|
|
|
||||
|
||||||
|
|
|
|
|
||
|
|
|
|
|
|
||
|
||||||
 |
        |
    |
Substance Profiles for The
Challenge
Toluene Diisocyanates
The Canadian Environmental Protection Act, 1999 (CEPA 1999) required the Minister of Health and Minster of the Environment to categorize the approximately 23 000 substances on the Domestic Substances List (DSL). Categorization involved identifying those substances on the DSL that are a) considered to be persistent (P) and/or bioaccumulative (B), based on criteria set out in the Persistence and Bioaccumulation Regulations (Government of Canada, 2000), and “inherently toxic” (iT) to humans or other organisms, or b) that present, to individuals in Canada, the greatest potential for exposure (GPE). Further to this activity, the Act requires the Minister of the Environment and the Minister of Health to conduct screening assessments of substances that meet the categorization criteria. A screening assessment involves a scientific evaluation of available information for a substance to determine whether the substance meets the criteria set out in section 64 of CEPA 1999. Based on the results of a screening assessment, the Ministers can propose taking no further action with respect to the substance, adding the substance to the Priority Substances List (PSL) for further assessment or recommending the addition of the substance to the List of Toxic Substances in Schedule 1 of CEPA 1999 and, where applicable, the implementation of virtual elimination of releases to the environment. A number of substances have been identified by the Ministers as high priorities for action based on the information obtained through the categorization process. This includes substances:
Based on a consideration of the ecological and/or human health concerns associated with these substances, and the requirement under section 76.1 of CEPA 1999 for the Ministers to apply a weight of evidence approach and the precautionary principle when conducting and interpreting the results of an assessment, sufficient data are currently available to consider these substances as meeting the criteria under Section 64 of CEPA 1999. As such, the Ministers have issued a Challenge to industry and other interested stakeholders through publication in Canada Gazette Part I December 9, 2006 to submit, within the timelines stated in the Challenge section of this publication of this document below, specific information that may be used to develop and benchmark best practices for risk management and product stewardship. The Toluene diisocyanate substances were identified as high priorities for action as they were determined to have a high potential for exposure to individuals in Canada (GPE or IPE), and are considered to present a high hazard to human health. The technical human health and ecological information that formed the basis for concern associated with this substance is contained in Appendices I and II, respectively. Substance Identity For the purposes of this document, the term Toluene diisocyanate (TDI) is used to refer to all three substances in this document.
All three Chemical Abstract System numbers representing the two isomers of Toluene diisocyanate (TDI) and mixtures of the two isomers were notified to the DSL. Depending on the TDI compound, between 6 to 9 companies notified these substances to the Domestic Substances List, reporting from 12,000 to 30,200 tonnes in commerce in 1986. These compounds were notified for a variety of uses including; adhesives, binders, sealants, formulation components for polymers, paint and coating additives and in a variety of industrial sectors including; automotive, aircraft, and watercraft, electrical and electronic products, paint and coating and the plastic and synthetic coatings sectors. Recent information on TDI indicates that it is used primarily in the production of polyurethane foams. The flexible and semi-rigid polyurethane foams have a variety of industrial applications including use in furniture, carpet underlay, bedding, and by the transportation sector (e.g. panels, padding and bumpers). The rigid polyurethane foams also have applications reported for thermal insulation in housing, refrigerated trucks, rail cars and containers, refrigerators and freezers, and in pipe insulation. THE CHALLENGE
Respecting direction under section 76.1 of CEPA 1999, information obtained during conduct of categorization is sufficient to conclude that criteria under Section 64 of CEPA 1999 are met for this substance in that it “may enter the environment in a quantity or concentration or under conditions that constitute or may constitute a danger in Canada to human life or health”. As such, the Ministers are prepared to recommend to the Governor in Council that this substance be added to the List of Toxic Substances in Schedule 1 of CEPA 1999 with the intent of initiating the development of risk management measures taking into account socio-economic considerations. The measures will be subject to review in light of new scientific information, including monitoring and ongoing assessment activities. Section 71 Notice Information needed for improved decision-making with regard to risk assessment and management of this substance is being gathered using section 71 of CEPA 1999. This notice applies to any person who, during the 2006 calendar year, manufactured or imported a total quantity greater than 100 kilograms of the substance, whether alone, in a mixture, in a product or in a manufactured item. The 2006 information mandated through the notice relates to, among other things, quantity of the substance imported, manufactured or used, types of uses