Background 3. Regulatory History for Assessments of Ethers 5

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2 Contents Background 3 Regulatory History for Assessments of Ethers 5 A. Classification for environmental hazards using Limited categories 5 B. Classification for human health and physicochemical hazards using Limited categories 7 C. Read-across to fill data gaps for three HPV ethers 16 D. Use of analogue searches to find suitable chemicals for read-across 19 A Systematic Approach to Chemical Categories Defining a Systematic Ether Category Identifying Important Category Endpoints Filling the Data Gaps for Narcotic Effects Application to Classification and Labelling 35 Discussion 40 Acknowledgements 41 References 42 2

3 Background Grouping chemicals in order to bring together tested and untested chemicals to evaluate trends and estimate the missing values for untested chemicals has been a routine practice in chemical engineering and physical chemistry for more than a half-century. The approaches for grouping chemicals are generally based on the premise that similar chemicals will behave similarly. Defining the basis for judging similarity of the chemicals has been left to the discretion of the chemist. As the need arose for estimating more complex biological activity and more complex chemicals, the factors involved in grouping similar chemicals become more complex, and the study of those factors evolved into the science of quantitative structure-activity relationships, or QSAR. The recognition that similar chemicals behave in consistent patterns and trends was also quickly applied in regulatory settings where data are scarce and hazard assessments are expensive. That similar chemicals would have similar hazards was recognised by the inclusion of groups of chemicals in both United Nations (UN) Transport Model Regulations and in the European Union (EU) classification and legislation that had grown out of this. In particular for metal compounds, it was generally agreed that they should be regarded as similar. This approach was already agreed in EU legislation in the mid-1970 s. A more formal regulatory application of grouping chemicals in order to reduce the cost of hazard assessments was proposed by the United States Environmental Protection Agency (US EPA) in the early 1990 s. That program ( called for the formation of chemical categories and the assessment of categories instead of individual chemicals. The success of that chemical categories program was due, in part, to the fact that the approach was already a common practice in the chemical industry. However, use of categories was limited largely by the methods of judging chemical similarity in terms relevant to hazard assessment. To enhance the international use of chemical categories in hazard assessment, the Organization for Economic Cooperation and Development (OECD) developed guidance for the formation of chemical categories as well as the use of approximation methods for filling data gaps with reasonable estimated values. The OECD guidance serves as a model for using grouping methods and filling data gaps for other regulatory applications, such as evaluation of High Production Volume chemicals. Moreover, OECD is incorporating many of the scientific tools needed for the formation of chemical categories into a QSAR Application Toolbox being distributed to all OECD stakeholders. The EU recently adopted a regulation on the Registration, Evaluation and Authorisation of Chemicals (REACH) 1. Article 13 of the Regulation (General requirements for generation of information on intrinsic properties of substances) states: 1. Information on intrinsic properties of substances may be generated by means other than tests, provided that the conditions set out in Annex XI are met. In particular for human toxicity, information shall be generated whenever possible by means other than vertebrate animal tests, through the use of alternative methods, for example, in vitro methods or qualitative or quantitative structure-activity relationship models or from information from structurally related substances (grouping or read-across). The use of non-testing approaches is the first requirement of this Article on data generation, and precedes the requirements of the test methodology to be used when tests are conducted. Annex XI to the Regulation covers a number of different aspects of non-testing methodology. Point 1.5 contains the following specific guidance for the use of chemical categories: 1 3

4 Grouping of substances and read-across approach. Substances whose physico-chemical, toxicological and ecotoxicological properties are likely to be similar or follow a regular pattern as a result of structural similarity may be considered as a group, or category of substances. Application of the group concept requires that physico-chemical properties, human health effects and environmental effects or environmental fate may be predicted from data for reference substance(s) within the group by interpolation to other substances in the group (read-across approach). This avoids the need to test every substance for every endpoint. The Agency, after consulting with relevant stakeholders and other interested parties, shall issue guidance on technically and scientifically justified methodology for the grouping of substances sufficiently in advance of the first registration deadline for phase-in substances. THE SIMILARITIES MAY BE BASED ON: a common functional group, the common precursors and/or the likelihood of common breakdown products via physical and biological processes, which result in structurally similar chemicals, or a constant pattern in the changing of the potency of the properties across the category. If the group concept is applied, substances shall be classified and labelled on this basis. IN ALL CASES RESULTS SHOULD: be adequate for the purpose of classification and labelling and/or risk assessment, have adequate and reliable coverage of the key parameters addressed in the corresponding test method referred to in Article13(3) cover an exposure duration comparable to or longer than the corresponding test method referred to in Article 13(3) if exposure duration is a relevant parameter, and adequate and reliable documentation of the applied method shall be provided. To facilitate implementing the legislation, the European Commission has commissioned a number of REACH Implementation Projects (RIPs), in particular to develop the guidance documents and tools needed for industry to fulfil their obligations under the legislation. RIP 3.3 focuses specifically on the information requirements for substances, and has been carried out by a group including CEFIC, the European Commission (DG JRC ECVAM, DG JRC ECB and DG Enterprise), the Danish EPA, ECETOC, INERIS, KemI, OECD, RIVM, TNO, UK Environment Agency and Eurométaux. The drafting group for developing guidance on categories was led by the ECB and included representatives from the OECD Secretariat, RIVM, KemI, UK Environment Agency, Danish EPA, Eurométaux, ECE- TOC, CEFIC, CONCAWE, RIFM, American Chemistry Council and the US EPA. As part of this work, a number of appendices were drafted by different authors to provide illustrations and case studies to apply the guidance to practical problems. A number of these appendices are published as a report by the JRC. This report was originally created as one of the appendices which would accompany the guidance on the formation of categories. Because of the interest in the approaches outlined herein, we are making a revised version of the illustration and analysis available on the website of the International QSAR foundation to Reduce Animal Testing () or at /documents/aliphaticethers.pdf. 4

