Screening Assessment for the Challenge

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N-[4-(acetylamino)phenyl]-4-[[5-(aminocarbonyl)-2-chlorophenyl]azo]-3-hydroxynaphthalene-2-carboxamide
(Pigment Orange 38)

Chemical Abstracts Service Registry Number
12236-64-5

Environment Canada
Health Canada

July 2008

(PDF Version - 280 KB)

Table of Contents

• Synopsis
• Introduction
• Substance Identity
• Physical and Chemical Properties
• Sources
• Uses
• Releases to the Environment
• Environmental Fate
• Persistence and Bioaccumulation Potential
• Potential to Cause Ecological Harm
• Conclusions
• References
• Appendix 1: Robust Study Summaries

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-Naphthalenecarboxamide, N-[4-(acetylamino)phenyl]-4-[[5-(aminocarbonyl)-2-chlorophenyl]azo]-3-hydroxy- (Pigment Orange 38), Chemical Abstracts Service Registry Number 12236-64-5. This substance was identified as a high priority for screening assessment and included in the Ministerial 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 Pigment Orange 38 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 (i.e., it did not meet the criteria of both being considered to present greatest or intermediate potential for exposure and having been classified by another national or international regulatory agency on the basis of carcinogenicity, genotoxicity, developmental toxicity or reproductive toxicity). Therefore, this assessment focuses on information relevant to the evaluation of ecological risks.

Pigment Orange 38 is an organic substance that is used in Canada primarily as a colour pigment in plastics and inks. The substance is not naturally produced in the environment. It is not reported to be manufactured in Canada; however, between 100 and 1000 kg of the pigment were imported into the country in 2006 for use in the manufacturing of various coloured products.

Based on certain assumptions and reported use patterns in Canada, most of the substance ends up in waste disposal sites. Assumptions and input parameters used in making these estimates are based on information obtained from a variety of sources including responses to regulatory surveys, Statistics Canada, manufacturer’s websites and technical databases. About 5% is estimated to be released to water, and no releases are predicted to air and soil. Pigment Orange 38 presents very low experimental solubilities in water and octanol (new data: range of 10–100 µg/L). It is present in the environment primarily as micro-particulate matter that is not volatile, is rather chemically stable, and it has a tendency to partition by gravity to sediments if released to surface waters, and to soils if released to air.

Based on its physical and chemical properties, Pigment Orange 38 is expected to be persistent in the environment. However, new experimental data relating to its solubility in octanol and water suggest that this pigment has a low potential to accumulate in the lipid tissues of organisms. The substance therefore meets the persistence criterion but does not meet the bioaccumulation criterion as set out in the Persistence and Bioaccumulation Regulations. In addition, new experimental toxicity data for a chemical analogue, as well as new toxicity predictions that take into account revised estimates of bioaccumulation potential, suggest that saturated solutions of the substance do not cause acute harm to aquatic organisms.

For this screening assessment, a very conservative exposure scenario was selected in which an industrial operation (user of the pigment) discharges Pigment Orange 38 into the aquatic environment. The predicted environmental concentration in water was many orders of magnitude below predicted no-effect concentrations calculated for fish, daphnids and algae.

This substance will be included in the Domestic Substances List inventory update initiative, to be launched in 2009. In addition and where relevant, research and monitoring will support verification of assumptions used during the screening assessment.

Based on the information available, Pigment Orange 38 does not meet any of the criteria set out in section 64 of the Canadian Environmental Protection Act, 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 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 these substances identified as high priorities.

The substance Pigment Orange 38 was identified as a high priority for assessment of ecological risk as it was found to be persistent, bioaccumulative and inherently toxic to aquatic organisms and is believed to be in commerce in Canada. The Challenge for Pigment Orange 38 was published in the Canada Gazette on February 3, 2007 (Canada 2007a). 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 Orange 38 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.

Screening assessments under CEPA 1999 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

“64. [...] a substance is toxic if it is entering or may enter the environment in a quantity or concentration or under conditions that

Screening assessments examine scientific information and develops 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 July 2007. 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. The critical information and considerations upon which the assessment is based are summarized below.

