Environmental Risk Assessment of Coal-Ash-Amended Soil Based on Continuous Planting of Pakchoi

The agricultural application of coal ash which contains a variety of chemical nutrients may also cause heavy metal pollution of crops and soil. In this study, pakchoi was cultivated for four consecutive seasons in pots of brown soil amended with fly ash or bottom ash. With subsequent plantings, the total concentrations in the four fractions of Pb, Cr and Cu decreased, while the concentrations of Pb, Cr and Zn dissolved in acetic acid increased. The lowest fresh weight of pakchoi were seen when 15% fly ash was applied. The edible parts of pakchoi contained more heavy metals than the roots. Calculating the Nemerow Pollution Index (NPI) according to the Environmental Protection Standards, the risk of heavy metals in coal ash-amended soils was low. With subsequent plantings, the Risk Assessment Code (RAC) of Pb, Cr and Zn increased gradually and Zn eventually reached a medium level. The study confirmed that coal ash had phytotoxic effects on pakchoi and application of coal ash confered a risk of soil pollution.