Bioavailability of Heavy Metals in Biosolids‐Amended Soil

Abstract

A single biosolids application was made to 1.5×2.3 m confined plots of a Davidson clay loam (Rhodic Kandiudult) in 1984 at 0, 42, 84, 126, 168, and 210 Mg ha⁻¹. The highest biosolids application supplied 750 and 600 kg ha⁻¹ of Cu and Zn, respectively. Corn (Zea mays L.), from 1984 to 2000, and radish (Raphanus sativus L.) and romaine lettuce (Lactuca sativa var. longifolia), from 2001 to 2004, were grown at the site to assess heavy‐metal bioavailability. Extractable (0.005 diethylenetriamine (DTPA) and Mehlich 1) Cu and Zn were determined on 0 to 15‐cm depth samples from each plot. Corn yield increased with biosolids rate each year until 1993 to 1997, when yield decreased with biosolids rate because of phytotoxicity induced by low (<5.0) soil pH. The corn yield reduction was reversed between 1998 and 2000 upon raising the soil pH to approximately 6.0 by limestone addition following the 1997 season. Between 2001 and 2004, radish and lettuce yields were either not affected or slightly increased with biosolids rate, even as soil pH declined to below 5.5. Plant‐tissue metal concentrations increased with biosolids rate and as pH declined but were always within the normal range of these crops. Mehlich 1 and DTPA extractable metals increased linearly with biosolids rate. Extractability of Cu and Zn decreased approximately 50% over the past 20 years despite a decrease in soil organic matter concentration and greater than 95% conservation of the metals.

Keywords:

• Copper
• corn
• Cu
• lettuce
• organic matter
• pH
• radish
• zinc
• Zn

Acknowledgments

The authors thank the Metropolitan Washington Council of Governments for funding of this research. We also wish to acknowledge the assistance of the staff of the Northern Piedmont Agricultural Research and Education Center, Dave Starner, Denton Dixon, Steve Gulick, and Alvin Hood for their support of this work.