5 Regulatory History for Assessments of Ethers Low molecular weight aliphatic ethers are one group of chemicals that have been evaluated using a number of different techniques. This section summarises the techniques used by different EU working groups in the past decade, and the regulatory conclusions that were drawn. The practices described here illustrate the importance of using a systematic approach to grouping chemicals, of showing how the hazards within a general category can shift among the subgroups, and of basing the classifications on mechanistic arguments. A. Classification for environmental hazards using Limited categories Classification and labelling requirements for substances in the EU are set by Directive 67/548/EEC. This Directive includes definitions of what is considered as a hazard, and includes an Annex (Annex VI, the so-called Labelling Guide ) with more elaborated criteria for the different effects regarded as hazards. In addition, the Directive includes a list of the harmonised classifications that are agreed by the EU and legally binding in all EU Member States. Following the introduction of criteria for classification of hazards to the environment in Directive 67/548/EEC in 1992, the environmental classification of existing Annex I entries was reviewed in order to update the entries where relevant for effects on the aquatic environment. That review required the collection of data on the individual Annex I entries. Initially, the data collection was carried out on an ad hoc or chemical-by-chemical basis; however, a more systematic approach was adopted later to group entries. This approach was simplified because the numbering of entries in the Annex is itself based on a grouping approach, allocating to chemicals included in the Annex an Index number based on the chemical group (element, type of organic compound) that is considered to be most characteristic of the substance s properties. The Index numbers that start with 603 are alcohols and their derivatives. Ethers are included as derivatives of alcohols, and hence the 603 group includes a number of aliphatic ethers as well as more complex ethers such as vinyl, glycol and allyl glycidyl ethers. The Annex I entries in the 603 group that includes the aliphatic ethers were reviewed in September 1997 (ECBI/48/97 Rev. 1) in the relevant EU Technical Committee, including representatives of the EU Member States as well as observers from industry. The aliphatic ethers in Annex I include dimethyl ether ( ), ethyl methyl ether ( ), diethyl ether ( ), di-n-propyl and di-isopropyl ether ( X) and din-butyl ether ( ). Member States volunteered to collect available data for the compounds. For these five ether entries, data was collected by Denmark, Germany, France, Spain and Sweden, either specifically for this evaluation or as part of a classification proposal for specific substances 2. That evaluation was mainly based on the available data; however, the data were compared with the results of the relevant QSAR model estimates for each individual substance. As will be discussed below, the practice of assessing a few chemicals of regulatory importance without considering all category members often makes it difficult to observe the trends in the data needed to appropriately classify the selected members of the category. Lacking the ability to quantify trends, QSAR estimates were made using the hazard assessment endpoints for which QSAR models existed (ECBI/20/97 - Add. 5). A qualitative prediction of biodegradability was calculated by the US EPA BIODEG Probability Program (BBP) developed by Howard and Meylan (Syracuse Research Corporation, 1992). The BBP1 and BBP2 degradation models produced consistent results for all chemicals, but the computation that an ether was readily degradable was not always in agreement with experimental data. Aquatic toxicity was predicted by the US EPA ECOSAR program developed by Clements and Nabholz (EPA-OPPT, Washington, 1993). In this program, different models have been developed for different chemical classes and for different aquatic species. 2 A list of the documents used for this discussion is shown in the References section. A limited number of the documents used are available on the ECB website. 5

6 The QSARs for nonpolar narcosis that were deemed appropriate for ethers are based on linear relationships with log Kow of the form: Log LC50 (mmol/l) = A - B log Kow For the first three entries dimethyl ether, ethyl methyl ether and diethyl ether the data collected by France, Spain, Belgium and Sweden showed that these substances should not be classified for dangers to the environment. The QSAR estimates showed that the chemicals would have a low probability of exceeding the classification criteria and thus supported the conclusion. For di-n-propyl ether and di-isopropyl ether, France proposed classification with R , while Sweden recommended no classification for dangers to the environment based on interpretations of available data. Sweden noted that there were contradictory values for fish toxicity for di-iso-propyl ether and used the higher toxicity values, > 100 mg/l. France believed that the data < 100 mg/l was valid. The QSAR results showed that the substances have a low probability of exceeding the classification criteria, which supported Sweden s conclusion. Therefore, the no classification proposal was proposed on a weight of evidence argument involving QSAR estimates. The United Kingdom (UK) noted Table A.1: QSARs for alcohols and their derivatives acting by nonpolar narcosis Organism duration endpoint A B n r2 Fish 96h LC Daphnia 48h LC Algae 96h EC Fish > 14 d ChV Daphnia 16 d EC Algae > 96 h ChV that the biodegradation data suggested no classification and the QSAR estimate of a NOEC of > 1 mg/l. The committee concluded that the substances should not be classified as dangerous to the environment. For di-n-butyl ether, Denmark and France recommended classification with R based on the data. Denmark noted there was ecotoxicity data for all three trophic levels and, in a Japanese Ministry for International Trade and Industry (MITI) biodegradability test, the substance was not shown to be really biodegradable. The QSAR calculations showed acute toxicity values in the range of 1 10 mg/l (so the substance could be classified as N; R51-53) and chronic values for fish and algae > 1 mg/l (which, together with acute toxicity in the mg/l range, would lead to no classification). The committee concluded that the substance should be classified with R This revision was included in the 29th ATP. Assessment Conclusions. The classifications of the five ethers were mainly based on the available data, but using a comparison with the QSAR estimates. For the three lower molecular weight ethers (with 2 to 4 carbon atoms), neither the data nor the QSAR estimates indicated that the substances should be classified for R For the two dipropyl ethers (n = 6), the QSAR estimates were consistent with the final no classification conclusion, and were cited as reasons for drawing that conclusion. For the di-n-butyl ether (n = 8), the data showed acute toxicity in the mg/l range, whilst the QSAR estimates were in the 1 10 mg/l range. 3 The EU criteria are based on (a) toxicity in the range mg/l, and (b) the substance s not being readily biodegradable. The classification need not be applied if additional scientific evidence is available concerning degradation and/or toxicity, such as a proven potential to degrade readily in the environment or a NOEC > 1 mg/l in a prolonged toxicity study with fish or daphnia. Classification with R52-53 corresponds to the Global Hazard System (GHS) Chronic Category 3 (Milieu, 2005b). 6