of the substance, and releases of the substance to the environment. Copies of the section 71 notice and guidance on how to comply with it are available from the Government of Canada Chemicals Portal (www.chemicalsubstanceschimiques.gc.ca/en/index.html), or from the contact provided below. Responses to the section 71 notice must be received at the address provided below by June 5, 2007. Opportunity to Submit Additional Information on Current Uses and Existing Control Measures to Inform the Risk Management Approach for this Substance The Ministers of Health and Environment are inviting the submission of additional information that is deemed beneficial by interested stakeholders, relating to the extent and nature of the management/stewardship of substances listed under the Challenge. Organizations that may be interested in submitting additional information in response to this invitation include those that manufacture, import, export or use this substance whether alone, in a mixture, in a product or in a manufactured item. Additional information is being invited in the following areas:
A questionnaire is available which provides a detailed template as an example for the submission of this information. Guidance on how to respond to the challenge questionnaire is also available. Interested stakeholders are invited to provide available additional information, recognizing that not all questions in the questionnaire may be relevant to a particular substance, use, or industrial sector. Copies of the questionnaire and associated guidance are available from the Government of Canada Chemicals Portal (www.chemicalsubstanceschimiques.gc.ca/en/index.html), or from the contact provided below. Responses to the questionnaire should be received at the address provided below by June 5, 2007. Request for Documents and Submission of Information Documents and instructions may be requested from the following contact. Information in response to the above Challenge must be submitted to this address. DSL Surveys Coordinator Appendix
I
Introduction Under the Canadian Environmental Protection Act, 1999 (CEPA, 1999), Health Canada undertook to categorize all substances on the Domestic Substances List (DSL) to identify those representing the greatest potential for human exposure (GPE) and those among a subset of substances considered persistent (P) and/or bioaccumulative (B) by Environment Canada that are also considered to be “inherently toxic” to humans. In order to efficiently identify substances that represent the highest priorities for screening assessment from a human health perspective, Health Canada developed and applied a Simple Exposure Tool (SimET) to the DSL to identify those substances that meet the criteria for GPE, Intermediate Potential for Exposure (IPE) or Low Potential for Exposure (LPE), and a Simple Hazard Tool (SimHaz) to identify those substances that pose a high or a low hazard. Mixed isomers of toluene diisocyanate, CAS No. 26471-62-5, are considered to meet the criteria for GPE under SimET and for high hazard under SimHaz. The 2,4- and 2,6- isomers of toluene diisocyanate, when considered separately were each deemed to meet the criteria for IPE under SimET and high hazard under SimHaz. This document summarizes the currently available information used to support the inclusion of these substances in the Challenge. Exposure Information from Health Related Components of DSL Categorization As mentioned above, SimET was developed and used to identify substances on the DSL considered to represent GPE. This approach was based on three lines of evidence: 1) the quantity in commerce in Canada, 2) the number of companies involved in commercial activities in Canada (i.e., number of notifiers), and 3) the consideration by experts of the potential for human exposure based on various use codes. The proposed approach was released for public comment in November 2003 and also enabled designation of substances as presenting an Intermediate (IPE) or Lowest Potential for Exposure (LPE), based on criteria for quantity and nature of use (Health Canada, 2003) Results of the Application of SimET Mixed isomers of toluene diisocyanate have been determined to be GPE and the 2,4- and 2,6- isomers of toluene diisocyanate, when considered separately were each deemed to meet the criteria for IPE under SimET based on a consideration of the DSL nomination information listed below. Nomination Information for DSL Quantity in Commerce The quantity of
26471-62-5 reported to be manufactured, imported or in commerce in Canada during
the calendar year 1986 was 24 000 000 kg Number of Notifiers The number of notifiers for
the calendar years 1984-86 for 91-08-7 was six. Use Codes and Description The following DSL use codes have been identified for the substances represented by the three CAS numbers: CAS No. 26471-62-5
CAS No. 584-84-9
CAS No. 91-08-7 (Note: pure 2,6-toluene diisocyanate is not commercially available)
Potential Uses in Canada Mixtures of 2,4- and 2,6-toluene diisocyanate
