substances identified as high priorities.

The substance 1,4-dioxane was identified as a high priority for assessment of human health risk because it was considered to present GPE and had been classified by other agencies on the basis of carcinogenicity. The Challenge for this substance was published in the Canada Gazette on August 30, 2008 (Canada 2008). A substance profile was released at the same time. The substance profile presented the technical information available prior to December 2005 that formed the basis for categorization of this substance. As a result of the Challenge, submissions of information were received.

Although 1,4-dioxane was determined to be a high priority for assessment with respect to human health and met the ecological categorization criteria for persistence, it did not meet the criteria for bioaccumulation potential or inherent toxicity to aquatic organisms. Therefore, this assessment focuses principally on information relevant to the evaluation of risks to human health.

Screening assessments focus on information critical to determining whether a substance meets the criteria set out in section 64 of CEPA 1999. Screening assessments examine scientific information and develop conclusions by incorporating a weight of evidence approach and precaution.

This final screening assessment includes consideration of information on substance properties, hazards, uses and exposure, including the additional information submitted under the Challenge. Data relevant to the screening assessment of this substance were identified in original literature, review and assessment documents and stakeholder research reports and from recent literature searches, up to April 2009 for both the exposure section and ecological section of the document and up to February 2009 for the health effects section. During the public comment period on the final screening assessment, a two-year inhalation study was identified and included in the toxicological dataset. Key studies were critically evaluated; modelling results may have been used to reach conclusions.

Evaluation of risk to human health involves consideration of data relevant to estimation of exposure (non-occupational) of the general population, as well as information on health hazards (based principally on the weight of evidence assessments of other agencies that were used for prioritization of the substance). Decisions for human health are based on the nature of the critical effect and/or margins between conservative effect levels and estimates of exposure, taking into account confidence in the completeness of the identified databases on both exposure and effects, within a screening context. The final screening assessment does not represent an exhaustive or critical review of all available data. Rather, it presents a summary of the critical information upon which the conclusion is based.

This final screening assessment was prepared by staff in the Existing Substances Programs at Environment Canada and Health Canada and incorporates input from other programs within these departments. The ecological and human health portions of this assessment have undergone external written peer review/consultation. Comments on the technical portions relevant to human health were received from scientific experts selected and directed by Toxicology Excellence for Risk Assessment (TERA), including Michael Jayjock (The Lifeline Group), Glenn Talaska ( University of Cincinnati) and Chris Bevan (CJB Consulting LLC). Additionally, the draft of this screening assessment was subject to a 60-day public comment period. While external comments were taken into consideration, the final content and outcome of the screening risk assessment remain the responsibility of Health Canada and Environment Canada.

The critical information and considerations upon which the final assessment is based are summarized below.

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Substance Identity

For the purposes of this document, this substance will be referred to as 1,4-dioxane. Its substance identity is summarized in Table 1.

Table 1. Substance identity for 1,4-dioxane

Chemical Abstracts Service Registry Number (CAS RN)	123-91-1
DSL name	1,4-Dioxane
NCI names	1,4-Diethylene dioxide (ECL, PICCS) Diethylene ether (PICCS) Diethylene oxide (PICCS) 1,4-Dioxane (English, French) (AICS, ASIA-PAC, DSL, EINECS, ENCS, NZIoC, PICCS, SWISS, TSCA) Dioxane (PICCS) Dioxane, para- (PICCS) p-Dioxane (PICCS)
Other names	Diethylene dioxide; 1,4-Diethyleneoxide; 1,4-Dioxacyclohexane; 1,4-Dioxan; Dioxan; p-Dioxan; Dioxane, 1,4-; Dioxano ioxyethylene ether; 1,4-Dioxin, tetrahydro-; NE 220; NSC 8728; UN 1165; UN 1165 (DOT)
Chemical group (DSL stream)	Discrete organics
Major chemical class or use	Heterocyclic organic
Major chemical subclass	Heterocyclic organic (oxygen)
Chemical formula	C4H8O2
Chemical structure
SMILES1	C1OCCOC1
Molecular mass	88.11 g/mol
Abbreviations: AICS, Australian Inventory of Chemical Substances; ASIA-PAC, Asia-Pacific Substances Lists; CAS RN, Chemical Abstracts Service Registry Number; DSL, Domestic Substances List; ECL, Korean Existing Chemicals List; EINECS, European Inventory of Existing Commercial Chemical Substances; ENCS, Japanese Existing and New Chemical Substances; NCI, National Chemical Inventories; NZIoC, New Zealand Inventory of Chemicals; PICCS, Philippine Inventory of Chemicals and Chemical Substances; SMILES, simplified molecular input line entry specification; SWISS, Swiss Giftliste 1 and Inventory of Notified New Substances; TSCA, Toxic Substances Control Act Chemical Substance Inventory. Source: NCI 2006 1 Simplified Molecular Input Line Entry Specification

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Physical and Chemical Properties

Table 2 contains experimental physical and chemical properties of 1,4-dioxane that are relevant to its environmental fate.

Table 2. Experimental physical and chemical properties of 1,4-dioxane

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Sources

No natural sources of 1,4-dioxane have been identified. However, in the case of food, there have been limited data suggesting that 1,4-dioxane is a natural constituent of the volatile fraction occurring at low concentrations in some food items (Chung et al. 1983; Hartung 1989). Although these studies point to its presence, it is not known whether this occurrence is due to natural production or contamination, as 1,4-dioxane is known to be an impurity in ethoxylated food additives and pesticides and may be found in environmental media (NICNAS 1998; 2009 personal communication from Pest Management Regulatory Agency, Health Canada; unreferenced; 2009 personal communication from the Food Directorate, Health Canada; unreferenced).

Anthropogenic emissions of 1,4-dioxane may occur during its direct production or processing. Another main source of 1,4-dioxane in Canada is its unintentional formation as a by-product in ethoxylation reactions where ethylene oxide or ethylene glycol is condensed, during the development of ethoxylated polymers used in a variety of industrial and consumer applications (Figure 1) (Robinson and Ciurczak 1980; NICNAS 1998; Black et al. 2001). Despite vacuum stripping, trace amounts of 1,4-dioxane will remain (Robinson and Ciurczak 1980).

Figure 1. General mechanism for 1,4-dioxane formation through ethoxylation (Robinson and Ciurczak 1980). [EtO = ethylene oxide; EFA = ethoxylated fatty acid; 1,4-D = 1,4-dioxane]

Based on information submitted under section 71 of CEPA 1999, 10 000–100 000 kg of 1,4-dioxane were manufactured in Canada in 2006; in addition, between 10 000 and 100 000 kg were imported during the same year. Canadian companies also reported using between 10 000 and 100 000 kg of 1,4-dioxane in 2006 (Environment Canada 2008).

