RECOVERY OF BIOSOLIDS-APPLIED HEAVY-METALS 16 YEARS AFTER APPLICATION

Little is known of the long-term fate of biosolids-applied heavy metal s in soil. The objective of this study was to quantify percent recover y of biosolids-applied heavy metals in a well-drained soil. Three annu al applications of biosolids resulted in cumulative biosolids loadings of 0, 60, 120, and 180 Rig ha(-1). Cumulative metal loadings for the 180 Big ha(-1) biosolids rate were 25, 141, 127, 43, 173, and 348 kg h a(-1) fur Cd, Cr, Cu, Ni, Pb, and Zn, respectively. Soils were sampled to a depth of 0.9 m. Soil organic carbon (OC) was measured. Soil was extracted with 1 M IINO3 and metals were determined in the supernatant s. Soil OC concentrations were linearly correlated to biosolids loadin gs and did not change significantly during die 16 yr after biosolids a pplications. Concentrations of extractable Cd, Cr, Cu, Ni, ph, and Zn in biosolids-treated soils were much greater than the control to a dep th of 0.30 m (P < 0.01), slightly greater at 0.30 to 0.45 nl (P < 0.05 ) and same as the control below 0.45 m. For the 180 Mg ha(-1) biosolid s loading, percent recoveries for Cd, Cr, Cu, Ni, ph, and Zn were 112, 59, 119, 114, 102, and 97%, respectively. Low recovery of Cr was prob ably due to incomplete extraction from the soil. These results show th at complete recovery of biosolids-applied heavy metals is possible whe n plot size is large enough to prevent cross-mixing of treated soils d uring tillage operations and when sediment losses are minimal.