Screening Assessment for the Challenge Benzenamine, 4-[(2,6-dichloro-4-nitrophenyl)azo]-N-(4-nitrophenyl)-

Chemical Abstracts Service Registry Number 72927-94-7

Environment Canada
Health Canada

August 2009

Table of Contents

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. Conclusion
12. References
13. Appendix I - Robust Study Summaries for Key Studies

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 on benzenamine, 4-[(2,6-dichloro-4-nitrophenyl)azo]-N-(4-nitrophenyl)- (DNAN), Chemical Abstracts Service Registry Number 72927-94-7. This substance was identified as a high priority for screening assessment and included in the Challenge because it had been found to meet the ecological categorization criteria for persistence, bioaccumulation potential and inherent toxicity to non-human organisms and is believed to be in commerce in Canada.

The substance DNAN was not considered to be a high priority for assessment of potential risks to human health, based upon application of the simple exposure and hazard tools developed by Health Canada for categorization of substances on the Domestic Substances List. Therefore, this assessment focuses on information relevant to the evaluation of ecological risks.

DNAN is an organic substance that has been previously reported to be used in Canada as a colorant. The substance is not naturally produced in the environment. No manufacturing or importation of this substance in Canada was reported for the years 2005 and 2006 above the section 71 reporting threshold of 100 kg per year. Based on known use patterns of structurally-similar azo dyes, the assumption is made in this assessment that DNAN is used in textiles.

Based on reported use patterns in Canada and certain assumptions, most of the substance ends up in solid waste disposal sites (85.2%) but a significant amount is released to sewer water (14.8%). DNAN is not expected to be soluble in water or volatile, but is expected to partition to particles because of its hydrophobic nature. For these reasons, after release to water, DNAN will likely end up mostly in sediments, and possibly to a much lesser extent, in agricultural soil that has been amended with sewage sludge. It is not expected to be significantly present in other media. It is also not expected to be subject to long-range atmospheric transport.

Based on its physical and chemical properties, DNAN is expected to be persistent in the environment (in water, sediment and soil). However, new experimental data relating to the bioaccumulation potential of a relatively close structural analogue suggests that this dye has a low potential to accumulate in the lipid tissues of organisms. The substance therefore meets the persistence criteria but does not meet the bioaccumulation criteria as set out in the Persistence and Bioaccumulation Regulations. In addition, experimental toxicity data for chemical analogues suggest that DNAN does not harm aquatic organisms exposed at low concentrations.

For this screening assessment, a very conservative exposure scenario was developed in which an industrial operation (i.e. the largest importer of the dye) discharges DNAN into a relatively small receiving water body at one discharge point. The predicted environmental concentration in water was below the predicted no-effect concentrations calculated for sensitive aquatic species. Additionally, since DNAN may be used in consumer products, a conservative consumer release scenario was developed based on an estimate of the quantity of DNAN in Canadian commerce. This scenario indicated that all modelled watercourses would have predicted environmental concentrations below the predicted no-effect concentrations.

This substance will be included in the upcoming Domestic Substances List inventory update initiative. In addition and where relevant, research and monitoring will be undertaken to confirm assumptions used during the screening assessment.

Based on the information available, it is concluded that DNAN does not meet any of the criteria set out in section 64 of CEPA 1999.

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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 human health. Based on the results of a screening assessment, the Ministers can propose to take no further action with respect to the substance, to add the substance to the Priority Substances List (PSL) for further assessment, or to recommend that the substance be added to the List of Toxic Substances in Schedule 1 of the Act and, where applicable, the implementation of virtual elimination.

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 2006a), that 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 benzenamine, 4-[(2,6-dichloro-4-nitrophenyl)azo]-N-(4-nitrophenyl)- (DNAN) was identified as a high priority for assessment of ecological risk as it had been found to be persistent, bioaccumulative and inherently toxic to aquatic organisms and was believed to be in commerce in Canada. The Challenge for this substance was published in the Canada Gazette on February 16, 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 pertaining to the uses of the substance were received.

Although DNAN was determined to be a high priority for assessment with respect to the environment, it did not meet the criteria for GPE or IPE and high hazard to human health based on classifications by other national or international agencies for carcinogenicity, genotoxicity, developmental toxicity or reproductive toxicity. Therefore, this assessment focuses principally on information relevant to the evaluation of ecological risks.

Under CEPA 1999, screening assessments focus on information critical to determining whether a substance meets the criteria for defining a chemical as toxic as set out in section 64 of the Act, where

Screening assessments examine scientific information and develop conclusions by incorporating a weight of evidence approach and precaution.

This screening assessment includes consideration of information on chemical 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, stakeholder research reports and from recent literature searches, up to August 2008 for exposure, effects and ecological sections of the document. Key studies were critically evaluated and generally only results from studies of good quality were used to reach conclusions, although other studies and modelling results may have been considered as part of the weight of evidence. When available and relevant, information presented in hazard assessments from other jurisdictions was considered. The screening assessmentdoes not represent an exhaustive or critical review of all available data. Rather, it presents the most critical studies and lines of evidence pertinent to the conclusion.

