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ARS Home » Pacific West Area » Kimberly, Idaho » Northwest Irrigation and Soils Research » Research » Publications at this Location » Publication #223245
Title: Fate of biosolids trace metals in a dryland wheat agroecosystem

Author
item Ippolito, James
item BARBARICK, K - COLORADO STATE UNIVERSITY

Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/5/2008
Publication Date: 10/27/2008
Citation: Ippolito, J.A., Barbarick, K.A. 2008. Fate of biosolids trace metals in a dryland wheat agroecosystem. Journal of Environmental Quality. 37:2135-2144.

Interpretive Summary: Biosolids land application for beneficial reuse applies varying amount of trace metals to soils. Measuring plant-available or total soil metals is typically performed to ensure environmental protection, yet these techniques do not quantify which soil phases play important roles in terms of metal release or attenuation. Ippolito and Barbarick report that trace metals were concentrated in the zone of incorporation in long-term (20 yr) research plots, as measured using 4 M nitric acid digestion and sequential extraction. The sequential extraction showed nearly all measurable Cd present in relatively mobile forms, and Cr, Cu, Mo, Ni, Pb, and Zn present in resistant phases. Biosolids application increased relatively immobile Cu, Mo, and Zn phases, and relatively mobile Cu, Ni, and Pb pools. The mobile phases have not contributed to significant downward metal movement.

Technical Abstract: Biosolids land application for beneficial reuse applies varying amounts of trace metals to soils. Measuring plant-available or total soil metals is typically performed to ensure environmental protection, yet these techniques do not quantify which soil phases play important roles in terms of metal release or attenuation. The study objective was to assess the distribution of Cd, Cr, Cu, Mo, Ni, Pb, and Zn associated with soluble/exchangeable, specifically adsorbed, easily-reducible Fe/Mn oxides, Fe/Mn oxides and acid replaceable (organically complexed), residual organic, and residual inorganic phases. Biosolids were applied every two years from 1982 to 2002, except in 1998, at rates of 0, 6.7, 13.4, 26.8 and 40.3 dry Mg biosolids per ha to 3.6 by 17.1 m plots. In 2003, 0-20 and 20-60-cm soil depths were collected and subjected to 4 M nitric acid digestion and sequential extraction. Trace metals were concentrated in the 0-20-cm depth with no observable downward movement using either 4 M nitric acid or sequential extraction. The sequential extraction showed nearly all measurable Cd present in relatively mobile forms, and Cr, Cu, Mo, Ni, Pb, and Zn present in more resistant phases. Biosolids application did not affect Cd or Cr fractionation, but did increase relatively immobile Cu, Mo, and Zn phases, and relatively mobile Cu, Ni, and Pb pools. The mobile phases have not contributed to significant downward metal movement. Long-term, repeated biosolids applications at rates considered several times greater than agronomic should not contribute to downward metal transport and groundwater contamination for soils under similar climatic, agronomic practices, and histories.