7 B. Classification for human health and physicochemical hazards using Limited categories At the same time as Annex I was being revised to include the environment classification, a number of Annex I entries were also reviewed under the terms of both the Treaty for the Accession of Sweden and Austria to the EU and the EEA Agreement with Norway. Negotiations on the accession of Austria, Finland and Sweden to the EU had shown that there were certain differences between the national legislation for chemicals classification and labelling in Sweden and Austria and the EU legislation then in effect. There was agreement that these differences, together with those between the Norwegian chemicals legislation covered by the EEA agreement, should be discussed in the EU Classification and Labelling groups. One important concern for a number of Annex I entries was the difference between Swedish and EU legislation with respect to the Swedish Moderately Harmful classification. This Moderately Harmful category 4 was mainly related to three hazards: compounds that show acute toxicity above the EU cut-off of 2000 mg/kg 5 ; certain inhalation hazards 6, and chemicals which show certain irritation effects on the skin 7. Further, these three effects were also a subject of concern with a number of solvents. Thus, after a discussion of these issues at a meeting of the Commission Working Group on the Classification and Labelling of Dangerous Substances at Ispra, April 1997 (ECBI/21/97 Rev 2), it was decided to discuss these possible changes as part of a widerranging review of the relevant Annex I entries. These entries were reviewed at meetings of the Commission Working Group on the Classification and Labelling of Dangerous Substances at Ispra, October 1997 (ECBI/51/97 Rev 3) and January 1998 (ECBI/01/98 Rev 1); in Copenhagen on March 1998 (ECBI/16/98 Rev 1); and in Ispra on 6 8 May, 1998 (ECBI/18/98 Rev. 1) 8. A list of hydrocarbons, alcohols, ethers, and esters was prepared, based on the substances included in Annex I (ECBI/22/96 Add 18 Rev. 2). The five ethers entries were the same Annex I entries as the five described in section A above. Using a similar approach to that used to revise the entries for environmental classification, Member States volunteered to collect data on different endpoints. The endpoints considered were physicochemical properties (in particular, flammability) (ECBI/22/96 Add. 20); acute oral (ECBI/22/96 Add. 25), dermal (ECBI/22/96 Add. 26) and inhalational toxicity (ECBI/22/96 Adds. 30, 31, 37 and 42); skin (ECBI/22/96 Add. 36), eye (ECBI/22/96 Add. 27) and lung (ECBI/22/96 Add. 34) irritation, as well as harm to breast-fed babies 9. Before this discussion, all five ether entries had been classified for flammability 10 and for concerns that they could produce explosive peroxides 11. The di-n-butyl ether was the only compound classified for human health concerns as a skin, eye and lung irritant 12. Three of these five entries, ethyl methyl ether, diethyl ether and dipropyl ether, had additional classifications in Swedish legislation. 4 Note that the term category in this context refers to a hazard classification class, and not to category in the primary sense used in this report of a group of chemicals with similar chemical structures. 5 R322 in Swedish legislation. This corresponds to the GHS Acute toxicity Cat. 5 (oral) (Milieu, 2005b) 6 R320 in Swedish legislation 7 R313 in Swedish legislation 8 The discussion of the ether entries was concluded in May Discussions of some of the other entries continued at the meeting at Ispra on 1 3 July, 1998 (ECBI/27/98 Rev. 2). 9 R64 is the EU phrase for harm to breast-fed babies. An earlier report had suggested that this might be relevant for some of the compounds considered. However, preliminary discussions indicated that this was unlikely to be a serious concern for many of these compounds, and this discussion was not pursued. R64 corresponds to the GHS Effects on or via lactation (Milieu, 2005b). 10 F+ R12 for dimethyl ether and ethylmethyl ether corresponds to either GHS Flammable gas Cat. 1 or 2 and for diether ether to Flammable liquid Cat. 1. F; R11 corresponds to GHS Flammable liquid Cat. 2; R10 to GHS Flammable liquid Cat. 3 (Milieu, 2005b). 11 EU risk phrase R19: May form explosive peroxides. This does not have any equivalent in the GHS system, although substances having explosive properties although not classified as explosives are currently under consideration for inclusion in GHS (Milieu, 2005a). 12 EU R-phrases Xi; R36/37/38. These three R-phrases correspond in the GHS system to Eye irritant, category 2; STOST category 3 and skin irritant, category 2 respectively (Milieu, 2005b). 7