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Uses

Historically, the use of 1,4-dioxane centred predominantly around its application as a stabilizer for 1,1,1-trichloroethane. This function has been phased out due to controls placed on 1,1,1-trichlorethane use under the Montreal Protocol ( Canada 1998). Currently in Canada , 1,4-dioxane is used extensively as a solvent for pharmaceutical processing and research and development and as an analytical reagent for laboratory use (Environment Canada 2008). 1,4-Dioxane is used as a carrier solvent in the manufacture of pharmaceuticals, veterinary drugs and natural health products. In pharmaceuticals, it is classified as a Class 2 residual solvent with a concentration limit of 380 mg/kg if the maximum daily exposure of the product containing 1,4-dioxane is not greater than 10 g; for products that are administered in doses greater than 10 g/day, the permitted daily exposure should not exceed 3.8 mg/day. An identical concentration limit and permitted daily exposure has been set for residual 1,4-dioxane in both natural health products and veterinary medicinal products (2009 personal communication from Natural Health Products Directorate, HealthCanada ; unreferenced; 2009 personal communication from Therapeutic Products Directorate, Health Canada ; unreferenced). 1,4-Dioxane is also a component of industrial agents that are used as corrosion inhibitors, antioxidants and heavy equipment degreasers (Environment Canada 2008).

As mentioned previously, residual 1,4-dioxane is formed during the production of ethoxylated substances used in a variety of applications, such as cosmetics, detergents, food packaging, agricultural products and industrial processes (EURAR 2002). In Canada , ethoxylated substances containing 1,4-dioxane as a by-product are produced and used as surfactants, emulsifiers, wetting agents and foaming agents in various industries (Environment Canada 2008). 1,4-Dioxane is also found as a formulant impurity in 168 pest control products that have both food and non-food uses (2009 personal communication from Pest Management Regulatory Agency, Health Canada ; unreferenced). Furthermore, 1,4-dioxane is found as an impurity in solvents used in the
formulation of ingredients and processing aids that are employed in the manufacture of food packaging materials such as paper and shrink films, although exposure to 1,4-dioxane from these materials was deduced to be minimal (2009 personal communication from Food Directorate, Health Canada; unreferenced). 1,4-Dioxane may also be present as an impurity in the food additives polysorbate 80, polysorbate 65, polysorbate 60, and polyethylene glycol, at a maximum residue limit of 10 mg/kg in accordance with the specifications for these chemicals in the Food Chemicals Codex (FCC, 6^th Ed., 2008) (2009 personal communication from Food Directorate, Health Canada; unreferenced). The aforementioned food additives in which 1,4-dioxane may be present as an impurity, may be present only in those foods for which provision exists for the use of these additives in accordance with the Food and Drug Regulations (2009 personal communication from Food Directorate, Health Canada; unreferenced).

Currently, 1,4-dioxane is present on Health Canada ’s Cosmetic Ingredient “Hotlist”, prohibiting its intentional use as an ingredient in cosmetics; however, it may be present as a manufacturing impurity (Health Canada 2007).

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Releases to the Environment

Information reported under section 71 of CEPA 1999 indicated that 10 000–100 000 kg of 1,4-dioxane were released into the environment in 2006. The majority of releases were to water and air, with a small fraction released to land (Environment Canada 2008). Amounts of 1,4-dioxane released to the air and water ranged between 10 000 and 100 000 kg each in 2006. Environmental releases reported under the National Pollutant Release Inventory (NPRI) indicated that 13 800 kg of 1,4-dioxane were released to air and 6 500 kg were released to water in 2006; however, releases to land were not reported (NPRI 2006).

In 2006, the US Toxics Release Inventory (TRI) reported a total of 56 tonnes released to air, 22 tonnes released to water and 64 tonnes released by underground injection (TRI 2006). The high release quantities are likely due to greater use of 1,4-dioxane in theUnited States compared with Canada .

In addition to environmental releases, information submitted under section 71 of CEPA 1999 show that 100–1000 kg of 1,4-dioxane were transferred to hazardous waste facilities. Less than 100 kg were transferred to non-hazardous waste facilities (Environment Canada 2008).

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Environmental Fate

Based on its physical and chemical properties (Table 2), 1,4-dioxane is characterized by high water solubility (1 000 000 mg/L), high vapour pressure (5080 Pa), low log K_ow (-0.42 to -0.27) and moderate Henry’s Law constant (0.49 Pa·m³/mol). The results of Level III fugacity modelling (Table 3) suggest that significant mass fractions of the substance will reside in the compartment of release and that partitioning of 1,4-dioxane to the water compartment is potentially significant, whereas partitioning to sediments is expected to be negligible.

Table 3. Results of the Level III fugacity modelling (EQC 2003) for 1,4-dioxane

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Persistence and Bioaccumulation Potential

Environmental Persistence

Table 4a presents empirical biodegradation data that show 0 % biodegradation over 14 days in a ready biodegradation test for 1,4-dioxane (MITI 1992). This study reported a negative value for biodegradation, indicating that the substance might be lost during the test. Therefore the reported data is considered of low confidence. However EURAR (2002), based on an earlier review by BUA (1991), reported no biodegradation of 1,4-dioxane under both standardized (Organisation for Economic Co-operation and Development) and non-standardized test conditions. This result is supported by contaminated site remediation experts who report limited biodegradation of 1,4-dioxane (Steffan 2007).

The substance does not have functional groups expected to undergo hydrolysis, nor direct photolysis in aquatic media. It is also resistant to biodegradation in water under ambient conditions (CCME 2008).

Also presented in Table 4a is an empirically derived atmospheric half-life of = 1 day by photooxidation with hydroxyl (OH) radicals, which is considered to be the primary loss mechanism in air (Atkinson 1989).

Table 4a. Empirical data for degradation of 1,4-dioxane

As experimental data on the degradation of 1,4-dioxane are limited, a quantitative structure–activity relationship (QSAR)-based weight of evidence approach (Environment Canada 2007) was also applied using the biodegradation models shown in Table 4b. Given the ecological importance of the water compartment, the fact that most of the available models apply to water and the fact that 1,4-dioxane is expected to be released to this compartment, biodegradation was examined primarily in water.

Table 4b. Modelled data for degradation of 1,4-dioxane

In air, a predicted atmospheric oxidation half-life of 0.38 day (see Table 4b) demonstrates that this chemical is likely to be rapidly oxidized. The compound may also be subject to photolysis and react with other photo-oxidative species in the atmosphere, such as ozone (EURAR 2002). With an empirically derived half-life of 0.98 day and an estimated half-life of 0.38 day via reactions with hydroxyl radicals, 1,4-dioxane is considered not to be persistent in air.