(TDI) isomers dominate industrial use of TDI. TDI is reacted with a polyol in the presence of surfactant, catalyst and blowing agent to form polyurethane foam (PUF). Production of PUF accounts for about 90% of TDI supply, the majority of which is used in flexible foam. The distribution of use of flexible PUF is as follows, furniture 32%, transportation 30%, carpet underlay 20%, bedding 10%, packaging 8%, other 10% (Chemexpo, 1999). Rigid PUF panels are used for thermal insulation in housing, refrigerated trucks, rail cars and containers, refrigerators and freezers, and in pipe insulation. Semi-flexible and semi-rigid PUF are used in automotive panels, padding and bumpers. TDI may be used as part of the isocyanate component, together with other isocyanates in semi-rigid and semi-flexible foams. (NLM 2006, Allport et al., 2003) TDI is used for producing material other than PUF in approximately these proportions: polyurethane coatings 4%, cast elastomers 2%, sealants 2%, miscellaneous including fibres 2%. (Chemexpo, 1999) TDI or a TDI adduct is used in polyurethane-modified alkyd paints and coatings including automotive and marine paint, wood varnish, floor treatment, wire and powder coating. Castable urethane elastomers are used in adhesives, sealants, automotive parts, shoe soles, wheels, pond liners, blood bags, and other products. Sealants and adhesives may be produced from TDI or a TDI adduct. TDI is used in the production of coatings for textiles for durability and waterproofing and in the production of polyurethane used to make the fabric Spandex. TDI may be used as a cross-linking agent in nylon 6 production. (NLM 2006, NTP 2005) Methylene diisocyanate has replaced TDI in some applications. The extent of the substitution is not known. Hazard Information from Health Related Components of DSL Categorization Simple Hazard Tool (SimHaz) SimHaz is a tool that has been used to identify, among all of the approximately 23 000 substances on the DSL, those considered to present either high or low hazard to human health based on formalized weight of evidence criteria and/or peer review/consensus of experts. This tool has been developed through extensive compilation of hazard classifications of Health Canada and other agencies and consideration of their robustness based on availability of transparent documentation of both process and criteria (Health Canada, 2005). Results of the Application of SimHaz The 2,4- and 2,6- isomers and mixed isomers of toluene diisocyanates are considered to be potentially high hazard substances based on the following classifications for carcinogenicity. The International Agency for Research on Cancer (IARC) has classified toluene diisocyanate as Carcinogenicity Group 2B (possibly carcinogenic to humans). IARC noted that there is inadequate evidence for the carcinogenicity of toluene diisocyanates in humans, but there is sufficient evidence for the carcinogenicity of toluene diisocyanates in experimental animals (IARC, 1999). The European Commission (EC) has classified toluene diisocyanate as Category 3 for carcinogenicity (Causes concerns for humans owing to possible carcinogenic effects) (European Commission, 1997; European Commission 2004; ESIS, 2006). The United States National Toxicology Program (NTP) has classified toluene diisocyanate as reasonably anticipated to be a human carcinogen based on sufficient evidence of carcinogenicity in experimental animals (NTP, 2005). Uncertainties SimET and SimHaz have been developed as robust tools for effectively identifying substances from the DSL considered to be human health related priorites for further consideration. It is recognized that they do not include a number of elements normally considered in a human health risk assessment such as a comprehensive characterization of exposure and hazard, a comparison of exposure metrics to hazard metrics and a detailed analysis of uncertainties. However, as a result of the combination of the severe hazard properties of these substances and their high potential for exposure to humans, evaluation of whether there is a need for preventative and protective actions is required. References Allport, D.C., Gilbert, D. and Outterside, S. eds. 2003. MDI and TDI: Safety, Health and the Environment: A Source Book and Practical Guide. Chichister, England, Wiley. Chemexpo. 1999. Chemical Profile on Toluene diisocyanate. Cited in
NLM, NIH Hazardous Substances Data Bank 2006. Toluene Diisocyanate. National
Library of Medicine, National Institutes of Health. European
Commission 1997. Toluene di-isocyanates. Summary Record. Commission Working
Group on the Classification and Labelling of Dangerous Substances. Meeting at
ECB Ispra, 15-21 October 1997. ECBI/51/97 - Rev. 3 European Commission 2004. 2-methyl-m-phenylene diisocyanate. 4-methyl-m-phenylene diisocyanate. M-tolylidene diisocyanate. Commission Directive 2004/73/EC of 29 April 2004. Annex 1A. Official Journal of the European Communities 16.6.2004. L 216/49. http://ecb.jrc.it/DOCUMENTS/Classification-Labelling/ATPS_OF_DIRECTIVE_67-548-EEC/29th_ATP.pdf ESIS
2006. CAS No. 91-08-7. 2-methyl-m-phenylene diisocyanate. CAS No. 584-84-9.
4-methyl-m-phenylene diisocyanate. CAS No. 26471-62-5. M-tolylidene
diisocyanate. ESIS Version 4.50. European Chemical Substances Information
System. Health Canada 2003. Proposal for Priority Setting for Existing Substances on the
Domestic Substances List under the Canadian Environmental Protection Act, 1999:
Greatest Potential for Human Exposure. Health Canada 2005. Proposed Integrated Framework for the Health-Related Components of Categorization of the Domestic Substances List under CEPA 1999, http://www.hc-sc.gc.ca/ewh-semt/alt_formats/hecs-sesc/pdf/contaminants/existsub/framework-int-cadre_e.pdf IARC
1999. IARC Monographs on the Evaluation of Carcinogenic Risks to Humans. Volume
71. Re-evaluation of some organic chemicals, hydrazine and hydrogen peroxide
(part two). World Health Organization. International Agency for Research on
Cancer. Lyon, France. Toluene Diisocyanates. p.865-879. NLM,
NIH Hazardous Substances Data Bank 2006. Toluene Diisocyanate. National Library
of Medicine, National Institutes of Health. NTP
2005. 11th Report on Carcinogens. US National Toxicology Program.