This screening assessment was prepared by staff in the Existing Substances Programs at Health Canada and Environment Canada and incorporates input from other programs within these departments. The assessment has undergone external written peer review.
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. Additionally, the draft of this screening assessment was subject to a 60-day public comment period. The critical information and considerations upon which the assessment is based are summarized below.

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Substance Identity

For the purposes of this document, the substance benzenamine, 4-[(2,6-dichloro-4-nitrophenyl)azo]-N-(4-nitrophenyl) will be referred to as DNAN. Information on substance identity is included in Table 1.

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Physical and Chemical Properties

No experimental data are available for DNAN. At the Environment Canada-sponsored Quantitative Structure-Activity Relationship (QSAR) Workshop in 1999 (Environment Canada 2000), Environment Canada and other invited modelling experts identified many structural classes of pigments and dyes as "difficult to model" using QSARs. The physical and chemical properties of many of the structural classes of dyes and pigments (including acid and disperse dyes) are not amenable to model prediction because they are considered "out of the model domain of applicability" (e.g., structural and/or property parameter domains). Therefore, to determine potential utility, the domains of applicability, Environment Canada reviews the applicability of QSAR models to dyes and pigments on a case-by-case basis. Environment Canada has considered it generally inappropriate to use QSAR models to predict the physical and chemical properties of DNAN. Consequently, a number of analogues were identified and "read-across" data has been used to determine the approximate physical and chemical properties in Table 2. These properties were subsequently used for further modeling and lines of evidence in this assessment.

An analogue is a chemical which is structurally similar to the substance under assessment and is therefore expected to have similar physical-chemical properties, behaviour in the environment and/or toxicity. Where there are experimental data for a given parameter for an analogue substance, these can be used directly or with adjustment as an estimate of that parameter value for the substance under assessment.

In order to find acceptable analogues, a review of data for several disperse azo dyes was performed (Anliker et al. 1981, Anliker and Moser 1987, Baughman and Perenich 1988, ETAD 1995, Brown 1992, Yen et al. 1989, Sijm et al. 1999). These compounds have structural similarities to DNAN but also share other important attributes that contribute to their suitability as analogues. This includes properties affecting their fate in the environment such as high molecular weights (generally greater than 300 g/mol), similar cross sectional diameters (1.31 - 2.05 nm) solid particulate structures, decomposition at greater than 74°C (to 236°C), and "dispersibility" in water (i.e. not truly soluble). In addition, they have low to moderate solubility in n-octanol, a negligible vapour pressure and are stable under environmental conditions. 

Table 2 contains analogue as well as read-across experimental and calculated physical and chemical properties of DNAN that are relevant to its environmental fate. No experimental values were found for DNAN.

Structural disperse azo analogues to DNAN are presented in Table 3a below. Certain empirical physical-chemical properties (Table 2), bioaccumulation data (Table 6) and toxicity data (Table 7) of these analogues were used in support of the weight of evidence and proposed decisions in this screening assessment. Specifically, data were obtained for the structural analogues: Disperse Orange 30, Disperse Blue 79, Disperse Blue 79:1, CAS RN 68877-63-4, Disperse Blue 165, Disperse Red 73, Disperse Orange 25 and Disperse Red 17.

It should be noted that there are several uncertainties associated with the use of physical-chemical, toxicological and bioaccumulation data available for the substances presented in Table 3a. All these substances belong to the same chemical class (disperse azo dyes with their characteristic azo bond) and are used for similar industrial purposes. However, there are differences between these substances associated with their unique functional groups (see Table 3b below) and for some of their molecular sizes. As a result, these analogues have empirical water solubilities that range over four orders of magnitude from 10^-4 to 1 mg/L and empirical log K_ow values that vary over two orders of magnitude from 2.5 to 5.4 (Table 2). Due to this variability, caution should be exercised when applying analogue values to DNAN as it would be preferable to use empirical water solubility and log K_ow data specific to the substance DNAN (Table 2).

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Sources

Recent information was collected through industry surveys conducted for the years 2005 and 2006 under Canada Gazette Notices issued pursuant to section 71 of CEPA 1999 (Canada 2006b and 2008). These Notices required submission of data on the Canadian manufacture and import of the substance. For 2006, data were also required on use quantities of DNAN.

In 2006, no companies reported importing or manufacturing DNAN above the prescribed reporting threshold of 100 kg/year in Canada. No companies reported using a total quantity greater than 1,000 kg of the substance, whether alone, in a mixture, in a product or in a manufactured item, at any concentration in 2006. In the Declaration of Stakeholder-Interest form associated with the section 71 survey for 2006, one company reported a stakeholder interest in this substance despite not meeting mandatory reporting requirements (Canada 2008).

In 2005, no companies reported manufacturing or importing DNAN in quantities above the prescribed reporting threshold of 100 kg/year. However, one company identified themselves as having a stakeholder interest in the substance (Canada 2006b).

The quantity reported during development of the Domestic Substances List (DSL) to be manufactured, imported or in commerce in Canada during the calendar year 1986 was 10,000 kg. The number of notifiers for the calendar years 1984-86 was fewer than four. 