In water, there are different conclusions indicated by the modelled data. Based on the modelled timeframe and probability of biodegradation values from BIOWIN (see Table 4b), the substance’s degradation half-life is <182 days. However, the modelled results from TOPKAT and CATABOL indicate that the half-life in water is >182 days (Table 4b). When concluding about persistence, greatest weight was given to the empirical data (Table 4a; EU RAR 2002; Staffen 2007; CCEM 2008) indicating that the half life of 1,4-dioxane is > 182 day, which is supported by the predictions from TOPKAT and CATABOL. Thus 1,4-dioxane is considered persistent in water.

To extrapolate a half-life in water to half-lives in soil and sediment, Boethling’s factors t_½ water:t_{½ soil}:t_{½ sediment} = 1:1:4 (Boethling et al. 1995) can be used. Therefore, based on the above empirically derived half-life in water of =182 days and an extrapolation factor of 1, the half-life in soil is expected to be =182 days. For sediment, the half-life is expected to be 4 times higher (i.e., =728 days). It may thus be concluded that 1,4-dioxane is persistent in soil and sediment.

Based on the empirical data and model predictions, it is concluded that 1,4-dioxane meets the persistence criteria for water, soil and sediment (half-lives in soil and water =182 days and half-life in sediment =365 days), but does not meet the persistence criterion for air (half-life ³2 days), as set out in the Persistence and Bioaccumulation Regulations (Canada 2000).

In addition, the long-range transport potential (LRTP) of 1,4-dioxane from its point of release to air is estimated to be low. The TaPL3 (2000) model was used to estimate characteristic travel distance (defined as the maximum distance travelled by 63% of the substance) of 95 km for 1,4-dioxane. Beyer et al. (2000) proposed characteristic travel distances of >2000 km as representing high LRTP, 700–2000 km as moderate LRTP and <700 km as low LRTP. Based on the model’s estimate, 1,4-dioxane is expected to have a low LRTP and to remain primarily in the areas close to its emission sources.

Potential for Bioaccumulation

Experimental log K_ow values for 1,4-dioxane suggest that this chemical does not have the potential to bioaccumulate in organisms (see Table 2 above). An experimental bioconcentration factor (BCF) value in fish is reported to be in the range of 0.2 – 0.7 L/kg wet weight (MITI 1992).

Since few experimental data on bioaccumulation were available, a QSAR-based weight of evidence approach was also applied using the bioaccumulation factor (BAF) and BCF models. Model outcomes are presented in Table 5.

Table 5. Modelled data for bioaccumulation of 1,4-dioxane

The modified Gobas BAF middle trophic level model for fish predicted a BAF of 0.96 L/kg, indicating that 1,4-dioxane does not have the potential to bioconcentrate and biomagnify in the environment. The results of BCF model calculations also provide weight of evidence to support the low bioconcentration potential of this substance (Table 5).

Based on the available empirical and modelled data, it is concluded that 1,4-dioxane does not meet the bioaccumulation criteria (BAF or BCF =5000) as set out in the Persistence and Bioaccumulation Regulations (Canada 2000).

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Potential to Cause Ecological Harm

The approach taken in this assessment was to examine the available scientific information and develop conclusions based on a weight of evidence approach and using precaution as required under CEPA 1999. Lines of evidence considered include results from a conservative risk quotient calculation as well as information on the persistence, bioaccumulation, toxicity, sources and fate of the substance.

There is experimental and modelled evidence that 1,4-dioxane does not cause harm to aquatic organisms at low concentrations (see Tables 6a and 6b).

Table 6a. Empirical data for aquatic toxicity of 1,4-dioxane

Table 6b. Modelled data for aquatic toxicity of 1,4-dioxane

A more comprehensive overview of the aquatic toxicity data is available from the International Uniform Chemical Information Database (ECB 2000) and the European Union risk assessment (EURAR 2002); these data are in the same range as those presented in Table 6a. The AQUIRE database (ECOTOX 2006) reports median acute aquatic toxicity values ranging from 2274 to 12 326 mg/L.

The lowest reported experimental aquatic toxicity value was 163 mg/L, based on a 48-hour median effective concentration (EC₅₀) for Ceriodaphnia dubia (TSCATS 1989). This value may be questioned, however, considering the other reported levels of toxicity and also because the original study could not be obtained and evaluated for quality. When Ceriodaphnia dubia was tested in long term static studies, the chronic no-observed-effect concentration (NOEC) reported were much higher (~630 mg/L). (Springborn Laboratories 1989, DOW 1995). Therefore, as in the European Union assessment (EURAR 2002), this result was not used as an effect measure for risk characterization. The second lowest toxicity value (575 mg/L from Table 6a) was thus selected as the critical toxicity value (CTV), as an indicator of potential for ecological effects to sensitive species.

Table 6b contains predicted ecotoxicity values that were considered to be reliable and were used in the QSAR weight of evidence approach for aquatic toxicity (Environment Canada 2007).

The range of empirical toxicity values, as well as the aquatic toxicity predictions obtained from the various QSAR models considered, indicates that the substance is not highly hazardous to aquatic organisms (i.e., acute LC₅₀ or EC₅₀ >> 1.0 mg/L).

A conservative predicted no-effect concentration (PNEC) is derived from the CTV identified from the empirical data. An assessment factor of 10 has been applied to the empirical chronic effect value of 575 mg/L--to account for inter- and intraspecies variations in sensitivity and to extrapolate from a laboratory-based endpoint to a chronic effect value in the field. This results in a PNEC of 57.5 mg/L.

Based on the section 71 survey, the majority of releases of 1,4-dioxane are to water and air. If released to water, the substance is expected to remain mainly within water (see Table 3). This substance has not been detected in surface water in eastern Canada (CCME 2008). For the purpose of the ecological assessment, two conservative aquatic exposure scenarios were developed to estimate the release into the aquatic environment from industrial operations and consumer uses, with the corresponding resulting aquatic concentrations.

The scenario to estimate the release from industrial operations is based on the largest total amount manufactured at a single facility, assuming that a conservative fraction is released to water (5%), no removal in a sewage treatment plant and discharge to a relatively small receiving water body. The predicted environmental concentration (PEC) is estimated to be 0.39 mg/L for this conservative scenario using Environment Canada’s Industrial Generic Exposure Tool – Aquatic. The resulting risk quotient (PEC/PNEC) is 0.007; indicating that the release of 1,4-dioxane from industrial operations is unlikely to cause ecological harm in Canada (Environment Canada 2009a).

As 1,4-dioxane can be found in consumer products, Mega Flush – Environment Canada’s spreadsheet model – was used for estimating down-the-drain releases from consumer products. Mega Flush provides an estimate of the maximum PEC as 0.004 mg/L and the resulting risk quotient (PEC/PNEC) is 0.0008; indicating that the release of 1,4-dioxane from consumer uses is unlikely to cause ecological harm in Canada (Environment Canada 2009b).