Department of Health and Human Services. Substance Profile: Toluene
Diisocyanate. Ontario Ministry of the Environment, 2005. Ontario Air Standards for Toluene Diisocyanate (TDI) Appendix
II
Introduction The information in this document will form the basis of a screening assessment under section 74 of CEPA, 1999. Data relevant to an ecological screening assessment were identified in original literature, review documents, commercial and government databases prior to December 2005. Properties and characteristics may also have been estimated using Quantitative Structure Activity Relationship (QSAR) models. Model predictions for all 3 TDI substances were identical, and therefore differences between TDI isomers were not observed in the output from these models. Physical and Chemical Properties Table 1 contains experimental and modelled physical-chemical properties of Mixed Isomers of toluene diisocyanate which are relevant to the environmental fate of all 3 TDI compounds. Table 1. Phys-chem properties for commercial mixture of 2,4 TDI and 2,6-TDI (80/20).
TDI is insoluble in water (hydrophobic) and is miscible in a number of common organic solvents including; alcohol, monoethyl ether, ether, acetone, carbon tetrachloride, benzene, chlorobenzene, kerosene and olive oil. TDI is highly volatile (IPCS PIM 1997). TDI has a characteristic odour which allows it to be detected readily (odour recognition at 2.10 ppm), however, at the maximum recommended concentration (0.02 ppm) TDI is not detectable by its smell (HSDB 2003). Manufacture, Importation, and Uses Manufacture and Importation Refer to Appendix I Uses Refer to Appendix 1 Releases, Fate and Presence in the Environment Releases Toluene diisocyanates are synthetic organic compounds and are not known to naturally occur in the environment (IPCS PIM 1997). Based on information collected from the National Pollutant Release Inventory (NPRI; see Table 2) most releases reported are to air, with no releases reported directly to water or land (excluding data collected by NPRI on disposal and recycling). The number of facilities reporting to NPRI has remained fairly constant from 1994-2002, with 27 to 38 facilities reporting in a given year. Table 2. Summary of Releases to Air Reported for TDI to NPRI 1999-2002
(Source NPRI)
Fate Environmental fate modelling requires knowledge of the physical-chemical properties of the TDI isomers. Table 3 reports the values relevant to assess the fate of TDI in a unit world environment. The extent to which modelling of the environmental distribution and partitioning between the various media is useful for this group of chemicals is questionable, by virtue of the reactivity of diisocyanates in water, soil (particularly moist soil) and sediment. Table 3: Results of the Level III fugacity modelling (EPIWIN V3.04)
Multimedia modelling of the partitioning of TDI indicates that, depending on the medium to which they are released, these compounds can partition to an appreciable extent into air, water and soil. When released to air the principle medium of initial released (based on NPRI data), it is expected that some TDI will partition to water and soil. Given that hydrolysis was not considered when generating the Level III fugacity results, the extent to which these results reflect the partitioning behaviour of these substances in the environment is questionable. In water, soil and sediment, and under conditions typical to the environment, it is expected that TDI’s affinity to react with amines more strongly than with water, combined with its relative insolubility in water, would result in reactions that lead to the formation of a solid crust of polyureas, encasing unreacted TDI. Hydrolysis in the presence of water in these three media, which acts as a catalyst for further reactions between the diisocyantes and amines, is expected to be the primary driver in the fate of TDI in the environment. The role hydrolysis plays in the environmental fate of these chemicals is described in further detail in the Rationale for P, B and iT Status section. Presence in the Environment As a result of its low aqueous solubility and inherent reactivity with water it is not expected that significant concentrations of TDI would be found in the water (or moist soil and sediment), and this has been seen to be the case. In fact, TDI has not been detected in any aquatic studies (Pemberton and Tury 2004). Evaluation of P, B and iT Properties Environmental Persistence The fate and behaviour of TDI in the atmosphere is an important factor influencing the persistence of these compounds in the environment. TDI is volatile, although emissions are generally regarded as low from industrial processes (IPCS PIM 1987, Tury et al 2003). Indirect photolytic degradation as a result of photogenerated hydroxyl radicals has been demonstrated to be a significant degradation pathway for these compounds (Pemberton and Tury 2004). Surprisingly, despite the reactivity of TDI with water, Tury et al (2003) observed that reaction (i.e. hydrolysis) with atmospheric