8 Physicochemical Properties The data collected for the ethers is shown in Table B.1. Table B.1: Physicochemical properties (from ECBI/22/96 - Add. 20) Name CAS No Current EU classification dimethyl ether F+, R12 flammable gas 1, 2 ethylmethyl ether F+; R12 flammable gas 2 diethyl ether F+; R12, R19 f.p.: 40 1, b.p di-n-propyl ether F; R11, R19 f.p.: -5 2, -17 (open cup) 3, -21 (closed cup) 3, di-iso-propyl ether F; R11, R19 f.p.: -24 1, -20 2, -9.4 (open cup) 3, (closed cup) 3. di-n-butyl ether R10 f.p.: 25 2 Notes to the Table: 1: IUCLID data 2: Chemsafe database, data supplied by Dr. Elisabeth Brandes, Physikalisch-Technische Bundesanstalt, Braunschweig und Berlin. 3: Swedish classification proposal, ECBI/43/95 - Add. 42. No changes to the current classification were proposed for any of the five entries. Acute oral toxicity The acute oral toxicity data collected by the UK is shown in Table B.2. Table B.2: Acute oral toxicity (from ECBI/22/96 Add 25) Name CAS No Current EU classification Experimental data Suggested classification dimethyl ether no data (gas) None ethylmethyl ether no data (gas) None diethyl ether Extensive information supporting Xn; R22 Xn; R22 di-n-propyl ether Rat LD50: 4646, 8470, 11616, mg/kg None di-iso-propyl ether di-n-butyl ether Rat LD50: 7400 mg/kg (Sax) None Only diethyl ether was considered to be concern for acute oral toxicity. The compound was classified with R322 in the Swedish legislation. In the EU Working Group discussion, France questioned whether R22 was appropriate as the LD50 value was > 2000 mg/kg and only 4 out of 60 animals had died at the highest dose. However, Belgium noted that there was an LD50 value of 1200 mg/kg, which warranted the R22 classification. Sweden pointed out that the repeated oral toxicity study was done with corn oil, which affects uptake, and that the value for acute oral toxicity should be taken into account, particularly as this substance was also a concern for children. The UK agreed with the Swedish comments, and the Working Group agreed to the classification with Xn; R22 13 (ECBI/21/97 rev 2). This change was subsequently agreed as part of the 25th ATP. Acute inhalational toxicity The document summarising data on inhalational toxicity was prepared by Sweden (ECBI/22/96 Add 42), complementing the document with acute inhalational classification prepared by Denmark (ECBI/22/96 Add 30). The information on ethers is shown in Table B.3 below. 13 Corresponds approximately to the GHS Acute toxicity Cat. 4 (oral), although the cut-off values are slightly different. (The lower limit is 200 mg/kg in the EU system and 300 mg/kg in GHS) (Milieu, 2005a,b).13 8

9 Table B.3: Acute inhalational toxicity SUBSTANCE dimethyl ether* ethylmethyl ether diethyl ether di-n-propyl di-isopropyl ether di-n-butyl ether* ether CAS No PHYSICOCHEMICAL DATA Molecular weight Vapour pressure, kpa at ( C) 531 (20) 144 (20) 58,6 (20) 6,76 (20) 15,9-17,3 (20) 0,64 (20) Sat. vap. conc (mg/l) Log Pow -0,23; -0,18; 0,07 0,34-0, ,5-1,8 3.2 Other part. coeff NA LETHALITY LC50 (mg/l) 313 (3%) duration; remarks R 4h M 15 min. M 90min, R 4h, (5,6%) M 15 min M 15 min M 15 min (35 C) LC low (mg/l) 840 NA ,6 (LC33); 130 duration; remarks M; 15 min.; LC1-5 M 15 min M 15 min R 4h; M 15 min (35 C) CNS DEPRESSION: ACUTE EXPOSURE NARCOSIS Animal; effect narcosis loss right. refl. (AC50) narcosis anaesthesia loss right.refl. loss right.refl. conc. (mg/l) 94 (1%) (4-6%) 30 (10%) duration; remarks R,<=30 min. M;15 min. M, Rb, dog, 3-5 min M 2h M 15 min M 15 min (35 C) Human; effect unconsciousness anaesthesia NA NA NA conc. (mg/l) (3,3%) duration; remarks 26 min min (?) 9

10 OTHER EFFECTS Animal; effect behav., neuroendocr. loss right. refl. confus. semi-stupor conc. (mg/l) 9 (0,5%) duration; remarks M 30 min M, 15 min monkey 10 min Human; effect reduction in alertness suppr. evok. resp, conc. abil, time percept., amnesia conc. (mg/l) 143 (1,4%) 30 (1,6%) duration; remarks 12 min 3 h (or longer) CNS DEPRESSION; PROLONGED/REPEATED EXPOSURE Animal; effect incoordination, lethargy conc. (mg/l) 95.5 duration; remarks R, 6h/day/5d/w./2 w. Human; effect headache, dizzin, loss balance conc. (mg/l) 1,2 and/or above duration; remarks occup. exp. OTHER NEUROTOXIC/TOXIC EFFECTS Animal; effect disturb. equil. syst (VOR) conc. (mg/l) 150μM/kg/min duration; remarks cr, iv., 1 h Human; effect hearing loss complaints conc. (mg/l) 1,02 duration; remarks workday S basis for evaluation (for details see classification forms or basis documents for moderately harmful substances) Narcotic prop. in animals and humans, gas (b.p C) (Not in EINECS) Narcotic prop. in animals, gas (b.p. 10,8 C) Narcotic prop.in animals and humans, very high volat., readily absorb., impaired nerophysiol. and neurobehav (animals, humans), CNS depr. of occup. exp. Narcotic prop., high volatil. and log Pow, high part. coeffic. oil/blood Narcotic prop., very high volatil. and log Pow 10 Narcotic prop. only demonstrated at 35 C in mice

