The chemistry of a submerged idol
Plaster of Paris is calcium sulphate hemihydrate. When it enters water, it does not dissolve the way salt does. It absorbs water, hardens briefly, then breaks into fine particulate matter that suspends in the water column and settles into the riverbed. A study published in the journal Environmental Monitoring and Assessment found that after Ganesh Chaturthi immersions in the Mula-Mutha river in Pune, total dissolved solids spiked by over 400 percent in the days immediately following the festival. The river bottom becomes layered with calcium sulphate sediment that smothers benthic organisms, the invertebrates, insect larvae, and small crustaceans that live in and on the riverbed and form the base of the aquatic food chain.
