Screening Assessment for the Challenge 2-Naphthalenol, 1-[(4-chloro-2-nitrophenyl)azo]- (Pigment Red 6)

Chemical Abstracts Service Registry Number 6410-13-5

Environment Canada
Health Canada

February 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 (n = 8)

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 2-Naphthalenol, 1-[(4-chloro-2-nitrophenyl)azo]- (Pigment Red 6), Chemical Abstracts Service Registry Number 6410-13-5. 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 was believed to be in commerce in Canada.

The substance Pigment Red 6 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.

Pigment Red 6 is not naturally produced in the environment. It is an organic substance that has been used in Canada in the past as a solvent/carrier, printing agent/de-inker and in electrical or electronic products. Elsewhere it may be used in paints, printing inks, paper, board and plastics, and for colouring leather and textile printing. No reports of the manufacture of Pigment Red 6 in or import into Canada were received for the 2005 or 2006 calendar years. Therefore, releases of this substance to the Canadian environment are expected to be very low.

Pigment Red 6 is a solid particle that is not volatile and not soluble in water. If released to water, Pigment Red 6 will likely accumulate mostly in sediments and if released to terrestrial environments, it will tend to remain in soil. 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, Pigment Red 6 is determined to be persistent in all environmental media. New experimental data relating to the solubility of analogues in water and octanol suggest that this pigment has a low potential to accumulate in the lipid tissues of organisms. The substance therefore meets persistence criteria but does not meet bioaccumulation criteria as set out in the Persistence and Bioaccumulation Regulations. In addition, new experimental toxicity data on structurally similar pigments, as well as new toxicity predictions that take into account revised estimates of bioaccumulation potential, suggest that the substance has a negligible to low potential for toxicity to aquatic organisms.

No environmental monitoring data relating to the presence of Pigment Red 6 in the Canadian environment have been identified. For this screening assessment, a conservative, generic scenario was designed in which it is assumed that all industrial operations (users of the dye) discharge Pigment Red 6 into the aquatic environment at the Section 71 reporting threshold of 100 kg. The predicted environmental concentration in water was below the predicted no-effect concentration calculated for sensitive aquatic organisms. Considering these findings, Pigment Red 6 is unlikely to be causing ecological harm in Canada.

This substance will be included 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.

Based on the information available, it is concluded that Pigment Red 6 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; 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 theCanada Gazette, Part I, on December 9, 2006 (Canada 2006), 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 2-Naphthalenol, 1-[(4-chloro-2-nitrophenyl)azo]- 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 Pigment Red 6 was published in the Canada Gazette on August 18, 2007 (Canada 2007). 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 Pigment Red 6 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 March 2008. Key studies were critically evaluated; modelling results may have been used to reach conclusions. When available and relevant, information presented in hazard assessment from other jurisdictions was considered. The screening assessment does 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. 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 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, this substance will be referred to as Pigment Red 6, derived from the common name.

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Physical and Chemical Properties

The pigment industry synthesizes organic pigments that have low to very low solubilities in nearly all solvents (i.e., less than 1 mg L to less than 0.01 mg L). This arises from the desire of the industry to produce chemicals that will retain their colour for a long time and in any type of material. Low solubility is enhanced by designing chemicals that have strong interactive forces within and between molecules. For Beta Naphthol compounds, this is achieved by the intramolecular, bifurcated hydrogen bonds. Although the structure of Pigment Red 6 is often depicted as in Table 1, based on the measured bond lengths, the keto-hydrazone tautomer was found to be favoured. The keto-hydrazone tautomer is different with respect to certain bonds. Namely, there is a ketone oxygen on the naphthalene ring instead of the hydroxyl group, a double bond exists between the nitrogen and the naphthalene ring and the azo bond is a single bond (Figure 1). This structure creates bifurcated hydrogen bonds between the ortho substituents on the phenyl ring (like -Cl, or -NO₂), the azo group and the ketone oxygen on the naphthalene group. The molecules may be linked by weak van der Waals forces and charge-transfer forces causing the molecules to stack in columns within a crystal. (Herbst and Hunger 2004; Whitaker 1978; Lincke 2003).