water was not significant. There is good agreement between the modelled and experimental atmospheric half life data for these compounds with AOPWIN v1.91 predicting a half-life of 1.7 days using the default global average concentrations for hydroxyl radicals 1.5E6 OH radicals/cm3 (12h day). Experimentally Tury et al (2003) reported a half life of 1.4 days for TDI based on experimental reaction rates and also noted that photooxidation did not appear to lead to the formation of toluene diamines (TDA) (<0.05%) (Tury et al 2003). Atkinson (1989) also calculated a half life in air for the three TDI compounds of 1.5 days based on experimental reaction rates with hydroxyl radicals (Atkinson, 1989). Based on the evidence available, it is believed that TDI should not be considered persistent in the atmosphere based on reactions with photogenerated hydroxyl radicals. The TDI compounds also do not appear to persist in water, soil, or sediment, and in fact, their residence time in these media may be quite short, relatively speaking. However, given the reactive nature of these compounds the degradation products from these reactions in the environment, namely polyureas and toluene diamines (TDA) were also examined. TDI compounds are considered transient in media where water is present (e.g. water, moist soils, sediment) with half-lives of under a minute noted (Yakabe et al, 1999). However, the reaction of an amine with isocyanate is faster then the hydrolysis reaction of water with isocyanate, which, in the case of a diisocyanate like TDI, leads primarily to reactions forming polyureas (Yakabe et al 1999, Pemberton and Tury 2004). Polyureas are generally considered to be inert, insoluble solids; albeit persistent for millennia. As previously described, under conditions typical to the environment it is expected that TDI’s affinity to react with amines more strongly than with water, and its relative insolubility in water, would result in reactions that lead to the formation of a solid crust of polyureas encasing the unreacted material (TDI). This crust serves to limit the contact of the unreacted TDI with the surrounding water, while simultaneously limiting the egress of amine, thereby enhancing the reactions with amines within this encrusted region, which then leads to an even higher yield of polyureas (Pemberton and Tury 2004). This phenomenon has been observed in a number of studies including those by Yakabe et al (1999) and Tury et al (2003). It is well documented in numerous studies that the aromatic diisocyanates will hydrolyze and react rapidly in both water and soil (Pemberton and Tury 2004, Heimbach et al 1996, Yakabe et al 1999, Tury et al 2003). In addition, hydrolysis predictions generated using the HYDROWIN model (part of the EPIWIN suite) are in agreement with the conclusions of the experimental data. Although the model does not predict a hydrolysis half-life, it does state that substance contains an isocyanate group and that the t1/2 is expected to be < 10 minutes (Hydrowin v1.67 results). As noted, the major transformation product of TDI is inert polyureas, which are both insoluble and anticipated to persist in the environment for millennia. Polyureas have been identified as polymers of low ecological concern, both because of their inert characteristics, and based on the expectation that they are not bioavailable, and thus unlikely to accumulate in organisms and food chains, and subsequently exert effects, in the environment. Besides polyureas, however, there is also the potential for TDA to form as a by-product of the hydrolysis of TDI, although the formation of TDA is generally considered negligible relative to the formation of polyureas in aqueous media. Yakabe et al (1999) conducted a series of experiments to determine under which scenarios it can be anticipated that TDA may form to a significant extent. Overall, Yakabe et al (1999) observed that TDA production is markedly less under static, unstirred conditions, and that only with good agitation and low loadings of TDI is TDA a major reaction product. In all other cases, the major reaction product was a solid material, found to be polyurea under further analysis (Yakabe et al 1999). I should also be noted that the scenarios which resulted in a significant, albeit low, concentration of TDA in the water column would occur under what would normally be considered unnaturally high dispersion/agitation, and therefore, are not likely to occur in nature. Nonetheless, appreciable TDA yields were noted with loadings less then 10 mg/L, therefore TDI under certain release scenarios could be viewed as a significant source of TDA to aquatic environments. As a result, it was deemed necessary to consider the persistence of TDA in its evaluation of TDI compounds. Studies provided showed extensive biodegradation under various OECD test protocols. Data provided from the panel showed that for both TDA and MDA (a close analog of TDA) > 70% DOC removal was observed in OECD 302B and 302C inherent biodegradability tests performed by BASF and reported in the European Union Risk Assessment for 4, 4-MDA. Substances such as 2,4-TDA were observed to have 93-100% DOC removal rate in 6 days, and >70% DOC removal in 3 days for 4,4-MDA (BASF AG, 1988, BASF AG, 1993 and ECB 2001). Based on the weight of evidence approach developed for categorization, these TDA substances would not meet the persistence criteria. As a result, it is believed that these TDA chemicals are not persistent based on experimental and modeled data. Table 3a. Modeled Data for Persistence of TDI
