Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/15/2005
Publication Date: 9/8/2005
Citation: Sukkariyah, B.F., Evanylo, G., Zelazny, L., Chaney, R.L. 2005. Recovery and distribution of biosolids-derived trace metals in a davidson clay loam soil. Journal of Environmental Quality. 34(5):1843-1850. Interpretive Summary: Because biosolids have higher concentrations of trace metals than most other soil amendments, research has been conducted to better understand the fate and potential effects of metals applied in biosolids. Some researchers added metal salts to soils to simulate biosolids added metals, but it is clear that this approach over-estimates the potential adverse effects. Consensus supports examination of metals in soils of long term biosolids utilization field plots to assess potential plant uptake, leaching, and chemical forms in soil over time after application. One long term study site in VA was studied by sampling soils with depth 17 years after a relatively high Zn and Cu containing biosolids was applied to a major soil of the Virginia piedmont, the Davidson clay loam. Over the 17 years of the experiment, the treated soils were constrained within fixed plot borders made from non-contaminating materials to prevent dispersal of the treated soil by tillage. Soil pH was maintained at 6.5-7 for about 10 years, and then allowed to drop with fertilizer-derived acidity. Analysis of the soil layers for total metals indicated that 95% or greater of applied metals were still present in the soil profile. For less strongly adsorbed metals (Zn), some of the applied metal had leached to the 10 cm layer below the plot layer depth. For most elements, leaching was not evident, either from solubilized metals, or from illuviation of fine particles with adsorbed metals. These results indicate little risk of applied metals leaching thru soils to comprise risk to groundwater quality. Crop uptake of metals by sensitive vegetable crops will be reported in a subsequent manuscript.
Technical Abstract: The long-term mobility of trace metals has been cited as a potential hazard by critics of EPA 503 rule governing the land application of biosolids. The objectives of this study were to assess the accumulation of Cu, Ni, Cd, and Zn within the soil profile, the distribution of exchangeable, specifically adsorbed, organic and oxide fractions of each metal and mass balance of Cu and Zn 17 years after biosolids application. Biosolids were applied to 1.5 x 2.3 m confined plots of a Davidson clay loam (clayey, kaolinitic, thermic, Rhodic Paleudult) in 1984 at 0, 42, 84, 126, 168, and 210 Mg ha-1. The highest biosolids application supplied 4.5, 750, 43, and 600 kg ha-1 of Cd, Cu, Ni, and Zn, respectively. Soils were sampled to a depth of 0.9 m and sectioned into 5-cm increments after separating the Ap horizon. Total (EPA 3050B), bioavailable (Mehlich-1), sequential extraction, and dispersible clay analysis were performed on samples from the control, 126 t/ha and 210 t/ha treatments. Trace metals are still concentrated in the top 0.2 m with slight enrichment down to 0.3 m. More than 85% of applied Cu and Zn are still found in the topsoil where biosolids was incorporated. Mehlich-1 results showed a slight increase in metal concentration down to 0.35 m. Biosolids application increased the concentration of trace metals in all the extracted fractions, with a large portion of Zn and Cd in readily extractable forms. The major portion of Cu, Zn, and Ni is associated with the metal-oxides fraction. Dispersible clay content and water-soluble metal contents were low and were not affected by biosolids application. Results from this study showed that 17 years after biosolids application there was negligible movement of trace metals through the soil profile and consequently, there is little risk of contamination of groundwater at this site.