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Substance Identity

For the purpose of this document, this substance will be referred to as Pigment Orange 38. This pigment belongs to the group of Naphthol AS III organic pigments, for which the basic entity is the anilide of 2-hydroxy-3-naphthoic acid (Table 1; Herbst and Hunger 2004).

Source: National Chemical Inventories (NCI), 2007: AICS (Australian Inventory of Chemical Substances); ECL (Korean Existing Chemicals List); EINECS (European Inventory of Existing Chemical Substances); ENCS (Japanese Existing and New Chemical Substances); PICCS (Philippine Inventory of Chemicals and Chemical Substances); TSCA (Toxic Substances Control Act Chemical Substance Inventory); ASIA-PAC (Combined Inventories from the Asia-Pacific Region).

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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., < 1 mg L^-1 to < 0.01 mg L^-1). 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 between molecules. For Naphthol AS compounds, this is achieved by the introduction of substituents like -CONH₂, -SO₂NH-, or -Cl in the molecule (Herbst and Hunger 2004; Lincke 2003). The resulting intermolecular bonds, in turn, generate a crystal structure that is at the origin of the stability of organic pigments (Lincke 2003).

As is the case with the majority of organic pigments, Naphthol AS III 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 2). 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 2 contains modelled and experimental physical and chemical properties of Pigment Orange 38 that are relevant to its environmental fate. Modelled estimates for these properties, as well as for rate constants and environmental partitioning 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 5.79 (KOWWIN 2000) implies that the solubility of Pigment Orange 38 is much higher in octanol than in water. Experimental solubility data, however, reveals that the substance is approximately equally soluble in the two solvents, indicating that the modelled partition coefficient is likely overestimated. The modelled estimate of log K_OW has therefore been disregarded for this assessment.

The experimental solubilities in Table 2 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 chemicals of known solubilities, they were determined to have a satisfactory degree of reliability for the present risk assessment.

^[1] NA: not applicable.
^[2] An acid-base property is required for a chemical to be an uncoupler of oxidative phosphorylation (section on Ecological Effects Assessment below). Values reported here are for the individual, solubilised molecule.

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Sources

Pigment Orange 38 is not known to be formed in nature. In Canada, no manufacture of this substance was reported in response to a CEPA section 71 survey notice for the 2006 calendar year in a quantity meeting the 100 kg reporting threshold. One company reported importing this substance for use in the manufacturing of various coloured products, with an importation volume in the 100–1000 kg/year range (Environment Canada 2007a).

Products containing Pigment Orange 38 may enter the country even if they are not identified as such in the section 71 survey. These quantities are currently not known. According to information from the United States Environmental Protection Agency (US EPA 2002), the import and production of Pigment Orange 38 in that country was in the order of 4.5–225 tonnes per year during 1986 and 1994, but no import/production was reported in 1990, 1998, and 2002. The Substances in Preparations in Nordic Countries (SPIN) database indicated its consumption in Denmark decreased from 6.8 tonnes in 2000 to 0.8 tonne in 2001 and 2002. Use was also reported in Sweden from 1999 to 2004 and in Denmark in 2003–2004, but quantities were not specified (SPIN 2006).

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Uses

According to submissions made under Section 71 of CEPA 1999, the only known current use pattern code for Pigment Orange 38 in Canada is as a colourant/pigment/stain/dye/ink (Environment Canada 2007a). In Canada, Pigment Orange 38 is regulated under the Food and Drug Act for use in one ink system for packaging material that would not contact food (Health Canada 2007).

Internationally, uses of Pigment Orange 38 include:

• as a pigment for plastics (CII 2007; Clariant 2007; Herbst and Hunger 2004);
• as a colourant for PVC, olefins and unsaturated polyester. It is also used for crayons and wax dispersions (Heitzman 2007; Herbst and Hunger 2004);
• as a colourant in printing inks (CII 2007; Herbst and Hunger 2004);
• in spin dyeing for colouring filament, fibres, and films made of secondary acetate (Herbst and Hunger 2004); and
• as a colourant in paints and coatings: this pigment is used in the areas of treatment and coating of fabricated metal products, machinery and equipment, or in areas of the construction industry (Herbst and Hunger 2004; SPIN 2006).

