Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/29/2009
Publication Date: 2/26/2010
Citation: Kukier, U., Chaney, R.L., Ryan, J.A., Daniels, W.L., Dowdy, R.H., Granato, T.C. 2010. Phytoavailability of Cadmium in Long-Term Biosolids Amended Soils. Journal of Environmental Quality. 39:519-530. Interpretive Summary: Information about the long-term availability of biosolids-applied metals has indicated that for at least high Fe biosolids, increasing rates of application actually reduce the potential for plant uptake of applied metals such as Cd. Some authors have disputed this interpretation based on their analysis of others experiments. In order to clarify this issue, we conducted an experiment using improved techniques. We obtained soils from long term field experiments where biosolids were applied to field plots used in agricultural tests so that the quality and quantity and timing of applications were well defined. Because soil pH can strongly affect metal uptake by plants, we adjusted all soils to the same pH. To estimate the potential for plant uptake of Cd, we added 5 rates of Cd nitrate with a stable isotope tracer to each soil, incubated and mixed the soils, and then grew Romaine lettuce to maturity. We analysed the lettuce and soil for total metals and for stable isotopes. By measuring the ratio of stable isotopes, we could estimate the amount of Cd in the soil which was potentially available to the plants, also called the “labile pool”. Plant uptake of Cd was a linear function of the added Cd nitrate for all treatments, but the slope of uptake was lower for the biosolids amended soils than the unamended soils from each location. For the low metal limed-composted biosolids and heat-treated biosolids applied in Beltsville, MD, in 1976, the slope was decreased 80-90% compared to the control. For all biosolids treated soils except those from the Fulton Co. plots of the Metropolitan Water Reclamation District of Greater Chicago, the labile pool was 80-90% of the total soil Cd, but for the Fulton Co. biosolids amended soil, the labile fraction was only 61% of the total Cd indicating that some of the Cd was present in forms not available to plants. Present findings suggest that adding Fe during biosolids processing can significantly reduce the plant availability of Cd and other biosolids metals, and improve their quality for use in remediation of metal toxic soils.
Technical Abstract: Agronomic use of biosolids has raised concern that plant availability of biosolids-Cd will increase with time following cessation of biosolids application. But it was demonstrated that long-term biosolids-amended soils have greater sorptive capacity for Cd than non-biosolids-amended soils. This study tested if Cd phytoavailability in the long-term biosolids-amended soils is also persistently decreased. Paired control and biosolids-amended soils were collected from 3 experimental sites where large cumulative rates of biosolids were applied about 20 years ago. The pH of all soils [in 0.01 M Ca(NO3)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 111Cd stable isotope were added to all soils, and Romaine lettuce (Lactuca sativa L. var. longifolia Lam.) was grown in pots. After harvest, Cd concentrations in shoots, and labile pool of Cd (L) in soils were determined. The relationship between total soil Cd and Cd concentrations in lettuce shoots was linear for all soils tested. Cd uptake slopes were highest in the control soils. Biosolids amendment decreased Cd uptake slopes to various extent depending on biosolids source, properties and rate. The decrease in slope 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).