Figure 1. Beta-Naphthol pigment structure (Whitaker 1978)

As is the case with the majority of organic pigments, Beta Naphthol pigments generally do not exist as individual molecules but are principally particles in the submicron range. The pigment powder is typically composed of primary particles (i.e., the crystal lattice of a pigment), aggregates and agglomerates. Manufacturers usually provide the physical specifications of their pigments, which include the average particle size of the pigment powder (see Table 2a). In doing so, users can determine which pigment is the most appropriate to colour their product(s), since performance is chiefly controlled by the particle size distribution (Herbst and Hunger 2004).

Table 2a contains modelled physical and chemical properties of Pigment Red 6 that are relevant to its environmental fate. Modelled estimates for these properties are typically generated using quantitative structure-activity relationship (QSAR) models. These models, in turn, base their predictions on the characteristics of the individual molecules. The modelled log K_ow of 6.55 (KOWWIN 2000) used for categorization implies that the solubility of Pigment Red 6 is much higher in octanol than in water. Experimental solubility data have been obtained for a close structural analogue, Pigment Red 4 (CAS RN 2814-77-9), which is a positional isomer of Pigment Red 6. These data reveal that the difference in the solubility in the two solvents is not that sizeable, indicating that the modelled partition coefficient is likely overestimated (Table 2a). In place of the model-derived log K_ow for this pigment, the ratio log (C_O/C_W) is preferred. The log (C_O/C_W) method is calculated from the experimental solubilities of the analogue Pigment Red 3 in octanol (C_O) and water (C_W) determined separately. This ratio is used as a surrogate for experimentally derived log K_ow using the standard method of the substance being exposed to octanol and water concurrently. The same interpretation for low, medium and high values is applied to log (C_O/C_W as for log K_ow. The modelled estimate of log K_ow has therefore been disregarded for this assessment, and the ratio log (C_o/C_w) has been presented instead (Table 2a).

The experimental solubilities in Table 2a have been determined using an aggressive approach with long contact times between pigment particles and the solvent, and a filtration step removing as much of the particulate matter in the suspension as possible. These studies have been critically reviewed and, although none reported using reference compounds of known solubilities, they were determined to have a satisfactory degree of reliability for the present risk assessment.

Octanol and water solubility studies were also performed on another structurally less closely related substance, Pigment Orange 5 CAS RN (3468-63-1). The results support the low water solubility and octanol solubility obtained from the closer analogue Pigment Red 3. The ratio log (C_o/C_w) has been presented as surrogate for the log K_ow of these substances (Table 2b).

Chemical structures for analogues Pigment Red 3, Pigment Orange 5 and Pigment Red 4

Analogue Pigment Red 3
CAS RN 2425-85-6

Pigment Red 3 differs from Pigment Red 6 in one chemical feature: a methyl group is substituted for a Cl on the terminal benzene ring.

Analogue Pigment Orange 5
CAS RN 3468-63-1

Pigment Orange 5 differs from Pigment Red 6 in one chemical feature: a NO₂ is substituted for a Cl on the terminal benzene ring.

Analogue Pigment Red 6
CAS RN 584-84-9

Pigment Red 4 differs from Pigment Red 6 in one chemical feature: it is a structural isomer.

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Sources

Pigment Red 6 is not naturally produced in the environment.

Recent information was collected through an industry survey conducted for the years 2005 and 2006 under Canada Gazettenotices issued pursuant to section 71 of CEPA 1999 (Canada 2006 and 2007). These notices requested data on the Canadian manufacture and import of the substance.

No reports of manufacture in or import into Canada of this substance at or above the reporting threshold of 100 kg in the 2005 or 2006 calendar years were received in response to the notices published under section 71 of CEPA 1999 (Canada 2006 and 2007). However, the Declaration of Non-Engagement and/or Stakeholder Interest forms associated with these notices further invited any companies to identify themselves as stakeholders if they had an interest in a listed substance. One stakeholder interest submission was received in response to the 2005 section 71 notice. Four companies have identified themselves as having a stakeholder interest in the substance in 2006 (Canada 6b2007).

