Zebrafish assays as developmental toxicity indicators in the green design of TAML oxidation catalysts

TAML activators promise a novel approach to water treatment by efficiently catalysing peroxide degradation of chemicals of high concern, including developmental toxicants. Seven TAML activators were subjected to zebrafish toxicity assays (1) to determine if developmental toxicity might be present to avoid in water treatment the very same problem that the catalysts have been designed to reduce/eliminate, and (2) to look for relationships between the structure, the known reactivity in peroxide catalysis and the toxicity. Differential toxicity within the studied TAML group and an interpretable design relationship have been revealed. Electron-withdrawing groups (EWGs) on the TAML macrocycle are known to increase the oxidative aggression of TAML/peroxide in the order Cl < CN < NO2 with the most reactive NO2-substituted catalysts being the most useful for degrading trace contaminants. The toxicity toward zebrafish was found to increase in the reverse order, NO2 < CN < Cl, the most positive possible result. While all the catalysts tested as possessing negligible toxicity at typical TAML/peroxide operating concentrations, three exhibited sufficient toxicity at higher concentrations to convey green design insight by indicating that these variants should be avoided in water treatment.