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United States Department of Agriculture

Agricultural Research Service

Title: Recovery of Biosolids Applied Heavy Metals Sixteen Years after Application

Authors
item Sloan, John
item Dowdy, Robert
item DOLAN, MICHAEL

Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 27, 1998
Publication Date: N/A

Interpretive Summary: Agricultural utilization of biosolids, a byproduct of municipal waste water purification, improves soil tilth and provides essential plant nutrients. However, it can also significantly increase heavy metal concentrations in soils. There is a general concern over the long-term fate of these heavy metals in the environment. Many researchers are unable to completely account for biosolids-derived heavy metals in soils subsequent to application. This suggests possible movement of metals into groundwater through leaching. Our study found that careful selection and layout of biosolids research plots combined with precise and accurate biosolids application rates can greatly improve the ability to account for the long-term fate of biosolids-applied heavy metals. We found that sixteen years after application, more than 90 percent of biosolids-applied heavy metals remained in upper 30 cm of the soil and 100 percent in the upper 45 5cm. Loss of heavy metals due to leaching and plant uptake were negligible These results provide valuable information to regulators, both federal and state, on the long-term fate of biosolids-applied heavy metals. The information can be used to development sensible guidelines for agricultural utilization of municipal biosolids.

Technical Abstract: The ability to account for biosolids-applied heavy metals subsequent to application provides information on their fate in the environment. The objective of this study was to quantitatively recover biosolids-applied heavy metals from a well-drained soil sixteen years after application. Three annual biosolids applications resulted in cumulative biosolids loadings of 0, 60, 120, and 180 Mg/ha. Cumulative heavy metal loadings for the 180 Mg/ha biosolids rate were 25, 141, 127, 43, 173, and 348 kg/ha for Cd, Cr, Cu, Ni, Pb, and Zn, respectively. Soils were sampled in 0.15 m increments to a depth of 0.9 m. Soil samples were extracted for 20 h with 1 M HNO3 and metals were determined in the supernatants by ICP-AES. Concentrations of extractable Cd, Cr, Cu, Ni, Pb, and Zn in biosolids-treated soils were much greater than the control to a depth of 0.30 m (p less than 0.01) and slightly greater at 0.30-0.45 m (p less than 0.05). There was no difference in soil metal concentrations between control and biosolids-treated soils below 0.45 m. For the 180 Mg/ha biosolids loading, percent recoveries for Cd, Cr, Cu, Ni, Pb, and Zn were 112 plus or minus 21, 59 plus or minus 18, 119 plus or minus 26, 114 plus or minus 7, 102 plus or minus 30, and 97 plus or minus 19 percent, respectively. These results suggest that biosolids-applied heavy metals are relatively immobile in soil and remain near the zone of incorporation. Complete recovery of biosolids-applied heavy metals is possible from large plots with well-documented heavy metal loading rates.

Last Modified: 9/29/2014
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