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Uses

No uses in Canada were identified through searches of the available scientific and technical literature. Elsewhere, Pigment Red 6 may be used in paints, printing inks, paper, board and plastics, and for colouring leather and textile printing (CII 2002). However, according to Herbst and Hunger (2004), it has lost most of its commercial market. In 1986, the uses reported during DSL nomination included solvent/carrier, stripper/etcher/discharge printing agent/de-inker and in electrical or electronic products (Environment Canada 1988).

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Releases to the Environment

Since there were no reports of import or manufacture at or above the reporting threshold of 100 kg in 2005 or 2006 in response to the section 71 notices (Canada 2006 and 2007), releases of this substance to the Canadian environment are expected to be very low.

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Environmental Fate

The very low modelled vapour pressure of 2.066 × 10^-8 Pa and a negligible Henry's Law constant of ~10^-8 Pa·m³/mol for Pigment Red 6 are consistent with the fact that it is a large and complex molecule (Baughman and Perenich 1988; Danish EPA 1998). This pigment is not expected to volatilize at environmentally realistic temperatures, and will thus not be subject to long range atmospheric transport.

The particulate character of Pigment Red 6 should have a key influence on its fate in the environment. Its particle size and density (1230 kg/m³), which is 1.2 times greater than that of water (1000 kg/m³, cf.: Reynolds et al 1987; Wetzel 2001), together with its chemical stability and low aqueous solubility, indicate that it will partition by gravity to sediments if released to surface waters, and will tend to remain in soils if released to terrestrial environments.

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Persistence and Bioaccumulation Potential

Environmental Persistence

Because of its very low solubility in water, this pigment may be considered not available for aerobic biodegradation. Jaffe (1996) has stated that once a pigment is incorporated into a matrix (e.g., plastic), it is expected to be durable and withstand the combined chemical and physical stresses of weather, solar radiation, heat, water and industrial pollutants. Therefore, direct contact with biota probably does not occur when the pigment is sealed in the matrix of coloured items and it is not expected that the pigment would be susceptible to abiotic degradation.

Industries manufacturing pigments recognize that their substances are persistent. For example, the Color Pigments Manufacturers Association, Inc. (CPMA 2003) has indicated that pigments are designed to be durable or persistent in the environment in order to provide color to finished coatings, inks and paints.

The environmental persistence of Beta Naphthol pigments such as Pigment Red 6 in anoxic environments is an important area of uncertainty. Azo dyes are reported to be degraded in anoxic waters via anaerobic reduction of the azo bond (-N=N-)(Weber and Wolfe 1987). A mutagenic potential is attributed to their breakdown products, which include aromatic amines (Van der Zee 2002). Beta Naphthol pigments have azo chromophores in their structure as well. However, no documentation has been found regarding a possible degradation potential of these pigments in aqueous media in the absence of oxygen. In principle, the crystal would have to dissolve first, releasing its constituent molecules. Then, the azo bonds in these molecules would be available for reduction to substituted aromatic constituents. However given its limited solubility, it is expected that only a very small proportion of the pigment would be reduced in this manner.

Based on the weight of evidence provided by the above-described literature, Pigment Red 6 is considered to meet the persistence criteria defined in the Persistence and Bioaccumulation Regulations (Canada 2000).

Potential for Bioaccumulation

For most organic compounds there is a predictable relationship between K_ow and the bioconcentration factor in lipids (Mackay 1982). However, the model-derived K_ow value is not considered to be a good indicator of the bioaccumulation potential of Pigment Red 6.

The ratio log (C_O/C_W) has been estimated from the experimental solubilities of the analogue Pigment Red 4 in octanol (C_O) and water (C_W) (Table 2a) and this experimentally derived ratio has been preferred over the model-derived log K_ow for this pigment. This approach is supported by the observation that partitioning into octanol is a good indicator of a substance's potential to partition into the lipid phase of aquatic biota (Bertelsen et al. 1998) and, for pigments, the observation that a reduced solubility in octanol translates into a similarly reduced bioconcentration factor (BCF) and bioaccumulation factor (BAF) in an aquatic organism (Banerjee and Baughman 1991).

