Many trace elements such as chromium and mercury are toxic. The leaching of trace elements from fly ash is usually monitored at ash storage and disposal sites to ensure that they do not leak into the natural environment at elevated concentrations. Preparatory studies are commonly carried out to ensure that the use of fly ash and other coal by-products in agricultural applications such as soil amendment and landfill do not lead to contamination of soil or groundwater. The concentrations of chromium and radioactive trace elements are also limited in cement and concrete applications as a result of recently tightened . . .