ASSESSMENT OF TRANSFER OF RADIOACTIVITY TO SOIL AND CROPS FROM LONG TERM LAND APPLICATION OF CHICAGO BIOSOLIDS

Wastewater treatment at publicly owned treatment works (POTWs) produces a considerable amount of biosolids. These biosolids are rich in plant nutrients, and may be used for beneficial purposes such as application to agriculture fields and disturbed lands. The Metropolitan Water Reclamation District of Greater Chicago (District) is one of the largest municipal wastewater treatment agencies in the nation, and it produces about 190,000 dry tons of biosolids each year. The District monitors the quality of biosolids produced, and is committed to using it beneficially. One beneficial use is fertilizing or reclaiming disturbed lands (mine soil) for crop production. The District has made long-term applications of biosolids to mine soil at the Corn Fertility Experimental Plots in Fulton County, Illinois. Biosolids were applied annually at the rates of 16.8, 33.6, and 67.2 Mg ha-1 to replicated plots (4 times) from 1973 to 2000 along with commercial fertilizer, which was applied annually to control plots. The purpose of this study was to evaluate the effect of long-term applications of biosolids on the radioactivity concentration in biosolids-amended soil, and the uptake of radioactivity into corn grain and stover harvested from these plots. Radiological analyses show nearly the same consistent concentration of radioactivity in soil from the biosolids-amended plots as that found in the soil from control plots receiving commercial fertilizer. The same trend was observed for corn grain and stover harvested from these plots. Of the twenty-seven radionuclides studied, only potassium-40 was found in corn grain and stover, and a negligible amount of radium-226 was observed in corn grain. No other radionuclide was found in corn grain and stover. The results of this study show that long-term annual applications of biosolids did not increase the radioactivity in amended soil or result in increased uptake by corn. The low or non-detectable levels of radioactivity observed in soil and corn indicate that the District's land applied biosolids do not pose a threat to human and animal health or the environment from a radioactivity standpoint.