ABSTRACT
Trace elements are required in small amounts by plants or animals. Some of these have been identified while others may still be unknown. Heavy metals are a group of elements found in the periodic table with a relatively high molecular weight and, when taken into the body, can accumulate in specific body organs. Soils are derived from parent material as a result of weathering. Because many of the parent material minerals contain trace elements, natural soils will contain different amounts of trace elements depending on the type of mineral. Lead arsenate and calcium arsenate previously have been used in cotton and orchards. Biosolids contain trace elements and heavy metals primarily from industrial, commercial and residential discharges into the wastewater system. As a result of the Clean Water Act of 1972 restricting industrial discharge, the quality of the wastewater entering publicly owned treatment works systems has improved. Consequently, the quality of biosolids has improved.
