The challenges of hazard identification and classification of insoluble metals and metal substances

摘要

Procedures for aquatic hazard identification of organic and inorganic substances are currently being harmonized by the OECD for the purpose of classifying market-place substances. Such a system already exists in Europe and is evolving other countries (United States and Canada). One common theme in each of these systems is the use of toxicity, persistence and bioaccumulation measurements to estimate aquatic hazard. It is recognized a within the OECD and European Union systems that special attention must be given to metal elements and sparingly soluble metal-containing compounds. This recognition is based upon a common understanding that standard hazard testing procedures designed for soluble organic chemicals do not accommodate the special characteristics of sparingly soluble metals and metal compounds (SSMMCs). Toxicity - it is recognized that the toxicity of a metal is due predominantly to the free metal ion in solution (estimated by soluble metal). Most of the toxicity data available to date have been derived using soluble metal salts. The assumption is that the dissolved metal ion is completely available. The toxicity of most dissolved metal salts to sensitive species lies in the range of 0.1 to 1000 ug/L (Table 1). In order to assess the acute aquatic toxicity of SSMMCs the rate and extent of transformation of metal to a soluble form must be measured. Transformation of insoluble metal substances to soluble forms is a function of several key factors including particle size, surface area, ionic strength, and the pH of the test solution. A standard protocol for measuring transformation is currently being developed by the OECD. Initial results obtained using the protocol under development indicate that unrealistically high concentrations of soluble metal are obtained as compared to concentrations that occur in natural environments (Table 2). The protocol at present lacks complexing ligands. Further development of this protocol is planned.