The ecotoxicity of zinc and zinc‐containing substances in soil with consideration of metal‐moiety approaches and organometal complexes

Within Canada, screening-level assessments for chemical substances are required in order to determine whether the substances pose a risk to human health and/or the environment, and as appropriate, risk management strategies. In response to the volume of metal and metal-containing substances, process efficiencies were introduced using a metal moiety approach, wherein substances that contain a common metal moiety are assessed simultaneously as a group, wherein the moiety of concern would consist of the metal ion. However, for certain subgroups, such as organometals (OM) or organic metal salts (OMS), the organic moiety or parent substance may be of concern, rather than simply the metal ion. To further investigate the need for such additional consideration, zinc-containing inorganic (zinc chloride and zinc oxide) and organic (organometal: zinc diethyldithiocarbamate (Zn(DDC)2) and organic metal salts: zinc stearate (ZnSt) and 4-chloro-2-nitrobenzenediazonium tetrachlorozincate (BCNZ)) substances were evaluated. The toxicity of the substances were assessed using plant (Trifolium pratense and Elymus lanceolatus) and soil invertebrate (Folsomia candida and Eisenia andrei) tests in a sandy soil. Effect measures were determined based on total metal and total parent analyses (for organic substances). In general, the inorganic zinc substances were less toxic than the OM and OMS, with 50% effective concentrations ranging from 11 to > 5194 mg Zn kg-1 dry soil. The data demonstrate the necessity for alternate approaches in the assessment of organo-metal complexes wherein the organic moieties or parent substance warrant consideration, rather than solely the metal ion. In this instance, the OM and OMS were significantly more toxic than other test substances despite their low total Zn content. This article is protected by copyright. All rights reserved