A revised set of BCF and BAF estimates for Pigment Red 6, different from those used during categorization, have been obtained from quantitative structure-activity relationship (QSAR)-based bioaccumulation models, using the experimentally based value log (C_O/C_W) of the analogue Pigment Red 4 in place of the QSAR-estimated log K_ow (Table 3). Table 3 shows that the revised modelled BCF and BAF estimates, based on data for the analogue Pigment Red 4 (for structure, solubility and melting point refer to Table 2b), are below 1000 L/kg. In addition, similarily low log (C_O/C_W) values have been derived from experimental solubilities for reasonably close analogues, Pigment Red 3 and Pigment Orange 5, (Table 2b) supporting the low bioaccumulation potential of Pigment Red 4.

Pigment Red 6 is therefore expected to present a low bioaccumulation potential, because of its very limited affinity for the lipid phase of living organisms. Further support is provided by experimental determinations for six representative organic pigments, all with BCF values less than 100 wet wt (MITI 1992). This is in agreement with the conclusion of a Danish assessment report (Danish EPA 1998) that organic pigments are generally not bioaccumulative.

The weight of evidence indicates that the substance does not meet the bioaccumulation criterion (BCF, BAF greater than or equal to 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

There is experimental evidence that other structurally similar Beta Naphthol pigments do not cause harm to aquatic organisms at the level of saturation. Predicted ecotoxicity values were also generated for Pigment Red 6, using the experimental log (C_o/C_w) of Pigment Red 4 instead of the modelled log K_ow.

The effect of a saturated solution of the analogue, Pigment Red 3 (2425-85-6), on the immobilization of Daphnia magna was determined under static conditions over 48 hours (Study Submission 2007g). Twenty test organisms were exposed to the saturated solution and a control. Water quality parameters were measured at the start and end of the test. The pH was maintained between 7.8 and 7.88 and oxygen between 8.49 and 8.61 mg/L. The temperature ranged from 18 to 22ºC. Saturation was achieved by shaking the stock solution for 24 hours and removing undissolved particles by centrifugation. The concentration of the pigment in solution was measured by dissolved organic carbon (DOC) analysis at the start and end of the test. It was observed that 0.6 mg/L DOC were present at the beginning and end of the test, indicating that the concentration of the pigment was maintained throughout the test. Based on the measured DOC, the concentration of pigment at saturation is estimated to be approximately 0.9 mg/L (see Table 4a). No biologically significant effects (immobilization) were observed at saturation. This study is considered to be of high reliability for the present assessment as good laboratory practices (GLP) were followed, control and reference toxicants were used and the dissolved organic carbon concentration was measured at the beginning and end of the experiment. However, according to the guidance provided by the OECD for sparingly soluble substances, when a substance is found to have no effects at saturation, this saturation concentration is typically below the water solubility value obtained in a water solubility test (OECD 2000). The water solubility of Pigment Red 3 was measured to be 0.0033 mg/L; therefore the measured DOC in this test may not be representative of the dissolved concentration only, but a measure of the suspended pigment particles and perhaps a small fraction of dissolved pigment. It is not expected that the maximum solubility would have been achieved by shaking the stock solution for 24 hours as the pigment was shaken in water for 2 hours at 30ºC and then for 70 hours at 23-24ºC in the solubility test, which still resulted in a residue of undissolved colorant on the 0.05-µm filter. Therefore, it is expected that undissolved pigment was also present in the toxicity test. This assumption that the DOC was not representative of only the dissolved concentration is further supported by the results of a toxicity test for Pigment Orange 5.

In a similar toxicity test on the analogue, Pigment Orange 5 (3468-63-1), it was also found that no biologically significant effects were observed at saturation. This study (Study Submission 2007h) was also considered to be of high reliability. Rather than using centrifugation to separate the undissolved fraction, a 0.45-µm membrane filter was used. The average particle size for Pigment Orange 5 is 0.285 µm; therefore, the filter would not have removed most particles. The DOC was also measured in this test and was found to correspond to a concentration of 1.6 mg/L of pigment. Since the filter was too large to capture the pigment particles, it is expected that 1.6 mg/L is the concentration of the dissolved pigment and the suspended particles.

