The most common kinds of waste can be
classified into four types: agricultural, industrial,
municipal and nuclear (Alloway 1995).
Agricultural wastes include a wide range of
organic materials (often containing pesticides),
animal wastes, and timber by-products. Many
of these, such as plant residues and livestock
manure, are very beneficial if they are returned
to the soil. However, improper handling and
disposal may cause pollution.