Although no suitable ecological effect studies were found for this compound in media other than water, given the low aquatic toxicity of this substance and its short half-life in air, effects from exposure to 1,4-dioxane in air (the other main receiving medium) are unlikely.

It should be noted that this conclusion was reached despite the conservative assumptions that were made in response to uncertainties encountered in the assessment. Some uncertainty relates to the fact that 1,4-dioxane has not been detected in the aquatic environment in Canada , and to address this an exposure model was used to predict a worst case concentration of this substance in water. There is also some uncertainty associated with the choice of critical toxicity value and the associated PNEC used in the risk quotient calculation. This was addressed by dividing the empirical chronic critical toxicity value by an assessment factor of 10.

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Potential to Cause Harm to Human Health

Exposure Assessment

Environmental Media

The upper-bounding estimates of daily intake of 1,4-dioxane from ambient air, indoor air, soil and drinking water were calculated. These are summarized for all age groups in Appendix 1. The total upper-bounding estimates range from 0.19 µg/kg body weight (kg-bw) per day for breast-fed infants <6 months old to 1.26 µg/kg-bw per day for formula-fed infants <6 months old. Breast-fed infants and formula-fed infants were exposed to 1,4-dioxane mainly through air and drinking water (experimental detection of 1,4-dioxane has not been reported in breast milk or baby formula). Drinking water represented the predominant contribution to the total estimated daily intake for all age groups, followed by indoor air.

Several studies have been conducted in the United States and Canada that show detectable levels of 1,4-dioxane in ambient air (maximum 0.646 µg/m³) and indoor air (maximum 0.85 µg/m³), respectively from all collected data(Harkov 1984; Brown et al. 1994; Fellin and Otson 1997; Singhvi 1999). Canadian data were used in estimating the intake from both air sources: 0.646 µg/m³ (ambient air) and 0.685 µg/m³ (indoor air) (Fellin and Otson 1997). Soil studies are limited, with only a few studies fromJapan and Canada comprising the data set (Golder Associates 1987; Government of Japan 2004). 1,4-Dioxane was not detected in soils in Canada , with the detection limit (100 µg/kg) used for estimating exposure (Golder Associates 1987).

Several recent studies from Japan show the presence of detectable levels of 1,4-dioxane (maximum 16 µg/L) in surface water (Abe 1999; Kawata et al. 2003; Simazaki et al. 2006). However, 1,4-dioxane has not been detected in surface water in eastern Canada (CCME 2008). Canadian drinking water data were used for intake estimation. Otson (1987) showed that 1,4-dioxane was not detected in 42 raw and 42 treated samples of water from a municipal water treatment plant in the Great Lakes region. In this instance, the detection limit (10 µg/L) was used for estimating exposure.

Although no studies pertaining to 1,4-dioxane in food inCanada were found, data from Japan suggested that 1,4-dioxane was present in several food groups (Nishimura et al. 2004). However, after consultation with the Food Directorate of HealthCanada , reanalysis of the published concentrations indicated that they were all below the detection limit of 2 µg/kg cited in the study (2009 personal communication from Food Directorate, Health Canada ; unreferenced). A subsequent study by the same research group, sampling meals as prepared and consumed, detected 1,4-dioxane in 1 out of 27 samples (Nishimura et al. 2005). Taking into account that dietary intakes of certain foods differ between Canada and Japan, potential differences in 1,4-dioxane content of water between Canada and Japan (used in food processing and cooking), differing food additive provisions between these two countries at the time these Japanese studies were conducted, and the limitations in those two studies, the food data from these studies were not included in estimates of daily intake from environmental media (Appendix 1).

One study examined the likelihood of the presence of 1,4-dioxane in breast milk (using a physiologically-based pharmacokinetic model (PBPK)), particularly in regards to women with potential occupational exposure to this substance (Fisher et al. 1997). In this study an experimental milk/blood partition coefficient of 0.89 was observed, indicating that more 1,4-dioxane would be expected to be present in blood than milk. A Center for Disease Control and Prevention (CDC) study examined blood samples from more than 2000 individuals from the NHANES US biomonitoring study (2008-2008) and 1,4-dioxane was not detected in any of the blood samples taken (Blount et al. 2008). Therefore, based on this PBPK model, negligible amounts would be expected in milk. This is supported by the physical-chemical properties of 1,4-dioxane. Typically, lipophilic chemicals are preferentially taken up in breast milk due to their higher fat content. However, 1,4-dioxane is very hydrophilic (log KOW -0.27 to -0.42). Accordingly, exposure to 1,4-dioxane from breast milk is not expected.

1,4-Dioxane may be present as an impurity in the food additives polysorbate 80, polysorbate 65, polysorbate 60, and polyethylene glycol. Therefore, trace amounts of 1,4-dioxane could potentially be carried over into foods that are permitted to contain these additives or into processing aid formulations that might contain these additives (2009 personal communication from Food Directorate, Health Canada ; unreferenced). Estimated intakes of 1,4-dioxane resulting from its potential presence as an impurity in permitted food additives (polysorbates 80, 65 and 60 and polyethylene glycol) were calculated based on the maximum residue limit (not more than 10 mg/kg) of 1,4-dioxane in these additives according to the Food Chemicals Codex (FCC, 6^th Ed., 2008) and the maximum level of use for those foods in which these additives are permitted according to Tables IV and VIII of the Food and Drug Regulations (see Appendix 2). These estimates are considered very conservative, in that food additives (polysorbates and polyethylene glycol) and 1,4-dioxane residues were assumed to be present at their maximum permitted levels in foods (Food and Drug Regulations) and residual level in the food additives (Food Chemicals Codex), respectively (Canada [1978]) (2009 personal communication from Food Directorate, Health Canada; unreferenced). Furthermore, residual levels of 1,4-dioxane in foods are expected to be very low due to its volatility and, as such, even lower in foods processed and cooked at high temperatures (2009 personal communication from Food Directorate, Health Canada; unreferenced). Further details on the conservative nature of these estimates are provided in Appendix 2. It should be noted, however, that the estimated intakes of 1,4-dioxane from food additive use are lower than the total intake from environment media, with the highest estimate of 0.335 µg/kg-bw per day for children aged 1–4 years and if added to environmental media intake, do not impact the lowest or highest estimated intake from the environmental media.

Consumer Products

1,4-Dioxane has been found in various personal care products in varying concentrations (see Table 7a).

Table 7a. Concentration of 1,4-dioxane in various personal care products

Maximum concentrations reported in products (see Table 7a) were used to derive exposure estimates from use of personal care products (see Table 7b). In the absence of Canadian specific concentrations in products, non-Canadian data was used to estimate exposures. There is no indication that the ethoxylation process (source of 1,4-dioxane residual levels in products) is different in countries from which the data was chosen. A number of the products in these surveys may also be available on the Canadian market.