11 The lung irritation data collected by Germany (ECBI/22/96 Add 34) notes that toxic and narcotic effects are seen usually at nominal concentrations above 20 mg/l and near the lower explosivity limit. The discussion concerned the available data in the current EU classification criteria to address the wider issues raised by the Swedish Moderately Harmful classification. A number of ad hoc meetings on the human health problems associated with volatile substances were held to consider whether additional criteria were required. The conclusion, based on the outcome of discussions of the individual substances, was that additional criteria were required to extend the EU criteria to cover narcotic effects of volatile substances. A new R-phrase, R67 14, was included in the criteria. For dimethyl ether, Denmark proposed classification with R67 for inhalational toxicity, since ethers were well documented as having a narcotic effect, and the UK agreed that the effects were well known and warranted classification. CEFIC felt that, in general, the effects of ethers were only observed at high concentrations and were therefore outside the criteria, but could accept R67 for dimethyl ether (ECBI/51/97 Rev 3). At a subsequent meeting (ECBI/16/98), the UK felt that further investigation of available data might be needed. As this entry was not problematic under either the Accession Treaty or EEA, time constraints prevented any further discussion. No changes have since been made to the classification of this entry. Ethylmethyl ether is included in the Swedish legislation and classified with R320 for concerns for inhalational toxicity. Although there are no data for this particular substance, Denmark proposed classification with R67 for inhalational toxicity, since ethers were well documented as having a narcotic effect. The UK and CEFIC agreed that classification for this substance could only be based on SAR (ECBI/51/97 Rev 3). At a subsequent meeting (ECBI/16/98), the Group decided that the entry should be deleted, as the substance was not listed in EINECS 15. However, this decision has not been carried out, and the entry remains unchanged in Annex I. Diethyl ether is also included in Swedish legislation and classified with R320 for concerns for inhalational toxicity, whilst in Norwegian legislation it is classified more stringently as Xn; R Preliminary discussions of this classification were hindered by a lack of consensus on possible changes to the criteria (ECBI/21/97 rev 2). However, following further discussions on criteria for narcotic effects, Germany, supported by Denmark, suggested R67 based on significant narcotic effects (ECBI/01/98 Rev. 1). This was agreed and included in the 25th ATP. The two dipropyl ethers (npropyl and iso-propyl ethers) are also included in Swedish legislation and classified with R320 for inhalational toxicity. Following agreement on the criteria for narcotic effects, classification with R67 was agreed without further discussion (ECBI/16/98). Di-n-butyl ether was not considered for acute inhalational toxicity or narcosis at any point in these discussions. 14 This R-phrase, Vapours may cause drowsiness and dizziness, corresponds to the GHS STOST (Single exposure) Category 3 (Milieu, 2005b). This R-phrase is used in the following report of the discussions, although the actual phrase was not agreed until quite late in the discussions. 15 A substance not included in EINECS is subject under current EU legislation to the notification procedures also included in Directive 67/548/EEC. Since in general, placing a substance not included in EINECS on the market in the EU requires a notification, substances not included in EINECS need not be included in Annex I. 16 Xn; R20 corresponds to the GHS Acute toxicity Cat. 4 (inhalation) (Milieu, 2005b) 11

12 Acute dermal toxicity The acute dermal toxicity data collected by the UK are summarised in Table B.4. Table B.4: Acute dermal toxicity (from ECBI/22/96 Add 26) Name CAS No Current EU classification Experimental data Suggested classification dimethyl ether no data (gas) none ethylmethyl ether no data (gas) none diethyl ether no data none di-n-propyl ether Rabbit LD50: mg/kg none di-isopropyl ether di-n-butyl ether Rabbit LD50: mg/kg (Sax) none Acute dermal toxicity was not considered at any point in these discussions. Skin irritation The skin irritation data collected by Sweden (ECBI/22/96 Add 36) is shown in Table B.5, together with additional comments from Sweden. Table B.5: Skin irritation SUBSTANCE dimethyl ether* ethylmethyl ether diethyl ether di-n-propyl ether di-isopropyl ether di-n-butyl ether* CAS No PHYSICOCHEMICAL DATA Molecular weight Boiling point ( C) Vapour pressure, kpa at ( C) 531 (20) 144 (20 ) 58,6 (20) 6,76 (20) 15,9-17,3 (20) 0,64 (20) Sat. vap. conc (mg/l) Log Pow -0,23; -0,18; 0,07 0,34-0, ,5-1,8 3.2 Hildebrand Hansen solubility parameter ( /Mpa1/2) Dielectricity constant BASIS FOR CLASSIFICATION R38 Human experience single exposure repeated exposure Animal data R66 Human data test data practical experience X X X Animal data (X) SAR Solubility properties log P log P log P Used as solvent X X X Proposed classification: R38, R66 or none none none R66 R66 R66 R38 (existing classification) 12