The empirical and modelled data (Table 3a) demonstrate that these TDI substances do not meet the persistence criteria (half-lives in soil and water ≥ 182 days/ air ≥ 2 days) as set out in the Persistence and Bioaccumulation Regulations (Government of Canada 2000). Potential for bioaccumulation It is expected that these TDI substances do not bioaccumulate because their tendency to hydrolyze rapidly makes their uptake and accumulation virtually impossible. The 3 Toluene diisocyanates were not categorized as bioaccumulative, and this decision was reaffirmed by the additional information provided by industry as well as additional literature searches performed. While the models employed for categorization are likely not appropriate for highly reactive chemicals such as TDI in aqueous media, it is useful to summarize them to further the weight of evidence. Table 4a and b presents the bioaccumulation data for both TDI and TDA Table 4a. Empirical Data for Bioaccumulation of TDA
Table 4b. Modeled Data for Bioaccumulation of TDI
The BCF models predicted a BCF in the range of BCF 151-1183 and a BAF of BAF 380. All of which indicate that these substances have a low potential for bioaccumulation in aquatic organisms. The predicted log Kow for these substances is approximately 3.74. However, it is worth noting that both the log Kow predictions, and the BCF models which depend them, likely overestimate the lipophilicity of these compounds because of the rapid reactivity and hydrolysis in water. The Kow model KOWWIN v1.67 while providing a prediction also notes in its output that that isocyanates hydrolyze and therefore the estimates are questionable. This rapid hydrolysis with water also limits the determination of log Kow experimentally, and as a result reliable experimental log Kow’s are not readily available in the literature. A log Kow of 3.4 was determined experimentally using OECD methods, however, it was of uncertain significance in terms of TDI’s environmental fate and behaviour, again, because of TDI’s reactivity in the aquatic environment (Yakabe et al 1999, Pemberton and Tury 2004). TDI is expected to not only hydrolyze rapidly into its transformation products, making TDI generally unavailable to aquatic organisms, but that given the highly reactive properties of diisocyanates, the parent compounds are likely metabolized/degraded at rates significant enough to counter any potential for bioaccumulation or biomagnification. In addition, they are also likely hydrolyzed in the gastrointestinal tract, thereby reducing the potential for uptake of the parent chemical from the gut. TDI substances have been found to be highly reactive in body fluids, with a half life of less then 30 seconds in serum and less then 20 minutes in stomach contents (IPCS EHC 1987). TDI’s react easily with moist mucous membranes, forming primary amines, ultimately reacting further with TDI to form Urea compounds (Yakabe et al 1999, Pemberton and Tury 2004, IPCS PIM 1997). The IPCS (1997) reports that some studies on 2,6-TDI in rats showed that in the gastrointestinal tract primarily polymers were formed, and furthermore that most TDI derived material was eliminated by the organism (IPCS PIM 1997). It is believed that TDI reacts with the tissues they contact rather than being absorbed and distributed in the body (IPCS EHC 1987). The transient existence of TDI in water also makes estimating bioaccumulation experimentally equally difficult. As discussed previously, due to the rapid transformation of TDI into primarily inert polyureas, and in some cases TDA, bioaccumulation of TDI is not expected in organisms. However, there was concern with the potential accumulation of some of products of hydrolysis. It was determined during categorization that the polyureas are a group of low concern polymers with no, or negligible, potential for bioaccumulation in organisms and food chains. There was, however, a concern over the formation of toluene diamines (TDA) as a result of the hydrolysis of TDI in certain situations, primarily rapid dispersion at low release concentrations; other scenarios tended to lead overwhelmingly towards the formation of inert polyureas as opposed to TDA (Pemberton and Tury 2004, Yakabe et al 1999). Regardless of the extent of TDA formation from the reaction of TDI in water, experiments investigating the bioaccumulation of 2,4-TDA (CAS 95-80-7) found a BCF of <5 to <50. While these BCF are based on nominal concentrations, and therefore likely underestimating the true BCF, it is still provides