Predicting and comparing chronic water quality criteria from physicochemical properties of transition metals

Criteria continuous concentrations (CCCs) are the scientific basis for making sound environmental management decisions and assessing surface water quality. Transition metals are a group of elements, similar in physicochemical properties perpendicularly and horizontally across the Periodic Table, some of which are widely distributed in aquatic environments and can cause adverse effects on aquatic life and human health. Currently internationally recommended CCCs are available for only seven transition metals. It is challenging to derive CCCs for transition metals based on scarce empirical information. The present study found significant relationships between the suggested CCCs of transition metals and their nine physicochemical properties and an empirical model was developed to satisfactorily predict the CCCs of 56 transition metals by use of the most relevant parameter, r, for protecting aquatic ecosystems. Predicted values were largely consistent with the CCCs and CMCs predicted previously and over 80% predicted CMCs of transition metals are greater than or equal to their CCCs. The present study shows methodological advantages in obtaining CCCs, and provides reliable reference values for setting chronic WQC and assessing risk of transition metals.