Exposure was modelled using ConsExpo 4.1 software (ConsExpo 2006). Health Canada ’s Cosmetic Notification System (CNS) was used to determine if product types other than those summarized in Table 7b contained ingredients which could contain 1,4-dioxane as a by-product. Hair dye was identified as a product type containing ethoxylated alkyl sulphates. As measured concentrations of 1,4-dioxane in hair dye were not available, measurements of 1,4-dioxane in cosmetic ingredients from a recent FDA survey were used to estimate exposure from use of that product type. Black et al 2001 reported concentrations of 45-1102 ppm in ethoxylated alkyl sulphates and multiplying this maximum by-product concentration by the composition value reported in CNS for hair dye gives an estimation of 1,4-dioxane concentration.

1,4-Dioxane has been shown to have low skin absorption (3.4%: skin lotion vehicle) in monkey forearms (Marzulli et al. 1981), which is thought to be a function of evaporation (NICNAS 1998; EURAR 2002; VCCEP 2007). Also, when added to lotion-like material, 1,4-dioxane has been known to evaporate rapidly (90% in 15 minutes) in unoccluded conditions (Bronaugh 1982). Therefore when characterizing exposure it was assumed that 90% of 1,4-dioxane is available for inhalation, whereas 10% is available for dermal exposure. A distinction between rinse-off and stay-on products was also made; thus, various skin retention factors were used in the analysis (see Appendix 3).

Table 7b. Estimated adult female¹ exposure to 1,4-dioxane from personal care products

Exposure from personal care products was estimated for women, men and children (body weight 7.5 kg). However, after analysis, it was apparent that because of factors such as frequency of use, women were the most exposed group. In the interests of clarity, only the exposure estimates for women and children are presented in this report.

Using finished product concentrations of 1,4-dioxane in children’s products (see table 7a) exposure was estimated for 0- to 6-month-old children (Table 7c). Aggregate exposure for three products was estimated to be 4.2 x 10^-5 mg/kg/day.

Table 7c. Estimated Children’s¹ exposure to 1,4-dioxane in personal care products

1,4-Dioxane has also been detected in dishwashing liquid, detergents and other household products (Fuh et al. 2005; Tanabe and Kawata 2008). Due to the potential for daily exposure to hand dishwashing detergent, exposure was estimated for a 70.9-kg adult. Using CNS consumer product data (maximum concentration: 0.033%; CNS 2009), exposure was analysed using ConsExpo 4.1 software and found to be minimal (inhalation: 2.2 × 10^-4 mg/kg-bw per day; dermal: 6.5 × 10^-5 mg/kg-bw per day).

Confidence in the exposure estimates for environmental media and consumer products is high. All soil, air and water data are Canadian and considered adequate to permit quantification of exposure to 1,4-dioxane. The confidence in estimates of intake from food sources is low, as Canadian data on the levels of 1,4-dioxane in foods were unavailable and therefore not included in the intake estimate. However, as discussed previously, the estimated exposures from certain food additives are considered to be an overestimate, with actual levels in food expected to the very low (2009 personal communication from Food Directorate, Health Canada ; unreferenced). Although there is some uncertainty associated with concentration of 1,4-dioxane in some product types available in Canada, due to the limited information on the presence or concentrations of the substance in consumer products available in Canada, the estimates of exposure from the use of products containing 1,4-dioxane were based on conservative assumptions; therefore, there is confidence that the exposure estimates are conservative upper-bounding estimates.

Health Effects Assessment

The available health effects information for 1,4-dioxane is summarized in Appendix 4.

On the basis of investigations in experimental animals, 1,4-dioxane has been classified by the International Agency for Research on Cancer in Group 2B – “possibly carcinogenic to humans” (IARC 1999), by the European Commission as a Category 3 Carcinogen – “cause concern for humans owing to possible carcinogenic effects but in respect of which the available information is not adequate for making a satisfactory assessment” (European Commission 2000; ESIS 2009), by the US Environmental Protection Agency as Group B2 – “probable human carcinogen” (US EPA 1990) and by the US National Toxicology Program as “reasonably anticipated to be a human carcinogen” (NTP 2005). These classifications were based on observed hepatocellular adenomas and carcinomas in mice, tumours of the nasal cavity, liver subcutaneous tissues, mammary gland and peritoneal mesotheliomas in rats and tumours of the liver and gallbladder in guinea pigs orally exposed to 1,4-dioxane (US EPA 1990; IARC 1999).

When 1,4-dioxane was administered in drinking water, a significantly increased incidence of hepatocellular adenomas and carcinomas was consistently observed in both sexes of various strains of rats and mice and in male guinea pigs (female guinea pigs were not tested) in chronic carcinogenicity bioassays, whereas nasal cavity tumours were observed only in rats of both sexes exposed to 0.5% (240 –398 mg/kg-bw per day) 1,4-dioxane and above dose levels via drinking water for 2 years. Significantly increased incidences of liver tumours in both mice and rats were observed in animals administered 0.05–1% (77–1070 mg/kg-bw per day 1,4-dioxane and above dose levels in drinking water for 2 years (Kociba et al. 1974; National Cancer Institute 1978; Yamazaki et al. 1994; JBRC 1998c), whereas significantly increased incidences of peritoneal mesotheliomas in male rats and mammary gland tumours in female rats were observed in rats exposed to 0.5% (398–514 mg/kg-bw per day) 1,4-dioxane in drinking water for 2 years (Yamazaki et al. 1994; JBRC 1998c). At a dose of 0.01% (9.6–19 mg/kg-bw per day) 1,4-dioxane in drinking water for 2 years, no tumour formation or any exposure-related effects were observed in exposed rats (Kociba et al. 1974). Additionally, liver and/or nasal tumours were observed in rats exposed to 0.75–1.8% (approximately equivalent to 770–1850 mg/kg-bw per day) 1,4-dioxane in drinking water for relatively shorter periods--that is, 13 months (Hoch-Ligeti et al. 1970; Argus et al. 1973) or 63 weeks (Argus et al. 1965); no statistical analyses were provided. In a carcinogenicity bioassay conducted in male guinea pigs, 22 animals were exposed to varied doses of 0.5–2% (1200–4800 mg/kg-bw per day) 1,4-dioxane via drinking water for 23 months; three animals developed hepatomas, one developed kidney adenoma and two developed gallbladder carcinomas (Hoch-Ligeti and Argus 1970).

An older chronic inhalation study did not provide any evidence of carcinogenicity or other adverse effects in rats of both sexes exposed to 1,4-dioxane at 400 mg/m³ for 2 years (Torkelson et al. 1974). However, during the public comment period for this assessment, a two-year inhalation study in male F344 rats was published (Kasai et al., 2009). Dose-dependent and significant increases in incidences of nasal squamous cell carcinomas and hepatocellular adenomas were observed primarily in the 1250 ppm (4500 mg/m³) exposed rats and a significantly increased incidence of peritoneal mesotheliomas was observed at 250 ppm (900 mg/m³) and above. The incidences of renal cell carcinomas, fibroadenomas in the mammary gland and adenomas in the Zymbal gland also increased with dose, but were not statistically significant. Preneoplastic lesions in the nasal cavity, including significantly increased incidences of nuclear enlargement, atrophy and respiratory metaplasia, were observed at 50 ppm (180 mg/m³) and above.