DNAN is an existing chemical in Europe, but is not on the low or high production volume chemicals lists (ESIS 2008). The production volume of DNAN in the United States was 10,000 - 500,000 pounds/year in 1998 (US EPA 2007). The Substances in Preparation in Nordic Countries (SPIN) database indicates that this substance was in use in Sweden from 1999-2006 and in Norway in 2002, but the quantities in use in those countries were not stated (SPIN 2008).

No manufacturing, importation or use of this substance was reported for 2006. However the s.71 reporting threshold (i.e., 100 kg) was used throughout this screening assessment to capture the maximum potential mass of this substance that could be in use in Canada that would not subject to reporting.

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Uses

During the DSL nomination (1984-1986) DNAN was reported to be used in Canada as a colourant in pigments, stains, dyes and inks (Environment Canada 1988). However, no recent information on the use of this substance in Canada has been identified. No additional information on potential uses of DNAN was identified through searches of the available scientific and technical literature. Based on known use patterns of structurally-similar azo dyes, the assumption made in this assessment is that DNAN is used in textiles.

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Releases to the Environment

Mass Flow Tool

To estimate potential releases of the substance to the environment at different stages of its life cycle, a Mass Flow Tool is usually developed (Environment Canada 2008a). Empirical data concerning releases of specific substances to the environment are seldom available. Therefore, for each identified type of use of the substance, the proportion and quantity of release to the different environmental media are estimated, as is the proportion of the substance chemically transformed or sent for waste disposal. Unless specific information on the rate or potential for release of the substance from landfills and incinerators is available, the Mass Flow Tool does not quantitatively account for releases to the environment from disposal.

Assumptions and input parameters used in making the release estimates are based on information obtained from a variety of sources including responses to regulatory surveys, Statistics Canada, manufacturers' websites and technical databases and documents. Of particular relevance are emission factors, which are generally expressed as the fraction of a substance released to the environment, particularly during its manufacture, processing, and use associated with industrial processes. Sources of such information include emission scenario documents, often developed under the auspices of the Organization for Economic Cooperation and Development (OECD), and default assumptions used by different international chemical regulatory agencies. It is noted that the level of uncertainty in the mass of substance and quantity released to the environment generally increases towards the end of the life-cycle.

The Mass Flow Tool result for other in-commerce disperse azo dyes was used in this document to estimate the fraction of DNAN being released to the environment, since DNAN is structurally similar to other disperse azo dyes and their use patterns are also expected to be similar (textiles).

Based on Statistics Canada information and an analysis by Industry Canada (2008), it is proposed that DNAN may be imported in manufactured articles. A ratio of the amount of textiles manufactured in Canada relative to the amount imported textiles of 30/70 has been used to estimate the amount of dye imported in textiles (Environment Canada 2008b). This import quantity was included in the Mass Flow Tool calculations.

Results indicate that, like other disperse azo dyes, DNAN can be expected to be found largely in solid waste disposal sites (85.2%), due to the eventual disposal of manufactured items containing it. The calculations assume that there is no release of the substance from these sites, although long-term releases may be possible. A small fraction of solid waste is incinerated which is expected to result in chemical transformation of the substance. Based largely on information contained in OECD emission scenario documents for processing and uses associated with this type of substance, it is estimated that 14.8% of DNAN may be released to sewers (5.4% from industrial processing and 9.4% from consumer uses).

Based on the above, sewer water is the medium potentially receiving the greatest proportion of DNAN emitted during product use. It is anticipated that the majority of the substance bound in the product will be sent to landfills for disposal.

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Environmental Fate

As indicated by the results of the Mass Flow Tool (Table 4), the substance DNAN is expected to be released to waste water effluents during industrial processing and use. The moderate to high read-across log K_ow values (2.5 to 5.4) and high log K_oc (read-across 3.4 to 4.2) values (see Table 2) indicate that this substance may have affinity for solids. However, the log K_oc is a calculated value (see footnote 3 below Table 2) and the adsorption potential of disperse particulate dye structures is generally not well understood, therefore the degree of adsorption of DNAN is uncertain.

DNAN is expected to be mostly found in sediment or soil, and is not expected to be subject to long-range atmospheric transport.

According to aerobic biodegradation models, DNAN is not expected to biodegrade quickly (see Table 5 below). It may inadvertently be applied to agricultural soils and pasture lands in Canada as a component of biosludge which is commonly used for soil enrichment. Moreover, it may also be released from coloured textiles deposited in landfills.

In solution DNAN behaves as a neutral base with an estimated pKa that is very low (-4.63; see Table 2). Consequently dissolved forms of DNAN are not expected to ionize in water at environmentally relevant pHs. Based on the water solubility of various analogues (Table 2), DNAN is however expected to be only sparingly soluble. Thus, when released into water, this substance is expected to be mostly present as a particulate solid or adsorbed to suspended particles and to sink eventually to bed sediments where it is expected to remain in a relatively biologically unavailable form. Razo-Flores et al. (1997) have stated that due to the recalcitrant nature of azo dyes in the aerobic environment, they eventually end up in anaerobic sediments, shallow aquifers and in groundwater. In buried sediment DNAN may undergo anaerobic degradation, as described in the following section on Persistence.

