Performance of the GHS Mixtures Equation for Predicting Acute Oral Toxicity

Acute oral toxicity classifications are based on the estimated chemical dose causing lethality in 50 % of laboratory animals tested (LD₅₀). Given the large number of pesticide registration applications that require acute toxicity data, an alternative to the in vivo test could greatly reduce animal testing. The United Nations Globally Harmonized System of Classification and Labelling of Chemicals (GHS) Mixtures Equation estimates the acute toxicity of mixtures using the toxicities of mixture components. The goal of this study was to evaluate the concordance of LD₅₀s predicted using the GHS Mixtures Equation and LD₅₀s from the in vivo test results. Using the EPA classification system, concordance was 55 % for the full dataset (N = 671), 52 % for agrochemical formulations (N = 620), and 84 % for antimicrobial cleaning products (N = 51). Most discordant results were from substances LD₅₀ > 2000 mg/kg (limit test) or 2000 < LD₅₀ < 5000 mg/kg that were predicted as LD₅₀ > 5000 mg/kg. A supplementary analysis combining all formulations with an LD₅₀ > 500 mg/kg produced a concordance of 82 %. The lack of more toxic formulations in this dataset prevented a thorough evaluation of the GHS equation for such substances. Accordingly, our results suggest the GHS equation is helpful to predict the toxicity of mixtures, particularly those with lower toxicity.