Answer:
Nitrate from agriculture is now the most common chemical contaminant in the world’s groundwater aquifers. Aquatic ecosystems are affected by agricultural pollution; for example, eutrophication caused by the accumulation of nutrients in lakes and coastal waters impacts biodiversity and fisheries.
It will form HCN Hydrogen Cyanide.
This is more to do with Bioaccumulation of mercury, where the mercury is absorbed into the issue of animals, and so animals higher in the food chain consume a lot of tissue matter hence increasing mercury content in their system.
The melting of the ice cube indicates physical change has taken place