Baughman and Perenich (1988) state that volatilization from aquatic systems will not be an important loss process for disperse dyes which agrees with the low to negligible Henry's Law constant (10^-8 to 10^-1 Pa·m³/mol, read-across data in Table 2). Transport to air due to the loss of this substance from moist and dry soil surfaces is not likely to be important for this substance as indicated by the very low vapour pressure of DNAN (5.33 × (10^-12 to 10^-5) Pa; read-across data in Table 2). These data are consistent with the physical state (solid particle) of DNAN which does not make it a likely candidate for volatilization.

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Persistence and Bioaccumulation Potential

Persistence

No experimental degradation data for DNAN have been identified. No environmental monitoring data relating to the presence of DNAN in the Canadian environment (air, water, soil, sediment) have been identified.

According to the Ecological and Toxicological Association of Dyes and Organic Pigments Manufacturers, with some exceptions, dyes are considered essentially non-biodegradable under aerobic conditions (ETAD 1995). Repeated evaluation of ready and inherent biodegradability using accepted screening tests (see OECD Guidelines for Testing Chemicals) have confirmed this assumption (Pagga and Brown 1986; ETAD 1992). Based on the chemical structure of DNAN, there is no reason to suspect that biodegradation will be other than that described for dyes generally (ETAD 1995).

Some disperse azo dyes have been shown to undergo relatively rapid anaerobic degradation in sediment at depth where anoxic conditions persist (Yen et al. 1991, Baughman and Weber 1994, Weber and Adams 1995). Disperse dyes enter the aquatic system mostly as a dispersion of fine suspended particles, eventually settling to the aerobic layers of surface sediment where they will persist until sediment burial creates reducing conditions. The rate of sediment deposition and the extent of bioturbation varies from site to site and thus it is very difficult to ascertain the residence time of dyes in aerobic sediment layers. It is likely however, that in many cases this is greater than 365 days. Once under anaerobic or reducing conditions, azo dyes may undergo rapid degradation to substituted aromatic amine constituents as demonstrated by Yen et al. who measured reduction half-life values in compacted sediments at room temperature of 1.9-2.0 days for an azo benzothiazole dye (CAS 68133-69-7). However, in anoxic sediment, these biodegradation transformation products are not expected to present a high degree of exposure potential to most aquatic organisms, and therefore they are not likely to present an ecological concern.

Given the expected release of DNAN into wastewater, persistence was primarily examined using predictive QSAR models for aerobic biodegradation in water. The following analysis applies primarily to the portion of this substance that is present in the environment in the dissolved form, recognizing that a significant proportion would also likely exist in dispersed form as solid particles. DNAN does not contain functional groups expected to undergo hydrolysis in aerobic environments (dyes are designed to be stable in aqueous conditions). Table 5 summarizes the results of available QSAR models for biodegradation in water.

The results from Table 5 show that the majority of the biodegradation models (BIOWIN1, 2, 3, 5, 6 and 7) suggest this substance does not biodegrade fast. In fact all probability results are less than 0.3, the cut-off suggested by Aronson et al. (2006) to identify substances as having a half-life greater than 60 days (based on the MITI probability models). The half-life result from the primary survey model (BIOWIN 4) of "weeks-months" is suggested to mean approximately 37.5 days (US EPA 2002; Aronson et al. 2006); however, the nature of degradation products is unknown. The ultimate survey model (BIOWIN 3) result of "recalcitrant" is suggested to mean greater than 182 days by the US EPA (2002). The overall conclusion from BIOWIN is not readily biodegradable.

Another ultimate degradation model, CATABOL, predicts that DNAN will be persistent in water.

When the results of the probability models, the overall BIOWIN conclusion and ultimate degradation models are considered, there is greater model consensus suggesting the ultimate biodegradation half-life in water is greater than 182 days. This finding is consistent with what would be expected for this chemical structure (i.e., few degradable functional groups, solid sparingly soluble particle).

Using an extrapolation ratio of 1:1:4 for a water: soil: sediment biodegradation half-life (Boethling et al 1995), the ultimate degradation half-life in soil should be greater than 182 days and the half-life in aerobic sediments should be greater than 365 days. This suggests that DNAN is expected to be persistent in soil and sediment.

Based on modelled ultimate degradation data (see Table 5 above) and on expert judgment (ETAD 1995), DNAN meets the persistence criteria in water, soil and sediment (half-lives in soil and water 182 days and half-life in sediment 365 days) as set out in the Persistence and Bioaccumulation Regulations (Canada 2000).

Potential for Bioaccumulation

No experimental bioaccumulation data are available for DNAN. Since azo dyes fall outside the domains of applicability for available bioaccumulation models, predictions from such models are considered unreliable for this group of substances. As a result, in this assessment bioaccumulation modelling has not been used to evaluate the bioaccumulation status of DNAN.

