A new approach to the hazard classification of alloys based on transformation/dissolution
Authors: Skeaff James M , Hardy David J , King Pierrette 
Published: January 2008

Most of the metals produced for commercial application enter into service as alloys which, together with metals and all other chemicals in commerce, are subject to a hazard identification and classification initiative now being implemented in a number of jurisdictions worldwide, including the European Union Registration, Evaluation, Authorisation and Restriction of Chemicals (REACH) initiative, effective 1 June 2007. This initiative has considerable implications for environmental protection and market access. While a method for the hazard identification and classification of metals is available in the recently developed United Nations (UN) guidance document on the Globally Harmonized System of Hazard Classification and Labelling (GHS), an approach for alloys has yet to be formulated. Within the GHS, a transformation/dissolution protocol (T/DP) for metals and sparingly soluble metal compounds is provided as a standard laboratory method for measuring the rate and extent of the release of metals into aqueous media from metal-bearing substances. By comparison with ecotoxicity reference data, T/D data can be used to derive UN GHS classification proposals. In this study we applied the T/DP for the 1st time to several economically important metals and alloys: iron powder, nickel powder, copper powder, and the alloys Fe-2Cu-0.6C (copper =2%, carbon = 0.6%), Fe-2Ni-0.6C, Stainless Steel 304, Monel, brass, Inconel, and nickel-silver. The iron and copper powders and the iron and nickel powders had been sintered to produce the Fe-2Me-0.6C (Me = copper or nickel) alloys which made them essentially resistant to reaction with the aqueous media, so they would not classify under the GHS, although their component copper and nickel metal powders would. Forming a protective passivating film, chromium in the Stainless Steel 304 and Inconel alloys protected them from reaction with the aqueous media, so that their metal releases were minimal and would not result in GHS classification. For the other alloys, we developed a new critical surface area-toxic units (CSA-TU) approach to derive their GHS classification proposals. The CSA-TU approach can be readily applied to other multicomponent alloy systems, without the need to arbitrarily select a particular component among several as the determinant of toxicity. This paper shows how regulatory obligations, such as those mandated by REACH, can be met with a laboratory-based CSA-TU method for deriving hazard classification proposals for alloys, linking to attendant environmental protection management decisions. Drawing on T/D data derived from laboratory testing of the alloy itself, the CSA-TU approach can be applied to establish scientifically defensible decisions on hazard classification proposals for an alloy of interest. The resulting decisions can then be incorporated into environmental management measures in such jurisdictions as the European Union. Based on an approach developed specifically for alloys, the hazard classification decisions can be regarded as relevant, credible, and protective of the environment. Since alloys are usually more resistant to chemical attack than their components, this approach is a considerable improvement over the possibility provided for in the GHS of calculating a hazard classification level for an alloy from the classification levels of its components.