Uses in Canada as a colourant/pigment/stain/dye/ink are considered to be similar to those identified above. 

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Releases to the Environment

The company that reported importing this substance in 2006 did not indicate any releases of this chemical to the environment.

Mass Flow Tool

To estimate potential release of the substance to the environment at different stages of its life cycle, a mass flow tool was used. 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. Assumptions and input parameters used in making these estimates are based on information obtained from a variety of sources including responses to regulatory surveys, Statistics Canada, manufacturers’ websites and technical databases. 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 Organisation for Economic Co-operation 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 further down the life cycle. 

Results indicate that Pigment Orange 38 can be expected to be found largely in waste management sites (93%), 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 the transformation of the substance. Based largely on information contained in OECD emission scenario documents for processing and uses associated with this substance, it is estimated that 4.8 percent of Pigment Orange 38 may be released to water (Table 3).

Although no information is available on the volume of consumer products containing Pigment Orange 38 that are imported into Canada, it is anticipated that the quantities of Pigment Orange 38 that are released to the various environmental media would not be significantly different from those estimated here. However, the quantities sent for waste management would be higher if importation of these products were taken into consideration.

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Environmental Fate

The very low modelled vapour pressure and a negligible Henry's Law constant of ~ 10^-23 Pa·m³/mol for Pigment Orange 38 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.

Because of its very low solubility in water, this pigment may be considered not available for aerobic biodegradation. In addition, direct contact with biota probably does not occur when the pigment is sealed in the matrix of coloured items.

^[1] For Pigment Orange 38, information from the following OECD emission scenario documents was used to estimate releases to the environment and distribution of the substance as summarized in this table: (OECD 2006; 2004). Values presented for release to environmental media do not account for possible mitigation measures that may be in place in some locations (e.g., partial removal by sewage treatment plants). Specific assumptions used in derivation of these estimates are summarized in Environment Canada (2007b).
^[2] Applicable stage(s): production-formulation-industrial use-consumer use-service life of article/product-waste disposal.
^[3] Wastewater before any form of treatment

The particulate character of Pigment Orange 38 should have a key influence on its fate in the environment. Its particle size and density, which is 46 percent greater than that of water (cf.: Reynolds et al. 1987; Wetzel 2001), together with its chemical stability and low aqueous solubility, indicates 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

Persistence

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.

Industries that manufacture 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 colour to finished coatings, inks and paints.

The environmental persistence of Naphthol AS III pigments, such as Pigment Orange 38, 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-: Van der Zee 2002). Naphthol AS III 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 biotic reduction.

Based on the weight of evidence provided by the above-described literature, Environment Canada considers that Pigment Orange 38 meets the persistence criteria defined in the Persistence and Bioaccumulation Regulations (Canada 2000)

Bioaccumulation

There is a predictable relationship between K_OW and the bioconcentration factor in lipids (Mackay 1982). The ratio log (C_O/C_W) has been estimated from the experimental solubilities of Pigment Orange 38 in octanol (C_O) and water (C_W) (Table 2), 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 new set of BCF and BAF estimates for Pigment Orange 38 has been obtained from quantitative structure-activity relationship (QSAR)-based bioaccumulation models, using the experimentally based value log (C_O/C_W) in place of the overestimated log KOW by KOWWIN (2000). In addition, modelled BCF and BAF estimates have been obtained for a reasonably close analogue of Pigment Orange 38, namely Pigment Red 2 (CAS RN 6041-94-7), using a log (C_O/C_W) derived from experimental solubilities as well (Study Submission 2007b). Table 4 shows that the new modelled BCF and BAF estimates are well below 1000 (log BCF/BAF of 3) for both Pigment Orange 38 and its analogue, Pigment Red 2.