In the absence of experimental and modelled data for DNAN itself, bioconcentration (BCF) and bioaccumulation (BAF) factors for structural analogues were used to estimate DNAN's potential for bioaccumulation. To that end, a bioconcentration study submitted for a relatively close structural analogue, Disperse Orange 30, suggests that it is unlikely to accumulate in fish (Shen and Hu 2008). This test was performed according to OECD Guidelines for Testing of Chemicals, Test No. 305B-1996, Bioconcentration: Semi-Static Fish Test. The bioconcentration of Disperse Orange 30 in zebra fish (Brachydanio rerio) was determined in a 28-day semi-static test with test medium renewal every two days. An exposure test at a nominal concentration of 20 mg/L (mean measured concentration 0.028 - 0.28 mg/L) was performed in accordance with the result of the fish acute toxicity test to check the bioconcentration potential of the test substance. Samples from both test solutions and test organisms were taken daily from the 26^th day to the last day during the 28-day exposure test period. Samples were prepared by extracting the lipid component from the test fish. The measured concentration of test substance, fish lipid content and BCF calculation are reported in Table 6.

The Shen and Hu (2008) study has been reviewed and was considered acceptable (see Appendix 1). Lack of detection in fish extracts (less than 0.028 mg/L) suggests a limited solubility in lipids and/or limited potential to partition into fish tissue from aqueous systems. However, there is some uncertainty associated with limit bounded values in any study because the absolute value is not known. But given the structure and likely behavior of disperse dyes in aqueous systems, a low BCF result is expected. Most disperse dyes, as their name suggests, exist as fine dispersible particles with limited truly soluble fractions. Solubility, however, can be increased by adding polar functional groups to the molecule. While DNAN contains some of these solubilizing functional groups (nitro groups), experimental solubility values for analogues containing many of the same groups are quite low.

While the above study serves as primary evidence to support DNAN's lack of bioaccumulation potential, other research corroborates this conclusion. Anliker et al. (1981) reported experimental fish bioaccumulation values for 18 disperse monoazo dyes, performed according to test methods specified by the Japanese Ministry of International Trade and Industry (MITI). Expressed on the basis of wet body weight of the fishes, these log bioaccumulation factors ranged from 0.00 to 1.76 (Anliker et al. 1981). A lack of reporting of chemical registry numbers and chemical structures limited the utility of this study for read-across purposes to DNAN. However, follow-up studies, which provided the chemical structures for the disperse dyes tested, confirmed low bioaccumulation potential for ten nitroazo dyes, with reported log bioaccumulation factors ranging from 0.3 to 1.76 (Anliker and Moser 1987; Anliker et al. 1988). Studies available from MITI also support low bioaccumulation potential for disperse azo dyes. Reported BCFs for three disperse azo dyes (CAS Nos. 40690-89-9, 61968-52-3 and 71767-67-4) tested at a concentration of 0.01 mg/L were in the range of less than 0.3 to 47 (MITI 1992). An accumulation study by Brown (1987) also showed that none of the twelve disperse dyes tested accumulated during an eight week study with carp.

A high, median read-across log K_ow value of 4.3 for DNAN (Table 2) is the only line of evidence that suggests DNAN may have a high potential for bioaccumulation. In spite of the high K_ow values for DNAN' and other disperse azo dyes, evidence for bioaccumulation of such dyes is lacking (Anliker et al. 1981, Anliker and Moser 1987, Anliker et al. 1988, MITI 1992). Authors who have measured high log K_ows and concomitant low bioaccumulation factors for disperse azo dyes suggest the low accumulation factors may be due in some cases to their low absolute fat solubility (Brown 1987) or to their relatively high molecular weight (typically 450-550 g/mol) which may make transport across fish membranes difficult (Anliker et al. 1981, Anliker and Moser 1987). It is also likely that the lack of bioavailability and limited capacity to partition under BCF test conditions limits accumulation in fish lipids.

It has been stated by ETAD (1995) that the molecular characteristics indicating the absence of bioaccumulation are a molecular weight of greater than 450 g/mol and a cross-sectional diameter of greater than 1.05 nm. Recent investigation by Dimitrov et al. (2002), Dimitrov et al. (2005) and the BBM (2008) suggests that the probability of a molecule crossing cell membranes as a result of passive diffusion declines significantly with increasing maximum cross-sectional diameter (D_max). The probability of passive diffusion lowers appreciably when cross-sectional diameter is greater than ~1.5 nm and more significantly for molecules having a cross-sectional diameter of greater than 1.7 nm. Sakuratani et al. (2008) have also investigated the effect of cross-sectional diameter on passive diffusion from a test set of about 1200 new and existing chemicals, also observing that substances not having a very high bioconcentration potential often have a D_max greater than 2.0 nm and an effective diameter (D_eff) greater than 1.1 nm.

DNAN has a molecular weight of 432.2 g/mol (see Table 1) and its molecular structure is relatively uncomplicated; both these characteristics indicate a bioaccumulation capability of this substance if molecular weight is used as the only parameter. In addition, an Environment Canada (2007) report points out that there is no clear evidence for establishing strict molecular size cut-offs for assessing bioaccumulation potential. However, the report does not dispute the notion that a reduction in uptake rate can be associated with increasing cross-sectional diameter as demonstrated by Dimitrov et al. (2002, 2005). The maximum diameter of DNAN and its conformers ranges from 1.44 to 2.11 nm (BBM 2008) suggesting that a potential for a significantly reduced uptake rate from water and in vivo bioavailability exists with this dye.