Dermal application of 1,4-dioxane alone did not induce exposure-related skin or other types of tumours in mice (King et al. 1973; Perone et al. 1976). However, in the dermal tumour promoting assay, when mice were administered dimethylbenzanthracene prior to 1,4-dioxane application, skin tumours as well as tumours in lung, kidney, spleen and liver were observed (King et al. 1973). 1,4-Dioxane-induced lung tumours were also observed in male but not female mice when the substance was administered by intraperitoneal injection (Maronpot et al. 1986; Stoner et al. 1986).

In humans, although several epidemiological investigations did not provide evidence of 1,4-dioxane-induced tumour formation in occupational environments (Thiess et al. 1976, 1981; NIOSH 1977; Buffler et al. 1978; Kramer et al. 1978), a large comparative mortality study based on data in the Danish Cancer Registry showed that the standardized proportionate incidence ratios for liver tumours in male workers exposed to 1,4-dioxane and other chemicals in occupational settings were significantly higher than the expected rates, and an increase in liver cancer incidence of 50% was identified in one workplace where only 1,4-dioxane was used (Hansen 1993; Hansen et al. 1993).

The genotoxicity of 1,4-dioxane has been assessed in a range of in vitro and in vivo assays. All tests for mutagenicity were negative, including those in a variety of bacterial, yeast and mammalian cells, dominant lethal mutation assay in mice and recessive lethal mutation assay in Drosophila (BASF 1977, 1979a, b, c, 1991; Stott et al. 1981; Haworth et al. 1983; Nestmann et al. 1984; Yoon et al. 1985; Khudoley et al. 1987; Kwan et al. 1990; McGregor et al. 1991; Morita and Hayashi 1998). In addition, all mutagenicity tests with one of the metabolites of 1,4-dioxane, 1,4-dioxan-2-one, were also negative (Goldsworthy et al. 1991; EURAR 2002). For clastogenicity investigations, including chromosomal aberration, micronuclei induction and sister chromatid exchange, the in vitro results were principally negative, with one weak positive result, and the results of the in vivo micronuclei induction assays in both CD-1 and C57BL/6 mice were mixed (Galloway et al. 1987; McFee et al. 1994; Mirkova 1994; Tinwell and Ashby 1994; Morita and Hayashi 1998; Roy et al. 2005). Significantly increased chromosomal aberrations were observed in 11 workers exposed to alkylene oxides, including 1,4-dioxane, for more than 20 years in the occupational environment. However, workers were also exposed to known mutagens, such as ethylene oxide and propylene oxide (Thiess et al. 1981). Significantly increased aneuploidy was observed in Drosophila (Muñoz and Barnett 2002), but not in yeast (Zimmermann et al. 1985), exposed to 1,4-dioxane. 1,4-Dioxane was positive in some assays, but not in others, for effects on deoxyribonucleic acid (DNA), such as DNA strand breaks, enhanced DNA repair processes or cell proliferation (measured as replicative DNA synthesis) and cell transformation. However, these were typically significant only at higher doses or following prolonged exposure and often in the presence of cytotoxicity (Stott et al. 1981; Heidelberger et al. 1983; Sina et al. 1983; Sheu et al. 1988; Sai et al. 1989; Kitchin and Brown 1990; Goldsworthy et al. 1991; Hellmer and Bolcsfoldi 1992; Uno et al. 1994; Miyagawa et al. 1999; Sasaki et al. 2000). The European Commission has concluded that the total weight of evidence indicates that 1,4-dioxane is a non-genotoxic compound (EURAR 2002). The Agency for Toxic Substances and Disease Registry (ATSDR) has indicated that “collectively, the information available suggests that 1,4-dioxane is a non-genotoxic compound, or at best, a weakly genotoxic compound” (ATSDR 2007). The Government of Australia has concluded that “overall, the weight of evidence from in vitro and in vivo tests indicates that 1,4-dioxane is unlikely to be a mutagen” (NICNAS 1998).

Although potential modes of action of carcinogenicity of 1,4-dioxane have been examined by other agencies, these have not been fully elucidated, as data on dose–response and temporal progression with which to characterize and/or identify the key events in the processes of 1,4-dioxane-induced tumour formation and thus support any of the hypothesized carcinogenic modes of action are insufficient, inconsistent or not available. However, the collective evidence indicates that 1,4-dioxane is not genotoxic. Accordingly although the mode of induction of tumours in not fully elucidated, the tumours observed are not considered to have resulted from direct interaction with genetic material (NICNAS 1998; EURAR 2002; ATSDR 2007; VCCEP 2007). It has been suggested that the nasal tumour formation in rats exposed to 1,4-dioxane via drinking water may be due to the inspiration of water into the nasal cavity during drinking from sipper bottles, resulting in high doses applied directly to nasal tissue and subsequent cytotoxicity (Reitz et al. 1990; Goldsworthy et al. 1991; Stickney et al. 2003; Sweeney et al. 2008), which is related to the rat nasal anatomy and experimental methodology. However, in a recent two-year study in rats (Kasai et al., 2009), preneoplastic and neoplastic lesions in rat nasal cavity were observed via inhalation exposure, therefore the human relevance of nasal tumour induced by 1,4-dioxane can not be excluded. Additionally, 1,4-dioxane is not a complete carcinogen, as it exhibited only tumour promotion activity, not tumour initiation activity (Pereira et al. 1982; Bull et al. 1986; Stoner et al. 1986; Lundberg et al. 1987).