To identify chemical analogues, the guidance provided by the OECD (2007) has been generally followed. In the present case, the crystalline nature of the pigments (Re: OECD 2007), and therefore their solubilities in water and octanol, is a key factor when determining an analogue for use in read-across. Pigment Orange 38 and Pigment Red 2 have reasonably similar solubilities in water and octanol. For example, water and octanol solubilities of Pigment Red 2 are 5.4 and 8630 µg/L, respectively (Study Submission 2007b; solubilities of Pigment Orange 38 are given in Table 2).

Pigment Orange 38 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).

^[a] Pigment Orange 38 differs from Pigment Red 2 in two chemical features: an additional residue NHCOCH₃ on one terminal benzene ring, and a Cl substituted by a residue H₂NOC on the other terminal benzene ring.

 

^[b] Default value for non-ionizable azo pigments.

The above weight of evidence indicates that Pigment Orange 38 does not meet the bioaccumulation criterion (BCF, BAF > 5000) as set out in the Persistence and Bioaccumulation Regulations (Canada 2000).

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Potential to Cause Ecological Harm

A quantitative evaluation based on exposure and ecological effects was conducted for this pigment as part of the weight of evidence evaluation of its potential to cause harm.

First, a predicted environmental concentration (PEC) was determined based on an analysis of exposure pathways. Then, pertinent endpoint organisms were selected. For each endpoint organism, a conservative (reasonable worst-case) predicted no-effect concentration (PNEC) was derived. The PNEC is obtained by selecting the lowest critical toxicity value (CTV) for the organism of interest and dividing it by an application factor appropriate for the endpoint.

Ecological Exposure Assessment

No data have been found regarding concentrations of Pigment Orange 38 in the Canadian environment. The mass flow tool estimated that more than 90 percent of the mass of this pigment ends up in waste disposal facilities. Off-site chemical migration from these facilities is unlikely, or can be predicted to be minor, because of the negligible geochemical mobility of the pigment indicated by its very low solubility in water and in organic solvents. Consequently, it is anticipated that there are negligible releases associated with the waste management stage of this substance.

The mass flow tool estimated that up to about 5 percent of the total mass of Pigment Orange 38 in use could be released to water. In addition, available industrial information suggested that these releases would be generated by industrial users who employed the pigment to manufacture other coloured products (Environment Canada 2007a). The Industrial Generic Exposure Tool – Aquatic (IGETA) was selected to model the reasonable worst-case 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 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 PEC. The maximum mass, per year, purchased by an industrial facility (1000 kg: Environment Canada 2007a) was used to calculate the loading rate for the PEC estimation. Based on the IGETA results, the annual average PEC is 0.0056 mg/L in the receiving watercourse.

Ecological Effects Assessment

A – In the Aquatic Compartment

Although no experimental toxicity data were found for Pigment Orange 38, there are experimental toxicity data available for Pigment Red 2, which is a reasonably close analogue of Pigment Orange 38 (Table 4, CAS RN 6041-94-7). Furthermore, predicted ecotoxicity values were obtained using the experimental log (C_O/C_W) of Pigment Orange 38 (0.79). These experimental and predicted toxicity data (Table 5a and 5b) are considered reliable and have been used in the weight of evidence approach to determine the aquatic toxicity potential of this pigment.

Juveniles of Daphnia magna were exposed to a saturated solution of Pigment Red 2 for 48 hours under static conditions (Study Submission 2007c; Table 5a). The pH was maintained between 7.7 and 8.1, the temperature oscillated between 18 and 22°C and dissolved oxygen ranged between 8.1 and 8.9 mg/L. The test water had a hardness of ~ 250 mg CaCO₃/L. An experimental treatment consisted of five specimens placed in a 50-mL glass beaker. One test concentration of 100 mg/L was established, using four replicates per test. In order to make a saturated solution, a stock solution of 100 mg Pigment Red 2 in one litre of test water was made. The stock solution was shaken at room temperature at 20 rpm for 24 hours (rotating shaker). Undissolved particles were removed by filtration on 0.45-µm membrane. This approach followed the guidance provided by the OECD for sparingly soluble substances (OECD 2000). The chemical was not measured during the test. No biologically significant effects (immobilization) were observed at saturation.

