#chemistry

Lead is one of the oldest metals known to man and therefore it deserves special emphasis in the international year of the Periodic Table of the Elements (2019). Its essentiality has been discussed but not demonstrated, yet its toxicity has already been recognized by Greek and Arab scholars.

The legendary traffic lights in Berlin, the “Ampelmännchen”, symbolise the opposite biological functions of chromium compounds in two major oxidation states: one for health and the other for disease. In other words, green stands for “go and safe”, red stands for “stop and danger”.