Several investigations indicated that 1,4-dioxane was absorbed rapidly and completely following oral and inhalation exposure in both humans and rats, whereas much less absorption (overall 3.4%) occurred via dermal application in monkeys or through human skin in vitro (Young et al. 1976, 1977, 1978; Marzulli et al. 1981; Bronaugh 1982). Following intraperitoneal injection, 1,4-dioxane was distributed rapidly to, and has been detected in, all the tissues examined (Woo et al. 1977; Mikheev et al. 1990). In both rats and humans, the primary metabolite of 1,4-dioxane is ß-hydroxyethoxyacetic acid (HEAA), which has been detected in the urine (Young et al. 1976, 1977, 1978; Braun and Young 1977). 1,4-Dioxan-2-one has also been detected in rat urine, depending on the pH and temperature of the analytical conditions. At high pH, HEAA will be detected, and at low pH, HEAA will be converted to 1,4-dioxan-2-one (Braun and Young 1977; Woo et al. 1977, 1978). At lower doses, rapid elimination (half-life of approximately 1 hour) of 1,4-dioxane has been observed in humans exposed to 50 ppm (180 mg/m³) 1,4-dioxane by inhalation. A similar half-life was observed in rats given low oral or intravenous doses of 1,4-dioxane (less than 10 mg/kg-bw). However, non-linear toxicokinetics of 1,4-dioxane has been demonstrated in rats when the oxidation of 1,4-dioxane to its primary metabolites, HEAA and 1,4-dioxan-2-one, was saturated at doses greater than 50 ppm (180 mg/m³) in air or 10 mg/kg-bw orally and the accumulation of 1,4-dioxane was observed (Young et al. 1976, 1977, 1978; Stickney et al. 2003). In addition, enhanced metabolism in the liver did not increase the liver toxicity of 1,4-dioxane measured by hepatic glutathione content or serum alanine transaminase activity, indicating that the metabolites did not play a major role in the liver toxicity of 1,4-dioxane (Nannelli et al. 2005). Collectively, the evidence suggests that a threshold for toxicity and carcinogenicity may exist at doses at which 1,4-dioxane metabolism becomes saturated (VCCEP 2007).

Several physiologically based pharmacokinetic/pharmacodynamic models have been developed to predict the absorption, distribution, metabolism and elimination of 1,4-dioxane in rodents and humans (Young et al. 1977, 1978; Leung and Paustenbach 1990; Reitz et al. 1990; Fisher et al. 1997; Sweeney et al. 2008). The Fisher et al. (1997) model indicates that 1,4-dioxane may also be excreted into human milk, as discussed in the exposure assessment section. However, excretion of 1,4-dioxane into breast milk has not been assessed or predicted by other PBPK models. As described in the exposure assessment section, exposure to 1,4-dioxane from breast milk is not expected.

The primary non-neoplastic effects induced by 1,4-dioxane were liver and kidney damage, typically associated with high-dose exposure and cytotoxicity, which were observed by all routes of exposure that have been tested and in both humans and experimental animals. Other adverse effects induced by 1,4-dioxane include effects on central nervous, respiratory and blood systems and stomach. The oral lowest-observed-adverse-effect level (LOAEL) for non-neoplastic effects, based on liver lesions, was observed at 16 mg/kg-bw per day in rats exposed to 1,4-dioxane via drinking water for 2 years (Yamazaki et al. 1994; JBRC 1998c). In addition, the lowest oral LO(A)ELs identified from subchronic, short-term and acute studies are 130 mg/kg-bw per day (Kano et al. 2008), 400 mg/kg-bw per day (the only dose tested; Nannelli et al. 2005) and 1050 mg/kg-bw per day (Kanada et al. 1994), respectively (Appendix 4). A practical no-observed-adverse-effect level (NOAEL) for chronic effects and the lowest level in available studies in which tumours were not observed in rats is 0.01% in drinking water (equivalent to 9.6 and 19 mg/kg-bw per day for males and females, respectively), based on the aforementioned 2-year study (Kociba et al. 1974).

1,4-Dioxane vapour–induced non-neoplastic effects, such as histopathological changes in nasal cavity and liver, were observed in rats at 100 ppm (360 mg/m³) and above in a 13-week study (Kasai et al. 2008) and at 50 ppm (180 mg/m³) and above in a two-year study (Kasai et al., 2009), although in another inhalation study, no treatment-related effects were observed in rats exposed to 111 ppm (400 mg/m³) 1,4-dioxane vapour for 2 years (Torkelson et al. 1974). In addition, glutathione peroxidase activation in both brain and ovaries was observed in female rats exposed to 1,4-dioxane vapour at 100 mg/m³ for a month (Burmistrov et al. 2001). Irritation of the eye and respiratory system was observed following acute inhalation exposure in both humans and experimental animals. Central nervous system depression as well as liver and kidney lesions were observed in animals exposed to high concentrations of 1,4-dioxane vapour. In terms of acute exposure, a no-observed-adverse-effect concentration (NOAEC) of 20 ppm (72 mg/m³) was identified in humans (Ernstgård et al. 2006), whereas mild effects, such as serum enzyme activity changes, were observed in rats exposed to 1000 ppm (3600 mg/m³, the lowest acute lowest-observed-effect concentration [LOEC]) 1,4-dioxane vapour for 4 hours (Drew et al. 1978).

In regards to dermal exposure, although significant lesions were not observed in mice topically exposed to 0.2 mL 1,4-dioxane 3 times/week for 60 weeks or to 0.05 mL 1,4-dioxane 3 times/week for 78 weeks (King et al. 1973; Perone et al. 1976), these data are considered unsuitable to derive a NOAEL, as the dermal application in these studies might not have occurred under occlusion, and therefore the dermal applied dose levels might be greatly reduced by the fast evaporation of 1,4-dioxane.

1,4-Dioxane-induced reproductive and developmental effects were observed only at higher doses, based on limited available data. Effects on male reproductive organs, such as reduced mineralization of testis, were observed in mice exposed to 1,4-dioxane at 2000 mg/L via drinking water (250 mg/kg-bw per day) for 2 years, but not in rats exposed to 1,4-dioxane at doses up to 1015 mg/kg-bw per day orally or at 400 mg/m³ in air for 2 years (Kociba et al. 1974; Torkelson et al. 1974; Yamazaki et al. 1994; JBRC 1998c). Significantly reduced average live fetus weights and delayed fetal ossification in sternebrae were observed in rats exposed to 1035 mg 1,4-dioxane/kg-bw per day during the organogenesis period (Giavini et al. 1985). In addition, immunological effects such as suppressed T-cell responses and augmented B-cell responses were observed in murine and human lymphocytes in vitro and slightly lower lymphocyte response to mitogens was observed in mice exposed to 1,4-dioxane by intraperitoneal injection (1670 mg/kg-bw per day for 7 days) (Thurman et al. 1978).

The confidence in the toxicity database is high, as data on acute toxicity, carcinogenicity, repeated-dose toxicity, genotoxicity and developmental toxicity are available, although data on reproductive and dermal effects are limited, and there is uncertainty in the mechanism of tumorigenesis.