Based on a lack of accumulation observed in bioconcentration tests of Disperse Orange 30 and other related disperse azo dyes, and DNAN's large molecular size which likely limits its partitioning behavior, DNAN is expected to have low potential for bioaccumulation. Therefore, considering analogue BCF evidence, and structural and bioavailability considerations, DNAN does not meet the bioaccumulation criteria (BCF or BAF greater than 5000) as set out in the Persistence and Bioaccumulation Regulations (Canada 2000).

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Potential to Cause Ecological Harm

Ecological Effects Assessment

A - In the Aquatic Compartment

No empirical ecotoxicity data were identified for DNAN. A range of aquatic toxicity predictions for DNAN were obtained from various QSAR models. However, as with bioaccumulation, these QSAR ecotoxicity predictions are not considered reliable because of the potential error associated with input parameters and the unique nature of disperse dyes - specifically structural and/or physical-chemical properties which fall outside of the models' domain of applicability.

Ecotoxicological data have however been located for several analogues of DNAN. A study submitted on behalf of ETAD provides acute ecotoxicity data in fish, invertebrates, algae and bacteria for 5 nitroazo disperse dyes (Brown 1992). Acute zebra fish, Daphnia magna and Scenedesmus subspicatus toxicity for the 5 analogues ranged from 17 to 710 mg/L, 4.5 to 110 mg/L and 6.7 to 54 mg/L, respectively (Table 7). In addition, all bacteria tests had an IC₅₀ exceeding 100 mg/L. The experimental details for the dyes tested were not provided, which greatly limited evaluation of this study. However, these data were considered usable and are included in this screening assessment as part of the available weight of evidence.

Another acute fish toxicity study was submitted for Disperse Blue 79 (BASF 1990). According to the study, Disperse Blue 79 has a 96-hour LC₅₀ in golden orfe between 100 and 220 mg/L. However, due to lack of details, this study was considered of uncertain reliability (Appendix 1).

Environment Canada received ecotoxicological data for another structurally similar disperse azo dye through the New Substances Notification Regulations (Environment Canada 1995). An acute fish toxicity study submitted to meet notification requirements revealed this substance has a 96-hour LC₅₀ of 505 mg/L in rainbow trout (Table 7). The test was conducted according to OECD guideline No. 203. The Material Safety Data Sheet also contained information on bacterial toxic effects. The results indicate an activated sludge respiration inhibition EC₅₀ of greater than 100 mg/L. Based on the available ecotoxicity information, the notified substance is expected to be of low concern for toxic effects to aquatic organisms. Reliability of the study was assessed using a robust study summary and considered as satisfactory (Appendix 1).

Lastly, a chronic study submitted for Disperse Blue 79:1, revealed its no effect concentration (NOEC) in rainbow trout to be greater than 0.0048 mg/L (Table 7). Reliability of this study was assessed as high (Appendix 1). However, this value was not used to calculate the predicted no effect concentration because the value is a hypothesis-based unbounded result. When considering all structural analogue toxicity information, these data suggest that DNAN is not highly hazardous to aquatic organisms (i.e., acute LC₅₀ values are greater than 1 mg/L).

In general, due to their low solubility (less than 1 mg/L), disperse dyes are expected to have a low acute ecological impact (Hunger 2003). The results of empirical toxicity studies with several analogues of DNAN are consistent with this expectation, indicating fish LC₅₀s in the 17 to 505 mg/L range, withDaphnia being the most sensitive organisms tested (EC₅₀/LC₅₀s from 4.5 to 110 mg/L). Although interpretation of results from these tests is complicated by the fact that the reported effect values (i.e. EC₅₀ and LC₅₀s) are likely to be much greater than the solubility of the substances tested as well as of DNAN, the analogue data available do indicate that the toxicity of DNAN is likely to be low.

The available empirical ecotoxicity information for analogues of DNAN thus indicates that it is not likely to be highly hazardous to aquatic organisms.

B - In Other Environmental Compartments

Because DNAN could be released to soil from application of biosludge which is commonly used for soil enrichment as well as from the disposal of products that degrade and release DNAN, it would be desirable to obtain toxicity data for soil organisms. Although, no suitable ecological effects studies were found for this compound in soil, considering the toxicity data for aquatic organisms as well as the lack of bioaccumulation potential and its low bioavailability, potential for toxicity to soil- dwelling organisms is likely to be low. For the same reasons, the toxicity potential is also likely to be low for sediment dwelling organisms, although this cannot be substantiated due to lack of whole organism sediment toxicity data for DNAN or suitable analogues.