The degree of reliability of this study was deemed satisfactory for the present assessment. Notably, a reference toxicant was used and good laboratory practices (GLP) were followed.

Aquatic toxicity predictions, recalculated using log (CO/CW), were obtained using the ECOSAR program (ECOSAR 2004), which is based on the assumption that Pigment Orange 38 has a narcotic mode of action (MOA) similar to that of phenols. However, the ASTER (1999) model predicted the MOA to be the “uncoupling of oxidative phosphorylation” for this pigment, in addition to narcosis. An application factor of 100 (Environment Canada 2003) was therefore applied to extrapolate from baseline toxicity to this more toxic MOA. It should be noted that the above MOAs were predicted for the solubilized molecule (i.e., Table 1). Table 5b presents these modelled ecotoxicity results.

The model data are all well above the estimated water solubility of the substance, and therefore are consistent with results of the experimental acute toxicity test, which indicate no effects at saturation.

^[1] Immobilization

 

 

B – In Other Media

No empirical or predicted effects data for non-aquatic organisms were identified for this compound. However, given the current release scenarios and quantities used in Canada, exposures through soils, suspended solids and sediment are not likely to be significant at this time.

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 the precautionary principle as required under section 76.1 of CEPA 1999. Particular consideration has been given to risk quotient analysis, persistence, bioaccumulation, toxicity, sources and fate in the environment.

Pigment Orange 38 is determined to be persistent based on published evidence. 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, low modelled BCFs, and low experimental BCFs determined for a number of analogous organic pigments (MITI 1992).

Newly acquired empirical data for a chemical analogue, as well as modelled aquatic toxicity results, also suggest that this pigment is not very harmful, indicating no acute effects at saturation. There is uncertainty that effect concentrations are greater than the solubility of the compound; the OECD (2000) protocol is currently the best available approach for the evaluation of sparingly soluble substances.

Since Pigment Orange 38 is considered a persistent but not bioaccumulative substance, 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.

In view of the limited amount of empirical Canadian exposure data, the IGETA model was used, along with industrial information, to estimate worst-case PECs. Three categories of organisms were considered for derivation of PNECs: fish, daphnids and algae. An application factor of 100 was used to extrapolate from acute to chronic effects, and from laboratory species to different species in the field. CTVs and PNECs are based on the most conservative effect values and are presented in Table 6. The resulting risk quotients are in all cases much less than 1, suggesting that the substance is unlikely to be present at concentrations that could cause harm to aquatic organisms.

Given the high persistence of the substance in the environment, chronic exposure is likely to occur. However, in view of the absence of any acute effects at saturation, and taking into account the relatively low solubility of the substance (25 µg/L) and its low bioaccumulation potential, long-term environmental exposure to the substance is not expected to cause adverse effects to aquatic organisms.

Considering these findings and given that this chemical is imported in relatively low quantities, it is concluded that Pigment Orange 38 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 Orange 38.

Long-term stability of Pigment Orange 38 in anoxic sediments, as well as in anoxic layers in the soil column of waste disposal sites, is largely unknown.

Nanoscale materials are informally defined as substances having at least one dimension less than 100 nm. There is increasing evidence 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 Orange 38, typically have a certain proportion of their particle size spectra in the nanoparticle range (e.g., Table 2). 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 Orange 38 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.. Similarly, it is concluded that Pigment Orange 38 is persistent but does not meet the criterion for bioaccumulation as set out in the Persistence and Bioaccumulation Regulations (Canada 2000).

Therefore it is concluded that Pigment Orange 38 does not meet the definition of toxic as set out in paragraph 64(a) of the Canadian Environmental Protection Act, 1999.

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Appendix 1: Robust Study Summaries

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.
^[**] The reliability code for ecotoxicological studies of DSL categorization is used.

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.
^[**] The reliability code for ecotoxicological studies of DSL categorization is used.