Characterization of Risk to Human Health

Based principally on the weight of evidence–based assessments of several international agencies (International Agency for Research on Cancer, European Union, US Environmental Protection Agency and US National Toxicology Program) and available information, critical effects associated with exposure to 1,4-dioxane are tumorigenesis following oral and inhalation exposure, but not dermal exposure, and other systemic effects, primarily liver and kidney damage, via all routes of exposure (i.e., oral, dermal and inhalation). The collective evidence indicates that 1,4-dioxane is not a mutagen and exhibits weak clastogenicity in some assays, but not others, at high exposure levels often associated with cytotoxicity. Consideration of the available information regarding genotoxicity, and conclusions of other agencies, indicate that 1,4-dioxane is not likely to be genotoxic. Non-linear toxicokinetics of 1,4-dioxane have been observed in rats, and the existence of a threshold dose for toxicity and carcinogenicity was suggested, at which 1,4-dioxane metabolism becomes saturated. Although the available epidemiological data did not provide adequate evidence regarding 1,4-dioxane carcinogenicity in humans, the human relevance of 1,4-dioxane carcinogenicity, especially liver tumour induction, cannot be discounted, as similar metabolic pathways for 1,4-dioxane in humans and experimental animals have been found. Although the mode of induction of tumours is not fully elucidated, the tumours observed are not considered to have resulted from direct interaction with genetic material. Therefore a threshold approach is used to characterize risk to human health. Margins of exposure are derived between the level at which no tumours or any adverse effects were observed in experimental studies, as well as the lowest exposure level associated with adverse effects induced by 1,4-dioxane, and conservative estimates of the general population exposure to 1,4-dioxane (Appendix 5).

The principal routes of exposure to 1,4-dioxane for the general population are expected to be from the general environment (i.e., ambient air, indoor air and drinking water), from food and during the use of consumer products containing the substance. Comparison of the upper-bounding estimates of total daily intake from the general environment to both the level at which no tumours or any adverse effects were observed and the LOAEL for non-cancer effects result in margins of exposure ranging from 7000 to 84 000. Furthermore, pertaining to inhalation exposure, a comparison of the highest concentration of 1,4-dioxane in indoor air measured in the greater Toronto area over a period of 3 months in 1996with the lowest-observed-adverse-effect concentration (LOAEC) for non-cancer effects in rats, or eye irritation in humans, results in margins of exposure of 5 orders of magnitude. These margins are considered adequately protective to account for the uncertainties in the dataset for the human health risk assessment for both cancer and non-cancer effects.

In addition, a range of personal care products containing 1,4-dioxane as a manufacturing by-product have been identified. Inhalation and dermal contact through use of these products would contribute to exposure to 1,4-dioxane. For those products that may be used collectively by consumers on a daily basis, the aggregate upper-bounding estimates of daily exposure to 1,4-dioxane in various personal care products (i.e., shampoo, conditioner, shower gel and skin moisturizer) by the dermal and inhalation routes combined are compared to both the level at which no tumours or any adverse effects were observed and the LOAEL for non-cancer effects. This approach is considered conservative, as the available dermal data are inadequate to derive a dermal LOAEL, and the low dermal absorption rate has been taken into consideration in the dermal exposure estimates. The resulting margins of exposure are approximately 8000–13300. Use of a single personal care product or dishwashing liquid or children products (Table 7c) generates lower exposure levels and would result in even larger margins of exposure. For the less frequently used products, such as hair dye, the upper-bounding dermal and inhalation exposure estimates are compared with the lowest oral acute LOEL, based on the effects on the central nervous system in rats, resulting in a margin of exposure of 15 630– 52 000. Therefore, the margins of exposure for intake from combined inhalation and dermal exposure during use of consumer products are considered adequately protective.

In terms of inhalation exposure from products, a comparison of the conservative sum of upper-bounding estimates of inhalation exposure from personal care products used in close succession on a daily basis, with the LOAEC, based on nasal effects in rats, results in a margin of exposure of 15250. The upper-bounding estimate from use of hair dye compared with the acute LOEC, based on altered serum enzyme activity in rats, and with eye irritation in humans results in margins of exposure are approximately 40 (irritation in humans) to 780 (rats). As these estimates for hair dye are for a very conservative upper bound (i.e., 100% ethoxylated alkyl sulphate in final product, which is certainly an overestimate), the margins of exposure during use of consumer products are considered adequately protective.

Uncertainties in Evaluation of Risk to Human Health

There is a high rating of confidence pertaining to data on concentrations of 1,4-dioxane in environmental media in Canada . All soil, air and water data are Canadian and considered adequate to permit quantification of exposure to 1,4-dioxane. There is some uncertainty in estimating intake from food sources, as Canadian data on the levels of 1,4-dioxane in foods were unavailable and as a result were not included in the overall intake estimate. The exposures from certain food additives are considered to be an overestimate, with actual levels in food expected to be very low (2009 personal communication from Food Directorate, Health Canada ; unreferenced). Although there is some uncertainty due to the limited information on the presence or concentrations of the substance in consumer products available in Canada, the estimates of exposure from the use of products containing 1,4-dioxane were based on conservative assumptions.

There is uncertainty around the extent to which 1,4-dioxane, present as a residual solvent in health products (phamaceuticals, veterinary drugs and natural health products), may contribute to general population exposure.

There is uncertainty regarding the mechanism of 1,4-dioxane-induced tumorigenesis, as data on dose–response and temporal progression with which to characterize and/or identify the key events in the processes of 1,4-dioxane-induced tumour formation of different types and thus support any of the hypothesized carcinogenic modes of action are insufficient, inconsistent or not available. However, the collective evidence indicates that this substance may not directly interact with genetic material, and therefore a margin of exposure approach is used within the screening assessment to characterize risk. As well, there is uncertainty with respect to the human relevance of 1,4-dioxane carcinogenicity, as epidemiological investigations have not provided conclusive evidence; however, the potential relevancy was not discounted in the assessment. As to the non-neoplastic effects, there are some uncertainties concerning the critical exposure levels associated with these effects via dermal exposure to 1,4-dioxane, as the dermal dataset is limited. As well, data on reproductive toxicity associated with 1,4-dioxane exposure are limited, as there is no multigenerational study available.

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Conclusion

Based on the information presented in this final screening assessment, it is concluded that 1,4-dioxane is not entering 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 or that constitute or may constitute a danger to the environment on which life depends.

On the basis of the adequacy of the margins between conservative estimates of exposure to 1,4-dioxane and critical effect levels, it is concluded that 1,4-dioxane 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.

It is concluded that 1,4-dioxane does not meet any of the criteria in section 64 of CEPA 1999. While 1,4-dioxane does meet the criteria for persistence, it does not meet the criteria for bioaccumulation potential as set out in the Persistence and Bioaccumulation Regulations (Canada 2000).

This substance will be considered for inclusion in the upcoming Domestic Substances List inventory update initiative. In addition and where relevant, research and monitoring will support verification of assumptions used during the screening assessment.

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References

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Appendix 1: Upper-bounding estimates of daily intake of 1,4-dioxane by the general population in Canada

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Appendix 2: Estimated intake of 1,4-dioxane from food additive uses^1,2

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Appendix 3: ConsExpo sample calculation scenarios

Personal care product scenarios for adult women

Household product scenarios

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Appendix 4: Summary of effects information for 1,4-dioxane

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Appendix 5: Summary of margins of exposure for 1,4-dioxane

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Date modified:

2013-06-20