Ecological Exposure Assessment

No data concerning concentrations of this substance in water in Canada have been identified. Environmental concentrations are, therefore, estimated from available information, including estimated substance quantities, estimated release rates, and characteristics of receiving water bodies. Environment Canada's Industrial Generic Exposure Tool - Aquatic (IGETA) was employed to estimate the substance concentration (worst-case) in a generic water course receiving industrial effluents (Environment Canada 2008c). The generic scenario is designed to provide these estimates based on conservative assumptions regarding the amount of chemical processed and released, the number of processing days, sewage treatment plant (STP) removal rate, and the size of the receiving watercourse. The tool models an industrial-release scenario based on loading data from sources such as industrial surveys and knowledge of the distribution of industrial discharges in the country, and calculates a predicted environmental concentration (PEC). The equation and inputs used to calculate the PEC in the receiving water course are described in Environment Canada (2008d). In spite of the fact that no information was received to confirm DNAN's quantities in Canada, the s. 71 reporting threshold for import/manufacture (i.e. 100 kg) was used in the exposure models as a reasonable worst case scenario. As a conservative estimate, the release to water (sewer) from industrial activities only was set at 16% of the amount used as per previous experience of Environment Canada on assessing other disperse azo dyes. Conservative assumptions were made regarding receiving water body, by assuming the chemical is released to a very small river with no removal from sewage treatment plants. The conservative PEC for water was calculated to be 0.0018 mg/L (Environment Canada 2008d).

Environment Canada's spreadsheet model to estimate down-the-drain releases from consumer uses (Mega Flush) was further employed to estimate the potential substance concentration in multiple water bodies receiving sewage treatment plant effluents to which consumer products containing the substance may have been released (Environment Canada 2008e). The spreadsheet model is designed to provide these estimates based on conservative assumptions regarding the amount of chemical used and released by consumers. By default, primary and secondary STP removal rates are set at 0%, losses from use are set at 100%, the consumer use of the substance is assumed to extend over 365 days/year, and the flow rate used for receiving water bodies at all sites is a low-end (10th percentile) value. These estimates are made for approximately 1000 release sites across Canada, which account for most of the major STPs in Canada. These parameter values are considered to result in a very conservative scenario.

The equation and inputs used in Mega Flush to calculate the predicted environmental concentration (PEC) of DNAN in the receiving water bodies are described in Environment Canada (2008f). The predicted releases to water (sewers) from formulation use and from consumer use of products containing this substance were based on the Mass Flow Tool results for similar disperse azo dyes. A scenario was run assuming a total consumer use quantity of 281 kg/year (Environment Canada 2008f). This consumer use quantity was estimated conservatively using the upper bound mass of substance that could be in commerce in Canada (100 kg) and applying the 30/70 ratio for dyes in textiles manufactured/ imported in Canada. A 10% loss of dye was then assumed for the total amount of the substance being used by consumers (Øllgaard et al. 1998). That is, 28 kg of DNAN were predicted to be released to water as a result of loss to sewers during the laundering of manufactured articles that contain this dye (articles either imported or manufactured in Canada). Primary and secondary STP removal rates of 0% were used. These assumptions result in a very conservative scenario. Using this scenario, the Mega Flush model estimates that the PEC in the receiving water bodies ranges from 0.0000035 to 0.000043 mg/L

Characterization of Ecological Risk

A predicted no-effect concentration (PNEC) was estimated based on the 48-hour EC₅₀ of 4.5 mg/L in Daphnia magna for analogue Disperse Blue 79 (Table 7). A factor of 100 was then applied to account for acute to chronic toxicity and lab to field extrapolations and use of a surrogate substance. The resulting PNEC is 0.045 mg/L.

When compared to the conservative PEC calculated above for industrial releases using IGETA, the resulting risk quotient (PEC/PNEC) is 0.0018/0.045 = 0.04. Therefore, concentrations of DNAN in surface waters from industrial releases in Canada appear unlikely to cause adverse effects to aquatic organisms. Given that IGETA provides a conservative estimate of exposure and risk, the results indicate a low potential for ecological harm to the aquatic environment resulting from local exposure to a point source industrial release. A more realistic evaluation of risk resulting from this type of source is not necessary.

For exposure resulting from down-the-drain releases through consumer uses (conservative scenario), MegaFlush results estimate that the PEC will not exceed the PNEC at any sites (i.e., all risk quotients less than 1). This indicates that down-the-drain consumer releases of DNAN are not expected to harm aquatic organisms.

Based on the available information, DNAN is expected to be persistent in water, soil and sediment and it is expected to have a low bioaccumulation potential. The lack of reports of manufacturing or importation of DNAN into Canada, along with information on its physical and chemical properties and its uses, indicate a low to moderate potential for releases into the Canadian environment. If released into the environment, DNAN is expected to be discharged mainly to surface waters, although it is expected to ultimately be transferred to sediment. Through use of analogue data, DNAN has also been demonstrated to have only a low to moderate potential for acute toxicity to aquatic organisms. Risk quotients for aquatic exposures indicate that DNAN concentrations likely do not exceed concentrations associated with effects, even when using conservative scenarios and assumptions. Therefore, DNAN is unlikely to be causing harm to populations of aquatic organisms in Canada.