strong evidence that TDA compounds themselves are not bioaccumulative (MITI 1992). In addition, Log Kow predictions for these compounds are predicted to be very low (log Kow 0.16) which indicates these substances are not likely to accumulate in organisms in the environment. In light of this information, it is believed that given the highly reactive properties of diisocyanates, that the parent compounds (TDI) are likely metabolized/degraded at rates significant enough to counter any potential for bioaccumulation or biomagnification. In addition, they are likely hydrolyzed in the gastrointestinal tract, thereby reducing the potential for uptake of the parent chemical from the gut. The weight of evidence indicates that these substances do not meet the bioaccumulation criterion (BCF, BAF ≥ 5000) as set out in the Persistence and Bioaccumulation Regulations (Government of Canada, 2000). Ecological Effects of TDI compounds In the Aquatic Compartment Due to the anticipated transient existence of TDI in aqueous media, including moist soils, it is unlikely that ecological effects will be elicited by the parent TDI compounds. It is likely that test results for TDI in aquatic environments are actually testing the toxicity of the degradation products of TDI. Data on the ecological effects of TDI to sediment dwelling organisms is limited, but reactivity in this medium is expected to be similar to that observed in both the aquatic and moist soil environments. It is anticipated that TDI released to water will primarily form inert polyureas which have the potential to be deposited to sediment, forming an inert component of the sediment strata. While persistent, laboratory and field studies on these inert polyureas have indicated that in small quantities they pose virtually no potential for adverse impacts on the aquatic environment (Heimbach et al 1996). A submission by the Aromatic diisocyanates panel of the American Chemistry Council (ACC during DSL categorization addressed the issue of ecotoxicity of the aromatic Diisocyanate compounds, which include TDI. The panel’s proposal argued that because of the rapid hydrolysis of these substances any potential toxicity would be mitigated, and that this mitigation would be unlikely to be predicted by any of the QSARs employed for categorization (Tury et al 2003, Heimbach 1996, Yakabe et al 1999). Environment Canada agrees with this assessment by the panel. However, because of the expected rapid degradation of the parent in the aquatic environment, it was felt necessary to examine the hydrolysis degradation products for potential aquatic toxicity. Tables 5a and b presents the ecotoxicity data, both modeled and experimental for TDI and its degradation products to aquatic organisms. Table 5a. Empirical Data for TDI and its degradation products
Table 5b. Modeled Data for TDI and its degradation products
Results from the short term studies of TDI were considered reliable, although it is noted repeatedly in many of the studies that it is in fact the degradation products (hydrolysis) whose toxicity is being measured in the bioassays. In toxicity studies where TDA was measured, to establish how much had formed, levels of only 4-16 mg/l were measured, which is considerably lower then the LC50 values reported for these compounds to fish (Pemberton and Tury 2004). These levels of TDA are in the range of concentrations where effects to Daphnia magna have been observed in at least one study, and model predictions (Pederson et al 1998, Environment Canada QSAR predictions). While TDA appears to be toxic at quite low levels to Daphnia magna, the EC50 observed still falls outside the criteria for acute toxicity developed for inherent toxicity as part of categorization of ≤ 1 mg/L. As expected, there was an increased toxicity to fish when TDI was dispersed into the test medium via high speed shearing, which enhances the formation of TDA. However, these conditions do not reflect those expected in the natural environment and are, in that sense, of limited relevance (Pemberton and Tury 2004). Unfortunately, reliable long term studies on the toxicity of TDI to aquatic organisms are currently lacking; although it is expected that the rapid disappearance of TDI in the aqueous media would have a negligible impact on the overall ecotoxicity of the compounds. In the tests which are available studying the long term toxicity of TDI, it was observed that at a value of 10 mg/l, damage to the skin occured, this was attributed to irritation to the fish’s skin caused by direct contact with TDI (Pemberton and Tury 2004) Based on the available information TDI and its degradation products are expected to exhibit low to moderate acute toxicity to aquatic organisms. In Other Media Ecotoxicity data available for TDI in the terrestrial environment are limited. However, generally these compounds were found to have no acute effects to earthworms and the plants which were tested. NOEC’s, EC50 and LC50 results were all observed to be >1000 mg/kg dw soil by Van der Hoeven et al (1992a,b). Here