519 Agronomic use of biosolids has raised concern that plant availability of biosolids-Cd will increase with time after cessation of biosolids application. It has been demonstrated that chemical extractability of Cd is persistently decreased in biosolids- amended soils. Tis study was conducted to determine if Cd phytoavailability in long-term biosolids-amended soils was also persistently decreased. Paired control and biosolids-amended soils were collected from three experimental sites where large cumulative rates of biosolids were applied about 20 yr ago. Te pH of all soils [in 0.01 mol L −1 Ca(NO 3 ) 2 ] was adjusted to 6.5 ± 0.2. Increasing rates of Cd-nitrate (from 0 to 10.0 mg Cd kg −1 soil) enriched in 111 Cd stable isotope were added to all soils, and Romaine lettuce (Lactuca sativa L. var. longifolia Lam.) was grown in pots to bioassay phytoavailable Cd. After harvest, Cd concentrations in shoots and labile pool of Cd (Cd L ) in soils were determined. Te relationship between added salt-Cd and Cd concentrations in lettuce shoots was linear for all soils tested. Ratios of (shoot Cd):(soil Cd) slopes were highest in the control soils. Biosolids amendment decreased (shoot Cd):(soil Cd) slopes to varied extent depending on biosolids source, properties, and application rate. Te decrease in slope in comparison to the control was an indication of the lower phytoavailability of Cd in biosolids-amended soils. A significant negative correlation existed between Cd uptake slopes and soil organic matter, free and amorphous Fe and Al oxides, Bray-P, and soil and plant Zn. Biosolids-Cd was highly labile (%L 80–95) except for Fulton County soil (%L = 61). Phytoavailability of Cadmium in Long-Term Biosolids-Amended Soils Urszula Kukier Virginia Polytechnic Institute and State University Rufus L. Chaney* USDA–ARS James A. Ryan USEPA W. Lee Daniels Virginia Polytechnic Institute and State University Robert H. Dowdy USDA–ARS Thomas C. Granato Metropolitan Water Reclamation District of Greater Chicago C oncerns related to adverse environmental and food chain effects of trace elements in biosolids have a history as long as the history of using biosolids as agricultural soil amendments (Page, 1974; Beckett et al., 1979; Chaney, 1973; McBride, 1995), component of composts, and artificial soil mixtures used for resto- ration of drastically disturbed ecosystems (Li et al., 2000; Granato et al., 2004; Brown et al., 2005). Tese concerns encouraged years of research to define patterns of metal uptake by plants grown in biosolids-amended soils (Cunningham et al., 1975; CAST, 1976; Corey et al., 1981; Heckman et al., 1987; Smith, 1994; Sloan et al., 1997; Granato et al., 2004). When metal salts are added to soils with biosolids, they are less phytoavailable than when added alone (Mahler et al., 1987). Tis effect is attributed to the addition of sorptive phases as organic matter or as mineral components of biosolids includ- ing phosphates, silicates, and Fe and Mn oxides (Li et al., 2001; Hettiarachchi et al., 2006). Although inorganic phases of biosol- ids may be persistent in amended soils, biosolids organic matter decomposes, and with time its content in soil diminishes. Tis loss of applied organic matter has raised concern that the phytoavail- ability of biosolids-applied trace elements may increase in decades after biosolids application and that the biosolids-Cd rate that is safe today may prove to be harmful in the future (Chaney, 1973; Beckett et al., 1979; McBride, 1995). To address this concern, crop uptake of Cd has been monitored in controlled field plots with a history of long-term biosolids application. For example, Chaney and Hornick (1978) reported that fields where biosolids with high Cd levels were applied, especially where the soils were acidic, caused very high Cd uptake by a range of crops (Chaney et al., 2006). However, when biosolids with typical median metal levels were applied, no evidence of increased Cd uptake was found Abbreviations: MWRDGC, Metropolitan Water Reclamation District of Greater Chicago. U. Kukier and W.L. Daniels, Virginia Polytechnic Institute and State Univ., Dep. Crop and Soil Environmental Sciences, Blacksburg, VA 24061; R.L. Chaney, USDA–ARS, Environmental Management and Byproduct Utilization Lab., 10300 Baltimore Blvd., Beltsville, MD 20705. J.A. Ryan, USEPA, National Risk Management Research Lab., 5995 Center Hill Rd., Cincinnati, OH 45224; R.H. Dowdy, USDA–ARS, Soil and Water Management Res., Univ. of Minnesota, 458 Borlaug Hall, St. Paul, MN 55108; T.C. Granato, Metropolitan Water Reclamation District of Greater Chicago, Lue-Hing R&D Complex, 6001 W. Pershing Rd. Cicero, IL 60804. Use of trade or proprietary names or trademarks herein is for informational purposes only and does not imply any advertisement or endorsement by the agencies involved in this study. Copyright © 2010 by the American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America. All rights reserved. No part of this periodical may be reproduced or transmitted in any form or by any means, electronic or mechanical, including pho- tocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. Published in J. Environ. Qual. 39:519–530 (2010). doi:10.2134/jeq2007.0671 Published online 5 Jan. 2010 Received 27 Dec. 2007. *Corresponding author (Rufus.Chaney@ars.usda.gov). © ASA, CSSA, SSSA 677 S. Segoe Rd., Madison, WI 53711 USA TECHNICAL REPORTS: HEAVY METALS IN THE ENVIRONMENT