Uncertainties in Evaluation of Ecological Risk

An area of uncertainty for DNAN is associated with the use of read-across data for physical and chemical properties, as well as toxicity data from analogues. While the chemicals identified (Disperse Blue 79, Disperse Blue 79:1, Disperse Orange 30, Disperse Orange 25, Disperse Red 17 and Disperse Red 73), share many similarities with DNAN, including being azo dyes with high molecular weights, similar cross sectional diameters, having solid particulate structures that decompose at greater than 74 °C (to 240 °C), and being "dispersible" in water (i.e., not truly soluble), they do have some differences in functional groups. These differences in chemical structure add uncertainty because the properties and toxicity of DNAN may be somewhat different. However, it was reasoned that the similarities were sufficient to include the data from analogues to contribute to the weight of evidence in the assessment of DNAN.

The persistence assessment is limited by the absence of biodegradation data, which necessitated generation of model predictions. Although all model prediction has some degree of error, the aerobic biodegradation model outputs confirmed the expected persistence of DNAN given its uses and structural characteristics. In addition, the persistence assessment is limited by the uncertainty about the rate and extent to which degradation occurs in anaerobic sediments and whether the degradation products (e.g., amines) would be biologically available. Nevertheless it is clear that anaerobic degradation of the bioavailable portion azo dyes in sediments to constitutive amines is much faster (half-lives in the order of days) than aerobic biodegradation. Although the amine degradation products are not expected to be biologically available because they form only in relatively deep anoxic sediment and can be irreversibly bound to sediment through nucleophilic addition and oxidative radical coupling (Colon et al 2002, Weber et al 2001), this issue is a source of uncertainty in the assessment of DNAN.

The bioaccumulation assessment for this substance was limited by the lack of empirical data and the inability of available models to reliably estimate bioaccumulation for disperse azo dyes. Instead the assessment relied on the use of bioaccumulation data for a structural analogue.

Uncertainties are also present due to the lack of information on environmental concentrations in Canada for DNAN. However, the lack of reports of manufacturing or importation of DNAN into Canada above reporting thresholds, its high fixation rate to textiles and the anticipated high removal rate from sewage treatment plants suggests low to moderate potential for release of this chemical into the Canadian environment, even if it is used in Canada at levels below the reporting thresholds.

The experimental concentrations associated with inherent toxicity for aquatic organisms may have an additional source of uncertainty when these concentrations exceed the solubility of the chemical in water (either experimental or predicted). Despite this, the available data indicate that DNAN is not highly hazardous to aquatic organisms

Uncertainties are also associated with the fraction of the substance that is released, and with the fraction that is removed in sewage treatment plants. These uncertainties were addressed by making conservative assumptions. Best model estimates were thus required to fill these data gaps.

There were also uncertainties with respect to the use of the substance in Canada. Based on known use patterns of structurally-similar azo dyes, the assumption made in this assessment is that DNAN is used in textiles.

Regarding ecotoxicity, based on the predicted partitioning behaviour of this chemical, the significance of soil and sediment as important media of exposure is not well addressed by the effects data available. Indeed, the only effects data identified apply primarily to pelagic aquatic exposures.

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Conclusion

Based on the information presented in this screening assessment, it is proposed that DNAN 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. 

It is therefore proposed that DNAN does not meet the definition of toxic as set out in section 64 of CEPA 1999. Additionally, DNAN meets the persistence criteria but does not meet the bioaccumulation criteria as set out in the Persistence and Bioaccumulation Regulations.(Canada 2000).

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Appendix I - Robust Study Summaries for Key Studies

Table A-1. Robust Study Summaries Form: Aquatic B

Reference: Hu, Shuangqing and Shen, Genxiang (Environmental Testing Laboratory, Shanghai Academy of Environmental Sciences, Shanghai, China). 2008. Bioconcentration Test of C.I. Disperse Orange 30 in Fish. Prepared for Dystar in the name of Ecological and Toxicological Association of the Dyes and Organic Pigments Manufacturers (ETAD) Basel, Switzerland. Report No. S-070-2007. Submitted to Environment Canada in April 2008.

Table A-2. Robust Study Summaries Form: Aquatic B

Reference: Shen, Genxiang and Hu, Shuangqing. 2008. Bioconcentration Test of C.I. Disperse Orange 30 in Fish. Prepared by Environmental Testing Laboratory, Shanghai Academy of Environmental Sciences, Shanghai, China for Dystar in the name of Ecological and Toxicological Association of the Dyes and Organic Pigments Manufacturers (ETAD) Basel, Switzerland. Report No. S-070-2007. Submitted to Environment Canada in April 2008. Challenge Submission ID#8351

Table A-3. Robust Study Summaries Form: Aquatic iT

Reference: BASF 1990. Bericht uber die Prufung der akuten Toxizitit an der Goldorfe (Leuciscus idus L.,. Goldvariante. Submitted by ETAD to Environment Canada, August 2008.

Table A-4. Robust Study Summaries Form: Aquatic iT

Reference: Environment Canada. 1995. Acute fish toxicity test submission in fulfillment of new substances notification regulations to New Substances Branch, Environment Canada under New Substance Notification Program.

Table A-5. Robust Study Summaries Form: Aquatic iT

Reference: Cohle P, R Mihalik R. 1991. Early life stage toxicity of C.I. Disperse Blue 79:1 purified preecake to rainbow trout (Oncorhynchus mykiss) in a flow-through system. Final report. ABC Laboratories Inc. Columbia MO.