13 Summary of detailed comments on the individual compounds: Dimethyl ether and methyl ethyl ether are gases at room temperature. Gases and vapours may be irritating to the skin but probably not by a defatting mechanism. Diethyl ether is a good solvent for fats and is used as such both in industry and at laboratories. It is commonly stated in handbooks and safety data sheets that prolonged or repeated exposure may lead to skin dryness, cracking of the skin or dermatitis. In rabbits (New Zealand), 0.01 ml of diethyl ether on uncovered belly skin caused no irritation during 24 hours of exposure. However, considering the very high volatility of diethyl ether and the small amount applied, most of the test substance would probably have evaporated within a short time. Classification with R66 is proposed on the basis of good fat solubility properties of diethyl ether, as indicated by its use as a solvent for fats, and on the practical human experience of dermatitis caused by repeated or prolonged skin contact with diethyl ether. Isopropyl ether is an excellent solvent for oils and fats. It is commonly stated that prolonged or repeated exposure to isopropyl ether may cause defatting of the skin leading to dermatitis. Classification with R66 is proposed for di-n-propyl and di-isopropyl ether. It is based on the good fat solubility properties as indicated by their log P values as well as their technical applications. For di-isopropyl ether it is also known by experience that repeated or prolonged skin contact may defat the skin and cause dermatitis in humans. Animal test data also support that repeated exposure to di-isopropyl ether may cause dermatitis. Di-n-butyl ether is an experimental skin irritant. Exposure to 100 mg for 24 hours caused moderate irritation. Di-n-butyl ether appears to have a high fat solubility, as indicated by the high ph 17 value (3.2). Prolonged or repeated skin contacts with ethers cause tissue defatting and dehydration, leading to dermatitis. Classification with R67 is suggested based on the high potential of di-n-butyl ether to cause delipidisation of the skin as indicated by a high log Pow value, as well as general experience that repeated exposure to ethers may lead to dermatitis. 17 This would appear to be a mistake, and it would seem clear that a reference to log Pow is intended in the Swedish document. 13

14 Like the discussion on acute inhalational toxicity, this discussion was concerned with relating available data to the current EU classification criteria, as well as addressing wider issues raised by the Swedish Moderately Harmful category. Discussions were further complicated by the recognition that current criteria did not properly reflect concerns for prolonged or repeated exposure to compounds that might have irritating effects on the skin. As with the inhalational criteria, ad hoc meetings were also held to develop the criteria in parallel with discussion of the substances. The conclusion, based on both the outcome of the discussions of the individual substances and the more general aspects, was that additional criteria were required to extend the EU criteria to cover defatting effects. A new R-phrase, R66 18, was included in the criteria. Dimethyl ether was not discussed for this effect as it is a gas. Although ethylmethyl ether is also a gas, it is included in the Swedish legislation and classified with R313 for concerns for skin irritation. No formal proposal for classification of ethylmethyl ether for this effect was made. The Group decided that the entry should be deleted since the substance was not included in EINECS 19. Diethyl ether is also included in Swedish legislation and classified with R313 for concerns for skin irritation. The initial discussion turned around uncertainties as to whether classification as Xi; R38 20 was not justified instead of R66 as dermatitis was observed after repeated exposures. The discussion that followed suggested that when the effects seen were dermatitis, then this should lead to classification with Xi; R38, whilst if the effects seen were drying and cracking of skin only (defatting effects), then classification with R66 was appropriate (ECBI/51/97 Rev 3). At a subsequent meeting, and based on this distinction between the two types of effect, the UK felt that the handbook data available were not sufficient to justify classification with Xi; R38, and classification with R66 was agreed (ECBI/01/98 Rev.1). The two dipropyl ethers (npropyl and iso-propyl ethers) are also included in Swedish legislation and classified with R313 for concerns for skin irritation. Following agreement on the criteria for defatting, classification with R66 was agreed without further discussion (ECBI/16/98). Di-n-butyl ether was already classified with Xi; R38, and this classification was not questioned in the discussions. As this entry was not problematic under either the Accession Treaty or EEA, time constraints prevented any further discussion, and no changes have since been made to the classification of this entry except to implement the environmental classification in the 29th ATP. The discussion that followed suggested that when the effects seen were dermatitis, then this should lead to classification with Xi; R38, whilst if the effects seen were drying and cracking of skin only (defatting effects), then classification with R66 was appropriate (ECBI/51/97 Rev 3). 18 This R-phrase, Repeated exposure may cause skin dryness or cracking has no exact equivalent in GHS(Milieu, 2005a). This R-phrase is used in the following report of the discussions, although the actual phrase was not agreed until quite late in the discussions. 19 As noted earlier, this decision has not been carried out, and the entry remains unchanged in Annex I with classification for physicalchemical hazards only. 20 The EU R-phrase Xi; R38 corresponds to the GHS Skin irritant category 2 (Milieu, 2005b) 14

