Ash leachates from some recent eruptions of Mount Etna (Italy) and Popocatepetl (Mexico) volcanoes and their impact on a lacustrine biotic

Volcanic ash is the most widely distributed product of explosive volcanic eruptions, and areas hundreds of kilometres from an erupting volcano could receive ash falls. Even minor quantities of deposited ash represent a major hazard for the modern technical society and the environment. In particular, deposition of volcanic ash into aqueous environments leads to dissolution of adsorbed metal salts and aerosols, increasing the bioavailability of both key nutrients and pollutants. This is because acids, metal salts and adsorbed gases on tephra surfaces are highly soluble, dissolving rapidly on contact with water. The effects of ashfall on natural waters and water supplies have focused mainly on the consequences of increased levels of turbidity, acidity and fluoride. On the other hand, contamination of drinkable water is a major concern for public health, due to the potential for outbreaks of waterborne infectious diseases due to the inhibition of disinfection at high levels of turbidity, and elevated concentrations of fluoride increasing risks of dental and skeletal fluorosis. Other than fluoride and acidity, little attention has been paid to contamination of water supplies by other soluble components of ashfall. In order to supply new data useful for understanding the behaviour of release of water contaminants from fresh volcanic ash and their impact on water supplies and live biotic, we collected ash deposits from two recent eruptions of Mount Etna (Italy, August 2011 and April 2012) and from the eruption of May 2012 of Popocatepetl volcano (Mexico). The collected volcanic ash was washed using two different types of water (double de-ionised and natural lake water), and the released compounds analysed for major and trace elements. The results were discussed in the light of international and Italian drinkable limits for public waters. The ash leachates were also used for conducting toxicity laboratory experiments on living biotic (tadpole).