Quantitative Cationic Activity Relationships for Predicting Toxicity of Metal Ions from Physicochemical Properties and Natural Occurrence Levels

Quantitative Cationic Activity Relationships (QCARs) were developed to predict the toxicity of metal ions from physicochemical properties and natural occurrence levels. In vivo toxicity data for different concentrations of nitrate salts of 17 metal ions were developed based on germination of sunflower seeds (F.1. Helianthus annuus ‘Sunspot’) in distilled water. The EC50 data were reported as the concentration giving 50% inhibition of radicle growth 1 day after emergence. Stepwise regression of the toxicity data produced correlations with some physicochemical properties and natural occurrence levels. For physicochemical properties, good results were obtained with the density of the elements, enthalpy of formation of metal sulphides and the stability constants of metal ions with sulphate (r_adj.²=0.72−0.81). For natural occurrence levels, good results were obtained with metal concentrations in soil, the median elemental composition of soils and the calculated mean of the elemental content in land plants (r_adj.²=0.69−0.83).