15 Eye irritation. The eye irritation data collected by the UK are shown in the following Table B.6. Table B.6: Eye irritation data (from ECBI/22/96 Add 27) Name CAS No Current EU classification Human data Animal evidence Suggested classification dimethyl ether no data no data none ethylmethyl ether no data no data none Diethyl ether no data slight reversible irritation of rabbit eyes exposed to liquid or vapour (Grant, 1974) none Di-n-propyl ether Irritation of the eyes Method not stated: none? di-iso-propyl ether reported by volunteers exposed to 300 ppm for 15 minutes. Anecdotal data Irritation of the eyes was reported following irritating to eyes (secondary evidence di-n-butyl ether Xi; R36 Causes conjunctival irritation in humans (Sax) Xi; R36? Whilst there was some initial concern for eye irritation for the dipropyl ethers, this issue was not substantiated and the proposal was withdrawn (ECBI/01/98 Rev.1). Although classified with Xi; R36 in Annex I, this classification was questioned by the UK (ECBI/51/97 Rev 3.) but not discussed any further. Lung irritation The lung irritation data collected by Germany (ECBI/22/96 Add 34) does not recommend classification with R37, as there are no reliable data referring to sensory irritation. The only substance for which this was considered to be a concern was di-n-butylether, which is classified as Xi; R37. Germany questioned such a classification. A trend toward irritation of the respiratory tract was noted, although not confirmed (ECBI/51/97 Rev 3). Assessment Conclusions This is an example of a partial category approach where trends cannot be adequately evaluated. Rather than taking all possible members of a chemical category, certain compounds have been selected for review. In both the review for environmental and human health effects, the basis for the selection was the fact that the compounds were already included in Annex I. However, the use of this approach for the review of human health effects was also limited by pragmatic considerations related to the need to address specific issues connected with the Accession Treaty and the EEA, and not all potential changes were fully discussed and agreed. Nevertheless, this approach has shown certain trends in effects across the group. Flammability decreases (as the flash point rises) with increasing size of the molecule. Acute oral toxicity was only problematic for diethyl ether, and decreased with higher ethers, and acute dermal was not considered to be a concern for any of the substances. Narcotic effects are seen as problematic for all aliphatic ethers up to and including the two dipropyl ethers. Defatting effects are not considered of concern with the lower ethers (which are gases), but diethyl and the two dipropyl ethers show this effect, whilst di-n-butyl ether shows a more severe form of skin irritation. Eye irritation and lung irritation do not appear to be effects of concern, except possibly for the higher-chain length ethers. 15

16 C. Read-across to fill data gaps for three HPV ethers The EU Existing Substances Regulation (ESR) programme has evaluated a number of High- Production Volume ethers with Finland as the Rapporteur. The review originally included two fuel oxygenates, methyl tert-butyl ether (MTBE ) and tert-amyl methyl ether (TAME). In the course of the evaluation, it became clear that a third compound, ethyl tert-butyl ether (ETBE) was also used as a fuel oxygenate. MTBE was reviewed under the 3rd priority list, followed by TAME under the 4th priority list. Recognising that a third ether, ETBE, was gaining an increasing market share, additional data on this third compound were obtained using the provisions of Article 12(2) of the Existing Substances Regulation (EC, 2002). A targeted risk assessment was also carried out for this third compound by Finland. In the risk assessment of MTBE (EU RAR, 2002), data were adequate to evaluate effects on the aquatic environment, although effects on the terrestrial environment were estimated using EUSES-modelling based on aquatic toxicity data. Data were also adequate to evaluate acute toxicity or irritation (by all routes), sensitisation, repeated dose toxicity by the oral and inhalation routes, mutagenicity, carcinogenicity and reproductive toxicity. The only identified need for further data was for emission data to adequately characterise risks to the aquatic ecosystem. The risk assessment of TAME built on the experience gained with the evaluation of MTBE (EU RAR, 2006). Read-across from MTBE to TAME was used to estimate the exposure to TAME by inhalation and from tap water in assessing indirect exposure via the environment. Data for TAME were adequate to evaluate effects on the aquatic environment, although effects on the terrestrial environment were estimated using EUSES-modelling based on aquatic toxicity data. Data were also adequate for TAME to evaluate effects on human health. Before starting an assessment of the third ether, ETBE, data were required under Article 12(2) of the Existing Substances Regulation (EC, 2002). The information reporting requirements for manufacturers/- importers were annual production and import volumes, acute toxicity to daphnia, growth inhibition test on algae, a developmental toxicity study and a fertility study. Consequently, the use of read-across was greater in the risk assessment of ETBE than for TAME (EU Draft RAR, 2006). Whilst there were adequate data for acute toxicity to the aquatic environment, there were no data for the chronic effects of ETBE. Table C.1 Chronic toxicity of MTBE, TAME and ETBE to aquatic species MTBE TAME ETBE Chronic toxicity mg/l mg/l mg/l Fish IC20: Daphnia magna NOEC: Mysidopsis bahia (marine) NOEC: 26 NOEC: Algae IC20: 103 NOEC: 77-16

17 The QSAR calculations in Table C.2 are based on the assumption that ETBE acts by a non-specific mode of action, which is the case also with MTBE and TAME (EU Draft RAR, 2006). Table C.2 QSAR calculations on acute and chronic toxicity of MTBE, TAME and ETBE (calculated according to the ECOSAR developed by U.S. Environmental Protection Agency, 2000) MTBE TAME ETBE Acute toxicity LC/IC50 in mg/l LC/IC50 in mg/l LC/IC50 in mg/l Fish d: d: d: 389 Marine fish Daphnia d: d: d: 9.85 Mysidopsis bahia (marine) Algae Chronic toxicity Chronic value Chronic value Chronic value Fish Algae Whilst the Rapporteur evaluated the validity of the new studies for human health required under Article 12(2), the validity of the data presented in the IUCLID data set was not fully evaluated for the preliminary assessment. These unevaluated studies were compared with the information available for MTBE and TAME. ETBE does not appear to have higher toxic potency on the specific endpoints compared to MTBE or TAME (Table C.3) (EU Draft RAR, 2006). Table C.3 Comparison of properties of MTBE, TAME and ETBE Property MTBE TAME ETBE Production purity % >95 < Typical content in 95 octane petrol 0,5-8% <1-10 <10 Vapour pressure ( 1 at 25 ºC (ChemIDplus) Acute toxicity Low Low Low Irritation Yes No No Sensitisation No No No Repeated dose toxicity NOAEC/NOAEL 800 ppm / 300 mg/kg 250 ppm / <125 mg/kg 500 ppm / <250 mg/kg Mutagenicity No No No Carcinogenicity No reliable data No reliable data No reliable data Reproductive toxicity 250 ppm 3000 ppm 1000 mg/kg Developmental toxicity Effects seen at 4000 ppm 250 ppm 1000 mg/kg or higher only with maternal toxicity 17

