Pollution specifically air pollution can cause acid. Gases such as sulphur (IV) oxide and Nitrogen (IV) oxide when they are released into the atmosphere and comes into contact with precipitation, that is rain water causes acid rain. Sulphurous acid and Nitric acid is formed thus the rain falls in acidic form.
Acid rain when it falls on the leaves of the flora (plants) causes removal of the green colouring matter (chlorophyll) thus making plants to be deficient of food. Food in plants is made my the process of photosynthesis, removal of chlorophyll in plants kills them due to lack of food.
Also when acid rain finds it's way into the water bodies through surface runoff, aquatic animals such as fishes die due to lack of favourable environment and oxygen deficiency in water. Acidity in the soil also kills important decomposers therefore soil aeration is altered.