as well, it is anticipated that any ecotoxicity noted is due to soluble reaction products such as TDA. Studies described in the GIL Report (2004) indicate that ecotoxicity of TDA to the plants Avena sativa and Lactuca sativa was higher, with EC50’s of 320 and 1000 mg/kg dw soil reported, respectively (GIL Report, 2004). The European Union’s IUCLID (2000) dataset cites a number of oral LC50 test results for birds (Agelaius phoenicens) to 2,4-TDI and 2,6-TDI at >= 100 mg/kg body weight. Toxic effects from inhalation and dermal contact are better understood endpoints for TDI, however, these data have generally been produced to address human health concerns, occupational exposure in particular, and do not necessarily reflect exposure pathways anticipated for terrestrial non-human organisms in the environment. Potential to Cause Ecological Harm Based on the available information, the three TDI substances do not persist in the environment and are not bioaccumulative. Information on concentrations of toluene diisocyanate in the environment has not been identified at this time. The experimental and modeled ecotoxicological data does indicate that while toluene diisocyanate could cause low to moderate harm to aquatic organisms, at relatively low concentration in the water. Information on potential impacts in other environmental compartments has not been identified. 6. References Arnot, J.A. and Gobas, F.A.P.C. 2003. A Generic QSAR for Assessing the Bioaccumulation Potential of Organic Chemicals in Aquatic Food Webs. QSAR Comb. Sci. 22(3): 337-345. ASTER. Assessment Tools for the Evaluation
of Risk. U.S. Environmental Protection Agency. Environmental Research
Laboratory, Duluth, MN. 1993 BCFWIN 2000. Version 2.15. U.S. Environmental Protection Agency. http://www.epa.gov/oppt/exposure/pubs/episuite.htm BIOWIN 2000. Version 4.02. U.S. Environmental Protection Agency. http://www.epa.gov/oppt/exposure/pubs/episuite.htm CEMC (Canadian Environmental Modelling Centre). 2002. Level III v. 2.70 model. Version dated September 2003. Trent University, Peterborough, Ontario. http://www.trentu.ca/cemc/models/EQC2.html (downloaded March, 2004). Curtis, M.W., Copeland, T.L. and C.H. Ward. 1978. Aquatic toxicity of substances proposed for spill prevention regulation. In: Proc. Natl. Conf. Control of Hazardous Material Spills, Miami Beach, FL: 99-103. ECOSAR 2004. Version 0.99h. U.S. Environmental Protection Agency. http://www.epa.gov/oppt/exposure/pubs/episuite.htm EPIWIN
2000. Version 3.12 U.S. Environmental Protection Agency. Heimbach, F. et al. 1996. Fate and Biological Effects of Polymeric MDI (4,4-dphenylmethane diisocyanate and homologues) in small artificial ponds. Ecotox.Environ.Safety 33: 143-153 HENRYWIN. 2000. Version 1.90. U.S. Environmental Protection
Agency. HSDB 2003. CAS 26471-62-5. Hazardous Substances Data Bank.Generated on October 19, 2006. http://toxnet.nlm.nih.gov HYDROWIN v.1.67 model (part of the US EPA’s EPIWIN suite of QSAR models) IUCLID 2000. CAS RN. 26471-62-5. m-tolyidene diisocyanate. European Commission. European Chemicals Bureau. Creation date. 18 February 2000. KOWWIN. 2000. Version 1.67. U.S. Environmental Protection Agency. MITI. Ministry of International Trade & Industry. 1992. Biodegradation and Bioaccumulation Data of Existing Chemicals Based on the CSCL Japan. Chemical Products Safety Division Basic Industries Bureau, Ministry of International Trade & Industry, Edited by Chemicals Inspection & Testing Institute, Japan. MPBPWIN 2000. Version 1.41. U.S. Environmental Protection
Agency. NPRI.
National Pollutant Release Inventory. Environment Canada Oasis
Forecast 2005. Version 1.20. Laboratory of Mathematical Chemistry. Bourgas,
Bulgaria. Pedersen, F., et al., 1998. Immobilisation test of aniline compounds with the crustacean Daphnia magna. Pemberton, D. and Tury, B. 2004. TDI Industry Risk Assessment: Sections on physico-chemical properties, environmental exposures, and environmental effects. GIL Report 2004/E. Tadokora H, et al. 1997. Ecotoxicities of TDI and TDA to fish, algae and aquatic invertebrates. IN: Chemicals Inspection and Research Institute, Japan. III Report No. 11217 Topkat 2004. Version 6.2. Accelrys, Inc. Tury, B et al. 2003. Fate and Potential Environmental Effects of methylenediphenyl diisocyanate and toluene diisocyanate released into the atmosphere. J. Air & Waste Manage.Assoc. 53:61-66 Yakabe, Y. et al 1999. Fate of methylenediphenyl diisocyanate and toluene diisocyanate in the aquatic environment. Environ.Sci.Technol. 33 (15) 2579-2583 WSKOWWIN. 2000.
Version 1.41. U.S. Environmental Protection Agency. Disclaimer: Although care has been taken to ensure that the information found on this website accurately reflects the requirements prescribed in the Canadian Environmental Protection Act (1999), you are advised that, should any inconsistencies be found, the legal documents, printed in the Canada Gazette, will prevail. |
|
||
|
| Help
| Search
| Canada Site |
|
||
|
The Green LaneTM, Environment Canada's World Wide Web site
|
||
|
|
||
|
|
||