18 Whilst diethyl ether is the only compound in the previous series of ethers that is classified for acute oral toxicity, TAME has also been classified for this effect, based on a predicted value for female rats from a range-finding study. Neither MTBE nor ETBE fulfils the criteria for classification for this effect. TAME has also been classified with R67 for a narcotic effect, whilst MTBE has not. Finland has proposed that ETBE also be classified with R67 (ECBI/83/06). This proposal was discussed at the EU TC C&L meeting in October 2006 (ECBI/62/06 Rev. 3). The conclusion of this discussion was that the experimental data from a repeated dose toxicity did not support classification of ETBE with R67. However, this conclusion was subsequently questioned by Finland in the follow-up to the meeting (ECB Follow-up II). MTBE, like di-n-butyl ether, is classified with Xi; R38 for skin irritation. TAME is not irritating to skin in a properly performed OECD Guideline 404 test. ETBE does not irritate the skin or eye based on properly performed OECD tests, but after a longer dermal occlusive exposure, ETBE was an irritant. TAME slightly irritates the eye, and induced slight irritation of throat and nose at an air concentration of 60 mg/m3, but is not classified for either skin, eye or lung irritation. The values for the NOAECs for respiratory irritation used for TAME and ETBE in the risk assessment reports are similar. All three compounds have flash points corresponding to F; R11, consistent with the trend seen for the other ether compounds. None of the three compounds is classified for hazards to the aquatic environment. The information from the three risk assessment reports indicates that the trends seen in the earlier review of the Annex I entries are also seen here. Assessment Conclusions In subsequent discussions of the Finnish report on ETBE at the EU TC NES, the ECB viewed the discussion of ETBE as an exercise in read-across risk assessment (mi_etbe_tc0504_env_ hh_dr1). There was little actual discussion of read-across for either the effects or the exposure assessment, although there was agreement that the risk reduction strategy might be considered as valid for all of the three oxygenates (MTBE, TAME and ETBE), irrespective of the actual compound. 18

19 D. Use of analogue searches to find suitable chemicals for read-across Forming chemical categories is the critical first step in the process of filling data gaps for untested chemicals regardless of whether read-across, trend analysis or quantitative models are to be used within the category. The process of grouping analogous chemicals generally includes classbased definitions of the group, and, when the class is defined by simple functional groups like the ether moiety, the class-based search for analogues will invariably include chemicals that have substantially different toxicological behaviour. The most widely used method in the public domain has been the US EPA Analogue Identification Method (AIM). This method was demonstrated by the ECB at the EU Risk Assessment Working Group meeting in November 2005 (mainmin_0504_dr2) and identified ETBE as an analogue of MTBE and TAME (ETBE read-across). The illustration also found other chemicals which would not normally be considered analogues. The reliability of grouping chemicals based purely on statistical similarity analysis of simple fragments is generally lower, because the statistical methods cannot detect mechanistic shifts in these chemical substructures. Consequently, the use of analogue identification methods is usually followed by further screening of the preliminary analogues, and by removal of more complex structures. Without this further separation of subgroups within the category, grouping experiments may also lead to unrealistically large categories as reported for phthalate esters, which resulted in a category of several hundred chemicals (Worth A et al., 2007). For large classes of industrial chemicals such as the phthalate esters, inadequate analogue methods can produce enormous categories. That size ultimately reduces the reliability of filling data gaps due to the possibility of different chemical behaviours in large categories. To overcome many of the technical limitations associated with grouping chemicals in chemical inventories, with pruning chemicals which are likely to have anomalous behaviour, and with gathering available data for the final category members, the OECD has embarked on the development of a QSAR Application Toolbox. Following the regulatory workflow addressed in the OECD Guidance Document on the Formation of Chemical Categories, the Toolbox separates that workflow into a number of functions performed by experts. It also aligns the tools needed to: (1) quickly explore grouping approaches, (2) evaluate four levels of pruning anomalous chemicals, (3) establish a management system for categories and subcategories needed to cover SIDS endpoints, (4) permit database searching for measured values, and (5) provide a flexible report generator. A Systematic Approach to Chemical Categories Chemistry is inherently hierarchical, and the use of combinatorial approaches to generate new modifications to known chemical structures is commonplace in many chemicals discovery programs. The starting point is often a parent chemical with desirable attributes, and the systematic exploration of modifications is used to optimise those attributes. Although combinatorial methods are not universally realistic for forming chemical categories for hazard assessment, the systematic approach can overcome some of the difficulties illustrated above. The experience in the EU regulatory groups described in the foregoing sections has shown that grouping too few chemicals in a category makes it difficult to discover the trends between chemical structure and assessment endpoint activity due to the inherent variability in test data. It has also illustrated that forming large categories through simplistic class definitions or statistical grouping will obscure structureactivity trends by mixing mechanisms. The remainder of this report will focus on the potential advantages of using a systematic category approach for the hazard assessment of aliphatic ethers Defining a Systematic Ether Category The category for aliphatic ethers can be defined based on a simple combinatorial approach using SMILES notation, which creates greater opportunity to include empirical data into the read-across judgements in the category and to illustrate