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354User Guide for Thresholds and ClassificationsTwenty-eight–day transformation testIf the process described in for the 7-day transformation test results in the classification of 9.1A, no furtherassessment is required as the metal compound will be classified irrespective of any further information. In allother cases, further data may have been generated through the dissolution/transformation test for 28 days inorder to show that the classification may be amended. If for poorly soluble metal compounds classified as9.1B or 9.1C or 9.1D, the dissolved metal ion concentration at the low loading rate after a total period of 28days is less than or equal to the long-term NOECs, then classification is removed.Particle size and surface areaParticle size, or moreover surface area, is a crucial parameter in that any variation in the size or surface areatested may cause a significant change in the levels of metals ions released in a given time window. Thus,this particle size or surface area is fixed for the purposes of the transformation test, allowing the comparativeclassifications to be based solely on the loading level. Normally, the classification data would have used thesmallest particle size marketed to determine the extent of transformation. There may be cases where datagenerated for a particular metal powder is not considered as suitable for classification of the massive forms.For example, where it can be shown that the tested powder is structurally a different material (for example,different crystallographic structure) and/or it has been produced by a special process and cannot begenerated from the massive metal, classification of the massive can be based on testing of a morerepresentative particle size or surface area, if such data are available. The powder may be classifiedseparately based on the data generated on the powder. However, in normal circumstances it is notanticipated that more than two classification proposals would be made for the same metal.Metals with a particle size smaller than the default diameter value of 1 mm can be tested on a case-by-casebasis. One example of this is where metal powders are produced by a different production technique orwhere the powders give rise to a higher dissolution (or reaction) rate than the massive form leading to amore stringent classification.The particle sizes tested depend on the substance being assessed and are shown in Table 19D.3.Table 19D.3: Particle sizes tested depend on the substance being assessedType Particle size CommentsMetal compounds Smallest representative size sold Never larger than 1 mmMetals – powdersMetals – massiveSmallest representative size sold1 mmMay need to consider different sources ifyielding different crystallographic/morphologicpropertiesDefault value may be altered if sufficientjustificationFor some forms of metals, it may be possible, using the Transformation/Dissolution Protocol (see Appendix19G), to obtain a correlation between the concentration of the metal ion after a specified time interval as afunction of the surface area loadings of the forms tested. In such cases, it could then be possible to estimateJanuary 2012 EPA0109
355User Guide for Thresholds and Classificationsthe level of dissolved metal ion concentration of the metal with different particles, using the critical surfacearea approach as proposed by Skeaff et al (2000). That is, from this correlation and a linkage to theappropriate toxicity data, it may be possible to determine a critical surface area of the substance that deliversthe L(E)C 50 to the medium and then to convert the critical surface area to the low, medium and high massloadings used in hazard identification. While this approach is not normally used for classification it mayprovide useful information for labelling and downstream decisions.Figure 19D.1: Decision scheme for aquatic classification of metals and inorganic metal compoundsMetals or inorganic metal compoundsL(E)C 50 of soluble ion >100 mg/LNO (metals)Solubility of metal compound≥ L(E)C 50 from available dataNOYESYESNO (metal compounds)No classificationClassify based on L(E)C 50of metal ion correctedfor molecular weight24 hours transformation/dissolutionscreening test shows that concentration≥ L(E)C 50 of dissolved formThis box applies onlyto metal compoundsNO7 days transformation/dissolution full test data availableNOYESConcentrationat low loading rate≥ L(E)C 50of dissolved formNOConcentration YESat medium loading rate≥ L(E)C 50of dissolved formNOYESClassify as 9.1AClassify as 9.1B unless:(1) there is evidence of rapid partitioningand no bioacccumulation; or(2) transformation/dissolution full testshows that after 28 days, concentrationlong-term NOECs of dissolved formin which case classify as 9.1DConcentrationat high loading rate≥ L(E)C 50of dissolved formNOClassify as 9.1D unlesstransformation/dissolution full test showsthat after 28 days, concentrationlong-term NOECs of dissolved formin which case no classification appliesYESClassify as 9.1C unless:(1) there is evidence of rapid partitioningand no bioacccumulation; or(2) transformation/dissolution full testshows that after 28 days, concentrationlong-term NOECs of dissolved formin which case classify as 9.1DNote: L(E)C5o = median lethal concentration or median effect concentration; NOEC = no observable effectconcentration.January 2012 EPA0109
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