Aquatic toxicity predictions, recalculated using log (C_O/C_W) of Pigment Red 4 instead of the modelled log K_ow, were obtained from the ECOSAR program (ECOSAR 2004). It is assumed that Pigment Red 6 has a narcotic mode of action (MOA) similar to that of phenols. However, the ASTER (1999) model predicted the MOA uncoupling of oxidative phosphorylation for this pigment, in addition to narcosis. An application factor of 100 was therefore applied to extrapolate from baseline toxicity to this more toxic MOA. It should be noted that the MOAs are predicted for the solubilized molecule that is likely released in very low amounts in solution as suggested by the solubility test in water. Table 4b presents these modelled ecotoxicity results, which are consistent with the empirical studies indicating that there would be no acute effects at saturation.

As noted above, Pigment Red 6 is the structural isomer of Pigment Red 4. Although experimental toxicity data is not available for Pigment Red 4, experimental water solubility and octanol solubility data show that it has very similar properties to Pigment Red 3. This supports the assumption that toxicity data for Pigment Red 3 can be used as read-across for Pigment Red 6.

Chronic exposure to Pigment Red 6 is likely to be low in water due to its low water solubility, relatively low bioaccumulation potential, high molecular weight and particulate nature.

Overall, experimental and modelled toxicity data indicate that Pigment Red 6 is predicted to have a negligible to low potential for toxicity to aquatic organisms.

B - In Other Environmental Compartments

No empirical or predicted effects data for non-aquatic organisms were identified for this compound. Pigment Red 6 is expected to reside in sediment or soil; however, effect levels in these media have not been identified.

Ecological Exposure Assessment

Since there were no reports of import or manufacture at or above the reporting threshold of 100 kg in 2005 and 2006 (Canada 2006 and 2007), releases of this substance to the Canadian environment are expected to be very low.

The Industrial Generic Exposure Tool - Aquatic (IGETA) was selected to conservatively model the discharge of an industrial operation (user of the pigment) to the aquatic environment. IGETA is a modelling tool developed by Environment Canada to estimate surface water concentrations. 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, the sewage treatment plant 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 default inputs used to calculate the PEC in the receiving watercourse (a generic small river) are described in Environment Canada (2008). The maximum mass, per year, used by all industries in Canada was assumed to be the reporting threshold of 100 kg (the Section 71 reporting threshold) and was used to calculate the loading rate for the PEC estimation. The percentage loss from manufacturing or handling was estimated at 5%, the number of processing days per year was estimated at 150 while the estimated removal from sewage treatment was estimated to be 0 percent. Based on IGETA results, the annual average PEC (assuming instantaneous dilution) is 0.00056 mg/L in the receiving watercourse (Environment Canada 2008).

Characterization of Ecological Risk

The approach taken in this ecological screening 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. Particular consideration has been given to risk quotient analysis, persistence, bioaccumulation, inherent toxicity, sources and fate in the environment.

Pigment Red 6 is determined to be persistent, based on published evidence and industry comments. However, it has been determined not to be bioaccumulative in accordance with the Persistence and Bioaccumulation Regulations of CEPA 1999 (Canada 2000), based on observations of its very low solubility in octanol and low modelled BCFs.

Newly acquired empirical data on analogous substances and modelled aquatic toxicity results also suggest that this pigment is not very harmful, showing a negligible to low potential for toxicity to aquatic organisms (acute LC₅₀/EC₅₀s above saturation).

A quantitative evaluation of exposure and of ecological effects was conducted as part of the weight-of-evidence evaluation of this pigment's potential to cause harm.

The result of a modelled fish toxicity study was selected as the critical toxicity value (CTV), as it was the lowest modelled LC₅₀ (0.217 mg/L). Although experimental data is available, much of the substance from the experimental LC₅₀ data was in particulate form and there were no observable effects. The modelled result is felt to address an endpoint that is not captured by existing experimental results. For this CTV, an application factor of 100 was used to extrapolate from acute to chronic exposure and to account for uncertainty in using data for the analogue, Pigment Red 3. The resulting conservative PNEC is 0.00217mg/L.

The IGETA tool estimates that the risk posed by exposure to Pigment Red 6 is low, based on the generation of a conservative risk quotient of 0.26 for an industrial discharge point to a small river. A risk quotient of less than one indicates that predicted environmental concentration in water is below the predicted no-effect concentration calculated for sensitive aquatic organisms

Considering these findings, it is concluded that Pigment Red 6 is unlikely to be causing ecological harm in Canada.

Uncertainties in Evaluation of Ecological Risk

This section summarizes the key uncertainties associated with the risk assessment of Pigment Red 6.

There is uncertainty in the current assessment resulting from the use of analogue data to evaluate the bioaccumulation potential and aquatic toxicity of Pigment Red 6. As data were not available for Pigment Red 6, the modelled predictions for bioaccumulation and aquatic toxicity are based on experimental physical and chemical properties of analogues and the empirical toxicity data presented are based on studies of analogue substances.

Pigment Red 6 is expected to partition primarily to sediment; however, experimental data on its fate and toxicity in sediments are limited. Specifically, the long-term stability of Pigment Red 6 in anoxic sediments, as well as in anoxic layers in the soil column of waste disposal sites, has not been studied. It is however considered likely that the crystalline structure of Pigment Red 6 would be maintained in these compartments, and that the substance would remain unavailable to sediment and soil-dwelling organisms and unavailable for reduction of the azo bond, which could release bioavailable aromatic amines. Although acute and chronic toxicity data are not available for sediment or soil-dwelling organisms, toxicity is expected to be low based on information for aquatic organisms.

Nanoscale materials are informally defined as substances having at least one dimension less than 100 nm. Evidence accumulates to the effect that nanoparticles can be absorbed by non-specific biouptake pathways such as pinocytosis (Leroueil et al. 2007). Organic pigments, such as Pigment Red 6, may have a certain proportion of their particle size spectra in the nanoparticle range (e.g., Table 2a). Presently, the bioaccumulation mechanisms and potential of these particles is poorly understood, as is the nature of the relationship between their bioaccumulation and their toxicity. Furthermore, certain less commonly considered environmental fate processes may have an important influence on the propensity of the pigment nanoparticles to be taken up by biota (e.g., importance of aggregation in nature: Wiesner et al. (2006)).

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Conclusion

Based on the information presented in this screening assessment, it is concluded that Pigment Red 6 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 proposedconcluded that Pigment Red 6 does not meet the definition of "toxic" as set out in section 64 of CEPA 1999. Additionally, Pigment Red 6 meets the criteria for persistence but does not meet the criteria for bioaccumulation potential as set out in the Persistence and Bioaccumulation Regulations (Canada 2000).

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Appendix I. Robust study summaries (n = 8)

Evaluation of experimental data using Kollig's approach

Kollig, H.P. 1988. Criteria for evaluating the reliability of literature data on environmental process constants. Toxicol. Environ. Chem. 17: 287-311.

Table A-1. Evaluation of experimental data using Kollig's approach for 13365Submission013

Table A-2. Evaluation of experimental data using Kollig's approach for 13365Submission014

Table A-3. Evaluation of experimental data using Kollig's approach for 13365Submission011

Table A-4. Evaluation of experimental data using Kollig's approach for 13365Submission012

Table A-5. Evaluation of experimental data using Kollig's approach for 13365Submission016

Table A-6. Evaluation of experimental data using Kollig's approach for 13365Submission017

Robust Study Summary Forms - Aquatic iT

Table A-7. Robust Study Summary for 13365Submission015: Aquatic iT

Reference: 13365Submission015. Acute Immobilization Test (Static, 48 hr) to Daphnia magna, Limit Test

Table A-8. Robust Study Summary for 13365Submission020: Aquatic iT

Reference: 13365Submission020. Acute Immobilization Test (Static, 48 hr) to Daphnia magna, Limit Test